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phase4: COMPLETE — service latency win + mechanical ROI report; roadmap done

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phase4-cjson-service (ledger): the accepted batch win phase3-cjson-002
measured under a 150 rps coordinated-omission-correct replay (20 rounds,
40k requests, 0 drops). p50 latency +6.2%, 95% CI [+5.8%, +7.2%] —
accepted; p99 CI [0.07, 4.97] too noisy (single-worker loopback tail),
harness correctly rejected. ROI (500-core fleet, $0.04/core-hr): 27.5
cores / $9,621/year at the CI lower bound, report generated mechanically
(results/phase4/cjson-service-roi.md).

- results/phase4/: case study + README + the generated ROI report.
- CLAUDE.md: Phase 4 complete; Phases 0-4 all done.

All SPEC §5 exit criteria met across every phase; zero shipped false
accepts across the whole project.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2
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@@ -30,9 +30,7 @@ Full engineering spec: `SPEC.md`. Read it before starting any phase.
- `playbook/` — optimization classes, ordered, with preconditions and known risks
- `results/` — generated reports and flamegraphs
## Current phase
**Phase 3 COMPLETE — all SPEC §5 exit criteria met.** The trust layer went language-agnostic: build isolation moved from a cargo-specific `CARGO_TARGET_DIR` injection to an explicit `{out}` placeholder + optional `sanitizer`/`sanitizer_binary` templates (`crates/diff-test/src/target.rs`), proven zero-regression on tokei before any C target. **A C target joined the roster** — cJSON v1.7.19 (MIT): trust-layer harness driver compiled with the patched `cJSON.c`, hermetic Unity/CTest gate (19 tests), ASan+UBSan sanitizers, deterministic pinned corpus, own A/A calibration (0/20 FP, 20/20 injection), CI-gated. **First verified cross-language win:** phase3-cjson-002 (class 5+3, stack-buffer number parse + `strtod` round-trip) +8.85%, 95% CI [+7.5%, +10.0%] — banked, byte-identical golden replay, independent ASan+UBSan clean, 10k-input diff-fuzz (`scripts/diff-fuzz-cjson.py`) 0 divergences. **Four public case studies** in `results/phase3/` (tokei class-5 wins; build flags + allocators; the comrak caught false-accept; the cJSON cross-language proof). **Six playbook classes exercised (1–6)**; wins on classes 1/2(review)/3/5 across Rust *and* C. coz wired (`-DHOTPATH_COZ`, `just coz`, `scripts/coz-*`); its apt runtime aborts in init on this container's glibc, so callgrind cache-sim is the working profiler (documented). Zero regressions shipped. **Next: Phase 4** (load replay, latency mode under replayed traffic, mechanical ROI reports — SPEC.md §5; `crates/report` has the ROI math, needs the generator).
**Phase 4 COMPLETE — all SPEC §5 exit criteria met. Phases 0–4 are all done.** Service-mode latency benchmarking shipped: a coordinated-omission-correct, open-loop, fixed-rate load generator (`crates/bench-runner/src/service.rs`) measuring latency from each request's intended send time (queueing counted, not hidden), interleaved A/B, exact percentiles, bootstrap p50/p99 CIs. A real service target — `targets/cjson/service.c`, a minimal HTTP server wrapping the patched `cJSON.c` (trust-layer, outside the workspace allowlist). Service calibration PASS (0/10 A/A false-positive, 10/10 injected-5%-latency-regression detection; `results/calibration/cjson-service-aa.json`). **The verified batch win phase3-cjson-002 measured under a 150 rps replay (20 rounds, 40k requests, 0 drops): p50 latency +6.2%, 95% CI [+5.8%, +7.2%] — accepted (`phase4-cjson-service` ledger row); p99 NOT claimed (CI [0.07, 4.97], single-worker loopback tail jitter) — harness correctly rejected it.** Mechanical ROI report generator (`crates/report` bin, `just report`, SPEC §9): reads a ledger row + service-latency JSON → throughput→cores→dollars (27.5 cores / $9,621-per-year CI lower bound on a 500-core fleet) *and* latency percentiles, every figure with CI + workload + methodology inline; flags any non-accepted row. Case study: `results/phase4/`. **The roadmap is complete — the profile→hypothesize→patch→gated-verdict→ROI loop runs end to end across Rust and C, batch and service, with zero shipped false accepts across all phases. Open follow-ups: the standing human ruling on `phase0-comrak-002` (mimalloc, needs-human-review); SPEC §13 research forks (GPU lane, learned policies) remain out of scope.**
## Commands