ci(loop): mirror CI's non-test gates so cycles stop leaving master red

[rslayer]

Root cause (from this round's analysis)

The recurring "master is red after a loop cycle" problem: the loop's EVAL gate is pytest-only, but ci.yml — which runs on the loop/cycle-N PR the loop opens — also enforces ruff, mypy, an openapi.json drift check, and the frontend gen:api:check. The build agent's Python-only runner can't even regenerate the frontend types. So every cycle's PR lands red on those gates, and merging it reddens master (cleaned up manually in #69, and again this round).

The fix — close it at the source

• Node 20 setup step — needed to regenerate web/src/lib/api.gen.ts.
• "CI parity" step after BUILD that deterministically fixes the mechanical gates: ruff --fix (import order / unused), regenerate openapi.json, regenerate the frontend API types. Non-fatal by design (the loop must still open a PR for review); anything left red is surfaced as a ::warning and by ci.yml on the PR. Placed before EVAL and the product-snapshot so the changes are part of the reviewed cycle.
• Build-prompt HARD RULE: run ruff + mypy and fix real errors, and regenerate openapi.json on model changes (mypy / non-autofixable lint can't be fixed mechanically, so the agent must).

⚠️ Not merged — needs your review + a test dispatch

workflow_dispatch workflows can't be run from my environment, so this is static/YAML-validated only:

• YAML parses; 18 steps in the right order (CI-parity sits between Build and Eval).
• The ruff --fix and openapi export commands run clean (no-ops on green master).
• I could not exercise the Node setup, npm ci, or the full dispatch (needs secrets + the Actions env).

Please review and do one gh workflow run loop.yml to confirm before relying on it. I left it as a PR rather than merging blind.

Companion to the budget-fix PR from the same review round.

🤖 Generated with Claude Code