Prepare Sandwich Hime v1 release candidate source

docs/BENCHMARKS.md

@@ -9,6 +9,28 @@ synthetic cases under the published method. Only reproduced improvements become
 marketing claims. Microbenchmarks do not justify claims about request
 throughput, database-heavy pages, or whole-application latency.
 
+The threshold was fixed before measuring the RC. On each maintained native
+platform and toolchain, ten benchmark samples use the exact output-equivalent
+`BenchmarkV1Corpus*` pair. Sandwich Hime passes when its median `ns/op` and
+`B/op` are each no more than 125% of `html/template`, and its median
+allocations/op are no more than two allocations above `html/template`.
+Any failed platform/toolchain pair is a material regression. Timing is reviewed
+from raw samples rather than enforced in ordinary CI, where host contention
+would turn a performance policy into a flaky correctness gate.
+
+Run:
+
+```sh
+cd sando
+go test -run '^TestBenchmarkCorpusEquivalent$' \
+  -bench '^BenchmarkV1Corpus' -benchmem -benchtime=2s -count=10
+```
+
+`benchmarkSandoComponent` intentionally mirrors generated writer calls and
+captures the same typed view used by the parsed standard template. This is a
+runtime renderer microbenchmark; it excludes parsing, compiler execution,
+HTTP, routing, logging, databases, and deployment.
+
 Benchmark fixtures must be self-contained, synthetic, reviewable, and committed
 to this repository. Application-specific datasets and deployment measurements
 belong with their applications and are neither copied here nor treated as core