fix(FN-XXX): harden windows path handling

.changeset/fix-windows-path-handling.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Fix Windows path handling for worktree detection and home-directory lookups.

packages/cli/src/__tests__/bundle-output.test.ts

@@ -36,6 +36,9 @@ describe("CLI bundle output", () => {
     expect(content).not.toMatch(/from\s+["']@fusion\/core["']/);
     expect(content).not.toMatch(/from\s+["']@fusion\/dashboard["']/);
     expect(content).not.toMatch(/from\s+["']@fusion\/engine["']/);
+    expect(content).not.toContain('"@fusion/core"');
+    expect(content).not.toContain('"@fusion/dashboard"');
+    expect(content).not.toContain('"@fusion/engine"');
   });
 
   it("contains inlined workspace code", () => {

packages/core/src/__tests__/pi-extensions-format.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { formatPiExtensionSource } from "../pi-extensions.js";
+
+describe("formatPiExtensionSource", () => {
+  it("formats project-relative extension paths", () => {
+    expect(
+      formatPiExtensionSource(
+        "fusion-project",
+        "/repo/.fusion/extensions/tooling/index.ts",
+        "/repo",
+        "/Users/alice",
+      ),
+    ).toBe("fusion-project: .fusion/extensions/tooling/index.ts");
+  });
+
+  it("formats home-relative Windows extension paths", () => {
+    expect(
+      formatPiExtensionSource(
+        "fusion-global",
+        "C:\\Users\\alice\\.fusion\\agent\\extensions\\tooling\\index.ts",
+        "C:\\repo",
+        "C:\\Users\\alice",
+      ),
+    ).toBe("fusion-global: ~/.fusion/agent/extensions/tooling/index.ts");
+  });
+
+  it("does not treat prefix-matching sibling paths as inside the project or home", () => {
+    const projectLookalike = "C:\\repo-two\\.fusion\\extensions\\tooling\\index.ts";
+    const homeLookalike = "C:\\Users\\alice-dev\\.fusion\\agent\\extensions\\tooling\\index.ts";
+
+    expect(
+      formatPiExtensionSource("fusion-project", projectLookalike, "C:\\repo", "C:\\Users\\alice"),
+    ).toBe(`fusion-project: ${projectLookalike}`);
+    expect(
+      formatPiExtensionSource("fusion-global", homeLookalike, "C:\\repo", "C:\\Users\\alice"),
+    ).toBe(`fusion-global: ${homeLookalike}`);
+  });
+});

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

@@ -8,10 +8,12 @@ const TEMP_HOME_PREFIX = "fn-test-home-";
 describe("test isolation setup", () => {
   it("process.env.HOME is overridden to a temp directory", () => {
     const home = process.env.HOME;
+    const userProfile = process.env.USERPROFILE;
 
     expect(home).toBeDefined();
     expect(home).toContain(tmpdir());
     expect(home).toContain(TEMP_HOME_PREFIX);
+    expect(userProfile).toBe(home);
   });
 
   it("homedir() resolves to the temp HOME", () => {

packages/core/src/pi-extensions.ts

@@ -1,6 +1,6 @@
 import { existsSync, mkdirSync, readdirSync, readFileSync, statSync, writeFileSync } from "node:fs";
 import { homedir } from "node:os";
-import { basename, join, relative, resolve, sep } from "node:path";
+import { basename, isAbsolute, join, relative, resolve, sep, win32 } from "node:path";
 
 const FUSION_DISABLED_EXTENSIONS_KEY = "fusionDisabledExtensions";
 
@@ -276,13 +276,28 @@ export function reconcileClaudeCliPaths(
   return filtered;
 }
 
