Turn drafter-core PR rules off unless CATSTACK_DRAFTER_CORE=1

[EdbertChan]

Summary

The PR drafting tools now skip the outside PR rule package unless a new setting turns it on. When skipped, they print a clear "unchecked" line.

The repo's own summary checks still run. The template tool stops with an "unchecked" exit so nobody mistakes an empty template for a real one.

Review Claim

With the new setting off, the PR drafting tools skip the outside rule package and say so, and turn it back on when the setting is on.

Review Lane

behavior

Review Unit

engine-runtime

Safety Invariant

With CATSTACK_DRAFTER_CORE=1 every script runs the same drafter-core rules as before; with it off, no check reports clean for rules it skipped.

Slice Rationale

The flag and every script that reads it change together, so the setting means one thing. The README flag row is its own docs PR stacked on this one.

Non-goals

• Does not remove drafter-core from package.json or CI.
• Does not change preflight.py review-unit rules, which read drafter.config.json directly.
• Does not change the preflight parity test, which still calls drafter-core.

Test Plan

Test Plan

• New tests fail on the old scripts: python3 -m unittest -k flag_off engine/skills/draft-pr/tests/test_draft_pr_scripts.py tests/test_validate_pr_body_local.py → FAILED (failures=3)
• Same files with the change, plus preflight tests: Ran 60 tests ... OK
• bash scripts/test/run_all_tests.sh → exit 0, no FAILED lines
• Flag off by hand: lint-diff-atomicity.mjs prints UNCHECKED: drafter-core rules skipped (CATSTACK_DRAFTER_CORE is off; ...) exit 0; pr-body-template.mjs same line, exit 3
• Flag on by hand: Diff atomicity validation passed. exit 0; template prints ## Summary exit 0
• python3 engine/skills/make-pr/scripts/preflight.py --base origin/main --body-file <this body>

Revert Plan

Revert Plan

• Safe to revert? Yes
• Revert command: git revert <sha>
• Post-revert steps: None
• Data migration? No

🤖 Generated with Claude Code

[EdbertChan]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	Turn drafter-core PR rules off unless CATSTACK_DRAFTER_CORE=1	#742	👈
2	README: list the CATSTACK_DRAFTER_CORE flag	#743