diff --git a/ui-electrobun/tests/unit/hardening/backpressure.test.ts b/ui-electrobun/tests/unit/hardening/backpressure.test.ts
new file mode 100644
index 0000000..8b6b3cf
--- /dev/null
+++ b/ui-electrobun/tests/unit/hardening/backpressure.test.ts
@@ -0,0 +1,103 @@
+// Tests for backpressure guards — paste truncation and stdout buffer limits.
+// Uses bun:test. Tests the logic from Terminal.svelte and sidecar-manager.ts.
+
+import { describe, it, expect } from 'bun:test';
+
+// ── Constants (replicated from source) ──────────────────────────────────────
+
+const MAX_PASTE_CHUNK = 64 * 1024;           // 64 KB (Terminal.svelte)
+const MAX_LINE_SIZE = 10 * 1024 * 1024;       // 10 MB (sidecar-manager.ts)
+const MAX_PENDING_BUFFER = 50 * 1024 * 1024;  // 50 MB (sidecar-manager.ts)
+
+// ── Replicated truncation logic ──────────────────────────────────────────────
+
+function truncatePaste(payload: string): { text: string; wasTruncated: boolean } {
+  if (payload.length > MAX_PASTE_CHUNK) {
+    return { text: payload.slice(0, MAX_PASTE_CHUNK), wasTruncated: true };
+  }
+  return { text: payload, wasTruncated: false };
+}
+
+function applyBufferBackpressure(buffer: string): string {
+  // If buffer exceeds MAX_PENDING_BUFFER, keep only last MAX_LINE_SIZE bytes
+  if (buffer.length > MAX_PENDING_BUFFER) {
+    return buffer.slice(-MAX_LINE_SIZE);
+  }
+  return buffer;
+}
+
+function shouldTruncateLine(buffer: string): boolean {
+  // If buffer exceeds MAX_LINE_SIZE without a newline, truncate
+  return buffer.length > MAX_LINE_SIZE && !buffer.includes('\n');
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('paste truncation', () => {
+  it('passes through text under 64KB', () => {
+    const text = 'hello world';
+    const result = truncatePaste(text);
+    expect(result.wasTruncated).toBe(false);
+    expect(result.text).toBe(text);
+  });
+
+  it('passes through text exactly at 64KB', () => {
+    const text = 'x'.repeat(MAX_PASTE_CHUNK);
+    const result = truncatePaste(text);
+    expect(result.wasTruncated).toBe(false);
+    expect(result.text.length).toBe(MAX_PASTE_CHUNK);
+  });
+
+  it('truncates text over 64KB', () => {
+    const text = 'x'.repeat(MAX_PASTE_CHUNK + 1000);
+    const result = truncatePaste(text);
+    expect(result.wasTruncated).toBe(true);
+    expect(result.text.length).toBe(MAX_PASTE_CHUNK);
+  });
+
+  it('preserves first 64KB of content on truncation', () => {
+    const prefix = 'START-';
+    const text = prefix + 'x'.repeat(MAX_PASTE_CHUNK + 1000);
+    const result = truncatePaste(text);
+    expect(result.text.startsWith('START-')).toBe(true);
+  });
+});
+
+describe('stdout buffer backpressure', () => {
+  it('leaves buffer unchanged under 50MB', () => {
+    const buffer = 'x'.repeat(1000);
+    expect(applyBufferBackpressure(buffer)).toBe(buffer);
+  });
+
+  it('truncates buffer over 50MB to last 10MB', () => {
+    const buffer = 'x'.repeat(MAX_PENDING_BUFFER + 1000);
+    const result = applyBufferBackpressure(buffer);
+    expect(result.length).toBe(MAX_LINE_SIZE);
+  });
+
+  it('keeps tail of buffer (most recent data)', () => {
+    const head = 'H'.repeat(MAX_PENDING_BUFFER);
+    const tail = 'T'.repeat(MAX_LINE_SIZE);
+    const buffer = head + tail;
+    const result = applyBufferBackpressure(buffer);
+    // Result should be the last MAX_LINE_SIZE chars, which is all T's
+    expect(result).toBe(tail);
+  });
+});
+
+describe('line size guard', () => {
+  it('no truncation for buffer with newlines', () => {
+    const buffer = 'x'.repeat(MAX_LINE_SIZE + 100) + '\nmore data';
+    expect(shouldTruncateLine(buffer)).toBe(false);
+  });
+
+  it('truncates when buffer exceeds MAX_LINE_SIZE without newline', () => {
+    const buffer = 'x'.repeat(MAX_LINE_SIZE + 1);
+    expect(shouldTruncateLine(buffer)).toBe(true);
+  });
+
+  it('no truncation at exactly MAX_LINE_SIZE', () => {
+    const buffer = 'x'.repeat(MAX_LINE_SIZE);
+    expect(shouldTruncateLine(buffer)).toBe(false);
+  });
+});
diff --git a/ui-electrobun/tests/unit/hardening/channel-acl.test.ts b/ui-electrobun/tests/unit/hardening/channel-acl.test.ts
new file mode 100644
index 0000000..4df193e
--- /dev/null
+++ b/ui-electrobun/tests/unit/hardening/channel-acl.test.ts
@@ -0,0 +1,165 @@
+// Tests for channel ACL — membership-gated messaging.
