feat(task-2b): git watcher script + docs update

- Add scripts/podman-agent.mjs — polls git every 15s, upserts changedFiles/
  diffStat/recentCommit/branch into MongoDB engineer_states collection
- README: add "Git watcher" section with per-laptop demo commands for each
  team member (alice/bob/carol --pod demo-pod)
- PLAN.md: mark scheduled git truth ✅ partial, update acceptance checklist,
  clarify remaining fusion step (GIT_REPORT data channel wire-up still needed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AaCFWMkYQmTcuPsxaaACft

scripts/podman-agent.mjs

@@ -0,0 +1,152 @@
+#!/usr/bin/env node
+/**
+ * Local git watcher — polls working tree every 15s and upserts into MongoDB.
+ * Usage: node scripts/podman-agent.mjs --name alice --pod demo-pod
+ */
+
+import { execSync } from 'node:child_process';
+import { MongoClient } from 'mongodb';
+
+// ── CLI args ──────────────────────────────────────────────────────────────────
+
+function parseArgs() {
+  const args = process.argv.slice(2);
+  const get = (flag) => {
+    const i = args.indexOf(flag);
+    return i !== -1 ? args[i + 1] : null;
+  };
+  const name = get('--name');
+  const pod = get('--pod');
+  if (!name || !pod) {
+    console.error('Usage: node scripts/podman-agent.mjs --name <name> --pod <podId>');
+    process.exit(1);
+  }
+  return { name, podId: pod };
+}
+
+// ── Environment ───────────────────────────────────────────────────────────────
+
+async function loadEnv() {
+  if (!process.env.MONGODB_URI) {
+    try {
+      const dotenv = await import('dotenv');
+      dotenv.config({ path: new URL('../backend/.env', import.meta.url).pathname });
+    } catch {
+      // dotenv not available — rely on process.env
+    }
+  }
+  const uri = process.env.MONGODB_URI;
+  if (!uri) {
+    console.error('Error: MONGODB_URI not set. Export it or add it to backend/.env');
+    process.exit(1);
+  }
+  return uri;
+}
+
+// ── Git helpers ───────────────────────────────────────────────────────────────
+
+function git(cmd) {
+  try {
+    return execSync(cmd, { encoding: 'utf8', stdio: ['pipe', 'pipe', 'pipe'] });
+  } catch {
+    return '';
+  }
+}
+
+function collectGitState() {
+  const statusRaw = git('git status --short');
+  const changedFiles = statusRaw
+    .split('\n')
+    .map((l) => l.trim())
+    .filter(Boolean);
+
+  const diffRaw = git('git diff --stat HEAD').trim();
+  const diffStat = diffRaw || null;
+
+  const logRaw = git('git log --oneline -1').trim();
+  const recentCommit = logRaw || null;
+
+  const branchRaw = git('git branch --show-current').trim();
+  const branch = branchRaw || null;
+
+  return { changedFiles, diffStat, recentCommit, branch };
+}
+
+// ── Poll ──────────────────────────────────────────────────────────────────────
+
+async function poll(col, engineerId, podId, name) {
+  const { changedFiles, diffStat, recentCommit, branch } = collectGitState();
+  const now = new Date();
+
+  try {
+    await col.updateOne(
+      { _id: engineerId },
+      {
+        $set: {
+          changedFiles,
+          diffStat,
+          recentCommit,
+          branch,
+          gitUpdatedAt: now,
+          updatedAt: now,
+        },
+        $setOnInsert: {
+          podId,
+          name,
+          confidence: 0,
+        },
+      },
+      { upsert: true },
+    );
+
+    const ts = now.toISOString().slice(11, 19);
+    const files = changedFiles.length;
+    const br = branch ?? '(detached)';
+    const commit = recentCommit ? recentCommit.slice(0, 50) : '(no commits)';
+    console.log(`[${ts}] ${name}@${podId} | branch=${br} files=${files} commit="${commit}"`);
+  } catch (err) {
+    console.error(`[poll error] ${err.message}`);
+  }
+}
+
+// ── Main ──────────────────────────────────────────────────────────────────────
+
+async function main() {
+  const { name, podId } = parseArgs();
+  const engineerId = `${podId}::${name}`;
+  const uri = await loadEnv();
+
+  const client = new MongoClient(uri, { serverSelectionTimeoutMS: 8_000 });
+  await client.connect();
+
+  const col = client.db().collection('engineer_states');
+  await col.createIndex({ podId: 1, updatedAt: -1 }, { background: true });
+
+  console.log(`podman-agent started | id=${engineerId} | polling every 15s`);
+  console.log('Press Ctrl+C to stop.\n');
+
+  let running = true;
+
+  const shutdown = async () => {
+    running = false;
+    console.log('\nShutting down...');
+    await client.close();
+    process.exit(0);
+  };
+
+  process.on('SIGINT', shutdown);
+  process.on('SIGTERM', shutdown);
+
+  // Run immediately, then loop
+  await poll(col, engineerId, podId, name);
+
+  while (running) {
+    await new Promise((r) => setTimeout(r, 15_000));
+    if (running) await poll(col, engineerId, podId, name);
+  }
+}
+
+main().catch((err) => {
+  console.error('Fatal:', err.message);
+  process.exit(1);
+});