fix(FN-4884): finalize docs and keep workspace gates green

Fusion-Task-Id: FN-4884
Fusion-Task-Lineage: b906ade4-a9f1-4f2e-b684-4ebf49c3e7e6

packages/engine/src/branch-conflicts.ts

@@ -535,6 +535,13 @@ export interface ReanchorBranchToBaseResult {
   newTipSha: string;
 }
 
+/**
+ * Re-anchor a task branch to base while handling already-at-base worktrees.
+ *
+ * Fast-path: when both worktree HEAD and branch tip already equal baseSha,
+ * avoid detach/rebranch churn (`checkout -B` can fail with worktree-binding
+ * conflicts) and only attempt lightweight branch re-association.
+ */
 export async function reanchorBranchToBase(
   input: ReanchorBranchToBaseInput,
 ): Promise<ReanchorBranchToBaseResult> {

packages/engine/src/self-healing.ts

@@ -2020,10 +2020,11 @@ export class SelfHealingManager {
           });
           result.worktreeRemoved = true;
           if (task) {
-            const patch: Partial<Task> = { worktree: null };
-            if (task.branch === branchName) patch.branch = null;
-            await this.store.updateTask(task.id, patch);
-            task = { ...task, ...patch } as Task;
+            const patch = {
+              worktree: null as string | null,
+              ...(task.branch === branchName ? { branch: null as string | null } : {}),
+            };
+            await this.store.updateTask(task.id, patch as Partial<Task>);
           }
         } catch (err: unknown) {
           const errorMessage = err instanceof Error ? err.message : String(err);