feat(FN-2984): add droid CLI path reconciliation extension

The merge introduces a new droid CLI extension with path reconciliation across daemon, dashboard, and serve commands, along with supporting core and engine utilities. It also removes stale lint suppression comments (FN-2983). Tests cover the new CLI extension and path reconciliation logic.

Fusion-Task-Id: FN-2984

packages/core/src/__tests__/reconcile-droid-cli-paths.test.ts

@@ -0,0 +1,52 @@
+import { describe, it, expect } from "vitest";
+import { reconcileDroidCliPaths } from "../pi-extensions.js";
+
+const VENDORED = "/repo/packages/droid-cli/index.ts";
+const GLOBAL_NPM = "/opt/homebrew/lib/node_modules/droid-cli/index.ts";
+const PI_AGENT = "/Users/u/.pi/agent/extensions/droid-cli/index.ts";
+const UNRELATED = "/Users/u/.pi/agent/extensions/quota.ts";
+
+describe("reconcileDroidCliPaths", () => {
+  it("returns input unchanged when no vendored path is supplied", () => {
+    const input = [GLOBAL_NPM, UNRELATED];
+    expect(reconcileDroidCliPaths(input, null)).toEqual(input);
+  });
+
+  it("drops a globally-installed droid-cli and prepends the vendored path", () => {
+    const result = reconcileDroidCliPaths([GLOBAL_NPM, UNRELATED], VENDORED);
+    expect(result).toEqual([VENDORED, UNRELATED]);
+  });
+
+  it("drops droid-cli installed under .pi/agent/extensions/", () => {
+    const result = reconcileDroidCliPaths([PI_AGENT, UNRELATED], VENDORED);
+    expect(result).toEqual([VENDORED, UNRELATED]);
+  });
+
+  it("keeps the vendored path exactly once even if it appears in input", () => {
+    const result = reconcileDroidCliPaths(
+      [VENDORED, GLOBAL_NPM, UNRELATED],
+      VENDORED,
+    );
+    expect(result).toEqual([VENDORED, UNRELATED]);
+  });
+
+  it("preserves the relative order of unrelated extension paths", () => {
+    const a = "/ext/a.ts";
+    const b = "/ext/b.ts";
+    const c = "/ext/c.ts";
+    const result = reconcileDroidCliPaths([a, GLOBAL_NPM, b, c], VENDORED);
+    expect(result).toEqual([VENDORED, a, b, c]);
+  });
+
+  it("does not mistake substrings of droid-cli for the package", () => {
+    const looksLike = "/ext/some-droid-cli-helper/index.ts";
+    const result = reconcileDroidCliPaths([looksLike], VENDORED);
+    expect(result).toEqual([VENDORED, looksLike]);
+  });
+
+  it("matches case-insensitively (e.g. on macOS-cased filesystems)", () => {
+    const upper = "/opt/homebrew/lib/node_modules/DROID-CLI/index.ts";
+    const result = reconcileDroidCliPaths([upper], VENDORED);
+    expect(result).toEqual([VENDORED]);
+  });
+});