docs: freeze the public Tend CLI line

Identify v0.2.0-preview.2 as the final public CLI preview while preserving every published licence and artifact.

AI-Assisted: OpenAI Codex
Signed-off-by: Cole Speelman <crspeelman@gmail.com>

PUBLIC-SNAPSHOT.json

@@ -1 +1 @@
-{"schema_version":1,"source_commit":"8aab3db43f35e6a49aa497f45d73701b13fc9f32","source_tree":"992132ea4703437dc13ffdbb04a077816c02caf9","source_date_epoch":1787049308,"file_count":76}
+{"schema_version":1,"source_commit":"07c1655921f21ee5e4fc4d85639d199e8867b17d","source_tree":"0a27c7c0d2fb8954e326044d06826cf7e1a37818","source_date_epoch":1787103648,"file_count":81}

PUBLIC-SNAPSHOT.sha256

@@ -1 +1 @@
-9c6153ab5b861ec5818591269b2a38a14239f68e89911655aaebec444f54a26d  PUBLIC-SNAPSHOT.json
+a38ba7894dede461d7aec3f1b07c5c6f65728f2971b973fc81c469c32667d38e  PUBLIC-SNAPSHOT.json

README.md

@@ -1,5 +1,17 @@
 # Gamertan Tend
 
+## Final public CLI preview
+
+`v0.2.0-preview.2` is the final public Tend CLI preview. This repository and
+its published AGPL releases remain available as an archived record, but it is
+not accepting new feature development. Private research continues around a
+networked management experience; that work is not mirrored or published here
+and carries no public release commitment.
+
+Existing licences and release artifacts are unchanged. Do not interpret this
+notice as withdrawing rights already granted by the AGPL-3.0-only and 0BSD
+files in this repository.
+
 Tend is an opinionated release and deployment tool for small Go services on
 Linux, systemd, and Caddy. It packages a clean pushed commit, records exact
 build provenance, activates a health-checked candidate, and keeps rollback
@@ -18,15 +30,24 @@ shell hooks. Application-specific data activation remains application-specific.
 ```text
 tend check    --config tend.json
 tend package  --config tend.json --version v0.2.0-preview.2 --out dist
+tend inspect  --config tend.json --artifact FILE --sha256 HEX --approve-sha256 HEX
 tend push     --target tend-deploy@host --known-hosts FILE --service NAME --artifact FILE --sha256 HEX --approve-sha256 HEX
 tend receive  --policy /etc/tend/receive-policy.json
 tend check-server --policy /etc/tend/receive-policy.json
 tend deploy   --config /etc/tend/services/example-site.json --artifact FILE --sha256 HEX --approve-sha256 HEX
 tend status   --config /etc/tend/services/example-site.json
+tend reconcile --config /etc/tend/services/example-site.json --json
 tend rollback --config /etc/tend/services/example-site.json
 tend prune    --config /etc/tend/services/example-site.json --keep 3 [--apply]
 ```
 
+`inspect` performs the complete archive, checksum, approval, manifest, SBOM,
+and binary-identity validation without staging or activating a release.
+`reconcile` is also read-only: it compares Tend's journal with conventional
+release symlinks, systemd units, the installed release identity, and the Caddy
+handler. It reports drift and retained-candidate residue without silently
+"repairing" a service.
+
 `push` transfers one approved artifact through a pinned OpenSSH connection. A
 forced, no-shell receiver maps the service name to one root-owned configuration;
 it accepts no remote path, environment value, URL, or shell fragment. Production
@@ -47,6 +68,17 @@ origins for the activation window. Blue/green deployments simultaneously keep
 checking the previous slot, restoring the prior handler and inactive-slot state
 if routed traffic or continuity fails.
 
+Singleton activation and rollback candidates use an operation-scoped systemd
+unit and persist a bounded lease containing the operation, release, unit,
+address, and start time in a separate adjacent file. Conventional deployment
+state remains schema 1 so a retained older binary can still read active and
+previous release identities; operators must reconcile before downgrading while
+a lease exists. `tend
+reconcile --json` compares that lease with unit activity, release pointers, and
+the exact Caddy handler file without changing any of them. It deliberately does
+not stop or clear a retained candidate: that process may still be the only
+healthy route after an interrupted recovery.
+
 Dry-run and digest approval are intentional friction. See the
 [schema-2 migration guide](docs/SCHEMA_V2_MIGRATION.md) and the
 [two-service walkthrough](docs/WALKTHROUGH.md).
@@ -62,12 +94,10 @@ maintenance releases and explicit rollback/reactivation for both Gamertan and
 the Sandwich Hime website using one reviewed candidate. See the dated
 [dogfood evidence](docs/DOGFOOD_EVIDENCE.md) for exact scope and limitations.
 
-The additive `v0.2.0-preview.2` candidate keeps that transport and activation
+The additive `v0.2.0-preview.2` release keeps that transport and activation
 contract while adding bounded deployment-event JSONL, routed-origin continuity,
 rollback annotations, and the operational findings recorded through real
-dogfooding. Preview 1 remains unchanged. Preview 2 will not be tagged until one
-identical binary has deployed, rolled back, and reactivated Gamertan, the
-Sandwich Hime website, and Gamertan Observatory.
+dogfooding. Preview 1 remains unchanged.
 Operational friction discovered while applying the same contract to new
 services is tracked separately in the
 [dogfood friction ledger](docs/DOGFOOD_FRICTION.md). The ledger preserves the

RELEASE.md

@@ -32,6 +32,13 @@ Gamertan, the Sandwich Hime website, and Gamertan Observatory before the tag is
 created. EQL is not part of this generic gate; its SQLite/catalog publication
 needs a dedicated adapter rather than arbitrary hooks.
 
+The operation-scoped lease compatibility candidate at private commit
+`789976ce766fd457ca10762540135e4e0e74cfe3` has completed the Gamertan and
+Sandwich Hime deployment, rollback, reactivation, and failure gates. It has not
+completed the Observatory gate because the live service now uses Docker
+Compose, outside the released strategy contract. Do not create the Preview 2
+tag from this candidate until that explicit topology decision is resolved.
+
 `v0.1.0-preview.1` is immutable but withdrawn: its source and module checksums
 are valid, while a fresh `go install` reports the development identity because
 the CLI did not yet adopt the tagged module version from Go build information.

cmd/tend/main.go

@@ -43,6 +43,8 @@ func run() error {
 		return packageCommand(ctx, os.Args[2:])
 	case "deploy":
 		return deployCommand(ctx, os.Args[2:])
+	case "inspect":
+		return inspectCommand(ctx, os.Args[2:])
 	case "push":
 		return pushCommand(ctx, os.Args[2:])
 	case "receive":
@@ -51,6 +53,8 @@ func run() error {
 		return checkServerCommand(os.Args[2:])
 	case "status":
 		return statusCommand(ctx, os.Args[2:])
+	case "reconcile":
+		return reconcileCommand(ctx, os.Args[2:])
 	case "rollback":
 		return rollbackCommand(ctx, os.Args[2:])
 	case "prune":
@@ -62,7 +66,7 @@ func run() error {
 	}
 }
 func usage() error {
-	return errors.New("usage: tend <check|package|push|receive|check-server|deploy|status|rollback|prune|version> [options]")
+	return errors.New("usage: tend <check|package|inspect|push|receive|check-server|deploy|status|reconcile|rollback|prune|version> [options]")
 }
 
 func checkCommand(args []string) error {
@@ -146,6 +150,39 @@ func deployCommand(ctx context.Context, args []string) error {
 	return writeJSON(report)
 }
 
+func inspectCommand(ctx context.Context, args []string) error {
+	set := flag.NewFlagSet("inspect", flag.ContinueOnError)
+	set.SetOutput(os.Stderr)
+	path := set.String("config", "", "target configuration")
+	artifact := set.String("artifact", "", "release archive")
+	sha := set.String("sha256", "", "expected artifact SHA-256")
+	approved := set.String("approve-sha256", "", "separately reviewed artifact SHA-256")
+	if err := set.Parse(args); err != nil {
+		return err
+	}
+	if set.NArg() != 0 {
+		return errors.New("inspect accepts no positional arguments")
+	}
+	cfg, _, err := loadConfig(*path)
+	if err != nil {
+		return err
+	}
+	artifactAbs, err := filepath.Abs(*artifact)
+	if err != nil {
+		return err
+	}
+	report, err := newManager().Deploy(ctx, cfg, deploy.Request{
+		Artifact:       artifactAbs,
+		SHA256:         *sha,
+		ApprovedSHA256: *approved,
+		Activate:       false,
+	})
+	if err != nil {
+		return err
+	}
+	return writeJSON(report)
+}
+
 func pushCommand(ctx context.Context, args []string) error {
 	set := flag.NewFlagSet("push", flag.ContinueOnError)
 	set.SetOutput(os.Stderr)
@@ -249,6 +286,27 @@ func statusCommand(ctx context.Context, args []string) error {
 	}
 	return writeJSON(result)
 }
+func reconcileCommand(ctx context.Context, args []string) error {
+	set := flag.NewFlagSet("reconcile", flag.ContinueOnError)
+	set.SetOutput(os.Stderr)
+	path := set.String("config", "", "absolute target configuration")
+	_ = set.Bool("json", false, "emit the reconciliation report as JSON")
+	if err := set.Parse(args); err != nil {
+		return err
+	}
+	if set.NArg() != 0 {
+		return errors.New("reconcile accepts no positional arguments")
+	}
+	cfg, _, err := loadConfig(*path)
+	if err != nil {
+		return err
+	}
+	report, err := newManager().Reconcile(ctx, cfg)
+	if err != nil {
+		return err
+	}
+	return writeJSON(report)
+}
 func rollbackCommand(ctx context.Context, args []string) error {
 	set := flag.NewFlagSet("rollback", flag.ContinueOnError)
 	set.SetOutput(os.Stderr)

docs/ARCHITECTURE.md

@@ -49,8 +49,12 @@ Blue/green mode points the inactive slot at the new release, restarts and
 probes it, atomically replaces one imported Caddy handler, validates the full
 Caddy configuration, reloads Caddy, and records the prior active slot.
 
-Singleton mode starts the new release in a hardened transient systemd unit on a
-separate loopback address and probes it. Tend then validates and atomically
+Singleton mode starts the target release in a hardened transient systemd unit on a
+separate loopback address and probes it. The unit is named from the service and
+a fresh bounded operation ID; a separate strict candidate-lease file binds that
+unit to the candidate release, address, and start time without changing the
+schema-1 deployment-state contract used by retained recovery binaries. Tend
+then validates and atomically
 routes the imported Caddy handler to that candidate. While the candidate serves
 the canonical origin, Tend changes the current release pointer, restarts and
 probes the installed fixed-address unit, validates Caddy again, and routes back
@@ -69,6 +73,13 @@ over the recorded state. It rechecks local health/readiness and public reachabil
 but deliberately does not apply a future release's content marker to an older
 release whose routes may differ. Pruning preserves both active and previous releases.
 
+`tend reconcile` is a read-only observation boundary. It compares persisted
+state, systemd activity, current/previous release pointers, and exact handler
+file bytes. It does not claim to inspect Caddy's currently loaded in-memory
+configuration, and it never clears or stops a candidate. The report makes
+retained, inactive, ambiguous, and settled states legible before a future
+explicit recovery operation is approved.
+
 ## Evidence boundary
 
 Every attempted activation and explicit rollback emits bounded, versioned JSONL
@@ -76,5 +87,8 @@ events with an operation ID, service, approved artifact digest, source commit,
 release version, phase, slot, elapsed duration, and outcome. Values are
 validated rather than copied from command output. The log contains no
 environment values, arbitrary process output, HTTP bodies, or secret paths.
-Identity, entropy, file, and downstream observability failures are deliberately
-best effort and cannot control Tend's deployment or rollback result.
+Release-identity, event-file, and downstream observability failures are
+deliberately best effort and cannot control Tend's deployment or rollback
+result. A fresh operation identity is operationally required for a singleton
+candidate unit; entropy failure therefore stops either forward activation or
+rollback before a candidate process or traffic change.

docs/DOGFOOD_EVIDENCE.md

@@ -5,6 +5,67 @@ general reliability claim. It preserves each dated campaign and its limitations
 instead of rewriting earlier observations as though later fixes had already
 existed.
 