+function getDisplayPathWithinRoot(root: string, targetPath: string): string | null {
+  const usesWindowsPaths = /^[A-Za-z]:[\\/]/.test(root) || /^[A-Za-z]:[\\/]/.test(targetPath) || root.includes("\\") || targetPath.includes("\\");
+  const pathApi = usesWindowsPaths ? win32 : { relative, isAbsolute, sep };
+  const rel = pathApi.relative(root, targetPath);
+  if (rel === "") {
+    return "";
+  }
+  if (!rel || rel === ".." || rel.startsWith(`..${pathApi.sep}`) || pathApi.isAbsolute(rel)) {
+    return null;
+  }
+  return rel.split(pathApi.sep).join("/");
+}
+
 export function formatPiExtensionSource(source: PiExtensionSource, extensionPath: string, cwd: string, home?: string): string {
   const homeDir = getHomeDir(home);
   const projectRoot = resolvePiExtensionProjectRoot(cwd);
-  const relativePath = extensionPath.startsWith(homeDir)
+  const relativeToHome = getDisplayPathWithinRoot(homeDir, extensionPath);
-    ? `~${extensionPath.slice(homeDir.length)}`
+  const relativeToProject = getDisplayPathWithinRoot(projectRoot, extensionPath);
-    : extensionPath.startsWith(projectRoot)
+  const relativePath = relativeToHome !== null
-      ? relative(projectRoot, extensionPath).split(sep).join("/")
+    ? relativeToHome.length > 0 ? `~/${relativeToHome}` : "~"
+    : relativeToProject !== null
+      ? relativeToProject || "."
       : extensionPath;
   return `${source}: ${relativePath}`;
 }

packages/dashboard/app/utils/__tests__/pathDisplay.test.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from "vitest";
+import {
+  getDisplayDirname,
+  getParentDisplayPath,
+  getPathBasename,
+  getPathBreadcrumbs,
+  getTrailingPath,
+  joinDisplayPath,
+  normalizeDisplayPath,
+  splitPathSegments,
+} from "../pathDisplay";
+
+describe("pathDisplay", () => {
+  it("normalizes Windows separators for display", () => {
+    expect(normalizeDisplayPath("C:\\repo\\src\\file.ts")).toBe("C:/repo/src/file.ts");
+  });
+
+  it("extracts basenames and trailing paths across separators", () => {
+    expect(getPathBasename("C:\\repo\\.worktrees\\quiet-falcon")).toBe("quiet-falcon");
+    expect(getTrailingPath("C:\\Users\\alice\\project", 2)).toBe("alice/project");
+  });
+
+  it("builds relative display paths for file browser navigation", () => {
+    expect(splitPathSegments("src\\utils")).toEqual(["src", "utils"]);
+    expect(joinDisplayPath("src\\utils", "file.ts")).toBe("src/utils/file.ts");
+    expect(getParentDisplayPath("src\\utils")).toBe("src");
+    expect(getDisplayDirname("src\\utils\\file.ts")).toBe("src/utils/");
+  });
+
+  it("builds breadcrumbs for POSIX and Windows absolute paths", () => {
+    expect(getPathBreadcrumbs("/usr/local")).toEqual([
+      { label: "/", path: "/" },
+      { label: "usr", path: "/usr" },
+      { label: "local", path: "/usr/local" },
+    ]);
+
+    expect(getPathBreadcrumbs("C:\\Users\\alice")).toEqual([
+      { label: "C:", path: "C:/" },
+      { label: "Users", path: "C:/Users" },
+      { label: "alice", path: "C:/Users/alice" },
+    ]);
+  });
+});

packages/dashboard/app/utils/__tests__/worktreeGrouping.test.ts

@@ -25,6 +25,7 @@ describe("getWorktreeLabel", () => {
   it("extracts humanized worktree names", () => {
     expect(getWorktreeLabel(".worktrees/swirly-monkey")).toBe("swirly-monkey");
     expect(getWorktreeLabel("/tmp/project/.worktrees/quiet-falcon")).toBe("quiet-falcon");
+    expect(getWorktreeLabel("C:\\repo\\.worktrees\\quiet-falcon")).toBe("quiet-falcon");
     expect(getWorktreeLabel(".worktrees/bright-orchid-2")).toBe("bright-orchid-2");
   });
 });

