diff --git a/test/derive-project-path.test.js b/test/derive-project-path.test.js
new file mode 100644
index 00000000..1b848292
--- /dev/null
+++ b/test/derive-project-path.test.js
@@ -0,0 +1,107 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+
+const { deriveProjectPath, resolveWorktreePath } = require('../derive-project-path');
+
+function mkTmp() {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'switchboard-dpp-'));
+}
+
+function cleanup(dir) {
+  fs.rmSync(dir, { recursive: true, force: true });
+}
+
+test('resolveWorktreePath collapses /<repo>/.claude/worktrees/<name> back to <repo> when parent exists', () => {
+  const tmp = mkTmp();
+  try {
+    const repo = path.join(tmp, 'repo');
+    fs.mkdirSync(repo);
+    const worktree = path.join(repo, '.claude', 'worktrees', 'agent-abc');
+    assert.equal(resolveWorktreePath(worktree), repo);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('resolveWorktreePath collapses /<repo>/.claude-worktrees/<name> back to <repo>', () => {
+  const tmp = mkTmp();
+  try {
+    const repo = path.join(tmp, 'repo');
+    fs.mkdirSync(repo);
+    const worktree = path.join(repo, '.claude-worktrees', 'foo');
+    assert.equal(resolveWorktreePath(worktree), repo);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('resolveWorktreePath collapses /<repo>/.worktrees/<name> back to <repo>', () => {
+  const tmp = mkTmp();
+  try {
+    const repo = path.join(tmp, 'repo');
+    fs.mkdirSync(repo);
+    const worktree = path.join(repo, '.worktrees', 'bar');
+    assert.equal(resolveWorktreePath(worktree), repo);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('resolveWorktreePath handles trailing-slash variant', () => {
+  const tmp = mkTmp();
+  try {
+    const repo = path.join(tmp, 'repo');
+    fs.mkdirSync(repo);
+    const worktreeWithSlash = path.join(repo, '.worktrees', 'bar') + '/';
+    assert.equal(resolveWorktreePath(worktreeWithSlash), repo);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('resolveWorktreePath returns input unchanged when the parent dir does not exist on disk', () => {
+  // /nonexistent-xyzzy-12345/.claude/worktrees/agent-foo — regex matches, but parent dir absent
+  const fake = '/nonexistent-xyzzy-12345/.claude/worktrees/agent-foo';
+  assert.equal(resolveWorktreePath(fake), fake);
+});
+
+test('resolveWorktreePath returns input unchanged when the path does not match the worktree pattern', () => {
+  assert.equal(resolveWorktreePath('/repo/src/foo'), '/repo/src/foo');
+  assert.equal(resolveWorktreePath('/repo/.claude/agents/foo'), '/repo/.claude/agents/foo');
+  // Worktrees segment but two extra components (nested under worktree) — must not match
+  assert.equal(resolveWorktreePath('/repo/.worktrees/foo/bar'), '/repo/.worktrees/foo/bar');
+});
+
+test('resolveWorktreePath passes falsy input through unchanged without throwing', () => {
+  assert.equal(resolveWorktreePath(null), null);
+  assert.equal(resolveWorktreePath(undefined), undefined);
+  assert.equal(resolveWorktreePath(''), '');
+});
+
+test('deriveProjectPath end-to-end: jsonl with worktree cwd resolves to parent repo', () => {
+  const tmp = mkTmp();
+  try {
+    // Real on-disk repo so existsSync returns true
+    const repo = path.join(tmp, 'repo');
+    fs.mkdirSync(repo);
+    const worktreeCwd = path.join(repo, '.claude', 'worktrees', 'agent-x');
+    // worktreeCwd itself doesn't need to exist; only its derived parent does
+
+    // The folder we feed deriveProjectPath is a "projects/foo" style dir
+    // containing a single jsonl whose first cwd line points at the worktree.
