CL-7221 sidecars top-level SIGTERM/SIGINT handler has no error

[TheGreatAxios]

CL-7221

Fixes CL-7221

[TheGreatAxios]

Fixes CL-7221

[linear-code]

CL-7221

[TheGreatAxios]

Self-review

Fix is sound: the SIGTERM/SIGINT handlers now await a runSidecarShutdown that catches sync/async failures from close/drain and reports them, with attachShutdownRejectionHandler as a backstop against any residual unhandled rejection. Tests cover close-throw, drain-throw, clean-exit, and the rejection backstop.

• CONFIRMED-FIXED: outer catch in runSidecarShutdown called reportError directly instead of the injected report parameter, bypassing the test seam the other branch uses and diverging from the function's own DI pattern. Now uses report.
• DISMISSED: onShutdownRejection in index.ts calls reportError directly rather than taking an injectable report — this is top-level wiring (not unit-tested), consistent with how the rest of index.ts wires real dependencies, not a defect.
• DISMISSED: double-invocation guard (shuttingDown) still only guards the async body, not the signal listeners directly — unchanged from prior behavior and out of scope for this fix (handler already returns early via the flag).

Targeted tests: bun test test/shutdown.test.ts — 7 pass, 0 fail. bun run typecheck — clean.