+## Operation-scoped lease compatibility campaign — August 18, 2026
+
+The candidate-lease compatibility fix completed trusted verification, exact
+candidate reproduction, live activation, rollback, reactivation, and a bounded
+failure injection on the production Linux/systemd/Caddy host. Conventional
+deployment state remained schema 1 throughout. Singleton operation identity
+used the separate adjacent lease introduced by this candidate.
+
+### Assessed Tend candidate
+
+- Private implementation source commit:
+  `789976ce766fd457ca10762540135e4e0e74cfe3`.
+- Version: `v0.2.0-preview.2`.
+- Linux/amd64 binary SHA-256:
+  `d0109bf037e493c7a046defe37818c3c1811806360b99c9a0910213665bd95c5`.
+- Release-candidate archive SHA-256:
+  `2c225e0b9dd0be2d36fda62ab8d0b52cd9b28f9336c60dfb5edf3e715f450f95`.
+- Toolchain: Go 1.26.6, `CGO_ENABLED=0`, `-trimpath`.
+- Trusted verification run 366 and release-candidate run 369 passed for the
+  exact commit. The release workflow built the archive twice with identical
+  bytes and published checksums, build metadata, and an SPDX SBOM.
+- The forge upload action reported a finalized 3.18 MB artifact, but both
+  documented artifact-list endpoints returned an empty result. A clean
+  independent clone therefore built the package twice and reproduced the
+  workflow's exact archive digest before deployment. This is recorded as an
+  artifact-publication limitation, not described as a successful consumer
+  download.
+- The previous installed Tend binary remained retained by checksum before the
+  candidate replaced the active tool. Server policy validation then passed.
+
+### Live maintenance and failure evidence
+
+Gamertan activated archive
+`c17b4db1a4e2fd5406b392ec72195b947272097e4d1bfcec9d700d0889c3a4c6`,
+rolled back to its recorded previous archive, and reactivated the first archive.
+Both blue/green units remained active with zero restarts. Reconciliation was
+settled after every transition.
+
+The Sandwich Hime website performed the same sequence with archive
+`d418f93ced3307fa788f5d2209b5f09f16bceabec4a9698a9beec6a05e439f35`.
+Every successful forward and rollback operation removed its operation-scoped
+candidate lease and transient unit. A final intentional local-smoke failure
+asked the otherwise valid candidate for an impossible marker. The candidate
+failed before Caddy or release-pointer mutation, stopped, removed its lease,
+recorded the failed attempt without changing the active release, and reconciled
+as settled and consistent.
+
+After the campaign, Gamertan, its news and case-study indexes, Sandwich Hime,
+its documentation and tutorial, the Gamertan-mounted Sandwich route, and EQL
+health all returned HTTP 200. Caddy, both Gamertan slots, and the installed
+Sandwich Hime service were active with zero restarts and no warning-or-higher
+journal entries during the campaign.
+
+Observatory is not claimed by this candidate campaign. Its current dogfood
+deployment is a Docker Compose singleton, which remains outside Tend's
+versioned systemd/Caddy strategies. The earlier three-service campaign remains
+valid for its assessed candidate, but the current commit must not be tagged
+until Observatory either returns to a supported topology or a separately
+reviewed Compose strategy completes the same activation, rollback, and failure
+gates.
+
 ## Final Preview 2 code-candidate campaign — August 18, 2026
 
 The final v0.2 Preview 2 implementation candidate completed two explicit

docs/DOGFOOD_FRICTION.md

@@ -1,6 +1,6 @@
 # Dogfood friction ledger
 
-This document records friction observed through August 18, 2026 while using
+This document records friction observed through August 19, 2026 while using
 Tend for real maintenance releases. Friction is evidence about the product: it
 should become either a clearer contract, safer automation, or an explicit
 non-goal. It must not become application-specific shell lore.
@@ -22,6 +22,10 @@ A Tend workflow should make the secure path the short, documented path:
 - first installation, maintenance, activation, rollback, and pruning are
   distinct operations;
 - every mutation has a recorded prior state and a tested restoration path;
+- Tend-owned state is an evidence journal and reconciliation aid, not an
+  exclusive claim over an otherwise conventional systemd/Caddy service;
+- tool-owned transient resources are leased, inspectable, resumable, and safe
+  to reconcile without requiring operators to understand internal names;
 - unrelated services may build and prepare candidates concurrently, while the
   shared Caddy activation boundary remains serialized.
 
@@ -32,14 +36,23 @@ A Tend workflow should make the secure path the short, documented path:
 | F-01 | Workflow mitigation | CI packaging needs proof that the exact commit was pushed. | Packaging verifies the configured remote and fails if Git cannot authenticate. The trusted workflow retains only its job-scoped read-only checkout credential. | Make the proof credential or an authenticated source attestation an explicit Tend input and evidence boundary. |
 | F-02 | Open | Application-owned unit and configuration changes are outside the binary activation transaction. | Operators stage, validate, back up, and restore those files separately. | Add an allowlisted configuration transaction or record and validate exact configuration digests. |
 | F-03 | Open | A singleton candidate may not reproduce the installed unit's arguments and application configuration. | It receives the production environment file and an isolated listen override; activation still fails closed. | Add a bounded application preflight and explicit, validated candidate invocation. |
-| F-04 | Partially resolved | Artifact production, review, approval, transfer, and activation require several identity checks. | v0.2 standardizes the evidence bundle and restricted transfer; the operator still repeats the approved digest intentionally. | Add offline inspection and approval ergonomics without combining build authority and production authority. |
+| F-04 | Partially resolved in development | Artifact production, review, approval, transfer, and activation require several identity checks. | v0.2 standardizes the evidence bundle and restricted transfer; `tend inspect` now exposes the complete non-mutating artifact validation as a named workflow. | Preserve explicit approval while adding digest-bound publication receipts. |
 | F-05 | Partially resolved | Tend maintenance assumes an existing adopted service and current release. | `check-server` validates a prepared host, while first installation remains a separately reviewed operator procedure. | Define an explicit `install` or `adopt` transaction rather than silently treating bootstrap as maintenance. |
 | F-06 | Partially resolved | Binary rollback can be unsafe when service configuration has changed incompatibly. | v0.2 records desired, candidate, active, previous, and last-attempt releases, but external configuration compatibility is operator-owned. | Bind non-secret configuration identities and preflight results to release state. |
 | F-07 | Open | `GOPROXY=off` does not prove that every module metadata lookup is available locally. | Packaging stops before artifact creation when Go cannot resolve the complete pinned module graph. | Separate checksum-verified dependency resolution from a network-disabled, cache-completeness-checked build stage. |
-| F-08 | Open | Packaging an otherwise clean pushed commit from a linked Git worktree fails Go's required VCS-status stamp. | Tend stops before artifact creation; package the same exact commit from a clean standalone clone. | Detect linked worktrees during `check`/`package`, explain the supported source shape, and assess a provenance-preserving worktree build that does not weaken `-buildvcs=true`. |
+| F-08 | Partially resolved in development | Packaging an otherwise clean pushed commit from a linked Git worktree fails Go's required VCS-status stamp. | Tend now detects a linked worktree before remote proof and build work and gives an exact standalone-clone instruction. | Assess provenance-preserving linked-worktree support without weakening `-buildvcs=true`. |
 | F-09 | Resolved in Preview 2 | Restarting a fixed-address singleton briefly exposed Caddy to an unavailable upstream. | Tend now routes the imported handler to the candidate, restarts and proves the installed unit behind that handoff, then routes back while the candidate remains healthy through the activation window. | Preserve the production regression campaign and failure-injection matrix. |
 | F-10 | Resolved in Preview 2 | A hardened root umask could make an extracted application binary executable only by root. | Tend reapplies every validated archive mode explicitly; extraction is tested under umask `0077`. | Preserve the mode and non-root candidate tests. |
 | F-11 | Evidence practice | A single external observer can report common-mode client or network errors as apparent multi-service downtime. | Production campaigns retain server state and use an independent observer before classifying a continuity failure. | Standardize multi-vantage continuity evidence without making an observability dependency part of deployment authority. |
+| F-12 | Partially resolved in development | A deliberately retained singleton handoff candidate could occupy Tend's fixed transient-unit name and block the next valid activation. | Candidates now have operation-scoped unit identities and bounded persisted leases; `reconcile --json` reports release identity, unit, pointer, and handler-file facts without mutation. | Add an explicit, idempotent `resume`/repair operation only after its route-identity and failure-injection model is proven. |
+| F-13 | Open | A configured public-origin probe may resolve to a different deployment after a DNS or edge migration. | Operators separately verify local routed-origin identity and external DNS topology before activation. | Bind probes to expected release and edge identities; classify topology drift instead of treating a body marker as deployment proof. |
+| F-14 | Open | An application can bind durable data identity to an absolute path that a binary-only candidate never exercises. | Preserve the production path and run application-owned validation before traffic moves. | Add a bounded, explicitly read-only application preflight and record which configuration/data identities it assessed. |
+| F-15 | Product direction | Requiring Tend-specific residue and metadata to be perfect can make the facilitator feel like an exclusive deployment owner. | Conventional systemd/Caddy recovery remains authoritative and every manual intervention is captured as evidence. | Make state append-only and migratable, infer observed state safely, and keep Tend removable without making the service obscure or undeployable. |
+| F-16 | Open | A reusable Docker network alias can identify both the live service and a retained handoff candidate, making the routed target ambiguous during activation. | Pin the temporary Caddy handoff to the exact, observed candidate address and restore the reviewed application handler after activation. | Allocate operation-scoped network identities and reject any candidate or handler target that resolves to more than one container or release identity. |
+| F-17 | Open | A CI job can report a successful artifact upload while the forge artifact API exposes no retrievable artifact to the approval/deployment client. | Reproduce and verify the exact pushed commit locally, then compare two packages byte-for-byte before approving the digest; never guess an artifact URL. | Define a digest-bound artifact handoff with an independently readable receipt and fail the workflow unless the approval client can retrieve and inspect the exact uploaded bytes. |
+| F-18 | Open | Tend's current strategies do not model a Docker Compose singleton, so a manual Observatory replacement briefly exposed an unavailable upstream. | The exact image, data backup, rollback image, and health probes were preserved, but Compose replaced the only live container and an external observer saw a bounded `502`/`503` window. | Design an explicit Compose strategy with operation-scoped candidates, unambiguous routing, durable-data preflight, activation continuity, and automatic rollback; do not add arbitrary container hooks to the systemd strategies. |
+| F-19 | Open | A successful application schema migration can make the previous binary unreadable even when its image and service definition are intact. | Preserve verified database backups and prefer completing the proven forward activation; do not execute a binary-only rollback after a forward-only migration. | Make applications declare schema compatibility and an explicit data restoration or forward-recovery plan before Tend offers automatic rollback. |
+| F-20 | Open | A stateful migration can require bounded temporary scratch space that a stateless binary candidate never exercises. | Run the exact candidate against a copied production data set under its proposed resource limits; record the reviewed scratch budget in the service definition. | Bind resource/configuration digests to the candidate and add an application-owned stateful preflight contract without arbitrary hooks. |
 
 ## F-01: pushed-commit proof in CI
 
@@ -307,20 +320,335 @@ is closed. A Linux regression test sets umask `0077`, extracts the release, and
 requires the installed binary to remain executable by the service identity.
 The successful maintenance campaign used that corrected Tend binary.
 