packages/dashboard/src/__tests__/skills-adapter.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
-import { createSkillsAdapter } from "../skills-adapter.js";
+import { createSkillsAdapter, extractSkillName } from "../skills-adapter.js";
 import { writeFile, mkdir, access } from "node:fs/promises";
 import { join, dirname } from "node:path";
 import { tmpdir } from "node:os";
@@ -531,3 +531,10 @@ describe("createSkillsAdapter - readSkillContent", () => {
     await cleanup(skillDir);
   });
 });
+
+describe("extractSkillName", () => {
+  it("normalizes Windows separators before deriving the display name", () => {
+    expect(extractSkillName("skills\\tooling\\windows-fix", "npm")).toBe("tooling/windows-fix");
+    expect(extractSkillName("windows-fix", "npm")).toBe("windows-fix");
+  });
+});

packages/dashboard/src/__tests__/usage.test.ts

@@ -106,6 +106,24 @@ describe("usage", () => {
       expect(second).not.toBe(first);
       expect(second).toHaveLength(0);
     });
+
+    it("falls back to USERPROFILE when HOME is unset", async () => {
+      vi.stubEnv("HOME", "");
+      vi.stubEnv("USERPROFILE", "/profiles/test-user");
+
+      mockReadFile.mockImplementation(async () => {
+        return Promise.reject(new Error("File not found"));
+      });
+
+      await fetchAllProviderUsage();
+
+      const readPaths = mockReadFile.mock.calls.map(([filePath]) => String(filePath));
+      expect(readPaths).toContain("/profiles/test-user/.claude/.credentials.json");
+      expect(readPaths).toContain("/profiles/test-user/.config/claude/.credentials.json");
+      expect(readPaths).toContain("/profiles/test-user/.codex/auth.json");
+      expect(readPaths).toContain("/profiles/test-user/.gemini/oauth_creds.json");
+      expect(readPaths.some((filePath) => filePath.startsWith("/home/testuser/"))).toBe(false);
+    });
   });
 
   describe("fetchGitHubCopilotUsage (via fetchAllProviderUsage)", () => {

packages/dashboard/src/routes/register-settings-memory-routes.ts

@@ -40,6 +40,7 @@ import {
   writeProjectMemoryFile,
   updatePiExtensionDisabledIds,
 } from "@fusion/core";
+import { createFnAgent as engineCreateFnAgent } from "@fusion/engine";
 import { ApiError, badRequest } from "../api-error.js";
 import { generateRemoteToken, issueRemoteAuthToken, maskRemoteToken } from "../remote-auth.js";
 import { invalidateAllGlobalSettingsCaches } from "../project-store-resolver.js";
@@ -1008,7 +1009,6 @@ export function registerSettingsMemoryRoutes(ctx: ApiRoutesContext, deps: Settin
         // eslint-disable-next-line @typescript-eslint/no-explicit-any
         let session: any = null;
         try {
-          await initCreateFnAgentForInsights();
           if (!createFnAgentForInsights) {
             throw new ApiError(503, "AI service unavailable for dream processing");
           }
@@ -1070,20 +1070,8 @@ export function registerSettingsMemoryRoutes(ctx: ApiRoutesContext, deps: Settin
 
   // ── Memory Insights Routes ───────────────────────────────────────────
 
-  // Lazy-loaded createFnAgent for AI operations (same pattern as ai-refine.ts)
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  let createFnAgentForInsights: any;
+  const createFnAgentForInsights: any = engineCreateFnAgent;
-
-  async function initCreateFnAgentForInsights(): Promise<void> {
-    if (createFnAgentForInsights) return;
-    try {
-      // Use dynamic import with @vite-ignore to prevent static analysis issues
-      const engine = await import(/* @vite-ignore */ "@fusion/engine");
-      createFnAgentForInsights = engine.createFnAgent;
-    } catch {
-      createFnAgentForInsights = undefined;
-    }
-  }
 
