#7297 docs(recipe): Needs review is not shipped without tip-native proof

What & why

Adds one docs page: docs/proof-gate-needs-review-receipt.md.

Needs review on the board is not shipped. Tip-native proof (check runs or a receipt pinned to the exact branch-tip SHA) is required first. Without that bar, Operators treat chrome as done and the product keeps lying about finished work.

How I tested

• Docs-only diff vs main (single file)
• Stay DRAFT — no undraft without CoS→Owen

Checklist

• Thin docs brick only (no host-service / product code)
• Attested board nouns; no invented ReadyVerified column
• Fence Todd #7007 agentStatus SoT; no hooks #7252/#7263

Supersedes contaminated draft #7296 (same docs intent; #7296 head accidentally included terminal-agents files).

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Summary by cubic

Stops a parent terminal from announcing completion while its subagents are still running, and adds a docs rule that Needs review on the board is not shipped without tip-native proof.

Bug Fixes

• A parent Stop now waits until the last child exits; previously it flipped the terminal green while children still worked.
• A stopped child no longer revives when its own events straggle in after the stop, unless the harness opts in to revival (Codex send_input).
• Deferred completions fire exactly once when the roster drains, and are dropped when the parent starts a new turn or the terminal dies.
• A child that goes quiet without a stop hook now delays the completion by the stale window instead of losing it; the sidebar poll releases it.
• Permission requests still raise while children run.

Docs

• Adds docs/proof-gate-needs-review-receipt.md: Needs review means not shipped without a check run or receipt pinned to the branch-tip SHA.