+## F-12: retained-candidate reconciliation
+
+### Observation
+
+An Observatory activation failure intentionally left its proven handoff
+candidate routed and running for operator recovery. A later push transferred
+and validated a new content-addressed artifact, then stopped before candidate
+startup because systemd still had Tend's fixed candidate unit loaded:
+
+`Unit observatory-tend-candidate.service was already loaded or has a fragment file.`
+
+The artifact, application, and host were valid. The collision was Tend-owned
+residue from its own safe fallback behavior. Recovery required starting the
+same stateless fallback under an independently named hardened unit, proving it,
+routing Caddy to it, and only then stopping the old candidate and confirming
+its port and unit name were free. No accepted application state was lost, but
+the operator had to understand Tend's internal unit convention.
+
+### Implemented foundation
+
+- Transient candidate units are named by service plus the first 12 hexadecimal
+  characters of a fresh 128-bit operation identity.
+- Conventional deployment state remains schema 1 so the retained v0.1 binary
+  can still read active and previous release identities. Singleton operations
+  write a separate strict, adjacent candidate-lease file containing the
+  operation, release, unit, address, and start time.
+- `tend reconcile --json` reports persisted state, installed/candidate unit
+  activity, release pointers, and whether the exact handler file matches the
+  installed or candidate upstream. It explicitly distinguishes handler file
+  bytes from Caddy's loaded runtime configuration and performs no mutation.
+- A retained forward-activation or rollback candidate lease survives an
+  incomplete recovery instead of being erased by a generic failed-attempt path.
+  Older binaries ignore the additive lease file, so operators must reconcile
+  before downgrading or attempting another activation.
+
+### Remaining options to assess
+
+- Extend the candidate lease with separately observed health and loaded-route
+  evidence rather than inferring either from a successful file write.
+- Add an explicit `tend resume` operation that distinguishes active, routed,
+  rollback, abandoned, and unknown candidates without mutating by default.
+- Permit automatic cleanup only after Tend proves that Caddy, current/previous
+  pointers, and the installed unit do not reference the candidate and that a
+  healthy route remains.
+- Make a repeated activation of the same approved digest idempotently resume
+  the recorded operation instead of restaging or colliding with itself.
+
+Never resolve the collision by blindly stopping the loaded unit. A retained
+candidate may be the only healthy route after a failed singleton activation.
+
+## F-13: public-origin topology and release identity
+
+### Observation
+
+During the same recovery, the public DNS record had already moved to a new
+edge while the old host's Tend policy still named the canonical HTTPS origin
+as its post-activation smoke target. A request from the old host would therefore
+test a different deployment. It could fail even when the old host was healthy,
+or pass against a matching marker served by the new host. Neither result proves
+the release that Tend just activated.
+
+### Options to assess
+
+- Separate a local routed-origin probe—Caddy with the canonical Host/SNI on the
+  deployment host—from an external DNS-origin observation.
+- Bind local success to a non-secret application release identity such as the
+  approved artifact digest, commit, and version, not only a human page marker.
+- Record the expected public edge identity or resolved address set at approval
+  time. If it changes, classify the result as topology drift and require an
+  explicit migration decision instead of reporting an application failure.
+- Allow independent external observers as additional evidence, but never let
+  a response from an unidentified deployment authorize activation.
+
+Public reachability remains valuable; it must be evidence about the intended
+deployment rather than merely evidence that the hostname answered.
+
+## F-14: application data-path and preflight fidelity
+
+### Observation
+
+An exact, checksummed Observatory data copy was mounted at a different absolute
+path in a container. Raw objects and durable SQLite databases were byte
+identical, but the application catalogue intentionally compared stored segment
+paths with filesystem-derived identities and failed closed. Preserving the
+original in-container data path made the same Preview 15 binary ready in four
+seconds with zero restarts and bounded memory.
+
+This was an application portability constraint, not a reason for Tend to
+rewrite database state. It also demonstrates the limit of a binary-only
+stateless candidate: executable health cannot prove compatibility with the
+real configuration, credentials, mounts, or durable data.
+
+SQLite `-wal`, `-shm`, and process-lock files also changed during ordinary
+open/close behavior while raw segments and durable databases did not. Migration
+evidence should distinguish durable application truth from ephemeral runtime
+coordination files.
+
+### Options to assess
+
+- Support a fixed, bounded application-owned preflight argument vector with an
+  explicit non-mutating contract, timeout, output limit, and no shell.
+- Record the exact non-secret configuration digest, data-root identity, mount
+  identity, and checks performed alongside binary candidate evidence.
+- Let applications define their durable migration evidence set; Tend should
+  transport and report those digests but must not infer database semantics or
+  edit state.
+- Require rollback compatibility to be assessed against the same configuration
+  and data identities before an older binary is called safe.
+
+## F-15: facilitator rather than owner
+
+Tend's strict boundaries are valuable where authority changes hands: source
+provenance, artifact digest approval, restricted transport, secret references,
+path validation, traffic movement, and rollback. Strictness becomes harmful
+when Tend's internal names or stale metadata are treated as application
+requirements that an authorized maintainer must reverse-engineer.
+
+The target model is less invasive:
+
+- systemd units, Caddy handlers, environment files, release directories, and
+  application checks remain conventional and independently operable;
+- Tend records an append-only migration/deployment journal and derives an
+  observed state before proposing mutation;
+- schema migrations preserve old records and explain compatibility rather than
+  silently rejecting safe, recognizable state;
+- `check`, `status`, and `reconcile` show facts and proposed repairs without
+  mutation; approval is required for artifact selection and traffic movement,
+  not for Tend implementation trivia;
+- installation and adoption are explicit, while uninstalling Tend leaves an
+  understandable, runnable service and complete evidence trail.
+
+This does not relax hostile-input defenses. It moves strictness to the trust
+boundary and makes recovery humane for the authenticated operator.
+
+## F-16: ambiguous container-network identity
+
+### Observation
+
+During the Observatory Preview 16 activation, the retained stateless handoff
+container and the live Compose service both answered to the Docker network
+alias `observatory`. A Caddy target such as `observatory:8093` could therefore
+resolve to either release. Removing or restarting one container could also
+change which release received traffic. The application and both containers
+were healthy; the ambiguity existed solely in deployment identity.
+
+The activation used a separately validated Caddy fragment pinned to the exact
+candidate address, proved its release marker before traffic moved, replaced
+the live service, and then restored the reviewed application handler. No
+ambiguous alias was used for the handoff.
+
+### Options to assess
+
+- Give every candidate an operation-scoped container name, network alias, and
+  lease that bind directly to its artifact digest and expected address.
+- Resolve and inspect a proposed upstream immediately before Caddy validation;
+  reject zero, multiple, or identity-mismatched targets.
+- Prefer a dedicated candidate network or an address supplied by the container
+  runtime over a stable alias shared with the live service.
+- Record the exact routed target and release proof in activation state, then
+  verify that the restored production handler identifies the active release.
+
+Do not treat a healthy response from an ambiguous service name as release
+proof. Availability and deployment identity are separate properties.
+
+## F-17: CI artifact publication is not artifact availability
+
+### Observation
+
+The trusted Observatory release-candidate workflow completed its two builds,
+byte comparison, checksums, manifest, and SBOM, and its upload action reported
+success. The forge artifact API subsequently returned no artifact for that
+run. The deployment client therefore had no independently discoverable object
+to download and inspect. Guessing a web-interface route or treating a green
+upload step as possession of the bytes would have weakened the build-approve-
+deploy boundary.
+
+The release was instead reproduced twice from a fresh, clean clone of the
+exact pushed commit with the pinned toolchain. The packages compared
+byte-for-byte, their manifest, checksums, SBOM, version, commit, and tree were
+verified, and the approved digest was recorded. This preserved release
+identity, but it is an operator workaround rather than the desired CI handoff.
+
+### Options to assess
+
+- Require the publisher to return a versioned receipt containing forge, run,
+  artifact identifier, size, digest, retention, and retrieval endpoint.
+- Add a separate read-only verification step that downloads the artifact using
+  the same interface available to the approval client and reruns `tend
+  inspect` before the workflow is considered publish-complete.
+- Support a content-addressed, append-only artifact store whose object name is
+  the approved SHA-256 and whose credentials remain separate from production.
+- Let `tend push` accept only a locally present artifact plus an optional
+  verified publication receipt; never allow a successful CI status alone to
+  select bytes for deployment.
+
+Artifact availability must be proven from the consumer side. A successful
+upload log is evidence of an attempted publication, not evidence that the
+approved bytes can be recovered.
+
+The same failure repeated for Tend release-candidate run 369: the pinned job
+successfully built identical archives, recorded digest
+`2c225e0b9dd0be2d36fda62ab8d0b52cd9b28f9336c60dfb5edf3e715f450f95`,
+and finalized a 3.18 MB upload, while both repository-wide and run-scoped REST
+artifact listings returned no objects. An independent clean build reproduced
+the exact digest before dogfooding. This confirms the problem is a reusable
+forge-to-approval gap rather than an Observatory-specific packaging defect.
+
+## F-18: Docker Compose is not a systemd singleton
+
+### Observation
+
+Observatory Preview 18 was packaged reproducibly and its exact scratch image
+passed a constrained loopback candidate check. The production service on
+cliff-mads is a Docker Compose singleton, while Tend's supported strategies are
+systemd/Caddy blue-green and systemd singleton-candidate. Tend was therefore
+not used to pretend that an unsupported runtime had received a complete Tend
+activation proof.
+
+The manual Compose replacement retained the former image and online database
+backups and completed health, readiness, route, projection, agent, and log
+checks. An independent public observer nevertheless recorded `200`, then
+`502`/`503`, then `200` across an approximately 31.6-second replacement and
+startup window. No application restart loop or accepted-data loss was
+observed, but this is not continuous delivery.
+
+Preview.19 strengthened this finding. The exact candidate passed direct health
+and readiness, but an activation script treated the first transient routed
+`503` as final and attempted rollback before the proxy path had settled. The
+previous binary then correctly rejected the newly migrated control schema and
+entered a fail-closed restart loop. The operator recovered with the already
+proven forward candidate while the agent remained paused. This was a bounded,
+observable failure with intact backups, but it demonstrates that proxy
+settling and data-schema rollback are different gates and cannot share one
+generic failure branch.
+
+### Options to assess
+
+- Add a distinct, versioned Docker Compose strategy rather than arbitrary
+  command hooks or hidden container behavior inside existing strategies.
+- Allocate an operation-scoped candidate container and network identity that
+  cannot collide with the production alias.
+- Validate the exact image digest, non-secret Compose/configuration digest,
+  mounts, durable data identity, and application-owned read-only preflight
+  before moving traffic.
+- Route Caddy to the proven candidate, replace or promote the production
+  service while the candidate remains healthy, then restore the reviewed live
+  handler only after the final container proves its release identity.
+- Restore the prior handler and retained image automatically when any
+  activation-window probe fails; keep data rollback an explicit
+  application-owned decision.
+
+This strategy must remain optional. Tend should facilitate a conventional
+Compose service without requiring Tend-only container labels, aliases, or
+state for ordinary operator recovery.
+
+## F-19: binary rollback is not data rollback
+
+### Observation
+
+Observatory Preview.19 migrated its live control database from the schema
+understood by Preview.18 to schema 11 before activation. When a premature
+public-origin failure triggered binary rollback, Preview.18 rejected the new
+schema rather than interpreting unknown state. That fail-closed behavior was
+correct, but Tend-like orchestration cannot infer from two binary identities
+whether their durable schemas are mutually readable.
+
+The exact pre-migration control and projection databases had already been
+copied, integrity-checked, mode-restricted, and SHA-256 verified. The new
+candidate had also passed the migration on an isolated copy. Because the
+migration was forward-valid and the old agent was paused, completing the
+Preview.19 activation preserved more verified state than restoring the backup.
+
+### Options to assess
+
+- Let an application declare a versioned, bounded compatibility statement for
+  current-to-candidate and candidate-to-previous data access.
+- Treat migration completion as a journalled phase after which automatic
+  binary rollback is permitted only when backward readability was explicitly
+  proven.
+- Support an application-owned, separately approved data-restoration plan;
+  never infer one from release pointers or run an arbitrary rollback hook.
+- Keep verified backups and the proven forward candidate until the migration
+  soak closes, even when the previous binary remains retained.
+
+## F-20: stateful preflight needs its real resource envelope
+
+### Observation
+
+The Preview.19 stateless candidate and ordinary tests passed, but building a
+presence-only SQLite index over a copied production projection failed with
+`database or disk is full` under the service's 64 MiB `/tmp` tmpfs. The exact
+same candidate and data passed with a 512 MiB tmpfs and drained all pending raw
+segments. The projection database was healthy; the one-time index sort needed
+more bounded scratch space than steady-state operation.
+
+### Options to assess
+
+- Record the non-secret service configuration digest and resource envelope
+  beside the artifact digest.
+- Permit a strict application-owned preflight command selected from a reviewed
+  schema, never an arbitrary shell string.
+- Exercise migrations against a copied or snapshot-backed production data set
+  under the candidate's exact CPU, memory, temporary-storage, filesystem, and
+  credential boundaries.
+- Report resource exhaustion distinctly from corrupt data, failed health, or
+  incompatible schema so recovery guidance remains accurate.
+
 ## Prioritization
 
 The recommended implementation order is:
 
-1. final production proof of the singleton traffic handoff;
-2. a checksum-verified resolver and network-disabled package contract;
-3. an early linked-worktree diagnostic and a provenance-preserving support
-   decision;
-4. `tend inspect` and a standardized CI artifact/approval contract;
-5. exact release plus configuration identity in status and state;
-6. a bounded application preflight contract;
-7. restricted transfer and receive with host policy;
-8. explicit adoption for existing services;
-9. managed configuration only after its restoration and failure-injection
+1. operation-scoped candidate leases plus explicit resume/repair built on the
+   new read-only reconciliation report;
+2. migration compatibility and stateful-resource preflight contracts;
+3. a bounded Docker Compose strategy with operation-scoped container/network
+   identities and unambiguous upstream
+   resolution and release proof;
+4. release-bound local routed-origin proof separated from external DNS proof;
+5. a bounded application preflight and configuration/data identity record;
+6. a consumer-verifiable, digest-bound CI artifact publication receipt;
+7. final production proof of the singleton traffic handoff;
+8. a checksum-verified resolver and network-disabled package contract;
+9. a provenance-preserving linked-worktree support decision after the new
+   early diagnostic;
+10. a standardized CI artifact/approval contract building on `tend inspect`;
+11. exact release plus configuration identity in status and state;
+12. restricted transfer and receive with host policy;
+13. explicit adoption for existing services;
+14. managed configuration only after its restoration and failure-injection
    model is as strong as binary activation.
 
 Friction entries should be updated with the implementing version, tests, and

docs/SCHEMA_V2_MIGRATION.md

@@ -1,8 +1,17 @@
 # Schema 1 to schema 2
 
-Schema 2 is intentionally not loaded as schema 1. Keep the installed v0.1 Tend
-binary available until the first schema-2 activation and rollback have both
-been exercised.
+Configuration schema 2 and deployment state are separate versioned contracts.
+The service configuration moves to schema 2, while conventional deployment
+state deliberately remains schema 1 so the retained v0.1 binary can still read
+active and previous release identities during recovery.
+
+Singleton operations write an adjacent, strict
+`<state-file>.candidate-lease.json` file containing the operation, release,
+unit, address, and start time. Older binaries ignore that additive file. Do not
+downgrade or start another deployment while a lease is present: first use the
+new binary's `tend reconcile --json` report to establish which process and
+route are healthy. Tend does not silently invent a lease for a legacy
+interrupted operation.
 
 1. Move each configuration to `/etc/tend/services/<service>.json`.
 2. Set `schema_version` to `2`.

docs/WALKTHROUGH.md

@@ -24,6 +24,10 @@ binary at `/usr/local/bin/tend`; it does not need Git or Go.
 4. Pin the server host key in a dedicated client file. Do not accept a new key
    interactively during deployment.
 5. Run `sudo tend check-server` and inspect the allowlisted service names.
+6. Run `sudo tend reconcile --config /etc/tend/services/example-site.json
+   --json` before the first maintenance release. A settled report is expected;
+   any retained candidate or unknown handler must be understood before traffic
+   changes. The command is read-only.
 
 ## Build and approve
 
@@ -35,6 +39,23 @@ The maintainer reads the candidate report and copies the exact approved digest
 into the deployment command. Tend refuses a digest that is merely inferred from
 the local file or differs from the produced value.
 
