Make harness continuation retries idempotent

[actus7]

What changed

• makes POST /harness/agent-runs/:id/continue idempotent for terminal runs
• replays the terminal run status through the existing SSE protocol instead of returning a conflict
• removes the duplicate database lookup between route authorization and stream startup
• avoids persisting duplicate terminal status events on harmless retries
• adds regression coverage for an empty terminal continuation replay

Root cause

A continuation request can race with the worker that changes a yielded run to a terminal state. The endpoint rejected that retry instead of returning the already-known final state. A second lookup inside stream startup also left an unnecessary time-of-check/time-of-use gap.

Impact

The chat client now treats late or repeated continuation requests as successful terminal replays, so a completed, failed, or cancelled run cannot become a misleading raw continuation error in the interface.

Validation

• pnpm test — 464 passed, 1 skipped
• pnpm typecheck — passed
• pnpm build — passed
• pnpm lint — 0 errors; 1 pre-existing warning in .remember/tmp/last-ndc.ts

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Project	Deployment	Actions	Updated (UTC)
modelhub	Ready	Preview	Aug 19, 2026 7:07pm

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