[Chore] Remove the completion check

[mrubens]

Why

The completion check (#3071, #3083, #3085, #3113) set out to replace the judge's minutes-long completion pass with a sub-second decision-model check. The judge part worked; the check did not. On nightly it flagged 49-60% of coding turns, mostly wrongly, because its hardest questions (did the tests pass on the shipped code?) depended on reconstructing validation evidence from the transcript: a shell-command window, file fingerprints, staleness rules. Each fix to that evidence exposed another gap. CI and pull request review already answer those questions from the source of truth.

What this removes

• Turn-end check and reopen in the OpenCode harness, including the held-message and settle plumbing it needed.
• The roomote-completion-gate.js OpenCode plugin and the commands.checkCompletionBeforeTool sandbox procedure (tool-time holds).
• Command recording, diff collection, and code fingerprinting (completion-gate-runtime.ts, completion-gate-evidence.ts).
• POST /api/mcp/tasks/runs/:runId/completion_check, the server gate, its types, and the ROOMOTE_COMPLETION_GATE flag set at dequeue.
• Docs describing the check.

What stays

• The judge limited to visual proof: it runs only when capture-visual-proof kept screenshots or keyframes. That is what removed the multi-minute general completion pass, and it no longer mentions a platform check.
• Unrelated fixes that landed along the way: shell exit codes from metadata.exit ([Fix] Shell exit codes are always missing from task transcripts and the completion check #3080), source tags on harness-queued continuations ([Fix] The completion check skips every task delegated from a Session #3083).

Rollback

No schema involved. A worker from the previous release calling the removed route gets a 404, which it already treats as a skipped check.

Validation

pnpm lint:fast, pnpm check-types:fast, pnpm knip; worker sandbox-server and run-task suites (remaining failures are the known local-only command-executor, tail-file-path, and OpenRouter variant tests), cloud-agents workflows, sdk task-runs, api tasks.

[roomote-community]

No new code issues found. See task

• The judge's shared prompt still requests a full implementation review, so visual-proof runs retain the completion pass this change intends to remove. apps/worker/src/run-task/agent-home.ts:1389
• The proof-only judge no longer receives the final shipped diff, so it cannot detect source drift after capture begins. packages/cloud-agents/src/server/workflows/skills/standard/implement-changes/resources/default-workflow.md:37

_{Reviewed e118987}