+Inspect the exact downloaded bytes before transfer. This is a complete,
+read-only artifact validation and does not stage a candidate:
+
+```text
+tend inspect --config /review/example-site.json \
+  --artifact /approved/example-site.tar.gz \
+  --sha256 <produced> --approve-sha256 <reviewed>
+```
+
+On the host, compare Tend's journal with the conventional service state before
+and after activation. Reconciliation reports facts and never stops a unit,
+rewrites a pointer, or changes Caddy:
+
+```text
+sudo tend reconcile --config /etc/tend/services/example-site.json
+```
+
 ```text
 tend push --target tend-deploy@server.example \
   --known-hosts /secure/tend_known_hosts \
@@ -66,5 +87,12 @@ services share Caddy. Tend does not stop the other application.
   units, pointers, and public origin did not change.
 - Interrupt a transfer: no release becomes active and the incomplete incoming
   file is removed when the receiver exits.
+- Interrupt singleton recovery after the candidate is proven. `tend reconcile
+  --json` must name the operation-scoped candidate unit, report whether it is
+  active and whether the handler file targets it, and perform no stop, restart,
+  reload, pointer, or state mutation.
 
 After the soak, prune per service. Active and previous releases remain protected.
+If activation fails, run `reconcile` before manual recovery so the retained
+candidate, route, release pointers, and journal disagreement are preserved in
+one bounded report.

internal/deploy/deploy.go

@@ -25,12 +25,13 @@ type Request struct {
 	Activate       bool
 }
 type Report struct {
-	Validated       bool   `json:"validated"`
-	Mutation        string `json:"mutation"`
-	Release         string `json:"release,omitempty"`
-	ActiveRelease   string `json:"active_release,omitempty"`
-	PreviousRelease string `json:"previous_release,omitempty"`
-	EventWarnings   int    `json:"event_warnings,omitempty"`
+	Validated           bool   `json:"validated"`
+	Mutation            string `json:"mutation"`
+	Release             string `json:"release,omitempty"`
+	ActiveRelease       string `json:"active_release,omitempty"`
+	PreviousRelease     string `json:"previous_release,omitempty"`
+	EventWarnings       int    `json:"event_warnings,omitempty"`
+	LeaseCleanupPending bool   `json:"lease_cleanup_pending,omitempty"`
 }
 type Status struct {
 	State            *state.Record   `json:"state,omitempty"`
@@ -38,6 +39,11 @@ type Status struct {
 	StateInitialized bool            `json:"state_initialized"`
 }
 
+type retainedCandidateError struct{ cause error }
+
+func (e *retainedCandidateError) Error() string { return e.cause.Error() }
+func (e *retainedCandidateError) Unwrap() error { return e.cause }
+
 type Manager struct {
 	Operator     Operator
 	Now          func() time.Time
@@ -86,6 +92,9 @@ func (m Manager) Deploy(ctx context.Context, cfg config.Config, request Request)
 			operationID = ""
 		}
 	}
+	if cfg.Deployment.Strategy == "singleton_candidate" && operationID == "" {
+		return Report{}, errors.New("singleton activation requires a fresh operation identity")
+	}
 	emit := func(phase, slot, outcome string) {
 		if m.AppendEvent == nil || identityErr != nil || operationID == "" {
 			return
@@ -99,6 +108,17 @@ func (m Manager) Deploy(ctx context.Context, cfg config.Config, request Request)
 	if err != nil {
 		return Report{}, err
 	}
+	leasePath := state.CandidateLeasePath(cfg.Deployment.StateFile)
+	var candidateLease state.CandidateLease
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		_, exists, leaseErr := loadCandidateLease(cfg)
+		if leaseErr != nil {
+			return Report{}, leaseErr
+		}
+		if record.CandidateRelease != "" || exists {
+			return Report{}, errors.New("singleton candidate lease is unresolved; run tend reconcile --json before another activation")
+		}
+	}
 	attemptAt := m.Now().UTC().Format(time.RFC3339)
 	record.DesiredRelease = release
 	record.CandidateRelease = release
@@ -106,24 +126,52 @@ func (m Manager) Deploy(ctx context.Context, cfg config.Config, request Request)
 	record.LastAttemptOutcome = "running"
 	record.LastAttemptAt = attemptAt
 	record.UpdatedAt = attemptAt
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		candidateUnit, unitErr := singletonCandidateUnit(cfg.Service.Name, operationID)
+		if unitErr != nil {
+			return Report{}, unitErr
+		}
+		candidateLease = state.CandidateLease{SchemaVersion: state.CandidateLeaseSchemaVersion, Service: cfg.Service.Name, OperationID: operationID, Release: release, Unit: candidateUnit, Address: cfg.Deployment.Singleton.CandidateAddress, StartedAt: attemptAt}
+	}
 	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
 		return Report{}, err
 	}
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		if err := state.StoreCandidateLease(leasePath, cfg.Deployment.Root, candidateLease); err != nil {
+			failed := record
+			clearCandidateLease(&failed)
+			failed.LastAttemptOutcome = "failed"
+			failed.UpdatedAt = m.Now().UTC().Format(time.RFC3339)
+			if storeErr := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, failed); storeErr != nil {
+				return Report{}, errors.Join(err, storeErr)
+			}
+			return Report{}, err
+		}
+	}
 	emit("candidate", inactiveSlot(cfg, record), "running")
 	switch cfg.Deployment.Strategy {
 	case "blue_green":
 		err = m.deployBlueGreen(ctx, cfg, record, release)
 	case "singleton_candidate":
-		err = m.deploySingleton(ctx, cfg, record, release)
+		err = m.deploySingleton(ctx, cfg, record, release, candidateLease.Unit)
 	default:
 		err = errors.New("unsupported strategy")
 	}
 	if err != nil {
 		failed := record
-		failed.CandidateRelease = ""
+		var retained *retainedCandidateError
+		if !errors.As(err, &retained) {
+			if cleanupErr := state.RemoveCandidateLease(leasePath); cleanupErr != nil {
+				err = errors.Join(err, fmt.Errorf("candidate lease cleanup failed: %w", cleanupErr))
+			} else {
+				clearCandidateLease(&failed)
+			}
+		}
 		failed.LastAttemptOutcome = "failed"
 		failed.UpdatedAt = m.Now().UTC().Format(time.RFC3339)
-		_ = state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, failed)
+		if storeErr := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, failed); storeErr != nil {
+			err = errors.Join(err, storeErr)
+		}
 		emit("activation", inactiveSlot(cfg, record), "failed")
 		return Report{EventWarnings: eventWarnings}, err
 	}
@@ -132,7 +180,40 @@ func (m Manager) Deploy(ctx context.Context, cfg config.Config, request Request)
 	if err != nil {
 		return Report{}, err
 	}
-	return Report{Validated: true, Mutation: "activated", Release: release, ActiveRelease: updated.ActiveRelease, PreviousRelease: updated.PreviousRelease, EventWarnings: eventWarnings}, nil
+	report := Report{Validated: true, Mutation: "activated", Release: release, ActiveRelease: updated.ActiveRelease, PreviousRelease: updated.PreviousRelease, EventWarnings: eventWarnings}
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		if cleanupErr := state.RemoveCandidateLease(leasePath); cleanupErr != nil {
+			report.LeaseCleanupPending = true
+		}
+	}
+	return report, nil
+}
+
+func singletonCandidateUnit(service, operationID string) (string, error) {
+	if len(operationID) != 32 {
+		return "", errors.New("candidate operation identity is invalid")
+	}
+	for _, character := range operationID {
+		if !strings.ContainsRune("0123456789abcdef", character) {
+			return "", errors.New("candidate operation identity is invalid")
+		}
+	}
+	return service + "-tend-candidate-" + operationID[:12] + ".service", nil
+}
+
+func clearCandidateLease(record *state.Record) {
+	record.CandidateRelease = ""
+}
+
+func loadCandidateLease(cfg config.Config) (state.CandidateLease, bool, error) {
+	lease, err := state.LoadCandidateLease(state.CandidateLeasePath(cfg.Deployment.StateFile), cfg.Deployment.Root, cfg.Service.Name)
+	if err == nil {
+		return lease, true, nil
+	}
+	if os.IsNotExist(err) {
+		return state.CandidateLease{}, false, nil
+	}
+	return state.CandidateLease{}, false, fmt.Errorf("load singleton candidate lease: %w", err)
 }
 
 type releaseIdentity struct {
@@ -194,13 +275,13 @@ func loadOrBootstrap(cfg config.Config, now time.Time) (state.Record, error) {
 		if err != nil {
 			return state.Record{}, fmt.Errorf("bootstrap active slot: %w", err)
 		}
-		return state.Record{SchemaVersion: 1, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: slot, ActiveRelease: release, UpdatedAt: now.UTC().Format(time.RFC3339)}, nil
+		return state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: slot, ActiveRelease: release, UpdatedAt: now.UTC().Format(time.RFC3339)}, nil
 	case "singleton_candidate":
 		release, err := resolveReleaseLink(cfg.Deployment.Root, cfg.Deployment.Singleton.CurrentLink)
 		if err != nil {
 			return state.Record{}, fmt.Errorf("bootstrap singleton: %w", err)
 		}
-		return state.Record{SchemaVersion: 1, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, UpdatedAt: now.UTC().Format(time.RFC3339)}, nil
+		return state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, UpdatedAt: now.UTC().Format(time.RFC3339)}, nil
 	}
 	return state.Record{}, errors.New("unsupported strategy")
 }
@@ -275,18 +356,18 @@ func (m Manager) deployBlueGreen(ctx context.Context, cfg config.Config, record
 	if err = m.continuityWindow(ctx, cfg, previous.Address, true); err != nil {
 		return fmt.Errorf("activation continuity failed: %w", err)
 	}
-	next := state.Record{SchemaVersion: 1, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: inactive, ActiveRelease: release, PreviousSlot: record.ActiveSlot, PreviousRelease: record.ActiveRelease, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: record.LastAttemptAt, UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
+	next := state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: inactive, ActiveRelease: release, PreviousSlot: record.ActiveSlot, PreviousRelease: record.ActiveRelease, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: record.LastAttemptAt, UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
 	if err = state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, next); err != nil {
 		return err
 	}
 	return nil
 }
 
-func (m Manager) deploySingleton(ctx context.Context, cfg config.Config, record state.Record, release string) (err error) {
-	if err = m.activateSingletonRelease(ctx, cfg, release, true); err != nil {
+func (m Manager) deploySingleton(ctx context.Context, cfg config.Config, record state.Record, release, candidateUnit string) (err error) {
+	if err = m.activateSingletonRelease(ctx, cfg, release, candidateUnit, true); err != nil {
 		return err
 	}
-	next := state.Record{SchemaVersion: 1, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, PreviousSlot: "singleton", PreviousRelease: record.ActiveRelease, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: record.LastAttemptAt, UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
+	next := state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, PreviousSlot: "singleton", PreviousRelease: record.ActiveRelease, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: record.LastAttemptAt, UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
 	if err = state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, next); err != nil {
 		return err
 	}
@@ -306,12 +387,54 @@ func (m Manager) Rollback(ctx context.Context, cfg config.Config) (state.Record,
 	if record.PreviousRelease == "" {
 		return state.Record{}, errors.New("no previous release is recorded")
 	}
+	leasePath := state.CandidateLeasePath(cfg.Deployment.StateFile)
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		_, exists, leaseErr := loadCandidateLease(cfg)
+		if leaseErr != nil {
+			return state.Record{}, leaseErr
+		}
+		if record.CandidateRelease != "" || exists {
+			return state.Record{}, errors.New("singleton candidate lease is unresolved; run tend reconcile --json before rollback")
+		}
+	}
 	started := m.Now()
 	identity, identityErr := m.ReadIdentity(record.PreviousRelease)
 	digest, digestErr := releaseDigest(record.PreviousRelease)
 	operationID := ""
 	if m.OperationID != nil {
-		operationID, _ = m.OperationID()
+		operationID, err = m.OperationID()
+	}
+	if cfg.Deployment.Strategy == "singleton_candidate" && (err != nil || operationID == "") {
+		return state.Record{}, errors.New("singleton rollback requires a fresh operation identity")
+	}
+	candidateUnit := ""
+	rollbackAttempt := record
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		candidateUnit, err = singletonCandidateUnit(cfg.Service.Name, operationID)
+		if err != nil {
+			return state.Record{}, err
+		}
+		attemptAt := m.Now().UTC().Format(time.RFC3339)
+		rollbackAttempt.DesiredRelease = record.PreviousRelease
+		rollbackAttempt.CandidateRelease = record.PreviousRelease
+		rollbackAttempt.LastAttemptRelease = record.PreviousRelease
+		rollbackAttempt.LastAttemptOutcome = "running"
+		rollbackAttempt.LastAttemptAt = attemptAt
+		rollbackAttempt.UpdatedAt = attemptAt
+		if err = state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, rollbackAttempt); err != nil {
+			return state.Record{}, err
+		}
+		lease := state.CandidateLease{SchemaVersion: state.CandidateLeaseSchemaVersion, Service: cfg.Service.Name, OperationID: operationID, Release: record.PreviousRelease, Unit: candidateUnit, Address: cfg.Deployment.Singleton.CandidateAddress, StartedAt: attemptAt}
+		if err = state.StoreCandidateLease(leasePath, cfg.Deployment.Root, lease); err != nil {
+			failed := rollbackAttempt
+			clearCandidateLease(&failed)
+			failed.LastAttemptOutcome = "failed"
+			failed.UpdatedAt = m.Now().UTC().Format(time.RFC3339)
+			if storeErr := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, failed); storeErr != nil {