+    const folder = path.join(tmp, 'project-folder');
+    fs.mkdirSync(folder);
+    fs.writeFileSync(
+      path.join(folder, 'session-1.jsonl'),
+      JSON.stringify({ type: 'user', cwd: worktreeCwd }) + '\n',
+      'utf8'
+    );
+
+    assert.equal(deriveProjectPath(folder), repo);
+  } finally {
+    cleanup(tmp);
+  }
+});
diff --git a/test/session-transitions.test.js b/test/session-transitions.test.js
new file mode 100644
index 00000000..a0366188
--- /dev/null
+++ b/test/session-transitions.test.js
@@ -0,0 +1,197 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+
+const sessionTransitions = require('../session-transitions');
+const { detectSubagentTransitions, init } = sessionTransitions;
+
+function mkTmp() {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'switchboard-st-'));
+}
+
+function cleanup(dir) {
+  fs.rmSync(dir, { recursive: true, force: true });
+}
+
+/** Build a mock mainWindow that records every webContents.send call. */
+function makeMockWindow() {
+  const events = [];
+  return {
+    isDestroyed: () => false,
+    webContents: {
+      send: (channel, payload) => events.push({ channel, payload }),
+    },
+    _events: events,
+  };
+}
+
+/** Initialize the module with mocks. Returns the recorded-events array. */
+function setupModule() {
+  const win = makeMockWindow();
+  init({
+    PROJECTS_DIR: '/unused',
+    activeSessions: new Map(),
+    getMainWindow: () => win,
+    log: { info: () => {}, debug: () => {}, warn: () => {}, error: () => {} },
+    rekeyMcpServer: () => {},
+  });
+  return win._events;
+}
+
+/** Create N agent jsonl files under <folder>/<sessionId>/subagents/ and
+ *  set their mtimes to (now - ageMs). Returns the subagents dir. */
+function seedAgents(folder, sessionId, agents) {
+  const subDir = path.join(folder, sessionId, 'subagents');
+  fs.mkdirSync(subDir, { recursive: true });
+  for (const { id, ageMs = 0, content = '' } of agents) {
+    const filePath = path.join(subDir, `agent-${id}.jsonl`);
+    fs.writeFileSync(filePath, content, 'utf8');
+    if (ageMs) {
+      const t = (Date.now() - ageMs) / 1000;
+      fs.utimesSync(filePath, t, t);
+    }
+  }
+  return subDir;
+}
+
+test('bootstrap call with 5 pre-existing subagents emits zero events and populates the map', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent-session';
+    seedAgents(tmp, sessionId, [
+      { id: 'a1' }, { id: 'a2' }, { id: 'a3' }, { id: 'a4' }, { id: 'a5' },
+    ]);
+
+    const session = {}; // knownSubagents undefined → bootstrap
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 0, 'bootstrap must not emit IPC');
+    assert.ok(session.knownSubagents instanceof Map);
+    assert.equal(session.knownSubagents.size, 5);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('bootstrap marks an old-mtime agent (>60s) as completed: true', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent';
+    seedAgents(tmp, sessionId, [{ id: 'oldie', ageMs: 120_000 }]); // 2 minutes old
+
+    const session = {};
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 0);
+    const entry = session.knownSubagents.get('oldie');
+    assert.ok(entry, 'expected an entry for oldie');
+    assert.equal(entry.completed, true);
+    assert.ok(entry._completedAt, 'expected _completedAt to be stamped');
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('bootstrap marks a fresh-mtime agent as completed: false (lifecycle continues)', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent';
+    seedAgents(tmp, sessionId, [{ id: 'fresh', ageMs: 5_000 }]); // 5s old, well under 60s
+
+    const session = {};
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 0, 'bootstrap must still be silent for fresh agents');
+    const entry = session.knownSubagents.get('fresh');
+    assert.ok(entry);
+    assert.equal(entry.completed, false);
+    assert.equal(entry._completedAt, null);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('post-bootstrap: a brand-new agent file emits exactly one subagent-spawned event', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent';
+    // First, bootstrap with empty subagents dir
+    fs.mkdirSync(path.join(tmp, sessionId, 'subagents'), { recursive: true });
+    const session = {};
+    detectSubagentTransitions(sessionId, session, tmp);
+    assert.equal(events.length, 0);
+    assert.equal(session.knownSubagents.size, 0);
+
+    // Now drop in a new agent file and re-run
+    seedAgents(tmp, sessionId, [{ id: 'newcomer' }]);
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 1, `expected 1 event, got ${events.length}`);
+    assert.equal(events[0].channel, 'subagent-spawned');
+    assert.equal(events[0].payload.parentSessionId, sessionId);
+    assert.equal(events[0].payload.agentId, 'newcomer');
+    assert.equal(session.knownSubagents.get('newcomer').completed, false);
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('post-bootstrap with no new agents emits zero events (IPC-flood regression)', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent';
+    seedAgents(tmp, sessionId, [{ id: 'a' }, { id: 'b' }, { id: 'c' }]);
+
+    const session = {};
+    // Bootstrap absorbs all three silently
+    detectSubagentTransitions(sessionId, session, tmp);
+    assert.equal(events.length, 0);
+
+    // Subsequent flushes with no new files must stay silent
+    detectSubagentTransitions(sessionId, session, tmp);
+    detectSubagentTransitions(sessionId, session, tmp);
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 0, 'no events should fire when nothing changed');
+  } finally {
+    cleanup(tmp);
+  }
+});
+
+test('completion: agent alive on call N, stable mtime for >30s on call N+1, emits subagent-completed', () => {
+  const events = setupModule();
+  const tmp = mkTmp();
+  try {
+    const sessionId = 'parent';
+    const subDir = seedAgents(tmp, sessionId, [{ id: 'slow' }]);
+    const filePath = path.join(subDir, 'agent-slow.jsonl');
+    const mtimeMs = fs.statSync(filePath).mtimeMs;
+
+    // Pre-seed knownSubagents as if a prior call already saw this agent alive
+    // and started the stability timer 31 seconds ago. This skips bootstrap mode
+    // since knownSubagents is already defined.
+    const session = { knownSubagents: new Map() };
+    session.knownSubagents.set('slow', {
+      mtimeMs, // same as file's actual mtime → "mtime stable"
+      completed: false,
+      _stableStart: Date.now() - 31_000, // stability started >30s ago
+    });
+
+    detectSubagentTransitions(sessionId, session, tmp);
+
+    assert.equal(events.length, 1, `expected 1 completion event, got ${events.length}: ${JSON.stringify(events)}`);
+    assert.equal(events[0].channel, 'subagent-completed');
+    assert.equal(events[0].payload.parentSessionId, sessionId);
+    assert.equal(events[0].payload.agentId, 'slow');
+    assert.equal(session.knownSubagents.get('slow').completed, true);
+  } finally {
+    cleanup(tmp);
+  }
+});