fix(server): treat signal-killed Claude subprocess as interrupted

[marcoamt]

What Changed

ClaudeAdapter now recognizes "terminated by signal SIGTERM/SIGINT" messages from the Claude Agent SDK's ProcessTransport as a graceful interruption instead of surfacing a runtime.error. Added a regression test asserting no runtime.error is emitted and the turn completes with state interrupted.

Why

When the OS delivers SIGTERM/SIGINT directly to the Claude subprocess (e.g. on desktop app quit) ahead of our own stopSession()-driven close, the SDK's error message for the signal-killed process was being treated as a runtime error instead of a normal interruption.

UI Changes

When Cmd+Q app and reopen a Claude Code thread it looks like screenshot

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Note

Fix isClaudeInterruptedMessage to treat SIGTERM/SIGINT-killed subprocesses as interrupted

When the Claude CLI subprocess is killed by SIGTERM or SIGINT before stopSession() completes, the Claude Agent SDK surfaces an error message containing 'terminated by signal sigterm' or 'terminated by signal sigint'. Previously these were treated as runtime errors; now isClaudeInterruptedMessage matches these substrings and returns interrupted state instead.

^{Macroscope summarized e6c7331.}

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[macroscopeapp]

Approvability

Verdict: Approved 8f898ff

Straightforward bug fix that adds two string patterns to an existing pattern-matching function. The change correctly classifies SIGTERM/SIGINT subprocess terminations as 'interrupted' rather than runtime errors, following the same pattern already used for similar cases. Includes comprehensive test coverage.

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