feat(FN-4536): complete Step 2 — add branch worktree handler skeleton

Fusion-Task-Id: FN-4536
Fusion-Task-Lineage: 8d5615e4-e75d-413d-b3ab-0c4874b21fc5

packages/engine/src/auto-recovery-handlers/branch-worktree.ts

@@ -0,0 +1,35 @@
+import { exec } from "node:child_process";
+import { promisify } from "node:util";
+import type { TaskStore } from "@fusion/core";
+import type { AutoRecoveryContext, AutoRecoveryDecision, AutoRecoveryFailure } from "../auto-recovery.js";
+import type { Logger } from "../logger.js";
+import type { RunAuditor } from "../run-audit.js";
+
+const execAsync = promisify(exec);
+
+export interface BranchWorktreeRecoveryDeps {
+  taskStore: TaskStore;
+  runAudit: RunAuditor;
+  logger?: Logger;
+  spawnAiRecoverySession?: (
+    failure: AutoRecoveryFailure,
+    decision: AutoRecoveryDecision,
+    ctx: AutoRecoveryContext,
+  ) => Promise<{ outcome: "resolved" | "exhausted" | "error"; metadata?: Record<string, unknown> }>;
+  now?: () => Date;
+}
+
+export class BranchWorktreeAutoRecoveryHandler {
+  constructor(private readonly deps: BranchWorktreeRecoveryDeps) {
+    void this.deps;
+    void execAsync;
+  }
+
+  async issueRetry(_failure: AutoRecoveryFailure, _decision: AutoRecoveryDecision, _ctx: AutoRecoveryContext): Promise<void> {
+    // Implemented in FN-4536 Step 2.
+  }
+
+  async spawnAiRecovery(_failure: AutoRecoveryFailure, _decision: AutoRecoveryDecision, _ctx: AutoRecoveryContext): Promise<void> {
+    // Implemented in FN-4536 Step 4.
+  }
+}