+// Uses bun:test. Tests the logic from btmsg-db.ts channel operations.
+
+import { describe, it, expect, beforeEach } from 'bun:test';
+
+// ── In-memory channel store (replicated logic from btmsg-db.ts) ─────────────
+
+interface ChannelMessage {
+  id: string;
+  channelId: string;
+  fromAgent: string;
+  content: string;
+}
+
+function createChannelStore() {
+  const channels = new Map<string, { id: string; name: string }>();
+  const members = new Map<string, Set<string>>();    // channelId -> Set<agentId>
+  const messages: ChannelMessage[] = [];
+  let msgCounter = 0;
+
+  return {
+    createChannel(id: string, name: string): void {
+      channels.set(id, { id, name });
+      members.set(id, new Set());
+    },
+
+    joinChannel(channelId: string, agentId: string): void {
+      const ch = channels.get(channelId);
+      if (!ch) throw new Error(`Channel '${channelId}' not found`);
+      members.get(channelId)!.add(agentId);
+    },
+
+    leaveChannel(channelId: string, agentId: string): void {
+      members.get(channelId)?.delete(agentId);
+    },
+
+    sendChannelMessage(channelId: string, fromAgent: string, content: string): string {
+      const memberSet = members.get(channelId);
+      if (!memberSet || !memberSet.has(fromAgent)) {
+        throw new Error(`Agent '${fromAgent}' is not a member of channel '${channelId}'`);
+      }
+      const id = `msg-${++msgCounter}`;
+      messages.push({ id, channelId, fromAgent, content });
+      return id;
+    },
+
+    getChannelMembers(channelId: string): string[] {
+      return Array.from(members.get(channelId) ?? []);
+    },
+
+    getMessages(channelId: string): ChannelMessage[] {
+      return messages.filter(m => m.channelId === channelId);
+    },
+  };
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('channel membership', () => {
+  let store: ReturnType<typeof createChannelStore>;
+
+  beforeEach(() => {
+    store = createChannelStore();
+    store.createChannel('general', 'General');
+  });
+
+  it('joinChannel adds member', () => {
+    store.joinChannel('general', 'agent-1');
+    expect(store.getChannelMembers('general')).toContain('agent-1');
+  });
+
+  it('joinChannel to nonexistent channel throws', () => {
+    expect(() => store.joinChannel('nonexistent', 'agent-1')).toThrow('not found');
+  });
+
+  it('leaveChannel removes member', () => {
+    store.joinChannel('general', 'agent-1');
+    store.leaveChannel('general', 'agent-1');
+    expect(store.getChannelMembers('general')).not.toContain('agent-1');
+  });
+
+  it('leaveChannel is idempotent', () => {
+    store.leaveChannel('general', 'agent-1');
+    expect(store.getChannelMembers('general')).toHaveLength(0);
+  });
+
+  it('getChannelMembers returns all members', () => {
+    store.joinChannel('general', 'agent-1');
+    store.joinChannel('general', 'agent-2');
+    store.joinChannel('general', 'agent-3');
+    expect(store.getChannelMembers('general')).toHaveLength(3);
+  });
+
+  it('duplicate join is idempotent (Set semantics)', () => {
+    store.joinChannel('general', 'agent-1');
+    store.joinChannel('general', 'agent-1');
+    expect(store.getChannelMembers('general')).toHaveLength(1);
+  });
+});
+
+describe('channel message ACL', () => {
+  let store: ReturnType<typeof createChannelStore>;
+
+  beforeEach(() => {
+    store = createChannelStore();
+    store.createChannel('ops', 'Operations');
+    store.joinChannel('ops', 'manager');
+  });
+
+  it('member can send message', () => {
+    const id = store.sendChannelMessage('ops', 'manager', 'hello team');
+    expect(id).toBeTruthy();
+    const msgs = store.getMessages('ops');
+    expect(msgs).toHaveLength(1);
+    expect(msgs[0].content).toBe('hello team');
+    expect(msgs[0].fromAgent).toBe('manager');
+  });
+
+  it('non-member is rejected', () => {
+    expect(() => {
+      store.sendChannelMessage('ops', 'outsider', 'sneaky message');
+    }).toThrow("not a member");
+  });
+
+  it('former member is rejected after leaving', () => {
+    store.leaveChannel('ops', 'manager');
+    expect(() => {
+      store.sendChannelMessage('ops', 'manager', 'should fail');
+    }).toThrow("not a member");
+  });
+
+  it('rejoined member can send again', () => {
