Two fixes for E2E test reliability:
1. session-runner.ts: error_max_turns was misclassified as error_api
because is_error flag was checked before subtype. Now known subtypes
like error_max_turns are preserved even when is_error is set. The
is_error override only applies when subtype=success (API failure).
2. worktree.ts: pruneStale() now skips worktrees < 1 hour old to avoid
deleting worktrees from concurrent test runs still in progress.
Previously any second test execution would kill the first's worktrees.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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