test(server): mock cancelStaleQueuedRunsForIssue in route-level heartbeat mocks

The eager-cancel-on-reassignment call in routes/issues.ts (added by an
earlier commit on this PR for RENA-55610) invokes
heartbeat.cancelStaleQueuedRunsForIssue on every PATCH /api/issues/:id
that changes assigneeAgentId. Route test files that hoist their own
mockHeartbeatService double did not define that method, so any
reassignment-path test threw "cancelStaleQueuedRunsForIssue is not a
function" synchronously - before the route's own .catch() around that
call could ever run - and the request failed with a 500.

This surfaced as unrelated-looking failures across three "Verify
serialized server suites" shards in CI (issue-agent-mutation-ownership-routes,
issue-assignee-invokability-routes, issue-comment-reopen-routes), all
"expected 500 to be 200" on PATCH reassignment paths.

Add the missing mock (resolving to []) to every hoisted
mockHeartbeatService in server/src/__tests__ that mounts routes/issues.ts,
so reassignment tests exercise the real .catch()-guarded call path
instead of throwing before it. Verified locally (serialized, extended
timeouts to offset this box's resource contention): the three
previously-failing files now pass 174/174.

RENA-55706

Author: Paperclip-Paperclip

server/src/__tests__/document-annotation-routes.test.ts

@@ -37,6 +37,7 @@ const mockIssueReferenceService = vi.hoisted(() => ({
   syncIssue: vi.fn(async () => undefined),
 }));
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
 }));

server/src/__tests__/issue-activity-events-routes.test.ts

@@ -22,6 +22,7 @@ const mockAccessService = vi.hoisted(() => ({
   hasPermission: vi.fn(async () => false),
 }));
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),

server/src/__tests__/issue-agent-mutation-ownership-routes.test.ts

@@ -101,6 +101,7 @@ const mockTaskWatchdogService = vi.hoisted(() => ({
   disableForIssue: vi.fn(async () => null),
 }));
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),

server/src/__tests__/issue-assignee-invokability-routes.test.ts

@@ -33,6 +33,7 @@ const mockIssueService = vi.hoisted(() => ({
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),

server/src/__tests__/issue-closed-workspace-routes.test.ts

@@ -24,6 +24,7 @@ const mockAccessService = vi.hoisted(() => ({
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),

server/src/__tests__/issue-comment-cancel-routes.test.ts

@@ -16,6 +16,7 @@ const mockAccessService = vi.hoisted(() => ({
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   getRun: vi.fn(async () => null),
   getActiveRunForAgent: vi.fn(async () => null),
 }));

server/src/__tests__/issue-comment-reopen-routes.test.ts

@@ -22,6 +22,7 @@ const mockAccessService = vi.hoisted(() => ({
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),

server/src/__tests__/issue-document-restore-routes.test.ts

@@ -27,6 +27,7 @@ const mockAgentService = vi.hoisted(() => ({
 
 const mockLogActivity = vi.hoisted(() => vi.fn(async () => undefined));
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
 }));

server/src/__tests__/issue-execution-policy-routes.test.ts

@@ -17,6 +17,7 @@ const mockIssueService = vi.hoisted(() => ({
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   triggerIssueMonitor: vi.fn(async () => ({ outcome: "triggered" as const })),
   reportRunActivity: vi.fn(async () => undefined),

server/src/__tests__/issue-feedback-routes.test.ts

@@ -29,6 +29,7 @@ const mockAgentService = vi.hoisted(() => ({
   getById: vi.fn(),
 }));
 const mockHeartbeatService = vi.hoisted(() => ({
+  cancelStaleQueuedRunsForIssue: vi.fn(async () => []),
   wakeup: vi.fn(async () => undefined),
   reportRunActivity: vi.fn(async () => undefined),
   getRun: vi.fn(async () => null),