fix(edge-worker): suppress ede_diagnostic error on first-stop interrupt (CYPACK-1352)

[cyrusagent]

Summary

Fixes CYPACK-1352. When a user sends a single stop to interrupt Cyrus mid-turn, Linear showed a spurious red An error occurred activity containing internal SDK diagnostic text:

[ede_diagnostic] result_type=user last_content_type=n/a stop_reason=tool_use

Root cause (what changed)

PR #1109 (a7be6096, "warm sessions, interrupt-on-stop, and buffered response posting") introduced a two-phase stop: the first stop on a warm session now calls runner.interrupt() (abort the current turn, keep the session alive) instead of stop().

The pre-warm-session flow set a stop-request flag (requestSessionStop) so AgentSessionManager.completeSession() swallowed any error result. The new first-stop interrupt branch in EdgeWorker.handleStopSignal() never set a flag, so when the SDK surfaced the aborted turn as an error_during_execution result containing [ede_diagnostic] ..., consumeStopRequest() returned false and addResultEntry() posted it as a visible error.

For warm sessions, interrupt() does not throw (the keepSessionWarm loop stays alive), so the diagnostic arrives purely as a result message — fixing the completeSession path is sufficient. (Two prior fixes for this exact issue existed on the agent-sessions-warmup and cypack-1129 branches but were never merged to main; this ports the cleaner edge-worker-level approach.)

Fix

• Add requestSessionInterrupt() / consumeInterruptRequest() to AgentSessionManager (mirrors the existing stop-request mechanism).
• EdgeWorker.handleStopSignal() marks the session as interrupted before calling interrupt().
• completeSession() checks the interrupt flag first: if set, it swallows the error result and keeps the session Active (no status change) so the next prompt resumes normally. The interrupt acknowledgment ("Interrupted by …") is still posted.

Testing

• New unit test in AgentSessionManager.stop-session.test.ts asserts that after requestSessionInterrupt, an is_error ede_diagnostic result posts no error activity and leaves the session non-Error.
• pnpm --filter cyrus-edge-worker test → 729 passed.
• pnpm typecheck (full monorepo) → clean.

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