+    store.leaveChannel('ops', 'manager');
+    store.joinChannel('ops', 'manager');
+    const id = store.sendChannelMessage('ops', 'manager', 'back again');
+    expect(id).toBeTruthy();
+  });
+});
+
+describe('channel isolation', () => {
+  let store: ReturnType<typeof createChannelStore>;
+
+  beforeEach(() => {
+    store = createChannelStore();
+    store.createChannel('ch-a', 'Channel A');
+    store.createChannel('ch-b', 'Channel B');
+    store.joinChannel('ch-a', 'agent-1');
+  });
+
+  it('member of channel A cannot send to channel B', () => {
+    expect(() => {
+      store.sendChannelMessage('ch-b', 'agent-1', 'wrong channel');
+    }).toThrow("not a member");
+  });
+
+  it('messages are channel-scoped', () => {
+    store.joinChannel('ch-b', 'agent-2');
+    store.sendChannelMessage('ch-a', 'agent-1', 'msg in A');
+    store.sendChannelMessage('ch-b', 'agent-2', 'msg in B');
+    expect(store.getMessages('ch-a')).toHaveLength(1);
+    expect(store.getMessages('ch-b')).toHaveLength(1);
+    expect(store.getMessages('ch-a')[0].content).toBe('msg in A');
+    expect(store.getMessages('ch-b')[0].content).toBe('msg in B');
+  });
+});
diff --git a/ui-electrobun/tests/unit/hardening/durable-sequencing.test.ts b/ui-electrobun/tests/unit/hardening/durable-sequencing.test.ts
new file mode 100644
index 0000000..3ea7d83
--- /dev/null
+++ b/ui-electrobun/tests/unit/hardening/durable-sequencing.test.ts
@@ -0,0 +1,142 @@
+// Tests for durable sequencing — monotonic seqId assignment and deduplication.
+// Uses bun:test.
+
+import { describe, it, expect } from 'bun:test';
+
+// ── Replicated seqId counter from agent-store.svelte.ts ─────────────────────
+
+function createSeqCounter() {
+  const counters = new Map<string, number>();
+  return {
+    next(sessionId: string): number {
+      const current = counters.get(sessionId) ?? 0;
+      const next = current + 1;
+      counters.set(sessionId, next);
+      return next;
+    },
+    get(sessionId: string): number {
+      return counters.get(sessionId) ?? 0;
+    },
+    set(sessionId: string, value: number): void {
+      counters.set(sessionId, value);
+    },
+  };
+}
+
+// ── Deduplication logic ─────────────────────────────────────────────────────
+
+interface RawMsg {
+  msgId: string;
+  seqId: number;
+  content: string;
+}
+
+function deduplicateMessages(messages: RawMsg[]): { deduplicated: RawMsg[]; maxSeqId: number } {
+  const seqIdSet = new Set<number>();
+  const deduplicated: RawMsg[] = [];
+  let maxSeqId = 0;
+
+  for (const m of messages) {
+    const sid = m.seqId ?? 0;
+    if (sid > 0 && seqIdSet.has(sid)) continue;
+    if (sid > 0) seqIdSet.add(sid);
+    if (sid > maxSeqId) maxSeqId = sid;
+    deduplicated.push(m);
+  }
+
+  return { deduplicated, maxSeqId };
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('seqId monotonic assignment', () => {
+  it('starts at 1', () => {
+    const counter = createSeqCounter();
+    expect(counter.next('s1')).toBe(1);
+  });
+
+  it('never decreases', () => {
+    const counter = createSeqCounter();
+    let prev = 0;
+    for (let i = 0; i < 100; i++) {
+      const next = counter.next('s1');
+      expect(next).toBeGreaterThan(prev);
+      prev = next;
+    }
+  });
+
+  it('each call returns unique value', () => {
+    const counter = createSeqCounter();
+    const ids = new Set<number>();
+    for (let i = 0; i < 50; i++) {
+      ids.add(counter.next('s1'));
+    }
+    expect(ids.size).toBe(50);
+  });
+
+  it('independent per session', () => {
+    const counter = createSeqCounter();
+    expect(counter.next('a')).toBe(1);
+    expect(counter.next('b')).toBe(1);
+    expect(counter.next('a')).toBe(2);
+    expect(counter.next('b')).toBe(2);
+  });
+});
+
+describe('deduplication', () => {
+  it('removes messages with duplicate seqIds', () => {
+    const messages: RawMsg[] = [
+      { msgId: '1', seqId: 1, content: 'hello' },
+      { msgId: '2', seqId: 2, content: 'world' },
+      { msgId: '3', seqId: 1, content: 'hello-dup' }, // duplicate
+    ];
+    const { deduplicated } = deduplicateMessages(messages);
+    expect(deduplicated).toHaveLength(2);
+    expect(deduplicated.map(m => m.msgId)).toEqual(['1', '2']);