   /**
    * GET /api/memory/insights
@@ -1148,8 +1136,6 @@ export function registerSettingsMemoryRoutes(ctx: ApiRoutesContext, deps: Settin
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     let session: any = null;
     try {
-      await initCreateFnAgentForInsights();
-
       if (!createFnAgentForInsights) {
         throw new ApiError(503, "AI engine not available");
       }

packages/dashboard/src/skills-adapter.ts

@@ -546,9 +546,9 @@ export function createSkillsAdapter(options: {
 /**
  * Extract skill name from path and source.
  */
-function extractSkillName(skillPath: string, source: string): string {
+export function extractSkillName(skillPath: string, source: string): string {
   // Get the last two path components (category/name or just name)
-  const parts = skillPath.split("/").filter(Boolean);
+  const parts = skillPath.replace(/\\/g, "/").split("/").filter(Boolean);
   if (parts.length >= 2) {
     // Return last two parts joined
     return parts.slice(-2).join("/");

packages/dashboard/src/usage.ts

@@ -5,6 +5,10 @@ import * as https from "node:https";
 import * as child_process from "node:child_process";
 import { getAuthFileCandidates } from "./auth-paths.js";
 
+function getHomeDir(): string {
+  return process.env.HOME || process.env.USERPROFILE || os.homedir();
+}
+
 function execFileAsync(
   file: string,
   args: string[],
@@ -846,8 +850,8 @@ async function fetchClaudeUsage(): Promise<ProviderUsage> {
 
   // ── Credential reading for plan detection & auth check ──────────────
   const credPaths = [
-    path.join(os.homedir(), ".claude", ".credentials.json"),
+    path.join(getHomeDir(), ".claude", ".credentials.json"),
-    path.join(os.homedir(), ".config", "claude", ".credentials.json"),
+    path.join(getHomeDir(), ".config", "claude", ".credentials.json"),
   ];
 
   // eslint-disable-next-line @typescript-eslint/no-explicit-any -- untyped credentials JSON
@@ -1067,7 +1071,7 @@ async function fetchCodexUsage(): Promise<ProviderUsage> {
   };
 
   // Load Codex auth
-  const codexHome = process.env.CODEX_HOME || path.join(os.homedir(), ".codex");
+  const codexHome = process.env.CODEX_HOME || path.join(getHomeDir(), ".codex");
   const authPath = path.join(codexHome, "auth.json");
 
   // eslint-disable-next-line @typescript-eslint/no-explicit-any -- untyped auth JSON
@@ -1182,7 +1186,7 @@ async function fetchGeminiUsage(): Promise<ProviderUsage> {
   };
 
   // Load Gemini OAuth credentials
-  const oauthPath = path.join(os.homedir(), ".gemini", "oauth_creds.json");
+  const oauthPath = path.join(getHomeDir(), ".gemini", "oauth_creds.json");
   // eslint-disable-next-line @typescript-eslint/no-explicit-any -- untyped OAuth JSON
   let oauthCreds: any = null;
   try {
@@ -1204,7 +1208,7 @@ async function fetchGeminiUsage(): Promise<ProviderUsage> {
   }
 
   // Check auth type from settings
-  const settingsPath = path.join(os.homedir(), ".gemini", "settings.json");
+  const settingsPath = path.join(getHomeDir(), ".gemini", "settings.json");
   try {
     const settings = JSON.parse(await readFile(settingsPath, "utf-8"));
     const authType = settings?.security?.auth?.selectedType;

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

@@ -433,5 +433,20 @@ describe("HybridExecutor", () => {
         executor.updateProject("non-existent", { maxConcurrent: 4 })
       ).rejects.toThrow("Runtime not found");
     });
+
+    it("reuses the registered project path when isolation mode changes without an explicit working directory", async () => {
+      const manager = mockProjectManagerInstances[0];
+      manager?.addProject.mockClear();
+
+      await executor.updateProject("proj_test123", { isolationMode: "child-process" });
+
+      expect(mockCentralCore.getProject).toHaveBeenCalledWith("proj_test123");
+      expect(manager?.removeProject).toHaveBeenCalledWith("proj_test123");
+      expect(manager?.addProject).toHaveBeenCalledWith(expect.objectContaining({
+        projectId: "proj_test123",
+        workingDirectory: "/tmp/test-project",
+        isolationMode: "child-process",
+      }));
+    });
   });
 });

