test: preserve runner commit stall acknowledgement invariants (#20383)

Assert that stalled event commits do not advance acknowledgement or committed state. Clarify the limits of historical failure attribution. Preserve the production implementation already merged in #20385.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

doc/run-log-events.md

@@ -995,3 +995,6 @@ long cause chains stop at the same four-object limit.
 
 This only improves the recorded cause. Event acknowledgement, replay integrity,
 the bounded stall policy, and operator recovery requirements stay unchanged.
+
+A later successful continuation does not establish the cause of an earlier
+failure that recorded only `Error`.

packages/paperclip-runner/src/control-plane/durable-prp-control-plane.test.ts

@@ -1538,6 +1538,8 @@ it.each([
     expect(onProtocolIntegrityError).toHaveBeenCalledOnce();
     const failure = onProtocolIntegrityError.mock.calls[0]![0] as Error;
     expect(failure).toMatchObject({ reason: "runner_event_commit_stalled", detail: `${code} at source seq 1` });
+    expect(core.store.state.ackedSourceSeq).toBe(0);
+    expect(core.store.state.committedEvents).toHaveLength(0);
     expect(failure.message).toContain("runner_event_commit_stalled");
     expect(failure.message).not.toContain("private-host-fixture");
     expect(failure.message).not.toContain("private query");