feat(FN-2944): merge fusion/fn-2944

- test(FN-2944): cover already checked out worktree conflict recovery
- fix(FN-2944): recognize git already checked out worktree conflict
- fix(engine): auto-recover from squash-merge orphan rebase failures

Fusion-Task-Id: FN-2944

packages/engine/src/__tests__/executor.test.ts

@@ -966,6 +966,56 @@ describe("TaskExecutor worktree recovery", () => {
     expect(worktreeAddCalls).toHaveLength(1);
   });
 
+  it("extractWorktreeConflictInfo classifies already checked out errors as already-used", () => {
+    const store = createMockStore();
+    const executor = new TaskExecutor(store, "/tmp/test");
+
+    const error: any = new Error(
+      "fatal: 'fusion/fn-050' is already checked out at '/tmp/test/.worktrees/green-sage'",
+    );
+    error.stderr = Buffer.from(
+      "fatal: 'fusion/fn-050' is already checked out at '/tmp/test/.worktrees/green-sage'",
+    );
+
+    const conflictInfo = (executor as any).extractWorktreeConflictInfo(error);
+    expect(conflictInfo).toMatchObject({
+      type: "already-used",
+      path: "/tmp/test/.worktrees/green-sage",
+    });
+  });
+
+  it("recovers from already checked out worktree conflict and retries", async () => {
+    const store = createMockStore();
+    let callCount = 0;
+
+    mockedExecSync.mockImplementation((cmd: string | string[]) => {
+      const command = typeof cmd === "string" ? cmd : cmd[0];
+      if (command.includes("git worktree add") && callCount++ === 0) {
+        const error: any = new Error(
+          "fatal: 'fusion/fn-050' is already checked out at '/tmp/test/.worktrees/green-sage'",
+        );
+        error.stderr = Buffer.from(
+          "fatal: 'fusion/fn-050' is already checked out at '/tmp/test/.worktrees/green-sage'",
+        );
+        throw error;
+      }
+      return Buffer.from("");
+    });
+
+    const executor = new TaskExecutor(store, "/tmp/test");
+    await executor.execute(makeTask());
+
+    expect(store.logEntry).toHaveBeenCalledWith(
+      "FN-050",
+      expect.stringContaining("Cleaned up conflicting worktree, retrying"),
+      "/tmp/test/.worktrees/swift-falcon",
+    );
+    expect(store.updateTask).toHaveBeenCalledWith(
+      "FN-050",
+      expect.objectContaining({ worktree: expect.any(String) }),
+    );
+  });
+
   it("recovers from worktree conflict and retries", async () => {
     const store = createMockStore();
     let callCount = 0;

packages/engine/src/__tests__/setup-test-isolation.ts

@@ -10,3 +10,11 @@ import { join } from "node:path";
 
 const tempHome = mkdtempSync(join(tmpdir(), "fn-test-home-"));
 process.env.HOME = tempHome;
+process.env.USERPROFILE = tempHome;
+if (process.platform === "win32") {
+  const match = tempHome.match(/^([A-Za-z]:)(.*)$/);
+  if (match) {
+    process.env.HOMEDRIVE = match[1];
+    process.env.HOMEPATH = match[2] || "\\";
+  }
+}

packages/engine/src/executor.ts

@@ -5107,6 +5107,12 @@ and show an appropriate message to the user.\`
       return { type: "already-used", path: alreadyUsedMatch[1], message: output };
     }
 
+    // Pattern: already checked out at '/path/to/worktree'
+    const alreadyCheckedOutMatch = output.match(/is already checked out at '([^']+)'/);
+    if (alreadyCheckedOutMatch) {
+      return { type: "already-used", path: alreadyCheckedOutMatch[1], message: output };
+    }
+
     // Pattern: invalid reference: 'branch-name'
     // Also covers: unable to resolve reference, stale file handle, not a valid ref
     if (

packages/engine/src/pi.ts

@@ -792,8 +792,11 @@ async function registerExtensionProviders(cwd: string, modelRegistry: ModelRegis
  *   `/project` → null (not a worktree)
  */
 function getProjectRootFromWorktree(cwd: string): string | null {
-  // Match paths like /project/.worktrees/task-id or /project/.worktrees/task-id/...
-  const match = cwd.match(/^(.+?)\/\.worktrees\/[^/]+/);
+  // Match paths like:
+  //   /project/.worktrees/task-id
+  //   /project/.worktrees/task-id/src/file.ts
+  //   C:\project\.worktrees\task-id
+  const match = cwd.match(/^(.+?)[\\/]\.worktrees[\\/][^\\/]+(?:[\\/]|$)/);
   if (match) {
     return match[1]!;
   }

packages/engine/src/runtimes/__tests__/in-process-runtime.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
 import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { randomUUID } from "node:crypto";
 import type { Task, TaskStore, CentralCore, AgentStore, Agent } from "@fusion/core";
@@ -184,7 +185,7 @@ describe("InProcessRuntime", () => {
 
   beforeEach(() => {
     // Create a unique temp directory for this test run
-    testDir = mkdtempSync(join("/tmp", `fn-test-${randomUUID().slice(0, 8)}-`));
+    testDir = mkdtempSync(join(tmpdir(), `fn-test-${randomUUID().slice(0, 8)}-`));
 
     // Create mock CentralCore
     mockCentralCore = {
@@ -746,12 +747,12 @@ describe("InProcessRuntime", () => {
     it("should store projectId in config", () => {
       // Access via the constructor params - runtime is created with testDir
       expect(testDir).toBeDefined();
-      expect(testDir).toContain("/tmp/fn-test-");
+      expect(testDir).toContain("fn-test-");
     });
 
     it("should store workingDirectory in config", () => {
       expect(testDir).toBeDefined();
-      expect(testDir.startsWith("/tmp/")).toBe(true);
+      expect(testDir.startsWith(tmpdir())).toBe(true);
     });
 
     it("should store maxConcurrent in config", () => {

packages/engine/src/scheduler.ts

@@ -10,7 +10,7 @@ import {
 } from "@fusion/core";
 import { existsSync } from "node:fs";
 import { readFile } from "node:fs/promises";
-import { join } from "node:path";
+import { basename, join } from "node:path";
 import type { AgentSemaphore } from "./concurrency.js";
 import { generateReservedWorktreeName, slugify } from "./worktree-names.js";
 import { schedulerLog } from "./logger.js";
@@ -466,7 +466,7 @@ export class Scheduler {
     reservedNames: Set<string>,
   ): string {
     if (task.worktree) {
-      const existingName = task.worktree.split("/").pop();
+      const existingName = basename(task.worktree);
       if (existingName) reservedNames.add(existingName);
       return task.worktree;
     }
@@ -659,7 +659,7 @@ export class Scheduler {
       let started = 0;
       const reservedWorktreeNames = new Set(
         tasks
-          .map((task) => task.worktree?.split("/").pop())
+          .map((task) => (task.worktree ? basename(task.worktree) : undefined))
           .filter((name): name is string => Boolean(name)),
       );