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

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
-import { describeModel, compactSessionContext, COMPACTION_FALLBACK_INSTRUCTIONS, createFnAgent, promptWithFallback, type AgentOptions } from "../pi.js";
+import { describeModel, compactSessionContext, COMPACTION_FALLBACK_INSTRUCTIONS, createFnAgent, getProjectRootFromWorktree, promptWithFallback, type AgentOptions } from "../pi.js";
 import { createAgentSession, type AgentSession } from "@mariozechner/pi-coding-agent";
 import { piLog } from "../logger.js";
 
@@ -78,6 +78,18 @@ vi.mock("@mariozechner/pi-coding-agent", () => ({
 let resolveSessionSkillsMock: ReturnType<typeof vi.fn>;
 let createSkillsOverrideFromSelectionMock: ReturnType<typeof vi.fn>;
 
+describe("getProjectRootFromWorktree", () => {
+  it("detects POSIX worktree paths", () => {
+    expect(getProjectRootFromWorktree("/repo/.worktrees/fn-001")).toBe("/repo");
+    expect(getProjectRootFromWorktree("/repo/.worktrees/fn-001/src/file.ts")).toBe("/repo");
+  });
+
+  it("detects Windows worktree paths", () => {
+    expect(getProjectRootFromWorktree("C:\\repo\\.worktrees\\fn-001")).toBe("C:\\repo");
+    expect(getProjectRootFromWorktree("C:\\repo\\.worktrees\\fn-001\\src\\file.ts")).toBe("C:\\repo");
+  });
+});
+
 // Initialize mocks before first test
 beforeEach(() => {
   // Access mocks from the mocked module

packages/engine/src/hybrid-executor.ts

@@ -274,13 +274,19 @@ export class HybridExecutor extends EventEmitter<HybridExecutorEvents> {
         `Isolation mode changed for ${projectId}: ${currentMode} → ${config.isolationMode}`
       );
 
+      const project = await this.centralCore.getProject(projectId);
+      const workingDirectory = config.workingDirectory ?? project?.path;
+      if (!workingDirectory) {
+        throw new Error(`Project not found in CentralCore: ${projectId}`);
+      }
+
       // Stop old runtime
       await this.projectManager.removeProject(projectId);
 
       // Get the full current config
       const fullConfig: ProjectRuntimeConfig = {
         projectId,
-        workingDirectory: config.workingDirectory ?? "/tmp",
+        workingDirectory,
         isolationMode: config.isolationMode,
         maxConcurrent: config.maxConcurrent ?? 2,
         maxWorktrees: config.maxWorktrees ?? 4,

packages/engine/src/pi.ts

@@ -791,7 +791,7 @@ async function registerExtensionProviders(cwd: string, modelRegistry: ModelRegis
  *   `/project/.worktrees/fn-001/src/file.ts` → `/project`
  *   `/project` → null (not a worktree)
  */
-function getProjectRootFromWorktree(cwd: string): string | null {
+export function getProjectRootFromWorktree(cwd: string): string | null {
   // Match paths like:
   //   /project/.worktrees/task-id
   //   /project/.worktrees/task-id/src/file.ts

packages/pi-claude-cli/src/__tests__/setup-test-isolation.test.ts

@@ -7,10 +7,12 @@ const TEMP_HOME_PREFIX = "fn-test-home-";
 describe("test isolation setup", () => {
   it("overrides process.env.HOME to a temp directory", () => {
     const home = process.env.HOME;
+    const userProfile = process.env.USERPROFILE;
 
     expect(home).toBeDefined();
     expect(home).toContain(tmpdir());
     expect(home).toContain(TEMP_HOME_PREFIX);
+    expect(userProfile).toBe(home);
   });
 
   it("resolves homedir() to the temp HOME", () => {