fix(primer): resolve bundled codex JS launcher so the periodic primer fires

The Codex usage primer spawned a bare `codex` binary, but under bun/systemd
there is no global `codex` on PATH, so every slot failed with ENOENT and the
primer never ran. Resolve the vendored @openai/codex JS launcher and run it
through the current JS runtime (matching the codex-runner), with global-binary
and PATH fallbacks.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

src/codex-warmup.ts

@@ -1,7 +1,9 @@
 import { ChildProcess, spawn } from 'child_process';
 import fs from 'fs';
+import { createRequire } from 'module';
 import os from 'os';
 import path from 'path';
+import { fileURLToPath } from 'url';
 
 import { DATA_DIR } from './config.js';
 import type { AppConfig } from './config/schema.js';
@@ -87,9 +89,63 @@ function getPreferredCodexPathEntries(): string[] {
   return [...new Set(entries)];
 }
 
-function resolveCodexBinary(): string {
+const require = createRequire(import.meta.url);
+
+interface CodexLauncher {
+  command: string;
+  prefixArgs: string[];
+}
+
+/**
+ * Resolve how to spawn the Codex CLI for warm-up.
+ *
+ * The bot runs under bun/systemd where a global `codex` binary usually is NOT
+ * on PATH, so the old bare-`codex` fallback failed with ENOENT and the primer
+ * never fired. Prefer the bundled `@openai/codex` JS launcher (the same path
+ * the codex-runner spawns) and run it through the current JS runtime, falling
+ * back to a globally installed binary only when the package is unavailable.
+ */
+function resolveCodexLauncher(): CodexLauncher {
+  const launcherCandidates: string[] = [];
+  try {
+    launcherCandidates.push(
+      path.join(
+        path.dirname(require.resolve('@openai/codex/package.json')),
+        'bin',
+        'codex.js',
+      ),
+    );
+  } catch {
+    /* @openai/codex not resolvable from this module — try explicit paths */
+  }
+  // The codex-runner workspace always vendors @openai/codex.
+  const repoRoot = path.resolve(
+    path.dirname(fileURLToPath(import.meta.url)),
+    '..',
+  );
+  launcherCandidates.push(
+    path.join(
+      repoRoot,
+      'runners',
+      'codex-runner',
+      'node_modules',
+      '@openai',
+      'codex',
+      'bin',
+      'codex.js',
+    ),
+  );
+  for (const launcher of launcherCandidates) {
+    if (fs.existsSync(launcher)) {
+      return { command: process.execPath, prefixArgs: [launcher] };
+    }
+  }
+  // Fall back to a globally installed codex binary, then bare PATH lookup.
   const npmGlobalBin = path.join(os.homedir(), '.npm-global', 'bin', 'codex');
-  return fs.existsSync(npmGlobalBin) ? npmGlobalBin : 'codex';
+  if (fs.existsSync(npmGlobalBin)) {
+    return { command: npmGlobalBin, prefixArgs: [] };
+  }
+  return { command: 'codex', prefixArgs: [] };
 }
 
 function ensureAccountState(
@@ -219,7 +275,8 @@ function runCodexWarmupCommand(
     );
 
     try {
-      proc = spawn(resolveCodexBinary(), args, {
+      const launcher = resolveCodexLauncher();
+      proc = spawn(launcher.command, [...launcher.prefixArgs, ...args], {
         stdio: ['ignore', 'pipe', 'pipe'],
         env: spawnEnv,
       });