fix(edge-worker): suppress Finished activity when turn ends on tool call (CYPACK-1177)

[cyrusagent]

Assignee: @pauravhp (paurav)

Summary

Fixes CYPACK-1177.

When an SDK turn ended on a backgrounded tool call (ScheduleWakeup, Bash with run_in_background) and there was no trailing assistant text, Cyrus posted a "Finished" response activity to Linear whose body was the raw tool-input JSON.

Root cause: in AgentSessionManager.handleClaudeMessage, every assistant message — including tool-use messages — wrote its content into lastAssistantBodyBySession. But for a tool-use message, extractContent serializes the tool input via JSON.stringify(block.input, null, 2). When the result arrived without any trailing text message to overwrite the buffer, addResultEntry posted that JSON string as the response body.

Changes

1. AgentSessionManager.ts — Only buffer text-only, non-empty assistant content into lastAssistantBodyBySession. Tool-use messages no longer poison the response fallback.
2. AgentSessionManager.ts — In addResultEntry, skip emitting the response activity entirely when there is no real content to post (and the result is not an error). The session status is still set to Complete by completeSession, but no spurious "Finished" entry is created.
3. New regression test — AgentSessionManager.result-no-trailing-text.test.ts covers the ScheduleWakeup and background-Bash turn-ending cases, plus the happy path where trailing assistant text is still posted as a response.

Test plan

• New tests pass (pnpm vitest run test/AgentSessionManager.result-no-trailing-text.test.ts)
• Full edge-worker test suite passes (614 tests)
• pnpm typecheck clean
• pnpm lint clean (no new errors)

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