1.4b — CI gates: run smoke corpus + inspector-contract checks on PR

[aarontrowbridge]

Part of Phase 1.4 (Jack's Phase-1 kickoff, #amicode 2026-07-01). Complements #45 (VSIX gate): wire the smoke corpus (#61) into CI as a required PR gate, plus a contract check for the frozen RunInspector message/DOM schema (Jack's freeze step 2).

This is the enforcement layer for the run-dir contract — the required gate is the home for every producer↔consumer guard on that contract. Checks are added to the required set as each lands (this issue is not blocked on the ones still in flight).

Gate scope (required checks)

• Smoke corpus (1.4a — smoke corpus: minimal end-to-end solve fixtures #61 / 1.4a: smoke corpus — seconds-scale end-to-end fixtures (Scheduler → executor → RunsManager → Inspector) #78) — end-to-end Scheduler → executor → RunsManager → Inspector wiring.
• RunInspector message/DOM contract check — the frozen runId-keyed protocol + DOM ids (freeze step 2).
• Run-dir reader parity (Consolidate run-dir readers behind one readRunDir — kill the N-completion-path field drift #84) — the single readRunDir guard, so completion paths can't drop additive fields. Lands with feat(contract): pre-solve formulation.toml (additive; scoped counterpart to #64) #81; add on landing.
• AMICODE_ stdout fixture roundtrip* (Bring the AMICODE_* stdout grammar under the shared-fixture roundtrip discipline #83, test portion only) — template↔parser format drift. Lands with 1.4a: smoke corpus — seconds-scale end-to-end fixtures (Scheduler → executor → RunsManager → Inspector) #78; add on landing. The AmicoRunDir.jl package refactor in Bring the AMICODE_* stdout grammar under the shared-fixture roundtrip discipline #83 is out of scope here — it's deferred to the second template (WIP night spike: pulse-designer Layer-0 — interview → entities → solve, e2e green #75/Score runtime (D5): manifests, router, entitlements, stage guard, usage capture #76).

Dependencies

Blocked-by: #61
Blocked-by: #45
Part-of: Phase 1 (1.4)