[Improve] Show pull requests in Fast task updates

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote or in the web UI.

What changed

• Add structured pull request metadata to delegated-task settlement events so Fast closeouts can name and link every associated PR with its current status.
• Emit provider-neutral PR-opened events through the existing Fast parent event stream as soon as source-control delivery persists the task association.
• Deduplicate retries with durable per-run claims and stable Slack message IDs, while preventing terminal task events from being followed by stale PR-open notices.
• Bound PR-open Fast turn-lock waits to 30 seconds so an unrelated active turn cannot hold an already-persisted source-control mutation for the default ten-minute lock window.
• Propagate transient PR-open delivery failures after releasing their claim, allowing the next source-control attempt to update the existing PR and retry the early Fast event.
• Teach the Fast orchestrator to present PR-open and completion context without repeating “newly opened” wording.

Why this change was made

Delegated Slack tasks could open a pull request without giving the Fast orchestrator reliable structured context, leaving completion replies unable to mention the shipped PR. A separate direct Slack notification would recreate duplicate-message behavior, so this keeps lifecycle presentation in the existing parent event path.

Impact

Fast-mode Slack conversations now receive an early, linked PR update and retain authoritative PR context at task completion. Existing merge, close, and review notification paths are unchanged.

[roomote-community]

No code issues found. See task

• packages/sdk/src/server/lib/task-runs/notify-fast-agent-parent-on-pull-request-opened.ts:108 now bounds the Fast turn-lock wait to 30 seconds.
• packages/sdk/src/server/lib/pull-requests/source-control-pull-requests.ts:407 now propagates transient PR-open notification failures after releasing their claim, so a retry updates the existing PR and retries the early event.

_{Reviewed 2b82523}

[roomote-roomote]

Addressed all current review feedback in 224d4fd and 2b82523. PR-open delivery now has a 30-second lock bound, and transient failures propagate after claim release so an update retry can recover without creating another PR. Focused tests and the full pre-push suite pass; all 17 CI checks completed with 14 successes and 3 expected skips. Both review threads are resolved. See the task.