+  });
+
+  it('keeps first occurrence of duplicate seqId', () => {
+    const messages: RawMsg[] = [
+      { msgId: 'a', seqId: 5, content: 'first' },
+      { msgId: 'b', seqId: 5, content: 'second' },
+    ];
+    const { deduplicated } = deduplicateMessages(messages);
+    expect(deduplicated).toHaveLength(1);
+    expect(deduplicated[0].msgId).toBe('a');
+  });
+
+  it('preserves messages with seqId 0 (unsequenced)', () => {
+    const messages: RawMsg[] = [
+      { msgId: 'x', seqId: 0, content: 'legacy' },
+      { msgId: 'y', seqId: 0, content: 'legacy2' },
+    ];
+    const { deduplicated } = deduplicateMessages(messages);
+    expect(deduplicated).toHaveLength(2);
+  });
+
+  it('returns correct maxSeqId', () => {
+    const messages: RawMsg[] = [
+      { msgId: '1', seqId: 3, content: 'a' },
+      { msgId: '2', seqId: 7, content: 'b' },
+      { msgId: '3', seqId: 5, content: 'c' },
+    ];
+    const { maxSeqId } = deduplicateMessages(messages);
+    expect(maxSeqId).toBe(7);
+  });
+});
+
+describe('restore resumes from max seqId', () => {
+  it('counter resumes after restoring maxSeqId', () => {
+    const counter = createSeqCounter();
+    // Simulate: restored messages had max seqId 42
+    counter.set('session-1', 42);
+    expect(counter.next('session-1')).toBe(43);
+    expect(counter.next('session-1')).toBe(44);
+  });
+
+  it('handles empty restore (maxSeqId 0)', () => {
+    const counter = createSeqCounter();
+    counter.set('session-1', 0);
+    expect(counter.next('session-1')).toBe(1);
+  });
+});
diff --git a/ui-electrobun/tests/unit/hardening/file-conflict.test.ts b/ui-electrobun/tests/unit/hardening/file-conflict.test.ts
new file mode 100644
index 0000000..95ba3ed
--- /dev/null
+++ b/ui-electrobun/tests/unit/hardening/file-conflict.test.ts
@@ -0,0 +1,127 @@
+// Tests for file conflict detection via mtime comparison.
+// Uses bun:test. Tests the mtime-based conflict detection and atomic write logic
+// from ui-electrobun/src/bun/handlers/files-handlers.ts and FileBrowser.svelte.
+
+import { describe, it, expect } from 'bun:test';
+
+// ── Replicated conflict detection logic ──────────────────────────────────────
+
+interface FileStat {
+  mtimeMs: number;
+  size: number;
+  error?: string;
+}
+
+/**
+ * Check if the file was modified since we last read it.
+ * Returns true if conflict detected (mtime differs).
+ */
+function hasConflict(readMtimeMs: number, currentStat: FileStat): boolean {
+  if (readMtimeMs <= 0) return false;       // No baseline — skip check
+  if (currentStat.error) return false;       // Can't stat — skip check
+  return currentStat.mtimeMs > readMtimeMs;  // Modified since read
+}
+
+/**
+ * Simulate atomic write: write to temp file, then rename.
+ * Returns the operations performed for verification.
+ */
+function atomicWriteOps(filePath: string, _content: string): { tmpPath: string; finalPath: string } {
+  const tmpPath = filePath + '.agor-tmp';
+  return { tmpPath, finalPath: filePath };
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('mtime conflict detection', () => {
+  it('no conflict when mtime matches', () => {
+    const readTime = 1700000000000;
+    const stat: FileStat = { mtimeMs: readTime, size: 100 };
+    expect(hasConflict(readTime, stat)).toBe(false);
+  });
+
+  it('conflict detected when mtime is newer', () => {
+    const readTime = 1700000000000;
+    const stat: FileStat = { mtimeMs: readTime + 5000, size: 120 };
+    expect(hasConflict(readTime, stat)).toBe(true);
+  });
+
+  it('no conflict when readMtimeMs is 0 (first write)', () => {
+    const stat: FileStat = { mtimeMs: 1700000005000, size: 120 };
+    expect(hasConflict(0, stat)).toBe(false);
+  });
+
+  it('no conflict when stat returns error', () => {
+    const stat: FileStat = { mtimeMs: 0, size: 0, error: 'ENOENT: no such file' };
+    expect(hasConflict(1700000000000, stat)).toBe(false);
+  });
+
+  it('no conflict when file is older than read (edge case)', () => {
+    const readTime = 1700000005000;
+    const stat: FileStat = { mtimeMs: 1700000000000, size: 100 };
+    expect(hasConflict(readTime, stat)).toBe(false);
+  });
+
+  it('detects tiny mtime difference (1ms)', () => {
