feat(protocol): pivot to Passive Heartbeat for Windows stability

The previous background loop approach was disruptive on Windows (terminal pop-ups).
We collaborated to find a more robust, silent alternative:
- Removed all background heartbeat worker logic and PID management.
- Implemented 'Passive Heartbeat' in tools/bb.ts: every agent command now refreshes liveness as a side-effect.
- Updated bb-init.mjs to use explicit heartbeat calls for adoption/registration.
- Result is 100% silent observability: if an agent is working, they are Active. If they stop, they drift to Stale.

OPERATIVE: silver-castle
SESSION: 2026-02-14-1300

tests/scripts/bb-init.test.ts

@@ -0,0 +1,83 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { execSync } from 'node:child_process';
+import fs from 'node:fs/promises';
+import path from 'node:path';
+import os from 'node:os';
+
+const projectRoot = path.resolve(__dirname, '../../');
+const initScript = path.join(projectRoot, 'scripts', 'bb-init.mjs');
+
+async function withTempRegistry(run: (tempDir: string) => Promise<void>): Promise<void> {
+  const previous = process.env.USERPROFILE;
+  const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), 'bb-init-passive-'));
+  process.env.USERPROFILE = tempDir;
+
+  // Initialize a fake git repo
+  execSync('git init', { cwd: tempDir, stdio: 'ignore' });
+  await fs.writeFile(path.join(tempDir, 'dummy'), 'data');
+  execSync('git add dummy && git commit -m "initial"', { cwd: tempDir, stdio: 'ignore' });
+
+  try {
+    await run(tempDir);
+  } finally {
+    process.env.USERPROFILE = previous;
+    await fs.rm(tempDir, { recursive: true, force: true, maxRetries: 5 });
+  }
+}
+
+test('PASSIVE: bb-init --register updates liveness via side-effect', async (t) => {
+  await withTempRegistry(async (tempDir) => {
+    const agentId = 'passive-agent';
+    const cmd = `node ${initScript} --register ${agentId} --role backend --json`;
+    
+    const out = execSync(cmd, { 
+      cwd: tempDir, 
+      encoding: 'utf8',
+      env: { ...process.env, BB_REPO: projectRoot }
+    });
+    const result = JSON.parse(out);
+
+    assert.equal(result.ok, true);
+    assert.equal(result.heartbeat.status, 'passive');
+
+    // Verify Registry Entry exists and has a timestamp
+    const agentFile = path.join(tempDir, '.beadboard', 'agent', 'agents', `${agentId}.json`);
+    const agentData = JSON.parse(await fs.readFile(agentFile, 'utf8'));
+    assert.equal(agentData.agent_id, agentId);
+    assert.ok(agentData.last_seen_at);
+  });
+});
+
+test('PASSIVE: bb-init --adopt rejection still works with noise filtering', async (t) => {
+  await withTempRegistry(async (tempDir) => {
+    const agentId = 'noise-agent';
+    
+    // Register first
+    execSync(`node ${initScript} --register ${agentId} --role test --json`, { 
+      cwd: tempDir,
+      env: { ...process.env, BB_REPO: projectRoot }
+    });
+
+    // Rejects with only .beadboard noise
+    try {
+      execSync(`node ${initScript} --adopt ${agentId} --non-interactive --json`, { 
+        cwd: tempDir, 
+        stdio: 'pipe',
+        env: { ...process.env, BB_REPO: projectRoot }
+      });
+      assert.fail('Should have rejected adoption');
+    } catch (err: any) {
+      const res = JSON.parse(err.stdout.toString());
+      assert.equal(res.error.code, 'ADOPTION_REJECTED');
+    }
+
+    // Accepts with real change
+    await fs.writeFile(path.join(tempDir, 'real.ts'), 'code');
+    const adoptOut = execSync(`node ${initScript} --adopt ${agentId} --non-interactive --json`, { 
+      cwd: tempDir, 
+      env: { ...process.env, BB_REPO: projectRoot }
+    });
+    assert.equal(JSON.parse(adoptOut).ok, true);
+  });
+});