feat(FN-4904): complete Step 1 — promote worktree root resolver

Fusion-Task-Id: FN-4904
Fusion-Task-Lineage: 5da52c8c-0ed6-4e3a-920e-aa1b56d0b719

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

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+import { getProjectRootFromWorktree } from "../pi-extensions.js";
+
+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");
+  });
+
+  it("supports configured candidate worktrees dir paths", () => {
+    expect(
+      getProjectRootFromWorktree("/tmp/.fn-worktrees/repo/fn-001/src", {
+        worktreesDirCandidates: ["/tmp/.fn-worktrees/repo"],
+      }),
+    ).toBe("/tmp/.fn-worktrees");
+
+    expect(
+      getProjectRootFromWorktree("/tmp/repo.worktrees/fn-001", {
+        worktreesDirCandidates: ["/tmp/repo.worktrees"],
+      }),
+    ).toBe("/tmp");
+  });
+});

packages/core/src/index.ts

@@ -194,7 +194,7 @@ export {
   MasterKeyPermissionError,
   MasterKeyCorruptError,
 } from "./master-key.js";
-export { discoverPiExtensions, formatPiExtensionSource, getEnabledPiExtensionPaths, getFusionAgentDir, getFusionAgentSettingsPath, getLegacyPiAgentDir, getPiExtensionDiscoveryDirs, reconcileClaudeCliPaths, reconcileDroidCliPaths, resolvePiExtensionProjectRoot, updatePiExtensionDisabledIds } from "./pi-extensions.js";
+export { discoverPiExtensions, formatPiExtensionSource, getEnabledPiExtensionPaths, getFusionAgentDir, getFusionAgentSettingsPath, getLegacyPiAgentDir, getPiExtensionDiscoveryDirs, getProjectRootFromWorktree, reconcileClaudeCliPaths, reconcileDroidCliPaths, resolvePiExtensionProjectRoot, updatePiExtensionDisabledIds } from "./pi-extensions.js";
 export type { PiExtensionEntry, PiExtensionSettings, PiExtensionSource } from "./pi-extensions.js";
 export { canTransition, getValidTransitions, resolveDependencyOrder } from "./board.js";
 export { computeBlockerFanoutMap, BLOCKER_ESCALATION_COLUMNS, isStaleBlockedByBlocker } from "./blocker-fanout.js";

packages/core/src/pi-extensions.ts

@@ -36,7 +36,39 @@ export function getFusionAgentSettingsPath(home?: string): string {
   return join(getFusionAgentDir(home), "settings.json");
 }
 
+export function getProjectRootFromWorktree(
+  cwd: string,
+  opts?: { worktreesDirCandidates?: string[] },
+): string | null {
+  const legacyMatch = cwd.match(/^(.+?)[\\/]\.worktrees[\\/][^\\/]+(?:[\\/]|$)/);
+  if (legacyMatch) {
+    return legacyMatch[1]!;
+  }
+
+  for (const candidate of opts?.worktreesDirCandidates ?? []) {
+    const normalizedCandidate = resolve(candidate);
+    const normalizedCwd = resolve(cwd);
+    const rel = relative(normalizedCandidate, normalizedCwd);
+    if (rel !== "" && !rel.startsWith("..") && !isAbsolute(rel)) {
+      const firstSegment = rel.split(/[\\/]/).filter(Boolean)[0];
+      if (firstSegment) {
+        const parent = normalizedCandidate.split(/[\\/]/).slice(0, -1).join("/");
+        if (parent) {
+          return parent;
+        }
+      }
+    }
+  }
+
+  return null;
+}
+
 export function resolvePiExtensionProjectRoot(cwd: string): string {
+  const worktreeProjectRoot = getProjectRootFromWorktree(cwd);
+  if (worktreeProjectRoot && existsSync(join(worktreeProjectRoot, ".fusion"))) {
+    return worktreeProjectRoot;
+  }
+
   let current = resolve(cwd);
   while (true) {
     if (existsSync(join(current, ".fusion"))) {

packages/engine/src/pi.ts

@@ -34,7 +34,7 @@ import {
   type AgentSession,
   type ToolDefinition,
 } from "@mariozechner/pi-coding-agent";
-import { getEnabledPiExtensionPaths, getFusionAgentDir, getLegacyPiAgentDir, reconcileClaudeCliPaths, reconcileDroidCliPaths, resolvePiExtensionProjectRoot } from "@fusion/core";
+import { getEnabledPiExtensionPaths, getFusionAgentDir, getLegacyPiAgentDir, getProjectRootFromWorktree, reconcileClaudeCliPaths, reconcileDroidCliPaths, resolvePiExtensionProjectRoot } from "@fusion/core";
 import type {
   AgentPermissionPolicyActionCategory,
   PermanentAgentActionCategory,
@@ -1225,41 +1225,7 @@ async function registerExtensionProviders(cwd: string, modelRegistry: ModelRegis
 
 // ── Worktree Path Boundary Helpers ──────────────────────────────────────────
 
-/**
- * Detect if a path is a task worktree under `.worktrees/`.
- * Returns the project root if the path is a worktree, otherwise null.
- *
- * Examples:
- *   `/project/.worktrees/fn-001` → `/project`
- *   `/project/.worktrees/fn-001/src/file.ts` → `/project`
- *   `/project` → null (not a worktree)
- */
-export function getProjectRootFromWorktree(
-  cwd: string,
-  opts?: { worktreesDirCandidates?: string[] },
-): string | null {
-  const legacyMatch = cwd.match(/^(.+?)[\\/]\.worktrees[\\/][^\\/]+(?:[\\/]|$)/);
-  if (legacyMatch) {
-    return legacyMatch[1]!;
-  }
-
-  for (const candidate of opts?.worktreesDirCandidates ?? []) {
-    const normalizedCandidate = resolve(candidate);
-    const normalizedCwd = resolve(cwd);
-    const rel = relative(normalizedCandidate, normalizedCwd);
-    if (rel !== "" && !rel.startsWith("..") && !isAbsolute(rel)) {
-      const firstSegment = rel.split(/[\\/]/).filter(Boolean)[0];
-      if (firstSegment) {
-        const parent = normalizedCandidate.split(/[\\/]/).slice(0, -1).join("/");
-        if (parent) {
-          return parent;
-        }
-      }
-    }
-  }
-
-  return null;
-}
+export { getProjectRootFromWorktree };
 
 async function isRegisteredGitWorktree(projectRoot: string, worktreePath: string): Promise<boolean> {
   try {