fix(run): enforce read-only seat capability

[solomonneas]

Closes #377.

What changed

• Add read_only_capable to roster agents with strict boolean validation and a backward-compatible true default.
• Reject read-only plan assignments to incapable seats before dispatch, including direct-worker runs.
• Preserve the capability in roster snapshots and resumed runs.
• Mark direct Composer, Grok, and affected proxy seats as incapable in the documented roster examples.

Root cause

The roster had no machine-readable read-only capability. Planning treated every enabled seat as eligible, so the chef could assign read-only work to transports that cannot perform it.

Verification

• brigade work verify run --target . --command "./scripts/verify" --capture brigade-work
• Brigade receipt: 20260720-014716-work-verify-bbff39
• Result: 3,180 passed, 3 skipped, 82.19% coverage
• Independent review: no findings; conflict-free rebase followed by a full gate

Risk

Existing rosters remain compatible because omitted capability metadata defaults to true. Incorrect non-boolean values now fail roster validation with a field-specific message.

[coderabbitai]

Important

Review skipped

Auto reviews are limited based on label configuration.

🏷️ Required labels (at least one) (1)

• coderabbit-review

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Repository: escoffier-labs/coderabbit/.coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 8ab2b8a6-0755-4806-b3ca-7749ae657a66

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/issue-377

---

_{Comment @coderabbitai help to get the list of available commands.}