Return watch AbortController immediately to enable cancellation before first event

[Copilot]

Watch.watch() could block the returned Promise<AbortController> until the stream produced output, which made idle/dead-watch recovery hard when no events arrived (for example with resourceVersion-based watches). This change makes cancellation available immediately while preserving existing watch lifecycle/error semantics.

• Behavior change: make controller availability immediate

  • watch.watch(...) now returns the AbortController immediately after setup, instead of waiting for auth/fetch/stream startup.
  • Watch startup work (applySecurityAuthentication + fetch + stream wiring) now runs asynchronously, and still funnels failures through done(...) via existing doneCallOnce logic.

• Error/lifecycle handling preserved

  • Existing guarantees remain intact:
    • done is still single-invocation.
    • timeout and abort paths still map to the same error flow.
    • non-200 responses still surface through done with status-aware error construction.

• Targeted test updates

  • Added coverage for “controller is returned before any response data is received,” then aborting that controller and asserting AbortError.
  • Updated one pre-existing test to account for async startup timing (wait for done instead of assuming synchronous completion).

const controller = await watch.watch(
  '/api/v1/pods',
  { resourceVersion: rv },
  onEvent,
  onDone,
);

// now available immediately, even before first event arrives
controller.abort();

[k8s-ci-robot]

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