feat(FN-996): add in-review to todo retry transition with UI and state cleanup

- Add valid board transitions from todo to in-review and in-review to todo (retry)
- Clear transient fields (agentId, worktree, branch, prInfo, mergeRetries, etc.) on in-review→todo transition
- Add Retry button to TaskDetailModal for in-review tasks
- Add tests for retry transition and transient field cleanup in store

packages/core/src/board.test.ts

@@ -79,7 +79,7 @@ describe("board", () => {
     });
 
     it("returns correct transitions for in-review", () => {
-      expect(getValidTransitions("in-review")).toEqual(["done", "in-progress"]);
+      expect(getValidTransitions("in-review")).toEqual(["done", "in-progress", "todo"]);
     });
 
     it("returns correct transitions for done", () => {

packages/core/src/store.test.ts

@@ -2775,6 +2775,33 @@ Task with acceptance criteria
       expect(reopened.blockedBy).toBeUndefined();
       expect(reopened.workflowStepResults).toBeUndefined();
     });
+
+    it("allows retrying in-review tasks back to todo and clears transient fields", async () => {
+      const task = await store.createTask({ description: "test retry in-review task to todo" });
+      await store.moveTask(task.id, "todo");
+      await store.moveTask(task.id, "in-progress");
+      await store.moveTask(task.id, "in-review");
+      await store.updateTask(task.id, {
+        status: "completed",
+        error: "stale error",
+        worktree: "stale-worktree",
+        blockedBy: "FN-456",
+        workflowStepResults: [{
+          workflowStepId: "wf-1",
+          workflowStepName: "Workflow step 1",
+          status: "passed",
+          startedAt: new Date().toISOString(),
+        }],
+      });
+
+      const retried = await store.moveTask(task.id, "todo");
+      expect(retried.column).toBe("todo");
+      expect(retried.status).toBeUndefined();
+      expect(retried.error).toBeUndefined();
+      expect(retried.worktree).toBeUndefined();
+      expect(retried.blockedBy).toBeUndefined();
+      expect(retried.workflowStepResults).toBeUndefined();
+    });
   });
 
   describe("columnMovedAt", () => {

packages/core/src/store.ts

@@ -980,7 +980,7 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
       // preserved here — the recovery-policy module manages those fields. They are
       // only cleared on terminal transitions (in-review, done, archived).
       if (
-        (fromColumn === "in-progress" || fromColumn === "done")
+        (fromColumn === "in-progress" || fromColumn === "done" || fromColumn === "in-review")
         && (toColumn === "todo" || toColumn === "triage")
       ) {
         task.status = undefined;

packages/core/src/types.ts

@@ -1119,7 +1119,7 @@ export const VALID_TRANSITIONS: Record<Column, Column[]> = {
   triage: ["todo"],
   todo: ["in-progress", "triage"],
   "in-progress": ["in-review", "todo", "triage"],
-  "in-review": ["done", "in-progress"],
+  "in-review": ["done", "in-progress", "todo"],
   done: ["todo", "triage", "archived"],
   archived: ["done"],
 };