docs: publish Tend Compose continuity evidence

Export the reviewed allowlisted snapshot from private source commit 07c1655921f21ee5e4fc4d85639d199e8867b17d. This records the Docker Compose activation, schema-compatible rollback, and stateful migration resource findings from Observatory Preview 19 dogfooding.

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

internal/deploy/lock_linux.go

@@ -0,0 +1,32 @@
+//go:build linux
+
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package deploy
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+type fileLock struct{ file *os.File }
+
+func acquireLock(path string) (*fileLock, error) {
+	file, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
+	if err != nil {
+		return nil, err
+	}
+	if err := syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
+		_ = file.Close()
+		return nil, errors.New("deployment lock is held")
+	}
+	return &fileLock{file: file}, nil
+}
+func (l *fileLock) Close() error {
+	if l == nil || l.file == nil {
+		return nil
+	}
+	_ = syscall.Flock(int(l.file.Fd()), syscall.LOCK_UN)
+	return l.file.Close()
+}