CI lint: enforce the plan-template Verify deny-list (falsifiable-verify rules are advisory without it)

[lantisprime]

Summary

PR #51 added a Falsifiable Verify rule + deny-list to agents/PLAN_TEMPLATE.md so lower-capability executors can't ship hollow guards (the P6-0b run-p6-smoke.sh / --append-system-prompt /dev/null failure). But the template only describes the deny-list — nothing enforces it. This repo has no active hook/CI that checks plan tables, so the rules are advisory until a lint exists.

Per the repo principle "enforce rules in CI, not just docs," add a lint.

Root cause it closes

A low-capability executor produces the weakest artifact its verify command accepts. The deny-list only bites if a machine rejects a non-falsifiable Verify cell at authoring/PR time.

Proposed lint

A check (script + CI step) over Appendix B mechanical-spec tables in agents/docs/*PLAN*.md (and any plan using the template's step tables) that fails when a Verify cell:

• tests only an exit code with a tolerant comparison — test $? -ne 1, || true, ; true, && echo ok;
• contains no capture-and-compare (no named observed value: stdout/exit/file/return vs an expected concrete value) — e.g. bare "exits 0" / "script runs";
• (heuristic) greps for a string literal that also appears in an echo/comment the same step writes (self-fulfilling);
• belongs to a MUST requirement or Safety/Security mitigation row and is a command -v …-skippable smoke without an UNGUARDED-IN-CI tag.

Plus: every UNGUARDED-IN-CI row MUST name a covering manual step (the lint asserts the Notes column is non-empty).

Acceptance

• Lint script under scripts/ (or agents/), runnable locally, exits non-zero on a violating Verify cell with a clear message + file:line.
• Wired into .github/workflows/ci.yml.
• A regression fixture: a deliberately-hollow Verify cell (test $? -ne 1) that the lint catches, and a falsifiable one it passes. (Per repo rule: regression test in the same commit as the lint.)
• Run against existing P6 plan tables; fix or UNGUARDED-IN-CI-tag any current violators (0b.17's row is the known one).

Context

• Template rules: PR docs(plan-template): falsifiable-verify rules so weak executors can't ship hollow guards #51 (docs/plan-template-falsifiable-verify)
• Triggering failure: P6-0b smoke gate (review on feat/p6-intent-routing)
• Related CI gap: CI: agents/ extension test suites are not run in CI #49 (agents/ suites not run in CI) — this lint and CI: agents/ extension test suites are not run in CI #49 could share one new CI job.