+				return state.Record{}, errors.Join(err, storeErr)
+			}
+			return state.Record{}, err
+		}
 	}
 	emit := func(outcome string) {
 		if m.AppendEvent == nil || identityErr != nil || digestErr != nil || operationID == "" {
@@ -325,16 +448,41 @@ func (m Manager) Rollback(ctx context.Context, cfg config.Config) (state.Record,
 	case "blue_green":
 		err = m.rollbackBlueGreen(ctx, cfg, record)
 	case "singleton_candidate":
-		err = m.rollbackSingleton(ctx, cfg, record)
+		err = m.rollbackSingleton(ctx, cfg, record, candidateUnit)
 	default:
 		err = errors.New("unsupported strategy")
 	}
 	if err != nil {
+		if cfg.Deployment.Strategy == "singleton_candidate" {
+			failed := rollbackAttempt
+			var retained *retainedCandidateError
+			if !errors.As(err, &retained) {
+				if cleanupErr := state.RemoveCandidateLease(leasePath); cleanupErr != nil {
+					err = errors.Join(err, fmt.Errorf("candidate lease cleanup failed: %w", cleanupErr))
+				} else {
+					clearCandidateLease(&failed)
+				}
+			}
+			failed.LastAttemptOutcome = "failed"
+			failed.UpdatedAt = m.Now().UTC().Format(time.RFC3339)
+			if storeErr := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, failed); storeErr != nil {
+				err = errors.Join(err, storeErr)
+			}
+		}
 		emit("failed")
 		return state.Record{}, err
 	}
 	emit("succeeded")
-	return state.Load(cfg.Deployment.StateFile, cfg.Deployment.Root, cfg.Deployment.Strategy)
+	updated, loadErr := state.Load(cfg.Deployment.StateFile, cfg.Deployment.Root, cfg.Deployment.Strategy)
+	if loadErr != nil {
+		return state.Record{}, loadErr
+	}
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		if cleanupErr := state.RemoveCandidateLease(leasePath); cleanupErr != nil {
+			return updated, fmt.Errorf("rollback succeeded but candidate lease cleanup is pending; run tend reconcile --json: %w", cleanupErr)
+		}
+	}
+	return updated, nil
 }
 
 func releaseDigest(release string) (string, error) {
@@ -398,14 +546,14 @@ func (m Manager) rollbackBlueGreen(ctx context.Context, cfg config.Config, recor
 	if err = m.probePublic(ctx, cfg, false); err != nil {
 		return err
 	}
-	next := state.Record{SchemaVersion: 1, Strategy: record.Strategy, DesiredRelease: record.PreviousRelease, ActiveSlot: record.PreviousSlot, ActiveRelease: record.PreviousRelease, PreviousSlot: record.ActiveSlot, PreviousRelease: record.ActiveRelease, LastAttemptRelease: record.PreviousRelease, LastAttemptOutcome: "rolled_back", LastAttemptAt: m.Now().UTC().Format(time.RFC3339), UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
+	next := state.Record{SchemaVersion: state.SchemaVersion, Strategy: record.Strategy, DesiredRelease: record.PreviousRelease, ActiveSlot: record.PreviousSlot, ActiveRelease: record.PreviousRelease, PreviousSlot: record.ActiveSlot, PreviousRelease: record.ActiveRelease, LastAttemptRelease: record.PreviousRelease, LastAttemptOutcome: "rolled_back", LastAttemptAt: m.Now().UTC().Format(time.RFC3339), UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
 	return state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, next)
 }
-func (m Manager) rollbackSingleton(ctx context.Context, cfg config.Config, record state.Record) (err error) {
-	if err = m.activateSingletonRelease(ctx, cfg, record.PreviousRelease, false); err != nil {
+func (m Manager) rollbackSingleton(ctx context.Context, cfg config.Config, record state.Record, candidateUnit string) (err error) {
+	if err = m.activateSingletonRelease(ctx, cfg, record.PreviousRelease, candidateUnit, false); err != nil {
 		return err
 	}
-	next := state.Record{SchemaVersion: 1, Strategy: record.Strategy, DesiredRelease: record.PreviousRelease, ActiveSlot: "singleton", ActiveRelease: record.PreviousRelease, PreviousSlot: "singleton", PreviousRelease: record.ActiveRelease, LastAttemptRelease: record.PreviousRelease, LastAttemptOutcome: "rolled_back", LastAttemptAt: m.Now().UTC().Format(time.RFC3339), UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
+	next := state.Record{SchemaVersion: state.SchemaVersion, Strategy: record.Strategy, DesiredRelease: record.PreviousRelease, ActiveSlot: "singleton", ActiveRelease: record.PreviousRelease, PreviousSlot: "singleton", PreviousRelease: record.ActiveRelease, LastAttemptRelease: record.PreviousRelease, LastAttemptOutcome: "rolled_back", LastAttemptAt: m.Now().UTC().Format(time.RFC3339), UpdatedAt: m.Now().UTC().Format(time.RFC3339)}
 	return state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, next)
 }
 
@@ -413,9 +561,8 @@ func (m Manager) rollbackSingleton(ctx context.Context, cfg config.Config, recor
 // installed fixed-address unit changes release. The transient candidate first
 // receives traffic, remains healthy through the handoff, and is stopped only
 // after Caddy points back to the verified installed unit.
-func (m Manager) activateSingletonRelease(ctx context.Context, cfg config.Config, release string, checkMarkers bool) (err error) {
+func (m Manager) activateSingletonRelease(ctx context.Context, cfg config.Config, release, candidateUnit string, checkMarkers bool) (err error) {
 	single := *cfg.Deployment.Singleton
-	candidateUnit := cfg.Service.Name + "-tend-candidate.service"
 	env := map[string]string{single.ListenEnv: single.CandidateAddress}
 	binary := filepath.Join(release, cfg.Build.Binary)
 	if err = m.Operator.StartCandidate(ctx, candidateUnit, binary, cfg.Service.EnvironmentFile, env); err != nil {
@@ -484,7 +631,7 @@ func (m Manager) activateSingletonRelease(ctx context.Context, cfg config.Config
 		}
 		if recoveryErr != nil && handlerChanged {
 			stopCandidate = false
-			err = errors.Join(err, fmt.Errorf("singleton recovery incomplete; candidate remains routed for operator recovery: %w", recoveryErr))
+			err = &retainedCandidateError{cause: errors.Join(err, fmt.Errorf("singleton recovery incomplete; candidate remains routed for operator recovery: %w", recoveryErr))}
 		}
 	}()
 
@@ -556,6 +703,15 @@ func (m Manager) Status(ctx context.Context, cfg config.Config) (Status, error)
 		units = []string{cfg.Deployment.BlueGreen.Blue.Unit, cfg.Deployment.BlueGreen.Green.Unit}
 	} else {
 		units = []string{cfg.Deployment.Singleton.Unit}
+		lease, exists, leaseErr := loadCandidateLease(cfg)
+		if leaseErr != nil {
+			return Status{}, leaseErr
+		}
+		if exists {
+			units = append(units, lease.Unit)
+		} else if result.StateInitialized && record.CandidateRelease != "" {
+			return Status{}, errors.New("candidate release has no operation-scoped lease; run tend reconcile --json")
+		}
 	}
 	for _, unit := range units {
 		active, err := m.Operator.IsActive(ctx, unit)
@@ -590,6 +746,17 @@ func (m Manager) Prune(cfg config.Config, keep int, apply bool) ([]string, error
 	}
 	items := []candidate{}
 	protected := map[string]bool{record.ActiveRelease: true, record.PreviousRelease: true}
+	if cfg.Deployment.Strategy == "singleton_candidate" {
+		lease, exists, leaseErr := loadCandidateLease(cfg)
+		if leaseErr != nil {
+			return nil, leaseErr
+		}
+		if exists {
+			protected[lease.Release] = true
+		} else if record.CandidateRelease != "" {
+			protected[record.CandidateRelease] = true
+		}
+	}
 	for _, entry := range entries {
 		if !entry.IsDir() || entry.Type()&os.ModeSymlink != 0 || !strings.HasPrefix(entry.Name(), "sha256-") {
 			continue
@@ -725,7 +892,7 @@ func resolveReleaseLink(root, link string) (string, error) {
 		target = filepath.Join(filepath.Dir(link), target)
 	}
 	target = filepath.Clean(target)
-	probe := state.Record{SchemaVersion: 1, Strategy: "singleton_candidate", ActiveSlot: "singleton", ActiveRelease: target, UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
+	probe := state.Record{SchemaVersion: state.SchemaVersion, Strategy: "singleton_candidate", ActiveSlot: "singleton", ActiveRelease: target, UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
 	if err := probe.Validate(root, "singleton_candidate"); err != nil {
 		return "", err
 	}

internal/deploy/deploy_test.go

@@ -17,6 +17,16 @@ import (
 	"gamertan.com/tend/internal/state"
 )
 
+const testCandidateUnit = "example-site-tend-candidate-dddddddddddd.service"
+
+func storeTestCandidateLease(t *testing.T, cfg config.Config, release, startedAt string) {
+	t.Helper()
+	lease := state.CandidateLease{SchemaVersion: state.CandidateLeaseSchemaVersion, Service: cfg.Service.Name, OperationID: strings.Repeat("d", 32), Release: release, Unit: testCandidateUnit, Address: cfg.Deployment.Singleton.CandidateAddress, StartedAt: startedAt}
+	if err := state.StoreCandidateLease(state.CandidateLeasePath(cfg.Deployment.StateFile), cfg.Deployment.Root, lease); err != nil {
+		t.Fatal(err)
+	}
+}
+
 type fakeOperator struct {
 	failReload              bool
 	failReloadAt            int
@@ -296,30 +306,48 @@ func TestDeploymentEvidenceCanNeverBlockActivationOrRollback(t *testing.T) {
 	}
 }
 
-func TestDeploymentEvidenceIdentityAndEntropyAreBestEffort(t *testing.T) {
-	for _, test := range []struct {
-		name   string
-		damage func(*Manager)
-	}{
-		{"identity", func(manager *Manager) {
-			manager.ReadIdentity = func(string) (releaseIdentity, error) {
-				return releaseIdentity{}, errors.New("injected identity failure")
-			}
-		}},
-		{"entropy", func(manager *Manager) {
-			manager.OperationID = func() (string, error) { return "", errors.New("injected entropy failure") }
-		}},
-	} {
-		t.Run(test.name, func(t *testing.T) {
-			cfg, old, fresh := baseConfig(t, "singleton_candidate")
-			cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, old)
-			manager := manager(&fakeOperator{active: map[string]bool{}}, fresh)
-			test.damage(&manager)
-			report, err := manager.Deploy(context.Background(), cfg, Request{Activate: true, ApprovedSHA256: strings.Repeat("a", 64)})
-			if err != nil || report.EventWarnings != 1 || report.ActiveRelease != fresh {
-				t.Fatalf("report=%+v err=%v", report, err)
-			}
-		})
+func TestDeploymentEvidenceIdentityIsBestEffort(t *testing.T) {
+	cfg, old, fresh := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, old)
+	m := manager(&fakeOperator{active: map[string]bool{}}, fresh)
+	m.ReadIdentity = func(string) (releaseIdentity, error) {
+		return releaseIdentity{}, errors.New("injected identity failure")
+	}
+	report, err := m.Deploy(context.Background(), cfg, Request{Activate: true, ApprovedSHA256: strings.Repeat("a", 64)})
+	if err != nil || report.EventWarnings != 1 || report.ActiveRelease != fresh {
+		t.Fatalf("report=%+v err=%v", report, err)
+	}
+}
+
+func TestSingletonOperationIdentityIsRequiredBeforeCandidateStart(t *testing.T) {
+	cfg, old, fresh := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, old)
+	operator := &fakeOperator{active: map[string]bool{}}
+	m := manager(operator, fresh)
+	m.OperationID = func() (string, error) { return "", errors.New("injected entropy failure") }
+	if _, err := m.Deploy(context.Background(), cfg, Request{Activate: true, ApprovedSHA256: strings.Repeat("a", 64)}); err == nil || !strings.Contains(err.Error(), "operation identity") {
+		t.Fatalf("expected operation identity refusal, got %v", err)
+	}
+	if len(operator.starts) != 0 {
+		t.Fatalf("candidate started without an operation identity: %#v", operator.starts)
+	}
+}
+
+func TestSingletonUnresolvedLeaseBlocksReplacementBeforeCandidateStart(t *testing.T) {
+	cfg, old, fresh := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, old)
+	at := time.Unix(100, 0).UTC().Format(time.RFC3339)
+	record := state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: fresh, CandidateRelease: fresh, ActiveSlot: "singleton", ActiveRelease: old, LastAttemptRelease: fresh, LastAttemptOutcome: "failed", LastAttemptAt: at, UpdatedAt: at}
+	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
+		t.Fatal(err)
+	}
+	storeTestCandidateLease(t, cfg, fresh, at)
+	operator := &fakeOperator{active: map[string]bool{testCandidateUnit: true}}
+	if _, err := manager(operator, fresh).Deploy(context.Background(), cfg, Request{Activate: true, ApprovedSHA256: strings.Repeat("a", 64)}); err == nil || !strings.Contains(err.Error(), "run tend reconcile") {
+		t.Fatalf("expected unresolved lease refusal, got %v", err)
+	}
+	if len(operator.starts) != 0 || !operator.active[testCandidateUnit] {
+		t.Fatalf("existing candidate was disturbed: starts=%#v active=%#v", operator.starts, operator.active)
 	}
 }
 
@@ -380,7 +408,7 @@ func TestSingletonRestartFailureRestoresPointers(t *testing.T) {
 	if info, err := os.Stat(handler); err != nil || info.Mode().Perm() != 0o640 {
 		t.Fatalf("handler mode=%v err=%v", info.Mode().Perm(), err)
 	}
-	if operator.active["example-site-tend-candidate.service"] {
+	if operator.active[testCandidateUnit] {
 		t.Fatal("candidate was not stopped after successful restoration")
 	}
 }
@@ -398,9 +426,15 @@ func TestStateRecordsSuccessfulActivation(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if record.ActiveRelease != fresh || record.PreviousRelease != old {
+	if record.ActiveRelease != fresh || record.PreviousRelease != old || record.CandidateRelease != "" {
 		t.Fatalf("state=%+v", record)
 	}
+	if _, err := os.Lstat(state.CandidateLeasePath(cfg.Deployment.StateFile)); !os.IsNotExist(err) {
+		t.Fatalf("candidate lease was not removed: %v", err)
+	}
+	if len(operator.starts) != 1 || operator.starts[0] != testCandidateUnit {
+		t.Fatalf("candidate starts=%#v", operator.starts)
+	}
 	if operator.candidateFile != cfg.Service.EnvironmentFile || len(operator.candidateEnvironment) != 1 || operator.candidateEnvironment["EXAMPLE_LISTEN"] != "127.0.0.1:18092" {
 		t.Fatalf("candidate file=%q environment=%#v", operator.candidateFile, operator.candidateEnvironment)
 	}
@@ -408,9 +442,13 @@ func TestStateRecordsSuccessfulActivation(t *testing.T) {