+    const readTime = 1700000000000;
+    const stat: FileStat = { mtimeMs: readTime + 1, size: 100 };
+    expect(hasConflict(readTime, stat)).toBe(true);
+  });
+});
+
+describe('atomic write', () => {
+  it('uses .agor-tmp suffix for temp file', () => {
+    const ops = atomicWriteOps('/home/user/project/main.ts', 'content');
+    expect(ops.tmpPath).toBe('/home/user/project/main.ts.agor-tmp');
+    expect(ops.finalPath).toBe('/home/user/project/main.ts');
+  });
+
+  it('temp file path differs from final path', () => {
+    const ops = atomicWriteOps('/test/file.txt', 'data');
+    expect(ops.tmpPath).not.toBe(ops.finalPath);
+  });
+
+  it('handles paths with special characters', () => {
+    const ops = atomicWriteOps('/path/with spaces/file.ts', 'data');
+    expect(ops.tmpPath).toBe('/path/with spaces/file.ts.agor-tmp');
+  });
+});
+
+describe('conflict workflow', () => {
+  it('full read-modify-check-write cycle — no conflict', () => {
+    // 1. Read file, record mtime
+    const readStat: FileStat = { mtimeMs: 1700000000000, size: 50 };
+    const readMtimeMs = readStat.mtimeMs;
+
+    // 2. User edits in editor
+    // 3. Before save, stat again
+    const preSaveStat: FileStat = { mtimeMs: 1700000000000, size: 50 }; // unchanged
+    expect(hasConflict(readMtimeMs, preSaveStat)).toBe(false);
+
+    // 4. Write via atomic
+    const ops = atomicWriteOps('/test/file.ts', 'new content');
+    expect(ops.tmpPath).toContain('.agor-tmp');
+  });
+
+  it('full read-modify-check-write cycle — conflict detected', () => {
+    // 1. Read file, record mtime
+    const readMtimeMs = 1700000000000;
+
+    // 2. External process modifies the file
+    const preSaveStat: FileStat = { mtimeMs: 1700000002000, size: 80 };
+
+    // 3. Conflict detected — should warn user
+    expect(hasConflict(readMtimeMs, preSaveStat)).toBe(true);
+  });
+
+  it('after successful save, update readMtimeMs', () => {
+    let readMtimeMs = 1700000000000;
+
+    // Save succeeds, stat again to get new mtime
+    const postSaveStat: FileStat = { mtimeMs: 1700000003000, size: 120 };
+    readMtimeMs = postSaveStat.mtimeMs;
+
+    // No conflict on subsequent check
+    expect(hasConflict(readMtimeMs, postSaveStat)).toBe(false);
+  });
+});
diff --git a/ui-electrobun/tests/unit/hardening/retention.test.ts b/ui-electrobun/tests/unit/hardening/retention.test.ts
new file mode 100644
index 0000000..34871a4
--- /dev/null
+++ b/ui-electrobun/tests/unit/hardening/retention.test.ts
@@ -0,0 +1,151 @@
+// Tests for session retention — enforceMaxSessions logic.
+// Uses bun:test. Tests the retention count + age pruning from agent-store.svelte.ts.
+
+import { describe, it, expect, beforeEach } from 'bun:test';
+
+// ── Replicated types and retention logic ────────────────────────────────────
+
+interface SessionEntry {
+  sessionId: string;
+  projectId: string;
+  status: 'idle' | 'running' | 'done' | 'error';
+  lastMessageTs: number;
+}
+
+interface RetentionConfig {
+  count: number;
+  days: number;
+}
+
+function setRetentionConfig(count: number, days: number): RetentionConfig {
+  return {
+    count: Math.max(1, Math.min(50, count)),
+    days: Math.max(1, Math.min(365, days)),
+  };
+}
+
+function enforceMaxSessions(
+  sessions: SessionEntry[],
+  projectId: string,
+  config: RetentionConfig,
+): string[] {
+  const now = Date.now();
+  const maxAgeMs = config.days * 24 * 60 * 60 * 1000;
+
+  // Filter to this project's non-running sessions, sorted newest first
+  const projectSessions = sessions
+    .filter(s => s.projectId === projectId && s.status !== 'running')
+    .sort((a, b) => b.lastMessageTs - a.lastMessageTs);
+
+  const toPurge: string[] = [];
+
+  // Prune by count
+  if (projectSessions.length > config.count) {
+    const excess = projectSessions.slice(config.count);
+    for (const s of excess) toPurge.push(s.sessionId);
+  }
+
+  // Prune by age
+  for (const s of projectSessions) {
+    if (s.lastMessageTs > 0 && (now - s.lastMessageTs) > maxAgeMs) {
+      if (!toPurge.includes(s.sessionId)) toPurge.push(s.sessionId);
+    }
+  }
+
+  return toPurge;
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('setRetentionConfig', () => {
+  it('clamps count to [1, 50]', () => {
