skill: expose the trust layer as a consumable peltier skill

The reusable artifact here was never the vendored targets — it is the
discipline: prove equivalence, prove significance, or claim nothing. This
packages it as a Claude Code skill usable from any repo.

Two modes. `verify` works anywhere, on any two shell commands in any
language: equivalence before timing -> A/A calibration -> interleaved A/B
with a bootstrap CI -> a verdict decided by the CI lower bound, never the
median. `attempt` drives the full in-repo loop (gates, pristine-baseline
verdict, ledger row, ROI report).

It drives the real bench-runner binary and refuses rather than degrade: on
an unsupported host, or with no trust layer reachable, preflight stops and
says so instead of falling back to a hand-rolled timing loop. A second copy
of the statistics is a second thing that can lie. A refusal ends the claim,
not the work.

An adversarial review of the skill caught six high-severity defects, all
fixed here — several of them the very errors the skill exists to prevent:

- verify mode had no risk classification at all. bench-runner emits only
  accepted/rejected-bench; needs-human-review is minted by the in-repo
  verdict path, which verify does not run. A concurrency change with
  byte-identical output would have sailed through as "accepted". The skill
  now makes the agent the classifier and says so explicitly.
- the accept template exposed `pin_prefix`, which is inert for
  compare/aa/calibrate (only `verdict` reads it) — an agent would have set
  it and reported pinning that never happened. Now documents wrapping both
  sides in taskset instead.
- the equivalence gate compared stdout only, so two commands that write to
  stderr and a dist/ tree would "GOLDEN PASS" on two empty files. Now hashes
  stdout + stderr + exit code + artifact tree, and an empty diff over empty
  output is a failed gate, not a passed one.
- nothing told the agent to build two coexisting immutable artifacts, so a
  `cargo run` baseline could rebuild from the patched tree mid-bench — the
  exact trap phase1-verdict-smoke-001 recorded.
- service mode was documented as generic HTTP. It is not: the server must
  take <port> <doc> <iters>, print READY, and close the connection. A stock
  Express app hangs the harness forever. Contract now stated.
- the CI refusal test could not pass: preflight also walks up from its own
  location, so running it in-place found this very repo. The test now copies
  the skill out of the tree first.

CI job `skill-preflight` asserts the contract that matters — resolve when a
trust layer is reachable, REFUSE when it is not, and work when consumed from
another repo via PELTIER_HOME. It deliberately does not assert a statistical
outcome: a shared runner is too noisy for that, which is precisely why the
skill calibrates before it claims.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/skills/peltier/assets/accept.template.toml

@@ -0,0 +1,41 @@
+# peltier accept thresholds — consumer template.
+#
+# Copy this next to the code you are measuring and pass it with
+# `bench-runner --config <this-file>`. The defaults are peltier's own
+# published bar; loosening them to make a result pass is not measurement,
+# it is negotiation.
+
+# The bootstrap CI *lower bound* of the speedup ratio must clear 1 + threshold.
+# The median is not the claim. The lower bound is the claim.
+threshold = 0.02
+
+# Measured runs per side, interleaved ABAB (SPEC minimum: 30).
+runs_per_side = 30
+
+# Warm-up runs per side, discarded — they pay for cold caches and JIT.
+warmup_runs = 3
+
+# Bootstrap resamples for the ratio CI.
+bootstrap_iters = 10000
+
+# Confidence level for the ratio CI.
+confidence = 0.95
+
+# Fixed PRNG seed so a calibration run is reproducible by anyone.
+bootstrap_seed = 1887343589
+
+# CPU pinning. WARNING: this key is INERT for `compare`, `aa`, and `calibrate`
+# — it is read only by the in-repo `verdict` pipeline. Setting it here and then
+# reporting "pinned to core N" would be a claim about a run that never happened.
+#
+# To actually pin a compare/aa/calibrate run, wrap BOTH sides identically in
+# the command itself:  --baseline 'taskset -c 2 <cmd>' --candidate 'taskset -c 2 <cmd>'
+#
+# Pinning tightens the A/A confidence interval ~5x on peltier's calibration
+# hardware. An unpinned host is not disqualified; a NOISY one is, and the A/A
+# self-test decides that empirically. Leave this empty.
+pin_prefix = ""
+
+# Differential-fuzz iterations requested per gate run. Only used by the
+# in-repo `verdict` pipeline, which requires a target to declare [gates].fuzz.
+# fuzz_iters = 10000