fix(daemon): resolve tsx from the filesystem when Node's resolver cannot see node_modules (#28)

Inside a Bun-compiled pi binary (pi.exe), createRequire().resolve("tsx/cli") is rooted at the
embedded virtual filesystem and cannot see the extension's real node_modules, so browser_setup
failed instantly. The resolver result is now checked on disk and, when it fails, the tsx CLI is
found by walking up the node_modules chain. Under Bun the daemon runs on `node` from PATH
(process.execPath is the pi binary itself); PI_BROWSER_NODE overrides it.

Fixes #27

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

1 files changed, 79 insertions, 2 deletions

diff --git a/test/util/daemon-socket-test.ts b/test/util/daemon-socket-test.ts
index 80a03e4..2f9ce8d 100644
--- a/test/util/daemon-socket-test.ts
+++ b/test/util/daemon-socket-test.ts
@@ -1,11 +1,18 @@
 import { test, describe } from "node:test";
 import assert from "node:assert/strict";
 import { fileURLToPath } from "node:url";
-import { existsSync } from "node:fs";
+import { existsSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
 import { Type } from "typebox";
 import type { ExtensionAPI, ToolDefinition } from "@mariozechner/pi-coding-agent";
 import type { TSchema } from "typebox";
-import { daemonSocketMayExist, daemonSpawnCommand } from "../../src/daemon/spawn";
+import {
+  daemonNodeExecutable,
+  daemonSocketMayExist,
+  daemonSpawnCommand,
+  resolveTsxCliFromFilesystem,
+} from "../../src/daemon/spawn";
 import { type AnyBrowserToolDefinition, registerBrowserTool } from "../../src/util/tool";
 import type { BrowserClient } from "../../src/client";
 import { ok } from "../../src/util/result";
@@ -55,6 +62,76 @@ describe("daemon spawn command", () => {
   });
 });
 
+describe("daemon node executable", () => {
+  const nodeVersions = { node: "22.0.0" };
+  const bunVersions = { node: "22.0.0", bun: "1.3.14" };
+
+  test("a plain Node host reuses its own executable", () => {
+    assert.equal(daemonNodeExecutable({}, nodeVersions, "linux", "/usr/bin/node"), "/usr/bin/node");
+    assert.equal(daemonNodeExecutable({}, nodeVersions, "win32", "C:\\node\\node.exe"), "C:\\node\\node.exe");
+  });
+
+  test("a Bun-compiled host never spawns itself as node", () => {
+    assert.equal(daemonNodeExecutable({}, bunVersions, "linux", "/opt/pi/pi"), "node");
+    assert.equal(daemonNodeExecutable({}, bunVersions, "darwin", "/opt/pi/pi"), "node");
+    assert.equal(daemonNodeExecutable({}, bunVersions, "win32", "C:\\pi\\pi.exe"), "node.exe");
+  });
+
+  test("PI_BROWSER_NODE overrides on every runtime", () => {
+    const env = { PI_BROWSER_NODE: "/custom/node" };
+    assert.equal(daemonNodeExecutable(env, nodeVersions, "linux", "/usr/bin/node"), "/custom/node");
+    assert.equal(daemonNodeExecutable(env, bunVersions, "win32", "C:\\pi\\pi.exe"), "/custom/node");
+  });
+
+  test("an empty PI_BROWSER_NODE is ignored", () => {
+    assert.equal(daemonNodeExecutable({ PI_BROWSER_NODE: "" }, bunVersions, "linux", "/opt/pi/pi"), "node");
+  });
+});
+
+const withTree = (prefix: string, fn: (root: string) => void): void => {
+  const root = mkdtempSync(join(tmpdir(), prefix));
+  try {
+    fn(root);
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+};
+
+const touch = (file: string): void => {
+  mkdirSync(dirname(file), { recursive: true });
+  writeFileSync(file, "");
+};
+
+describe("tsx CLI filesystem fallback", () => {
+  // pi installs extensions into one flat tree, so tsx is a sibling of the package, not inside it.
+  test("finds a tsx hoisted beside the package, walking up from src/daemon", () => {
+    withTree("pbh-hoist-", (root) => {
+      const cli = join(root, "node_modules", "tsx", "dist", "cli.mjs");
+      touch(cli);
+      const start = join(root, "node_modules", "pi-browser-harness", "src", "daemon");
+      mkdirSync(start, { recursive: true });
+      assert.equal(resolveTsxCliFromFilesystem(start), cli);
+    });
+  });
+
+  test("prefers the package's own node_modules over a hoisted copy", () => {
+    withTree("pbh-local-", (root) => {
+      const hoisted = join(root, "node_modules", "tsx", "dist", "cli.mjs");
+      const local = join(root, "node_modules", "pi-browser-harness", "node_modules", "tsx", "dist", "cli.mjs");
+      touch(hoisted);
+      touch(local);
+      const start = join(root, "node_modules", "pi-browser-harness", "src", "daemon");
+      mkdirSync(start, { recursive: true });
+      assert.equal(resolveTsxCliFromFilesystem(start), local);
+    });
+  });
+
+  test("the fallback agrees with Node's resolver in this checkout", () => {
+    const viaResolver = daemonSpawnCommand()?.args[0];
+    assert.equal(resolveTsxCliFromFilesystem(), viaResolver);
+  });
+});
+
 type GateProbe = { readonly ran: ReadonlyArray<string>; readonly text: string };
 
 const runGate = async (ensureAlive: boolean | undefined): Promise<GateProbe> => {