+    expect(setRetentionConfig(0, 30).count).toBe(1);
+    expect(setRetentionConfig(100, 30).count).toBe(50);
+    expect(setRetentionConfig(5, 30).count).toBe(5);
+  });
+
+  it('clamps days to [1, 365]', () => {
+    expect(setRetentionConfig(5, 0).days).toBe(1);
+    expect(setRetentionConfig(5, 500).days).toBe(365);
+    expect(setRetentionConfig(5, 30).days).toBe(30);
+  });
+});
+
+describe('enforceMaxSessions — count-based pruning', () => {
+  it('keeps only N most recent sessions', () => {
+    const now = Date.now();
+    const sessions: SessionEntry[] = [
+      { sessionId: 's1', projectId: 'p1', status: 'done', lastMessageTs: now - 50000 },
+      { sessionId: 's2', projectId: 'p1', status: 'done', lastMessageTs: now - 40000 },
+      { sessionId: 's3', projectId: 'p1', status: 'done', lastMessageTs: now - 30000 },
+      { sessionId: 's4', projectId: 'p1', status: 'done', lastMessageTs: now - 20000 },
+      { sessionId: 's5', projectId: 'p1', status: 'done', lastMessageTs: now - 10000 },
+    ];
+    const config: RetentionConfig = { count: 3, days: 365 };
+    const toPurge = enforceMaxSessions(sessions, 'p1', config);
+    expect(toPurge).toHaveLength(2);
+    // s1 and s2 are oldest
+    expect(toPurge).toContain('s1');
+    expect(toPurge).toContain('s2');
+  });
+
+  it('does not purge when under limit', () => {
+    const now = Date.now();
+    const sessions: SessionEntry[] = [
+      { sessionId: 's1', projectId: 'p1', status: 'done', lastMessageTs: now },
+    ];
+    const config: RetentionConfig = { count: 5, days: 365 };
+    expect(enforceMaxSessions(sessions, 'p1', config)).toHaveLength(0);
+  });
+});
+
+describe('enforceMaxSessions — age-based pruning', () => {
+  it('prunes sessions older than retention days', () => {
+    const now = Date.now();
+    const oldTs = now - (31 * 24 * 60 * 60 * 1000); // 31 days ago
+    const sessions: SessionEntry[] = [
+      { sessionId: 's-old', projectId: 'p1', status: 'done', lastMessageTs: oldTs },
+      { sessionId: 's-new', projectId: 'p1', status: 'done', lastMessageTs: now },
+    ];
+    const config: RetentionConfig = { count: 10, days: 30 };
+    const toPurge = enforceMaxSessions(sessions, 'p1', config);
+    expect(toPurge).toEqual(['s-old']);
+  });
+
+  it('keeps sessions within retention window', () => {
+    const now = Date.now();
+    const recentTs = now - (5 * 24 * 60 * 60 * 1000); // 5 days ago
+    const sessions: SessionEntry[] = [
+      { sessionId: 's1', projectId: 'p1', status: 'done', lastMessageTs: recentTs },
+    ];
+    const config: RetentionConfig = { count: 10, days: 30 };
+    expect(enforceMaxSessions(sessions, 'p1', config)).toHaveLength(0);
+  });
+});
+
+describe('enforceMaxSessions — running sessions protected', () => {
+  it('never purges running sessions', () => {
+    const now = Date.now();
+    const sessions: SessionEntry[] = [
+      { sessionId: 's-running', projectId: 'p1', status: 'running', lastMessageTs: now - 999999999 },
+      { sessionId: 's-done', projectId: 'p1', status: 'done', lastMessageTs: now },
+    ];
+    const config: RetentionConfig = { count: 1, days: 1 };
+    const toPurge = enforceMaxSessions(sessions, 'p1', config);
+    expect(toPurge).not.toContain('s-running');
+  });
+});
+
+describe('enforceMaxSessions — project isolation', () => {
+  it('only prunes sessions for the specified project', () => {
+    const now = Date.now();
+    const sessions: SessionEntry[] = [
+      { sessionId: 'p1-s1', projectId: 'p1', status: 'done', lastMessageTs: now - 1000 },
+      { sessionId: 'p2-s1', projectId: 'p2', status: 'done', lastMessageTs: now - 1000 },
+    ];
+    const config: RetentionConfig = { count: 0, days: 365 }; // count 0 → clamped to 1
+    const actualConfig = setRetentionConfig(0, 365);
+    const toPurge = enforceMaxSessions(sessions, 'p1', actualConfig);
+    expect(toPurge).not.toContain('p2-s1');
+  });
+});
diff --git a/ui-electrobun/tests/unit/keybinding-store.test.ts b/ui-electrobun/tests/unit/keybinding-store.test.ts
new file mode 100644
index 0000000..15c964b
--- /dev/null
+++ b/ui-electrobun/tests/unit/keybinding-store.test.ts
@@ -0,0 +1,211 @@
+// Tests for Electrobun keybinding-store — pure logic.
