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benbrownandClaude Opus 4.8
899d55f4b6
An adversarial audit found the enforcement story ahead of the code: gates that were documented as hard gates were advisory, manual, or absent, and several human-facing claims outran the machine record. This makes the claims true. High findings - Differential fuzz was documentation, not enforcement: verdict hardcoded fuzz_iters=0 and diff-test hardcoded the gate to Skipped, while the case studies claimed 10k-iteration fuzz on the same wins. Fuzz is now a real pipeline gate (strict FUZZ-RESULT contract, executed count recorded), and it is inherently baseline-vs-candidate, so it runs on the accept path and reports Skipped in the standalone `just gates` flow. New hard rule: a machine `accepted` verdict is impossible unless the fuzz gate actually passed — otherwise it caps at needs-human-review. - The agent's system prompt claimed FP/concurrency/unsafe patches were "routed to human review automatically". No such mechanism existed. Added a conservative lexical risk classifier (crates/verdict/src/risk.rs) that forces needs-human-review on any would-be accept carrying those signals; fp-tolerance equivalence always signals. - The local verdict path ran agent-influenced code unsandboxed. It now runs under scripts/no-net.sh (network namespace) and fails closed. Upstream test suites are hash-verified against corpora/<t>/TESTSUITE.sha256 when present (scripts/pin-testsuite.sh generates them). Also fixed, found while fixing the above - The pipeline script's `set -e` was inert (brace group as the left operand of `&&`), so a failing candidate build did not abort the run and verdict could bench a stale binary. Now a scoped subshell whose status is branched on at top level. - A wrapper that exits before exec'ing (no-net.sh refusing, bad wrapper path) stranded RUNNING.lock and left read_verdict polling forever. Failure accounting now lives outside the wrapper. - harnessd's patch allowlist ignored git rename/copy headers and --no-prefix diffs; the rename-escape case is now a committed regression test. - The workspace did not compile on Windows (ungated Unix APIs). cfg-gated; 71 portable tests now run on both platforms. - pin-check regenerated the corpus manifest instead of verifying it; it is now verify-only, with a deliberate `just pin-corpus` to re-pin. - Max RSS is captured per run on Unix; PMU counters are opt-in diagnostics (compare --perf-stat), never part of the accept decision. Docs now match the code, including what is NOT yet enforced: no target ships a TESTSUITE.sha256 pin, no target declares [build].tsan, and matmul is not wired to the fp-tolerance gate — each is stated as mechanized-but-inert rather than done. Corrected the stale "33 ledger rows" (34), the playbook's class-3 cJSON win (rejected), adversarial-review.md's sanitizer-separation claim (five accepted rows carry sanitizers_clean=false), the unsupported "40,000 requests" figure, and the blanket "historical rows record fuzz_iters=0" (8 of 10; phase0-tokei-002/-003 record 4,332). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
74 lines
3.8 KiB
Markdown
74 lines
3.8 KiB
Markdown
# Case study 1 — tokei: compounding algorithmic wins (Rust, class 5)
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**Target:** [tokei](https://github.com/XAMPPRocky/tokei) v14.0.0 — a
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source-code line counter. **Workload:** 221 MB / 4360 files (8 replicas
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of the Pro Git book + comrak's own tree), single rayon thread, CPU
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pinned. **Result:** three independent, CI-verified class-5 wins on the
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same hot function — each proposed *by the unattended agent* and
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100%-audited. Multiplied together they are **~1.26× over the Phase-0
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baseline** (1.107 × 1.037 × 1.099), but that product is an
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approximation, not a measured figure: each speedup carries its own
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bootstrap CI against its own baseline, and confidence intervals do not
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compose through multiplication. The trustworthy claims are the three
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individual increments below.
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## The hot path
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tokei spends the overwhelming majority of its instructions in one
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function — `LanguageType::parse_lines` and the per-byte loop inside
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`SyntaxCounter::perform_multi_line_analysis`. The cache-sim profile put
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it at **55.9% of instructions, 62% of all branches, 44% of branch
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mispredicts** on the pinned corpus: for every byte of every line, the
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counter tested a stack of quote/comment token matchers.
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## The three wins
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| run | mechanism | speedup (median) | 95% CI |
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|---|---|---|---|
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| `phase0-tokei-002` (class 3) | read path: `fs::read` pre-sized, BOM-only decode | 1.099 | [1.080, 1.127] |
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| `phase2-tokei-001` (class 5) | 256-entry first-byte gate table for the token matchers | 1.107 | [1.084, 1.131] |
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| `phase2-tokei-003` (class 5) | forward-only whitespace break (drop the `rposition` rescan) | 1.037 | [1.027, 1.052] |
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| `phase2-tokei-008` (class 5) | streaming leftmost `important_syntax` scan (one vectorized pass, not per-line restart) | 1.099 | [1.073, 1.112] |
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Each is a **redundant-work elimination**: the first-byte gate replaces
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five per-byte matcher loops with one table load; the whitespace-break
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change drops a full backward scan of the file tail per byte; the
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streaming scan replaces a per-line aho-corasick restart (which kept
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memmem's SIMD prefilter in its short-haystack slow path) with a single
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leftmost search advanced by integer comparisons.
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## Why the numbers are trustworthy
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- **Byte-identical golden replay** on the pinned corpus for every win —
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a code counter that miscounts one line fails the gate.
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- **10,000-input differential fuzz** (`scripts/diff-fuzz-tokei.py`),
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pristine vs candidate, **0 divergences** — after canonicalizing
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tokei's benign parallel-walker output ordering (a real finding:
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raw-byte differential comparison over-counts when the target is
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legitimately nondeterministic in presentation).
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- **ASan/LSan clean** on the patched tree over the full corpus.
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- **Interleaved A/B** vs a pristine-rebuilt baseline, bootstrap 95% CI
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lower bound ≥ the 2% bar. `phase2-tokei-008` was the first accept
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through the *machine-enforced* sanitizer gate (see case study 3).
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## What it demonstrates
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The richest wins on a mature Rust binary were not exotic — they were
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"this loop does work it doesn't need to, on every byte." The agent found
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each by reading the cache-sim profile, checking the ledger to avoid
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re-attempting a class on the same hotspot, and proposing the cheapest
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untried mechanism. Three separate hypotheses, three separate verified
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increments, all on the same 40%-of-runtime function — and one honest
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rejection in between (`phase2-tokei-009`, a real +5.7% median whose
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noisy CI lower bound of +0.2% could not clear the bar, so it does not
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count).
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---
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> **Note (2026-07-13).** The 10,000-input differential fuzz cited above
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> ran **out-of-band** (`scripts/diff-fuzz-tokei.py`, per-attempt), not
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> inside the verdict pipeline — so these ledger rows record
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> `fuzz_iters=0` in their machine record. The fuzz gate is now
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> pipeline-integrated; rows written after this date record the
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> iteration count actually executed.
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