Record basic validation allocation savings

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 Implement the remaining local work in the [performance roadmap](performance.md)
 in order. Each sequential stage is scoped for one Luna coding-agent prompt.
-Stage 1 is complete; Stages 2–14 remain pending. Update status and evidence
+Stages 1–2 are complete; Stages 3–14 remain pending. Update status and evidence
 as each work unit lands.
 The completed inspection plan is preserved at
 `481e2d4:docs/roadmap/implementation.md` in Git history.
@@ -127,6 +127,11 @@ calls, allocation assertions, or source parsing hidden in the compiled path.
 
 ## Stage 2 — Check Basic Output Emptiness Without A String Copy
 
+**Status: Complete (2026-10-09).** Basic validation now checks the response
+bytes directly. Behavioral coverage includes empty bytes, ASCII and Unicode
+whitespace, ordinary text, and arbitrary non-UTF-8 bytes. The comparison with
+the Stage 1 benchmark fixture is recorded below.
+
 **Outcome:** Basic validation avoids a response-sized temporary string.
 
 **Work:**
@@ -576,6 +581,48 @@ conditional decisions, and final verification in this section as the remaining
 stages complete. Keep the feature roadmap focused on target state and progress
 rather than duplicating the staged procedure.
 
+### Basic-Validation Copy Comparison
+
+The before measurement uses the unchanged Stage 1 benchmark fixture at commit
+`05fe13d` (`Record validation and rendering baselines`), immediately before the
+production change. The after measurement uses the same fixture and benchmark
+implementation at `ed7c273` (`Avoid copying output during basic validation`).
+Environment and module versions match the baseline above: Linux/amd64, Intel
+Core i5-7260U @ 2.20 GHz, parallelism 4, Go 1.26.8, ConfigKit `v0.5.0`, JSON
+Schema `v6.0.2`, and backend modules `v3.20260930.0`.
+
+Command for both revisions (five 500 ms samples, without the race detector):
+
+```sh
+GOTOOLCHAIN=local GOWORK=off GOPROXY=off GONOPROXY=none GOSUMDB=off \
+  go test -mod=readonly -run '^$' -bench '^BenchmarkBasicValidation$' \
+  -benchmem -benchtime=500ms -count=5 ./internal/validate
+```
+
+Times list all five `ns/op` samples in command order, followed by median and
+range. Allocation figures are `B/op; allocs/op`.
+
+| Benchmark case | Before `ns/op` (median; range) | Before allocations | After `ns/op` (median; range) | After allocations |
+| --- | --- | --- | --- | --- |
+| Short text | 45.39, 45.10, 42.20, 44.19, 44.21 (44.21; 42.20–45.39) | 0; 0 | 41.80, 41.19, 39.90, 41.02, 39.18 (41.02; 39.18–41.80) | 0; 0 |
+| 1 MiB nonempty text | 216006, 220902, 226243, 228846, 184748 (220902; 184748–228846) | 1048576–1048577; 1 | 39.76, 42.16, 41.61, 40.79, 40.92 (40.92; 39.76–42.16) | 0; 0 |
+| ~1 MiB whitespace-only text | 766108, 709398, 731226, 915411, 787797 (766108; 709398–915411) | 1048592–1048594; 2 | 558919, 562202, 561004, 555487, 564593 (561004; 555487–564593) | 16; 1 |
+| Unicode whitespace | 126.6, 113.2, 116.7, 111.6, 115.2 (115.2; 111.6–126.6) | 16; 1 | 115.1, 116.9, 106.1, 111.2, 110.9 (111.2; 106.1–116.9) | 16; 1 |
+
+The 1 MiB nonempty case's median fell from 220902 ns/op to 40.92 ns/op while
+response-sized allocation fell from 1048576–1048577 bytes to zero. The
+whitespace case still scans the body and returns a small validation failure;
+its response-sized temporary string is gone, reducing allocation from about
+1 MiB and two allocations to 16 bytes and one allocation. Small-input timings
+and the Unicode case remain in the same order of magnitude. The benchmark no
+longer reports bytes per second because the nonempty fast path can classify a
+body from its boundary bytes without scanning the full body; latency and
+allocation comparisons remain meaningful.
+
+Focused verification passed on the implementation commit:
+`go test -mod=readonly ./internal/validate ./internal/usecase`. The benchmark
+family above was rerun on that commit with the recorded command.
+
 ## Open Questions
 
 No consumer-policy decisions remain open. File reservation and encoding error