skill: cross-OS preflight — ps1 entry point, one CI-enforced contract

On a Windows host the preflight's job is to deliver a structured refusal
(measurement is Linux/POSIX-only). But a Windows-native harness with no
POSIX shell never got that far: preflight.sh fails to LAUNCH, and an agent
staring at "sh: not found" is exactly the agent that hand-rolls a timing
loop. The refusal doctrine has to be as portable as the skill.

- scripts/preflight.ps1: faithful port of the preflight contract, runs on
  Windows PowerShell 5.1 and pwsh 7+ on any OS. Host check first (so
  Windows refuses before touching anything), same walk-up resolution, same
  always-build rule, same key=value output, same exit codes. The source is
  pure ASCII with the shared em dashes composed at runtime — Windows
  PowerShell 5.1 misdecodes BOM-less UTF-8, and that exact bug class
  already bit this machine once (the francis-watchdog parse failure).
- Two implementations of one contract is a drift risk, so it is gated like
  every other claim in this repo: the skill-preflight CI job now runs BOTH
  scripts on the same ubuntu host and byte-diffs their stdout on all three
  paths (in-checkout resolve, no-checkout refusal, PELTIER_HOME from a
  foreign repo). Disagreement is a red build, not a footnote.
- New skill-preflight-windows job (windows-latest): asserts the native
  refusal end-to-end under Windows PowerShell 5.1 AND pwsh (STATUS=refuse,
  nonzero exit, the 'unsupported host' reason), plus Git Bash sh for good
  measure. Verified live on a real Windows 11 box before shipping: 5.1
  parses the pure-ASCII source clean and refuses with exit 1.
- SKILL.md / references/verify.md: document the second entry point ("use
  whichever your host can launch; never both, never neither"); book chapter
  and CLAUDE.md updated to match. .agents mirror regenerated (identical).
  The ZeroClaw variant is unaffected: rm -rf scripts/ drops the ps1 too,
  and its audit still passes (7 files scanned).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CLAUDE.md

@@ -29,7 +29,7 @@ Full engineering spec: `SPEC.md`. Read it before starting any phase.
 - `targets/` — vendored OSS targets for case studies (permissive licenses only)
 - `playbook/` — optimization classes, ordered, with preconditions and known risks
 - `results/` — generated reports and flamegraphs
-- `.claude/skills/peltier/` — the trust layer packaged as a consumable **Agent Skill** (agentskills.io SKILL.md standard, spec-compliant frontmatter): `verify` mode (equivalence → A/A calibration → interleaved A/B + bootstrap CI) works in any repo against any two shell commands; `attempt` mode drives the full in-repo loop. Drives the real `bench-runner` binary and refuses on unsupported hosts rather than falling back to a second, forkable copy of the statistics. Cross-harness: mirrored byte-identically at `.agents/skills/peltier/` (the Codex/Zed/Cursor/Gemini/Copilot convergence path — CI enforces the mirror), `AGENTS.md` at the repo root points non-Claude harnesses here, and `scripts/install-skill.sh` stamps consumer repos (plus a script-less `--zeroclaw-variant`, since ZeroClaw blocks script files in skills by default — its preflight runs from the checkout). Preflight refusal, spec conformance, mirror equality, and the installer are all asserted in CI (`skill-preflight`).
+- `.claude/skills/peltier/` — the trust layer packaged as a consumable **Agent Skill** (agentskills.io SKILL.md standard, spec-compliant frontmatter): `verify` mode (equivalence → A/A calibration → interleaved A/B + bootstrap CI) works in any repo against any two shell commands; `attempt` mode drives the full in-repo loop. Drives the real `bench-runner` binary and refuses on unsupported hosts rather than falling back to a second, forkable copy of the statistics. Cross-harness: mirrored byte-identically at `.agents/skills/peltier/` (the Codex/Zed/Cursor/Gemini/Copilot convergence path — CI enforces the mirror), `AGENTS.md` at the repo root points non-Claude harnesses here, and `scripts/install-skill.sh` stamps consumer repos (plus a script-less `--zeroclaw-variant`, since ZeroClaw blocks script files in skills by default — its preflight runs from the checkout). Preflight ships as two entry points implementing one contract — `preflight.sh` (POSIX) and `preflight.ps1` (Windows PowerShell 5.1/pwsh; pure-ASCII source, em dashes composed at runtime) — CI byte-diffs their output on all three paths and a `windows-latest` job asserts the native refusal. Preflight refusal, sh↔ps1 equivalence, spec conformance, mirror equality, and the installer are all asserted in CI (`skill-preflight`, `skill-preflight-windows`).
 
 **Phase 4 COMPLETE — all SPEC §5 exit criteria met. Phases 0–4 are all done.** Service-mode latency benchmarking shipped: a coordinated-omission-correct, open-loop, fixed-rate load generator (`crates/bench-runner/src/service.rs`) measuring latency from each request's intended send time (queueing counted, not hidden), interleaved A/B, exact percentiles, bootstrap p50/p99 CIs. A real service target — `targets/cjson/service.c`, a minimal HTTP server wrapping the patched `cJSON.c` (trust-layer, outside the workspace allowlist). Service calibration PASS (0/10 A/A false-positive, 10/10 injected-5%-latency-regression detection; `results/calibration/cjson-service-aa.json`). **The verified batch win phase3-cjson-002 measured under a 150 rps-target replay (20 interleaved rounds, 0 drops — the `phase4-cjson-service` ledger row records sessions=20, rate_rps=150, drop_rate=0.0; total request count is not machine-recorded): p50 latency +6.2%, 95% CI [+5.8%, +7.2%] — accepted; p99 NOT claimed (CI [0.07, 4.97], single-worker loopback tail jitter) — harness correctly rejected it.** Mechanical ROI report generator (`crates/report` bin, `just report`, SPEC §9): reads a ledger row + service-latency JSON → throughput→cores→dollars (27.5 cores / $9,621-per-year CI lower bound on a 500-core fleet) *and* latency percentiles, every figure with CI + workload + methodology inline; flags any non-accepted row. Case study: `results/phase4/`. **The roadmap is complete — the profile→hypothesize→patch→gated-verdict→ROI loop runs end to end across Rust and C, batch and service, with zero shipped false accepts across all phases.**