 	if err != nil || string(body) != "reverse_proxy 127.0.0.1:8092\n" {
 		t.Fatalf("handler=%q err=%v", body, err)
 	}
-	if operator.reloads != 2 || operator.active["example-site-tend-candidate.service"] {
+	if operator.reloads != 2 || operator.active[testCandidateUnit] {
 		t.Fatalf("reloads=%d active=%#v", operator.reloads, operator.active)
 	}
+	reconciliation, err := m.Reconcile(context.Background(), cfg)
+	if err != nil || reconciliation.Mutation != "none" || reconciliation.Disposition != "settled" || reconciliation.Observed.CandidateLease || !reconciliation.Consistent {
+		t.Fatalf("reconciliation=%+v err=%v", reconciliation, err)
+	}
 }
 
 func TestSingletonContinuityFailureRestoresHandlerPointersAndService(t *testing.T) {
@@ -430,7 +468,7 @@ func TestSingletonContinuityFailureRestoresHandlerPointersAndService(t *testing.
 	if err != nil || string(body) != "reverse_proxy 127.0.0.1:8092\n" {
 		t.Fatalf("handler=%q err=%v", body, err)
 	}
-	if operator.active["example-site-tend-candidate.service"] {
+	if operator.active[testCandidateUnit] {
 		t.Fatal("candidate was not stopped after continuity restoration")
 	}
 }
@@ -453,7 +491,7 @@ func TestSingletonCaddyReloadFailuresRestorePriorRoute(t *testing.T) {
 			if err != nil || string(body) != "reverse_proxy 127.0.0.1:8092\n" {
 				t.Fatalf("handler=%q err=%v", body, err)
 			}
-			if operator.active["example-site-tend-candidate.service"] {
+			if operator.active[testCandidateUnit] {
 				t.Fatal("candidate was not stopped after route restoration")
 			}
 		})
@@ -469,7 +507,85 @@ func TestSingletonIncompleteRecoveryKeepsProvenCandidateRunning(t *testing.T) {
 	if err == nil || !strings.Contains(err.Error(), "candidate remains routed for operator recovery") {
 		t.Fatalf("expected explicit incomplete recovery, got %v", err)
 	}
-	if !operator.active["example-site-tend-candidate.service"] {
+	if !operator.active[testCandidateUnit] {
 		t.Fatal("proven candidate was stopped despite incomplete route restoration")
 	}
+	record, loadErr := state.Load(cfg.Deployment.StateFile, cfg.Deployment.Root, cfg.Deployment.Strategy)
+	lease, leaseErr := state.LoadCandidateLease(state.CandidateLeasePath(cfg.Deployment.StateFile), cfg.Deployment.Root, cfg.Service.Name)
+	if loadErr != nil || leaseErr != nil || record.CandidateRelease != fresh || lease.OperationID != strings.Repeat("d", 32) || lease.Unit != testCandidateUnit {
+		t.Fatalf("retained state=%+v err=%v", record, loadErr)
+	}
+}
+
+func TestReconcileReportsRetainedCandidateWithoutMutation(t *testing.T) {
+	cfg, old, fresh := baseConfig(t, "singleton_candidate")
+	settings, handler := singletonSettings(t, cfg, old)
+	cfg.Deployment.Singleton = settings
+	at := time.Unix(100, 0).UTC().Format(time.RFC3339)
+	record := state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: fresh, CandidateRelease: fresh, ActiveSlot: "singleton", ActiveRelease: old, LastAttemptRelease: fresh, LastAttemptOutcome: "failed", LastAttemptAt: at, UpdatedAt: at}
+	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
+		t.Fatal(err)
+	}
+	storeTestCandidateLease(t, cfg, fresh, at)
+	candidateHandler, err := renderHandler(settings.CaddyHandlerTemplate, settings.CandidateAddress)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(handler, candidateHandler, 0o640); err != nil {
+		t.Fatal(err)
+	}
+	operator := &fakeOperator{active: map[string]bool{settings.Unit: true, testCandidateUnit: true}}
+	reconciliation, err := manager(operator, fresh).Reconcile(context.Background(), cfg)
+	if err != nil || reconciliation.Mutation != "none" || !reconciliation.Observed.CandidateLease || reconciliation.Observed.CandidateUnitActive == nil || !*reconciliation.Observed.CandidateUnitActive || reconciliation.Observed.HandlerFileTarget != "candidate" || reconciliation.Disposition != "retained_candidate_handler_file" {
+		t.Fatalf("reconciliation=%+v err=%v", reconciliation, err)
+	}
+	if len(operator.stops) != 0 || len(operator.restarts) != 0 || operator.reloads != 0 {
+		t.Fatalf("reconcile mutated services: stops=%#v restarts=%#v reloads=%d", operator.stops, operator.restarts, operator.reloads)
+	}
+}
+
+func TestSingletonRollbackRetainsOperationLeaseWhenRecoveryIsIncomplete(t *testing.T) {
+	cfg, old, fresh := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, old)
+	operator := &fakeOperator{active: map[string]bool{cfg.Deployment.Singleton.Unit: true}}
+	m := manager(operator, fresh)
+	if _, err := m.Deploy(context.Background(), cfg, Request{Activate: true, ApprovedSHA256: strings.Repeat("a", 64)}); err != nil {
+		t.Fatal(err)
+	}
+	operator.failReload = true
+	if _, err := m.Rollback(context.Background(), cfg); err == nil || !strings.Contains(err.Error(), "candidate remains routed for operator recovery") {
+		t.Fatalf("expected retained rollback candidate, got %v", err)
+	}
+	record, err := state.Load(cfg.Deployment.StateFile, cfg.Deployment.Root, cfg.Deployment.Strategy)
+	if err != nil {
+		t.Fatal(err)
+	}
+	lease, leaseErr := state.LoadCandidateLease(state.CandidateLeasePath(cfg.Deployment.StateFile), cfg.Deployment.Root, cfg.Service.Name)
+	if record.ActiveRelease != fresh || record.CandidateRelease != old || leaseErr != nil || lease.OperationID != strings.Repeat("d", 32) || lease.Unit != testCandidateUnit || record.LastAttemptOutcome != "failed" {
+		t.Fatalf("rollback state=%+v", record)
+	}
+	if !operator.active[testCandidateUnit] {
+		t.Fatal("rollback candidate was stopped despite incomplete recovery")
+	}
+}
+
+func TestPruneProtectsOperationScopedCandidateRelease(t *testing.T) {
+	cfg, active, candidate := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, active)
+	at := time.Unix(100, 0).UTC().Format(time.RFC3339)
+	record := state.Record{SchemaVersion: state.SchemaVersion, Strategy: cfg.Deployment.Strategy, DesiredRelease: candidate, CandidateRelease: candidate, ActiveSlot: "singleton", ActiveRelease: active, LastAttemptRelease: candidate, LastAttemptOutcome: "failed", LastAttemptAt: at, UpdatedAt: at}
+	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
+		t.Fatal(err)
+	}
+	storeTestCandidateLease(t, cfg, candidate, at)
+	removed, err := manager(&fakeOperator{active: map[string]bool{}}, candidate).Prune(cfg, 2, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(removed) != 0 {
+		t.Fatalf("candidate release was selected for pruning: %#v", removed)
+	}
+	if info, err := os.Stat(candidate); err != nil || !info.IsDir() {
+		t.Fatalf("candidate release was not preserved: %v", err)
+	}
 }

internal/deploy/reconcile.go

@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package deploy
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os"
+
+	"gamertan.com/tend/internal/config"
+	"gamertan.com/tend/internal/state"
+)
+
+type Finding struct {
+	Code     string `json:"code"`
+	Severity string `json:"severity"`
+	Message  string `json:"message"`
+}
+
+type ObservedReleaseIdentity struct {
+	Version string `json:"version"`
+	Commit  string `json:"commit"`
+}
+
+type ObservedState struct {
+	ActiveRelease         string                   `json:"active_release,omitempty"`
+	PreviousRelease       string                   `json:"previous_release,omitempty"`
+	ActiveIdentity        *ObservedReleaseIdentity `json:"active_identity,omitempty"`
+	Units                 map[string]bool          `json:"units"`
+	CandidateLease        bool                     `json:"candidate_lease"`
+	CandidateUnit         string                   `json:"candidate_unit,omitempty"`
+	CandidateUnitActive   *bool                    `json:"candidate_unit_active,omitempty"`
+	LegacyCandidateUnit   string                   `json:"legacy_candidate_unit,omitempty"`
+	LegacyCandidateActive *bool                    `json:"legacy_candidate_unit_active,omitempty"`
+	RouteHandlerMatches   bool                     `json:"route_handler_matches"`
+	HandlerFileTarget     string                   `json:"handler_file_target,omitempty"`
+}
+
+type Reconciliation struct {
+	Service          string        `json:"service"`
+	Strategy         string        `json:"strategy"`
+	Mutation         string        `json:"mutation"`
+	Consistent       bool          `json:"consistent"`
+	StateInitialized bool          `json:"state_initialized"`
+	State            *state.Record `json:"state,omitempty"`
+	Observed         ObservedState `json:"observed"`
+	Disposition      string        `json:"disposition"`
+	Findings         []Finding     `json:"findings"`
+}
+
+// Reconcile observes configured units, release pointers, installed release
+// identity, and the imported Caddy handler. It never acquires the deployment
+// lock or mutates service state; proposed repairs remain an operator decision.
+func (m Manager) Reconcile(ctx context.Context, cfg config.Config) (Reconciliation, error) {
+	if err := cfg.Validate(); err != nil {
+		return Reconciliation{}, err
+	}
+	if m.Operator == nil || m.ReadIdentity == nil {
+		return Reconciliation{}, errors.New("reconciliation dependencies are unavailable")
+	}
+	report := Reconciliation{
+		Service: cfg.Service.Name, Strategy: cfg.Deployment.Strategy, Mutation: "none",
+		Observed: ObservedState{Units: map[string]bool{}}, Findings: []Finding{},
+	}
+	add := func(code, severity, message string) {
+		report.Findings = append(report.Findings, Finding{Code: code, Severity: severity, Message: message})
+	}
+	record, err := state.Load(cfg.Deployment.StateFile, cfg.Deployment.Root, cfg.Deployment.Strategy)
+	if err == nil {
+		report.State = &record
+		report.StateInitialized = true
+	} else if os.IsNotExist(err) {
+		add("state_uninitialized", "warning", "Tend has no validated state record for this service.")
+	} else {
+		add("state_invalid", "error", "The Tend state record could not be validated.")
+	}
+
+	activeSlot := ""
+	activeUnit := ""
+	activeAddress := ""
+	handler := ""
+	template := ""
+	var candidateLease *state.CandidateLease
+	switch cfg.Deployment.Strategy {
+	case "singleton_candidate":
+		single := *cfg.Deployment.Singleton
+		activeSlot = "singleton"
+		activeUnit = single.Unit
+		activeAddress = single.Address
+		handler, template = single.CaddyHandler, single.CaddyHandlerTemplate
+		report.Observed.ActiveRelease = observeReleaseLink(cfg, single.CurrentLink, true, add)
+		report.Observed.PreviousRelease = observeReleaseLink(cfg, single.PreviousLink, false, add)
+		legacyCandidateUnit := cfg.Service.Name + "-tend-candidate.service"
+		candidateUnit := legacyCandidateUnit
+		lease, leaseErr := state.LoadCandidateLease(state.CandidateLeasePath(cfg.Deployment.StateFile), cfg.Deployment.Root, cfg.Service.Name)
+		if leaseErr == nil {
+			candidateLease = &lease
+			report.Observed.CandidateLease = true
+			candidateUnit = lease.Unit
+		} else if !os.IsNotExist(leaseErr) {
+			report.Observed.CandidateLease = true
+			candidateUnit = ""
+			add("candidate_lease_invalid", "error", "The operation-scoped candidate lease could not be validated.")
+		} else if report.State != nil && report.State.CandidateRelease != "" {
+			report.Observed.CandidateLease = true
+			candidateUnit = ""
+			add("legacy_candidate_lease", "error", "The state records a candidate release without an operation-scoped lease and requires manual review.")
+		}
+		if candidateUnit != "" {
+			report.Observed.CandidateUnit = candidateUnit
+			candidateActive, candidateErr := m.Operator.IsActive(ctx, candidateUnit)
+			if candidateErr != nil {
+				add("candidate_unit_unobservable", "error", "The transient candidate unit state could not be observed.")
+			} else {
+				report.Observed.CandidateUnitActive = &candidateActive
+				report.Observed.Units[candidateUnit] = candidateActive
+			}
+		}
+		if candidateUnit != legacyCandidateUnit {
+			report.Observed.LegacyCandidateUnit = legacyCandidateUnit
+			legacyActive, legacyErr := m.Operator.IsActive(ctx, legacyCandidateUnit)
+			if legacyErr != nil {
+				add("legacy_candidate_unit_unobservable", "error", "The legacy fixed candidate unit state could not be observed.")
+			} else {
+				report.Observed.LegacyCandidateActive = &legacyActive
+				report.Observed.Units[legacyCandidateUnit] = legacyActive
+				if legacyActive {
+					add("legacy_candidate_unit_active", "error", "A legacy fixed-name candidate remains active beside an operation-scoped lease.")
+				}
+			}
+		}
+	case "blue_green":
+		blueGreen := *cfg.Deployment.BlueGreen
+		handler, template = blueGreen.CaddyHandler, blueGreen.CaddyHandlerTemplate
+		activeSlot = blueGreen.BootstrapActive
+		if report.State != nil {
+			activeSlot = report.State.ActiveSlot
+		}
+		active := slotConfig(blueGreen, activeSlot)
+		previousName := "blue"
+		if activeSlot == "blue" {
+			previousName = "green"
+		}
+		previous := slotConfig(blueGreen, previousName)
+		activeUnit, activeAddress = active.Unit, active.Address
+		report.Observed.ActiveRelease = observeReleaseLink(cfg, active.Link, true, add)
+		report.Observed.PreviousRelease = observeReleaseLink(cfg, previous.Link, false, add)
+		for _, slot := range []config.Slot{blueGreen.Blue, blueGreen.Green} {
+			observeUnit(ctx, m.Operator, slot.Unit, report.Observed.Units, add)
+		}
+	}
+	if _, exists := report.Observed.Units[activeUnit]; !exists {
+		observeUnit(ctx, m.Operator, activeUnit, report.Observed.Units, add)
+	}
+	if active, observed := report.Observed.Units[activeUnit]; activeUnit != "" && observed && !active {
+		add("active_unit_inactive", "error", "The configured active service unit is not active.")
+	}
+
+	if report.Observed.ActiveRelease != "" {
+		identity, identityErr := m.ReadIdentity(report.Observed.ActiveRelease)
+		if identityErr != nil {
+			add("active_identity_unreadable", "error", "The observed active release identity could not be validated.")
