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+# hotpath — profile-guided optimization agent
+
+> Working name. Rename freely; nothing depends on it.
+
+## Mission
+
+An agent that profiles real binaries and services, isolates hot paths, proposes optimizations, and accepts a change **only** when (a) behavioral-equivalence gates pass and (b) the benchmark improvement is statistically significant on trusted infrastructure. Output: verified performance deltas translated into ROI reports nobody can dispute.
+
+Full engineering spec: `SPEC.md`. Read it before starting any phase.
+
+## Non-negotiables (re-read every session)
+
+1. **No unverified performance claims.** A change without passing equivalence gates AND a significant bench delta does not exist. Discard it. Log it.
+2. **Measure before optimizing.** No patch is proposed until profile data identifies the hot path. Never trust a single benchmark run.
+3. **Cheap wins first, always.** Build flags → LTO → PGO → allocator swap → *then* code changes. Check the ledger before re-attempting any class of change on a target.
+4. **Equivalence gates are hard gates.** Changes touching floating-point ordering, concurrency primitives, or anything UB-adjacent are NEVER auto-accepted — verdict is `needs-human-review`.
+5. **Every attempt goes in the ledger**, including failures and rejections. Failures are future training data.
+6. **The agent never modifies the trust layer.** `crates/`, `config/`, `corpora/`, and upstream test suites are read-only to the agent. Patches may touch only allowlisted paths under `targets/<name>/`. See SPEC.md §10.
+7. **Sandbox everything.** Target code runs only inside no-network containers. Never on the host.
+8. **Statistical bar:** accept only if the bootstrap 95% CI lower bound of speedup ≥ threshold in `config/accept.toml` (default 2%), from interleaved A/B runs on the same pinned hardware.
+
+## Architecture map
+
+- `crates/bench-runner` — trust layer: containerized, CPU-pinned, interleaved A/B benchmarking with bootstrap confidence intervals and A/A self-tests
+- `crates/diff-test` — behavioral equivalence: upstream test suite + golden I/O replay + differential fuzzing of changed functions + sanitizers
+- `crates/ledger` — append-only SQLite record of every attempt: hypothesis, patch, gate results, bench deltas, verdict, cost
+- `crates/report` — ROI generator: cores saved × $/core-hr, latency percentile deltas, CIs, workload caveats printed on every number
+- `agent/` — Claude Agent SDK (Python) loop, prompts, tool definitions
+- `targets/` — vendored OSS targets for case studies (permissive licenses only)
+- `playbook/` — optimization classes, ordered, with preconditions and known risks
+- `results/` — generated reports and flamegraphs
+
+## Current phase
+
+**Phase 0 — manual dry run.** (Update this line as phases complete; exit criteria in SPEC.md §5.)
+
+## Commands
+
+Fill these in as the harness is built; keep them current:
+
+```
+just profile <target>       # perf record + flamegraph for a target's benchmark workload
+just bench <target> <ref>   # interleaved A/B: pristine baseline vs working tree
+just gates <target>         # test suite + golden replay + diff-fuzz + sanitizers
+just verdict <target>       # runs gates + bench, writes ledger row, prints verdict
+just report <run-id>        # ROI report from ledger
+just aa <target>            # A/A calibration run (must show null result)
+```
+
+Built so far (command-level, pre-target-integration):
+
+```
+just build / test / lint    # trust-layer workspace: cargo build/test/clippy+fmt
+just aa [cmd]               # A/A self-test of bench-runner on a shell command
+just compare <a> <b>        # interleaved A/B of two shell commands, bootstrap CI
+just pin-check <target>     # verify corpus MANIFEST.sha256
+```
+
+## Definition of done — one optimization attempt
+
+- [ ] Hypothesis logged in ledger *before* patching
+- [ ] Patch touches only allowlisted paths under `targets/<name>/`
+- [ ] Upstream test suite green
+- [ ] Golden replay byte-identical (or within the target's explicit FP tolerance policy)
+- [ ] Differential fuzz on changed functions: no divergence (60s or 10k iterations minimum)
+- [ ] ASan + UBSan clean; TSan if the patch touches anything threaded
+- [ ] Interleaved A/B bench passes the CI-lower-bound threshold
+- [ ] Ledger row written with verdict and full evidence
+- [ ] If FP-ordering / concurrency / UB-adjacent: verdict `needs-human-review`, never auto-accept
+
+An attempt that fails any gate is a **valid, complete outcome** — write the ledger row and move on. Do not iterate on a rejected patch more than twice without a new hypothesis.
+
+## Conventions
+
+- Rust workspace (edition 2021+) for all harness crates; `just` for task running
+- Python 3.11+ for `agent/`; Claude Agent SDK — verify current package name and API at https://docs.claude.com/en/docs/claude-code/overview before scaffolding
+- Every number shown to a human carries its confidence interval and workload description. No naked percentages, ever.
+- Commit style: `phase0:`, `bench:`, `gates:`, `agent:`, `playbook:` prefixes
+- When in doubt between shipping a feature and hardening measurement, harden measurement. The product is trust.