feat(FN-1152): add retry flows for failed AI planning sessions

- Keep errored AI sessions retryable in the session store and add backend retry handlers for planning, subtask breakdown, and mission interview flows
- Add retry API routes and dashboard API client helpers for planning, subtask, and mission interview session retries
- Update PlanningModeModal, SubtaskBreakdownModal, MissionInterviewModal, and background session handling to show error states with retry/cancel UX
- Expand unit and integration tests across store, services, routes, and modal components to cover retry success and failure paths

packages/dashboard/app/api.ts

@@ -1253,6 +1253,19 @@ export function respondToPlanning(
   });
 }
 
+/** Retry a failed planning session turn */
+export function retryPlanningSession(
+  sessionId: string,
+  projectId?: string,
+): Promise<{ success: boolean; sessionId: string }> {
+  return api<{ success: boolean; sessionId: string }>(
+    withProjectId(`/planning/${encodeURIComponent(sessionId)}/retry`, projectId),
+    {
+      method: "POST",
+    },
+  );
+}
+
 /** Cancel an active planning session */
 export function cancelPlanning(sessionId: string, projectId?: string): Promise<void> {
   return api<void>(withProjectId("/planning/cancel", projectId), {
@@ -1803,6 +1816,18 @@ export function startSubtaskBreakdown(description: string, projectId?: string):
   });
 }
 
+export function retrySubtaskSession(
+  sessionId: string,
+  projectId?: string,
+): Promise<{ success: boolean; sessionId: string }> {
+  return api<{ success: boolean; sessionId: string }>(
+    withProjectId(`/subtasks/${encodeURIComponent(sessionId)}/retry`, projectId),
+    {
+      method: "POST",
+    },
+  );
+}
+
 export function getSubtaskStreamUrl(sessionId: string, projectId?: string): string {
   return buildApiUrl(withProjectId(`/subtasks/${encodeURIComponent(sessionId)}/stream`, projectId));
 }
@@ -3235,6 +3260,19 @@ export function respondToMissionInterview(
   });
 }
 
+/** Retry a failed mission interview turn */
+export function retryMissionInterviewSession(
+  sessionId: string,
+  projectId?: string,
+): Promise<{ success: boolean; sessionId: string }> {
+  return api<{ success: boolean; sessionId: string }>(
+    withProjectId(`/missions/interview/${encodeURIComponent(sessionId)}/retry`, projectId),
+    {
+      method: "POST",
+    },
+  );
+}
+
 /** Cancel an active mission interview session */
 export function cancelMissionInterview(sessionId: string, projectId?: string): Promise<void> {
   return api<void>(withProjectId("/missions/interview/cancel", projectId), {