+		} else {
+			report.Observed.ActiveIdentity = &ObservedReleaseIdentity{Version: identity.Version, Commit: identity.Commit}
+		}
+	}
+	expectedHandler, renderErr := renderHandler(template, activeAddress)
+	actualHandler, readErr := os.ReadFile(handler)
+	if renderErr != nil || readErr != nil {
+		add("route_handler_unreadable", "error", "The configured Caddy handler or its template could not be validated.")
+	} else {
+		report.Observed.RouteHandlerMatches = bytes.Equal(expectedHandler, actualHandler)
+		if report.Observed.RouteHandlerMatches {
+			report.Observed.HandlerFileTarget = "installed"
+		} else if cfg.Deployment.Strategy == "singleton_candidate" {
+			candidateAddress := cfg.Deployment.Singleton.CandidateAddress
+			if candidateLease != nil {
+				candidateAddress = candidateLease.Address
+			}
+			candidateHandler, candidateErr := renderHandler(template, candidateAddress)
+			if candidateErr == nil && bytes.Equal(candidateHandler, actualHandler) {
+				report.Observed.HandlerFileTarget = "candidate"
+			} else {
+				report.Observed.HandlerFileTarget = "other"
+			}
+		}
+		if !report.Observed.RouteHandlerMatches {
+			add("route_handler_drift", "error", "The installed Caddy handler does not match the configured active upstream.")
+		}
+	}
+
+	if report.State != nil {
+		if report.State.ActiveSlot != activeSlot || report.State.ActiveRelease != report.Observed.ActiveRelease {
+			add("active_release_drift", "error", "Recorded active state does not match the observed active release pointer.")
+		}
+		if report.State.PreviousRelease != report.Observed.PreviousRelease {
+			add("previous_release_drift", "warning", "Recorded rollback state does not match the observed previous release pointer.")
+		}
+		if cfg.Deployment.Strategy == "singleton_candidate" {
+			leased := report.Observed.CandidateLease && candidateLease != nil
+			candidateActive := report.Observed.CandidateUnitActive != nil && *report.Observed.CandidateUnitActive
+			if candidateLease != nil && report.State.CandidateRelease == "" {
+				add("candidate_lease_without_running_attempt", "error", "An operation-scoped candidate lease remains after the recorded attempt settled.")
+			}
+			if candidateLease != nil && report.State.CandidateRelease != "" && candidateLease.Release != report.State.CandidateRelease {
+				add("candidate_lease_release_mismatch", "error", "The operation-scoped candidate lease does not match the recorded candidate release.")
+			}
+			if leased && report.Observed.CandidateUnitActive != nil && !candidateActive {
+				add("inactive_candidate_lease", "error", "State retains a candidate lease but its operation-scoped unit is inactive.")
+			}
+			if !report.Observed.CandidateLease && candidateActive {
+				add("unleased_candidate_active", "error", "A transient candidate unit is active without a matching running attempt.")
+			}
+			if leased && candidateActive && report.Observed.HandlerFileTarget == "candidate" {
+				add("retained_candidate_routed", "warning", "The retained candidate appears in the handler file; do not stop it before establishing another healthy route.")
+			}
+			if leased && candidateActive && report.Observed.HandlerFileTarget != "candidate" {
+				add("candidate_active_not_routed", "warning", "The leased candidate is active but the handler file does not target it; cleanup remains an explicit reviewed operation.")
+			}
+		}
+	}
+	switch {
+	case !report.StateInitialized:
+		report.Disposition = "state_uninitialized"
+	case report.Observed.CandidateLease && report.Observed.CandidateUnit == "":
+		report.Disposition = "legacy_or_invalid_candidate_lease"
+	case report.Observed.CandidateLease && report.Observed.CandidateUnitActive != nil && *report.Observed.CandidateUnitActive && report.Observed.HandlerFileTarget == "candidate":
+		report.Disposition = "retained_candidate_handler_file"
+	case report.Observed.CandidateLease && report.Observed.CandidateUnitActive != nil && *report.Observed.CandidateUnitActive:
+		report.Disposition = "candidate_active_not_in_handler_file"
+	case report.Observed.CandidateLease:
+		report.Disposition = "inactive_candidate_lease"
+	case len(report.Findings) == 0:
+		report.Disposition = "settled"
+	default:
+		report.Disposition = "manual_review_required"
+	}
+	report.Consistent = len(report.Findings) == 0
+	return report, nil
+}
+
+func observeReleaseLink(cfg config.Config, link string, required bool, add func(string, string, string)) string {
+	release, err := resolveReleaseLink(cfg.Deployment.Root, link)
+	if err == nil {
+		return release
+	}
+	if !required && os.IsNotExist(err) {
+		return ""
+	}
+	code := "previous_pointer_unreadable"
+	message := "The configured previous release pointer could not be validated."
+	severity := "warning"
+	if required {
+		code = "active_pointer_unreadable"
+		message = "The configured active release pointer could not be validated."
+		severity = "error"
+	}
+	add(code, severity, message)
+	return ""
+}
+
+func observeUnit(ctx context.Context, operator Operator, unit string, units map[string]bool, add func(string, string, string)) {
+	active, err := operator.IsActive(ctx, unit)
+	if err != nil {
+		add("unit_unobservable", "error", "A configured service unit state could not be observed.")
+		return
+	}
+	units[unit] = active
+}

internal/deploy/reconcile_test.go

@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package deploy
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"gamertan.com/tend/internal/config"
+	"gamertan.com/tend/internal/state"
+)
+
+func writeReleaseIdentity(t *testing.T, release, version, commit string) {
+	t.Helper()
+	body := `{"version":"` + version + `","commit":"` + commit + `"}`
+	if err := os.WriteFile(filepath.Join(release, "RELEASE.json"), []byte(body), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func storeSingletonState(t *testing.T, cfg config.Config, active, previous string) {
+	t.Helper()
+	record := state.Record{
+		SchemaVersion:      state.SchemaVersion,
+		Strategy:           "singleton_candidate",
+		DesiredRelease:     active,
+		ActiveSlot:         "singleton",
+		ActiveRelease:      active,
+		PreviousRelease:    previous,
+		LastAttemptRelease: active,
+		LastAttemptOutcome: "succeeded",
+		LastAttemptAt:      time.Unix(100, 0).UTC().Format(time.RFC3339),
+		UpdatedAt:          time.Unix(100, 0).UTC().Format(time.RFC3339),
+	}
+	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func reconciliationManager(operator Operator) Manager {
+	return Manager{Operator: operator, ReadIdentity: readReleaseIdentity}
+}
+
+func TestReconcileReportsHealthySingletonWithoutMutation(t *testing.T) {
+	cfg, active, previous := baseConfig(t, "singleton_candidate")
+	cfg.Deployment.Singleton, _ = singletonSettings(t, cfg, active)
+	if err := replaceSymlink(cfg.Deployment.Singleton.PreviousLink, previous); err != nil {
+		t.Fatal(err)
+	}
+	commit := strings.Repeat("a", 40)
+	writeReleaseIdentity(t, active, "v0.2.0-preview.2", commit)
+	storeSingletonState(t, cfg, active, previous)
+	operator := &fakeOperator{active: map[string]bool{
+		cfg.Deployment.Singleton.Unit:                true,
+		cfg.Service.Name + "-tend-candidate.service": false,
+	}}
+
+	report, err := reconciliationManager(operator).Reconcile(context.Background(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !report.Consistent || report.Mutation != "none" || !report.StateInitialized || len(report.Findings) != 0 {
+		t.Fatalf("report=%+v", report)
+	}
+	if report.Observed.ActiveRelease != active || report.Observed.PreviousRelease != previous || !report.Observed.RouteHandlerMatches {
+		t.Fatalf("observed=%+v", report.Observed)
+	}
+	if report.Observed.ActiveIdentity == nil || report.Observed.ActiveIdentity.Version != "v0.2.0-preview.2" || report.Observed.ActiveIdentity.Commit != commit {
+		t.Fatalf("identity=%+v", report.Observed.ActiveIdentity)
+	}
+	if !report.Observed.Units[cfg.Deployment.Singleton.Unit] || report.Observed.CandidateUnitActive == nil || *report.Observed.CandidateUnitActive {
+		t.Fatalf("units=%#v candidate=%v", report.Observed.Units, report.Observed.CandidateUnitActive)
+	}
+}
+
+func TestReconcileReportsHealthyBlueGreenDeployment(t *testing.T) {
+	cfg, active, previous := baseConfig(t, "blue_green")
+	handler := filepath.Join(cfg.Deployment.Root, "handler.caddy")
+	template := filepath.Join(cfg.Deployment.Root, "handler.template")
+	if err := os.WriteFile(handler, []byte("reverse_proxy 127.0.0.1:8090\n"), 0o640); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(template, []byte("reverse_proxy {{UPSTREAM}}\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	blue := filepath.Join(cfg.Deployment.Root, "slots", "blue")
+	green := filepath.Join(cfg.Deployment.Root, "slots", "green")
+	if err := replaceSymlink(blue, active); err != nil {
+		t.Fatal(err)
+	}
+	if err := replaceSymlink(green, previous); err != nil {
+		t.Fatal(err)
+	}
+	cfg.Deployment.BlueGreen = &config.BlueGreen{
+		CaddyConfig: filepath.Join(cfg.Deployment.Root, "Caddyfile"), CaddyHandler: handler,
+		CaddyHandlerTemplate: template, BootstrapActive: "blue",
+		Blue:  config.Slot{Unit: "example-blue.service", Address: "127.0.0.1:8090", Link: blue},
+		Green: config.Slot{Unit: "example-green.service", Address: "127.0.0.1:8091", Link: green},
+	}
+	writeReleaseIdentity(t, active, "v0.2.0-preview.2", strings.Repeat("c", 40))
+	record := state.Record{
+		SchemaVersion: state.SchemaVersion, Strategy: "blue_green", DesiredRelease: active,
+		ActiveSlot: "blue", ActiveRelease: active, PreviousSlot: "green", PreviousRelease: previous,
+		LastAttemptRelease: active, LastAttemptOutcome: "succeeded",
+		LastAttemptAt: time.Unix(100, 0).UTC().Format(time.RFC3339), UpdatedAt: time.Unix(100, 0).UTC().Format(time.RFC3339),
+	}
+	if err := state.Store(cfg.Deployment.StateFile, cfg.Deployment.Root, record); err != nil {
+		t.Fatal(err)
+	}
+	operator := &fakeOperator{active: map[string]bool{
+		"example-blue.service": true, "example-green.service": true,
+	}}
+
+	report, err := reconciliationManager(operator).Reconcile(context.Background(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !report.Consistent || report.Mutation != "none" || report.Observed.ActiveRelease != active || report.Observed.PreviousRelease != previous || !report.Observed.RouteHandlerMatches {
+		t.Fatalf("report=%+v", report)
+	}
+	if report.Observed.CandidateUnit != "" || report.Observed.CandidateUnitActive != nil {
+		t.Fatalf("unexpected candidate observation=%+v", report.Observed)
+	}
+}
+
+func TestReconcileExplainsDriftWithoutRepairingIt(t *testing.T) {
+	cfg, recorded, observed := baseConfig(t, "singleton_candidate")
+	var handler string
+	cfg.Deployment.Singleton, handler = singletonSettings(t, cfg, recorded)
+	if err := replaceSymlink(cfg.Deployment.Singleton.PreviousLink, observed); err != nil {
+		t.Fatal(err)
+	}
+	storeSingletonState(t, cfg, recorded, observed)
+	if err := replaceSymlink(cfg.Deployment.Singleton.CurrentLink, observed); err != nil {
+		t.Fatal(err)
+	}
+	writeReleaseIdentity(t, observed, "v0.2.0-preview.3", strings.Repeat("b", 40))
+	candidateHandler, err := renderHandler(cfg.Deployment.Singleton.CaddyHandlerTemplate, cfg.Deployment.Singleton.CandidateAddress)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(handler, candidateHandler, 0o640); err != nil {
+		t.Fatal(err)
+	}
+	beforeHandler, err := os.ReadFile(handler)
+	if err != nil {
+		t.Fatal(err)
+	}
+	operator := &fakeOperator{active: map[string]bool{
+		cfg.Deployment.Singleton.Unit:                false,
+		cfg.Service.Name + "-tend-candidate.service": true,
+	}}
+
+	report, err := reconciliationManager(operator).Reconcile(context.Background(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if report.Consistent || report.Mutation != "none" {
+		t.Fatalf("report=%+v", report)
+	}
+	codes := map[string]bool{}
+	for _, finding := range report.Findings {
+		codes[finding.Code] = true
+	}
+	for _, code := range []string{"active_release_drift", "active_unit_inactive", "route_handler_drift", "unleased_candidate_active"} {
+		if !codes[code] {
+			t.Fatalf("missing %s in %#v", code, report.Findings)
+		}
+	}
+	target, err := resolveReleaseLink(cfg.Deployment.Root, cfg.Deployment.Singleton.CurrentLink)
+	if err != nil || target != observed {
+		t.Fatalf("current=%q err=%v", target, err)
+	}
+	afterHandler, err := os.ReadFile(handler)
+	if err != nil || string(afterHandler) != string(beforeHandler) {
+		t.Fatalf("handler changed err=%v", err)
+	}
+}

internal/provenance/git.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -18,6 +19,17 @@ type Source struct {
 }
 
 func Inspect(ctx context.Context, runner process.Runner, dir, branch string) (Source, error) {
+	gitDir, err := gitPath(ctx, runner, dir, "--git-dir")
+	if err != nil {
+		return Source{}, fmt.Errorf("inspect Git directory: %w", err)
+	}
+	commonDir, err := gitPath(ctx, runner, dir, "--git-common-dir")
+	if err != nil {
+		return Source{}, fmt.Errorf("inspect Git common directory: %w", err)
+	}
+	if gitDir != commonDir {
+		return Source{}, errors.New("release packaging does not yet support linked Git worktrees; use a clean standalone clone of the exact pushed commit")
+	}
 	status, err := runner.Run(ctx, dir, nil, "git", "status", "--porcelain=v1", "--untracked-files=all")
 	if err != nil {
 		return Source{}, err
@@ -51,3 +63,18 @@ func Inspect(ctx context.Context, runner process.Runner, dir, branch string) (So
 	}
 	return Source{Commit: commit, Epoch: epoch}, nil
 }
+
+func gitPath(ctx context.Context, runner process.Runner, dir, argument string) (string, error) {
+	out, err := runner.Run(ctx, dir, nil, "git", "rev-parse", argument)
+	if err != nil {