+// Uses bun:test. Tests default bindings, chord serialization, conflict detection.
+
+import { describe, it, expect, beforeEach } from 'bun:test';
+
+// ── Replicated types ──────────────────────────────────────────────────────────
+
+interface Keybinding {
+  id: string;
+  label: string;
+  category: 'Global' | 'Navigation' | 'Terminal' | 'Settings';
+  chord: string;
+  defaultChord: string;
+}
+
+// ── Default bindings (replicated from keybinding-store.svelte.ts) ───────────
+
+const DEFAULTS: Keybinding[] = [
+  { id: 'palette',       label: 'Command Palette',       category: 'Global',     chord: 'Ctrl+K',       defaultChord: 'Ctrl+K'       },
+  { id: 'settings',      label: 'Open Settings',          category: 'Global',     chord: 'Ctrl+,',       defaultChord: 'Ctrl+,'       },
+  { id: 'group1',        label: 'Switch to Group 1',      category: 'Navigation', chord: 'Ctrl+1',       defaultChord: 'Ctrl+1'       },
+  { id: 'group2',        label: 'Switch to Group 2',      category: 'Navigation', chord: 'Ctrl+2',       defaultChord: 'Ctrl+2'       },
+  { id: 'group3',        label: 'Switch to Group 3',      category: 'Navigation', chord: 'Ctrl+3',       defaultChord: 'Ctrl+3'       },
+  { id: 'group4',        label: 'Switch to Group 4',      category: 'Navigation', chord: 'Ctrl+4',       defaultChord: 'Ctrl+4'       },
+  { id: 'newTerminal',   label: 'New Terminal Tab',        category: 'Terminal',   chord: 'Ctrl+Shift+T', defaultChord: 'Ctrl+Shift+T' },
+  { id: 'closeTab',      label: 'Close Terminal Tab',      category: 'Terminal',   chord: 'Ctrl+Shift+W', defaultChord: 'Ctrl+Shift+W' },
+  { id: 'nextTab',       label: 'Next Terminal Tab',       category: 'Terminal',   chord: 'Ctrl+]',       defaultChord: 'Ctrl+]'       },
+  { id: 'prevTab',       label: 'Previous Terminal Tab',   category: 'Terminal',   chord: 'Ctrl+[',       defaultChord: 'Ctrl+['       },
+  { id: 'search',        label: 'Global Search',           category: 'Global',     chord: 'Ctrl+Shift+F', defaultChord: 'Ctrl+Shift+F' },
+  { id: 'notifications', label: 'Notification Center',     category: 'Global',     chord: 'Ctrl+Shift+N', defaultChord: 'Ctrl+Shift+N' },
+  { id: 'minimize',      label: 'Minimize Window',         category: 'Global',     chord: 'Ctrl+M',       defaultChord: 'Ctrl+M'       },
+  { id: 'toggleFiles',   label: 'Toggle Files Tab',        category: 'Navigation', chord: 'Ctrl+Shift+E', defaultChord: 'Ctrl+Shift+E' },
+  { id: 'toggleMemory',  label: 'Toggle Memory Tab',       category: 'Navigation', chord: 'Ctrl+Shift+M', defaultChord: 'Ctrl+Shift+M' },
+  { id: 'reload',        label: 'Reload App',              category: 'Settings',   chord: 'Ctrl+R',       defaultChord: 'Ctrl+R'       },
+];
+
+// ── Chord serialization (replicated) ─────────────────────────────────────────
+
+interface MockKeyboardEvent {
+  ctrlKey: boolean;
+  metaKey: boolean;
+  shiftKey: boolean;
+  altKey: boolean;
+  key: string;
+}
+
+function chordFromEvent(e: MockKeyboardEvent): string {
+  const parts: string[] = [];
+  if (e.ctrlKey || e.metaKey) parts.push('Ctrl');
+  if (e.shiftKey) parts.push('Shift');
+  if (e.altKey) parts.push('Alt');
+  const key = e.key === ' ' ? 'Space' : e.key;
+  if (!['Control', 'Shift', 'Alt', 'Meta'].includes(key)) {
+    parts.push(key.length === 1 ? key.toUpperCase() : key);
+  }
+  return parts.join('+');
+}
+
+// ── Store logic (replicated without runes) ──────────────────────────────────
+
+function createKeybindingState() {
+  let bindings: Keybinding[] = DEFAULTS.map(b => ({ ...b }));
+
+  return {
+    getBindings: () => bindings,
+    setChord(id: string, chord: string): void {
+      bindings = bindings.map(b => b.id === id ? { ...b, chord } : b);
+    },
+    resetChord(id: string): void {
+      const def = DEFAULTS.find(b => b.id === id);
+      if (!def) return;
+      bindings = bindings.map(b => b.id === id ? { ...b, chord: def.defaultChord } : b);
+    },
+    findConflicts(chord: string, excludeId?: string): Keybinding[] {
