refactor(hooks): extract gate detection into invocable-command lib (U5a — PR3)

[dralgorhythm]

Summary

U5a (PR3, gates lane 1 of 3) from plan_framework_hardening.md: pure-structure extraction of gate detection into an invocable-command library. Zero behavior change — the prerequisite for PR4's blocking enforcement (U5b) and PR5's default task gate (U5c), which branch from main after this merges.

What changed

• New .claude/hooks/gate-lib.sh (108 LOC): gate_lib_detect(dir) fills parallel GATE_LABELS/GATE_COMMANDS arrays with runnable per-stack gate commands (TS/JS pnpm/npm-aware, Python uv-aware, Go, Rust) — today's inline block produced display labels only.
• pre-commit-verification.sh: sources the lib (BASH_SOURCE-relative, CWD-independent) and reconstructs its advisory output from the lib — byte-identical: old-vs-new stdout diffed empty across five fixture contexts (TS/pnpm, TS/npm, Python, Go, Rust); the untouched baseline harness case also passes.
• Lib commands proven invocable: the detected pnpm test in scripts/fixtures/failing-project executes and returns the fixture's deliberate nonzero.

Provenance

• Author: worker-builder (sonnet) via /swarm-execute, refactoring focus (Two Hats: structure only); orchestrator re-ran all gates independently on the lane tip.
• Gates: test-hooks.sh ALL GREEN (no skips); check-invariants.sh ALL GREEN; CI-equivalent shellcheck clean; bash -n clean.

Risk tier

low — behavior-identity is the acceptance criterion and is byte-diff proven; no wiring, docs, or settings changes (deliberately deferred to U5b/U5c).

Test plan

• Old-vs-new advisory stdout byte-identical across five stack fixtures
• Baseline harness case for this hook passes unedited
• Lib-derived command smoke-executed in the failing fixture (nonzero as designed)

🤖 Generated with Claude Code