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Claude 328aafae77 Bootstrap hotpath from engineering spec v0.1

Commit the spec and scaffold the system it describes:

- SPEC.md: the full v0.1 engineering spec
- crates/: trust-layer Rust workspace, unit-tested
  - bench-runner: interleaved ABAB scheduling with discarded warm-ups,
    deterministic bootstrap CIs over the ratio of medians,
    CI-lower-bound accept rule, env fingerprinting, and a CLI with
    compare + A/A self-test modes (A/A verified passing end-to-end)
  - diff-test: gate outcome model, sha256 corpus pin verifier that
    refuses on mismatch, per-target equivalence policy parser
    (byte-identical default, explicit fp-tolerance opt-in)
  - ledger: append-only SQLite attempt schema with UPDATE/DELETE
    refused by triggers, anti-double-attempt query
  - report: cores-saved and dollars/yr ROI math over speedup CIs,
    pricing.toml inputs
- playbook/: classes 1-7 with preconditions, procedure, verification
  notes, and known failure modes per class
- agent/: Python package skeleton — six-tool contract and prompting
  spine, harness IPC deferred to Phase 1
- config/: accept.toml (2% threshold, 30 runs/side), pricing.toml
- targets/, corpora/, results/calibration/: layout and policy docs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

2026-07-06 18:34:51 +00:00

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Class 2 — Allocator swap

Link-line only. With class 1, forms the "your 30% was a linker flag" tier that is always exhausted before touching source.

Preconditions

Profile signature: malloc/free/operator new or allocator-internal symbols (_int_malloc, tcache_*, page-fault handling) ≥5% of exclusive samples; or high syscall time in mmap/brk; or multithreaded target with allocator lock contention visible.

Procedure

Rust: add mimalloc (then jemallocator) as #[global_allocator] — two-line diff, still effectively link-level.
C/C++: LD_PRELOAD trial first (free experiment, no rebuild), then proper linking of the winner.
Bench each candidate allocator separately; do not stack with other changes.

Verification notes

Behavior-preserving by contract, so gates should pass trivially — but run them all anyway: allocator swaps change address-space layout and can unmask latent UB (use-after-free that "worked" under glibc). A sanitizer failure here is a pre-existing target bug: record it, route to needs-human-review, do not ship.
Max RSS is captured per run: an allocator that wins time but doubles memory is a trade-off the report must state, not hide.

Known failure modes

Wins on the bench box's core count that vanish (or invert) at the fleet's concurrency level.
LD_PRELOAD trial passing but static-link integration subtly failing (symbol interposition differences) — re-run full gates on the final link, not the trial.
Fragmentation pathologies on long-running services that a short bench window never sees; service-mode targets need soak evidence (Phase 4).

1.6 KiB Raw Blame History