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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 3 — Allocation churn

First source-touching class: reduce the number of allocations, not the allocator servicing them.

Preconditions

Class 2 helped but allocator symbols still hot, or allocation shows up as cache misses from pointer-chasing freshly allocated objects.
Profile signature: allocation inside hot loops; Vec/String reallocation churn; many short-lived objects of the same type.

Procedure (cheapest first)

Hoist allocations out of loops; reuse buffers via clear() instead of re-creation.
Vec::with_capacity / reserve where the size is known or bounded.
Small-vector types (smallvec, fixed inline buffers) for collections that are almost always tiny — confirm the size distribution from the profile or a counting instrument first.
Arena allocation (bumpalo, typed arenas) for phase-scoped object graphs with a clear reset point.

Verification notes

Buffer reuse is where stale-data bugs come from: golden replay must cover inputs of decreasing size across a session so a dirty buffer would surface. Add such a sequence to the corpus if missing.
Arenas change drop order; targets with observable Drop side effects (logging, flushing) can diverge on golden replay — that divergence is a real reject, not noise.

Known failure modes

with_capacity guesses that overshoot: RSS regression the wall-clock number won't show — check the captured max RSS.
smallvec inline sizes chosen by vibes: an inline buffer bigger than the cache line it saves. Measure, don't guess.
Reuse introducing borrow-checker contortions that force unsafe — unsafe introduction routes to needs-human-review (SPEC §8).

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