+		return "", err
+	}
+	path := strings.TrimSpace(string(out))
+	if path == "" {
+		return "", errors.New("Git returned an empty path")
+	}
+	if !filepath.IsAbs(path) {
+		path = filepath.Join(dir, path)
+	}
+	return filepath.Clean(path), nil
+}

internal/provenance/git_test.go

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package provenance
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+)
+
+type recordingRunner struct {
+	responses map[string][]byte
+	calls     []string
+}
+
+func (runner *recordingRunner) Run(_ context.Context, _ string, _ map[string]string, name string, args ...string) ([]byte, error) {
+	key := name + " " + strings.Join(args, " ")
+	runner.calls = append(runner.calls, key)
+	response, ok := runner.responses[key]
+	if !ok {
+		return nil, errors.New("unexpected command: " + key)
+	}
+	return response, nil
+}
+
+func TestInspectAcceptsStandaloneExactPushedCheckout(t *testing.T) {
+	commit := strings.Repeat("a", 40)
+	runner := &recordingRunner{responses: map[string][]byte{
+		"git rev-parse --git-dir":                          []byte(".git\n"),
+		"git rev-parse --git-common-dir":                   []byte(".git\n"),
+		"git status --porcelain=v1 --untracked-files=all":  nil,
+		"git rev-parse HEAD":                               []byte(commit + "\n"),
+		"git ls-remote --exit-code origin refs/heads/main": []byte(commit + "\trefs/heads/main\n"),
+		"git show -s --format=%ct " + commit:               []byte("1720000000\n"),
+	}}
+	result, err := Inspect(context.Background(), runner, "/source", "main")
+	if err != nil || result.Commit != commit || result.Epoch != 1720000000 {
+		t.Fatalf("result=%+v err=%v", result, err)
+	}
+}
+
+func TestInspectExplainsUnsupportedLinkedWorktreeBeforeRemoteOrBuildWork(t *testing.T) {
+	runner := &recordingRunner{responses: map[string][]byte{
+		"git rev-parse --git-dir":        []byte("/repo/.git/worktrees/release\n"),
+		"git rev-parse --git-common-dir": []byte("/repo/.git\n"),
+	}}
+	_, err := Inspect(context.Background(), runner, "/source", "main")
+	if err == nil || !strings.Contains(err.Error(), "linked Git worktrees") || len(runner.calls) != 2 {
+		t.Fatalf("calls=%#v err=%v", runner.calls, err)
+	}
+}

internal/state/lease.go

@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package state
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"regexp"
+	"time"
+)
+
+const CandidateLeaseSchemaVersion = 1
+
+var (
+	leaseOperationPattern = regexp.MustCompile(`^[0-9a-f]{32}$`)
+	leaseServicePattern   = regexp.MustCompile(`^[a-z][a-z0-9-]{1,62}$`)
+)
+
+type CandidateLease struct {
+	SchemaVersion int    `json:"schema_version"`
+	Service       string `json:"service"`
+	OperationID   string `json:"operation_id"`
+	Release       string `json:"release"`
+	Unit          string `json:"unit"`
+	Address       string `json:"address"`
+	StartedAt     string `json:"started_at"`
+}
+
+func CandidateLeasePath(statePath string) string { return statePath + ".candidate-lease.json" }
+
+func (l CandidateLease) Validate(root, service string) error {
+	if l.SchemaVersion != CandidateLeaseSchemaVersion {
+		return errors.New("candidate lease schema version is unsupported")
+	}
+	if !leaseServicePattern.MatchString(service) || l.Service != service {
+		return errors.New("candidate lease service does not match configuration")
+	}
+	if !leaseOperationPattern.MatchString(l.OperationID) {
+		return errors.New("candidate lease operation ID is invalid")
+	}
+	if err := releaseBelow(root, l.Release); err != nil {
+		return fmt.Errorf("candidate lease release: %w", err)
+	}
+	expectedUnit := service + "-tend-candidate-" + l.OperationID[:12] + ".service"
+	if l.Unit != expectedUnit {
+		return errors.New("candidate lease unit does not match its operation")
+	}
+	address, err := netip.ParseAddrPort(l.Address)
+	if err != nil || !address.Addr().IsLoopback() || address.Port() == 0 {
+		return errors.New("candidate lease address is invalid")
+	}
+	if _, err := time.Parse(time.RFC3339, l.StartedAt); err != nil {
+		return errors.New("candidate lease timestamp is invalid")
+	}
+	return nil
+}
+
+func LoadCandidateLease(path, root, service string) (CandidateLease, error) {
+	info, err := os.Lstat(path)
+	if err != nil {
+		return CandidateLease{}, err
+	}
+	if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 || info.Size() > 64<<10 {
+		return CandidateLease{}, errors.New("candidate lease must be a bounded regular file")
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		return CandidateLease{}, err
+	}
+	decoder := json.NewDecoder(bytes.NewReader(body))
+	decoder.DisallowUnknownFields()
+	var lease CandidateLease
+	if err := decoder.Decode(&lease); err != nil {
+		return CandidateLease{}, fmt.Errorf("decode candidate lease: %w", err)
+	}
+	var extra any
+	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
+		return CandidateLease{}, errors.New("candidate lease contains trailing data")
+	}
+	if err := lease.Validate(root, service); err != nil {
+		return CandidateLease{}, err
+	}
+	return lease, nil
+}
+
+func StoreCandidateLease(path, root string, lease CandidateLease) error {
+	if err := lease.Validate(root, lease.Service); err != nil {
+		return err
+	}
+	if info, err := os.Lstat(path); err == nil && (!info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0) {
+		return errors.New("candidate lease path must be a regular file, not a symlink")
+	} else if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	body, err := json.MarshalIndent(lease, "", "  ")
+	if err != nil {
+		return err
+	}
+	body = append(body, '\n')
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return err
+	}
+	temporary, err := os.CreateTemp(dir, ".tend-candidate-lease-")
+	if err != nil {
+		return err
+	}
+	name := temporary.Name()
+	complete := false
+	defer func() {
+		_ = temporary.Close()
+		if !complete {
+			_ = os.Remove(name)
+		}
+	}()
+	if err := temporary.Chmod(0o644); err != nil {
+		return err
+	}
+	if _, err := temporary.Write(body); err != nil {
+		return err
+	}
+	if err := temporary.Sync(); err != nil {
+		return err
+	}
+	if err := temporary.Close(); err != nil {
+		return err
+	}
+	if err := os.Rename(name, path); err != nil {
+		return err
+	}
+	complete = true
+	return syncDir(dir)
+}
+
+func RemoveCandidateLease(path string) error {
+	info, err := os.Lstat(path)
+	if os.IsNotExist(err) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	if !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 {
+		return errors.New("candidate lease path must be a regular file, not a symlink")
+	}
+	if err := os.Remove(path); err != nil {
+		return err
+	}
+	return syncDir(filepath.Dir(path))
+}

internal/state/lease_test.go

@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package state
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestCandidateLeaseRoundTripAndRemoval(t *testing.T) {
+	root := filepath.Join(t.TempDir(), "service")
+	release := filepath.Join(root, "releases", "sha256-"+strings.Repeat("a", 64))
+	if err := os.MkdirAll(release, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	path := CandidateLeasePath(filepath.Join(root, "state.json"))
+	operation := strings.Repeat("d", 32)
+	lease := CandidateLease{SchemaVersion: CandidateLeaseSchemaVersion, Service: "example-site", OperationID: operation, Release: release, Unit: "example-site-tend-candidate-" + operation[:12] + ".service", Address: "127.0.0.1:18092", StartedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
+	if err := StoreCandidateLease(path, root, lease); err != nil {
+		t.Fatal(err)
+	}
+	loaded, err := LoadCandidateLease(path, root, "example-site")
+	if err != nil || loaded != lease {
+		t.Fatalf("loaded=%+v err=%v", loaded, err)
+	}
+	if err := RemoveCandidateLease(path); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Lstat(path); !os.IsNotExist(err) {
+		t.Fatalf("lease remains: %v", err)
+	}
+}
+
+func TestCandidateLeaseRejectsCrossServiceAndSymlink(t *testing.T) {
+	root := filepath.Join(t.TempDir(), "service")
+	release := filepath.Join(root, "releases", "sha256-"+strings.Repeat("a", 64))
+	if err := os.MkdirAll(release, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	operation := strings.Repeat("d", 32)
+	lease := CandidateLease{SchemaVersion: CandidateLeaseSchemaVersion, Service: "example-site", OperationID: operation, Release: release, Unit: "example-site-tend-candidate-" + operation[:12] + ".service", Address: "127.0.0.1:18092", StartedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
+	if err := lease.Validate(root, "other-site"); err == nil {
+		t.Fatal("expected service mismatch")
+	}
+	path := CandidateLeasePath(filepath.Join(root, "state.json"))
+	if err := os.Symlink(filepath.Join(root, "elsewhere"), path); err != nil {
+		t.Fatal(err)
+	}
+	if err := StoreCandidateLease(path, root, lease); err == nil {
+		t.Fatal("expected symlink refusal")
+	}
+	if err := RemoveCandidateLease(path); err == nil {
+		t.Fatal("expected symlink removal refusal")
+	}
+}
+
+func TestCandidateLeasePreservesSchemaOneDeploymentState(t *testing.T) {
+	root := filepath.Join(t.TempDir(), "service")
+	release := filepath.Join(root, "releases", "sha256-"+strings.Repeat("a", 64))
+	if err := os.MkdirAll(release, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	at := time.Unix(1, 0).UTC().Format(time.RFC3339)
+	statePath := filepath.Join(root, "state.json")
+	record := Record{SchemaVersion: SchemaVersion, Strategy: "singleton_candidate", DesiredRelease: release, CandidateRelease: release, ActiveSlot: "singleton", ActiveRelease: release, LastAttemptRelease: release, LastAttemptOutcome: "running", LastAttemptAt: at, UpdatedAt: at}
+	if err := Store(statePath, root, record); err != nil {
+		t.Fatal(err)
+	}
+	operation := strings.Repeat("d", 32)
+	lease := CandidateLease{SchemaVersion: CandidateLeaseSchemaVersion, Service: "example-site", OperationID: operation, Release: release, Unit: "example-site-tend-candidate-" + operation[:12] + ".service", Address: "127.0.0.1:18092", StartedAt: at}
+	if err := StoreCandidateLease(CandidateLeasePath(statePath), root, lease); err != nil {
+		t.Fatal(err)
+	}
+	body, err := os.ReadFile(statePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Contains(body, []byte(`"schema_version": 1`)) || bytes.Contains(body, []byte("candidate_operation_id")) || bytes.Contains(body, []byte("candidate_unit")) {
+		t.Fatalf("deployment state contract changed: %s", body)
+	}
+	loaded, err := Load(statePath, root, "singleton_candidate")
+	if err != nil || loaded.SchemaVersion != 1 || loaded.CandidateRelease != release {
+		t.Fatalf("loaded=%+v err=%v", loaded, err)
+	}
+}

internal/state/state_test.go

@@ -17,7 +17,7 @@ func TestStoreLoadRoundTripAndRejectSymlink(t *testing.T) {
 	}
 	path := filepath.Join(root, "state.json")
 	at := time.Unix(1, 0).UTC().Format(time.RFC3339)
-	record := Record{SchemaVersion: 1, Strategy: "singleton_candidate", DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: at, UpdatedAt: at}
+	record := Record{SchemaVersion: SchemaVersion, Strategy: "singleton_candidate", DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, LastAttemptRelease: release, LastAttemptOutcome: "succeeded", LastAttemptAt: at, UpdatedAt: at}
 	if err := Store(path, root, record); err != nil {
 		t.Fatal(err)
 	}
@@ -42,13 +42,13 @@ func TestStoreLoadRoundTripAndRejectSymlink(t *testing.T) {
 func TestRecordRequiresCandidateForRunningAttempt(t *testing.T) {
 	root := filepath.Join(t.TempDir(), "service")
 	release := filepath.Join(root, "releases", "sha256-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
-	record := Record{SchemaVersion: 1, Strategy: "singleton_candidate", DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, LastAttemptRelease: release, LastAttemptOutcome: "running", LastAttemptAt: time.Unix(1, 0).UTC().Format(time.RFC3339), UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
+	record := Record{SchemaVersion: SchemaVersion, Strategy: "singleton_candidate", DesiredRelease: release, ActiveSlot: "singleton", ActiveRelease: release, LastAttemptRelease: release, LastAttemptOutcome: "running", LastAttemptAt: time.Unix(1, 0).UTC().Format(time.RFC3339), UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
 	if err := record.Validate(root, "singleton_candidate"); err == nil {
 		t.Fatal("expected missing candidate rejection")
 	}
 }
 func TestRecordRejectsReleaseOutsideRoot(t *testing.T) {
-	record := Record{SchemaVersion: 1, Strategy: "singleton_candidate", ActiveSlot: "singleton", ActiveRelease: "/tmp/other/release", UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
+	record := Record{SchemaVersion: SchemaVersion, Strategy: "singleton_candidate", ActiveSlot: "singleton", ActiveRelease: "/tmp/other/release", UpdatedAt: time.Unix(1, 0).UTC().Format(time.RFC3339)}
 	if err := record.Validate("/opt/example", "singleton_candidate"); err == nil {
 		t.Fatal("expected path refusal")
 	}

scripts/public-snapshot.allow

@@ -45,6 +45,8 @@ internal/deploy/operator.go
 internal/deploy/operator_test.go
 internal/deploy/ownership_linux.go
 internal/deploy/ownership_other.go
+internal/deploy/reconcile.go
+internal/deploy/reconcile_test.go
 internal/deploy/release.go
 internal/deploy/release_mode_linux_test.go
 internal/deploy/release_test.go
@@ -54,10 +56,13 @@ internal/packager/packager.go
 internal/packager/packager_test.go
 internal/process/run.go
 internal/provenance/git.go
+internal/provenance/git_test.go
 internal/serverpolicy/ownership_linux.go
 internal/serverpolicy/ownership_other.go
 internal/serverpolicy/policy.go
 internal/serverpolicy/policy_test.go
+internal/state/lease.go
+internal/state/lease_test.go
 internal/state/state.go
 internal/state/state_test.go
 internal/transport/protocol.go