+      return bindings.filter(b => b.chord === chord && b.id !== excludeId);
+    },
+  };
+}
+
+// ── Tests ───────────────────────────────────────────────────────────────────
+
+describe('default bindings', () => {
+  it('has exactly 16 default bindings', () => {
+    expect(DEFAULTS).toHaveLength(16);
+  });
+
+  it('all bindings have unique ids', () => {
+    const ids = DEFAULTS.map(b => b.id);
+    expect(new Set(ids).size).toBe(ids.length);
+  });
+
+  it('all chords match defaultChord initially', () => {
+    for (const b of DEFAULTS) {
+      expect(b.chord).toBe(b.defaultChord);
+    }
+  });
+
+  it('covers all 4 categories', () => {
+    const categories = new Set(DEFAULTS.map(b => b.category));
+    expect(categories.has('Global')).toBe(true);
+    expect(categories.has('Navigation')).toBe(true);
+    expect(categories.has('Terminal')).toBe(true);
+    expect(categories.has('Settings')).toBe(true);
+  });
+
+  it('command palette is Ctrl+K', () => {
+    const palette = DEFAULTS.find(b => b.id === 'palette');
+    expect(palette?.chord).toBe('Ctrl+K');
+  });
+});
+
+describe('chordFromEvent', () => {
+  it('serializes Ctrl+K', () => {
+    expect(chordFromEvent({ ctrlKey: true, metaKey: false, shiftKey: false, altKey: false, key: 'k' })).toBe('Ctrl+K');
+  });
+
+  it('serializes Ctrl+Shift+F', () => {
+    expect(chordFromEvent({ ctrlKey: true, metaKey: false, shiftKey: true, altKey: false, key: 'f' })).toBe('Ctrl+Shift+F');
+  });
+
+  it('serializes Alt+1', () => {
+    expect(chordFromEvent({ ctrlKey: false, metaKey: false, shiftKey: false, altKey: true, key: '1' })).toBe('Alt+1');
+  });
+
+  it('maps space to Space', () => {
+    expect(chordFromEvent({ ctrlKey: true, metaKey: false, shiftKey: false, altKey: false, key: ' ' })).toBe('Ctrl+Space');
+  });
+
+  it('ignores pure modifier keys', () => {
+    expect(chordFromEvent({ ctrlKey: true, metaKey: false, shiftKey: false, altKey: false, key: 'Control' })).toBe('Ctrl');
+  });
+
+  it('metaKey treated as Ctrl', () => {
+    expect(chordFromEvent({ ctrlKey: false, metaKey: true, shiftKey: false, altKey: false, key: 'k' })).toBe('Ctrl+K');
+  });
+
+  it('preserves multi-char key names', () => {
+    expect(chordFromEvent({ ctrlKey: false, metaKey: false, shiftKey: false, altKey: false, key: 'Escape' })).toBe('Escape');
+  });
+});
+
+describe('setChord / resetChord', () => {
+  let state: ReturnType<typeof createKeybindingState>;
+
+  beforeEach(() => {
+    state = createKeybindingState();
+  });
+
+  it('setChord updates the binding', () => {
+    state.setChord('palette', 'Ctrl+P');
+    const b = state.getBindings().find(b => b.id === 'palette');
+    expect(b?.chord).toBe('Ctrl+P');
+    expect(b?.defaultChord).toBe('Ctrl+K'); // default unchanged
+  });
+
+  it('resetChord restores default', () => {
+    state.setChord('palette', 'Ctrl+P');
+    state.resetChord('palette');
+    const b = state.getBindings().find(b => b.id === 'palette');
+    expect(b?.chord).toBe('Ctrl+K');
+  });
+
+  it('resetChord ignores unknown id', () => {
+    const before = state.getBindings().length;
+    state.resetChord('nonexistent');
+    expect(state.getBindings().length).toBe(before);
+  });
+});
+
+describe('conflict detection', () => {
+  let state: ReturnType<typeof createKeybindingState>;
+
+  beforeEach(() => {
+    state = createKeybindingState();
+  });
+
+  it('detects conflict when two bindings share a chord', () => {
+    state.setChord('settings', 'Ctrl+K'); // same as palette
+    const conflicts = state.findConflicts('Ctrl+K', 'settings');
+    expect(conflicts).toHaveLength(1);
+    expect(conflicts[0].id).toBe('palette');
+  });
+
+  it('no conflict when chord is unique', () => {
+    state.setChord('palette', 'Ctrl+Shift+P');
+    const conflicts = state.findConflicts('Ctrl+Shift+P', 'palette');
+    expect(conflicts).toHaveLength(0);
+  });
+
+  it('excludes self from conflict check', () => {
+    const conflicts = state.findConflicts('Ctrl+K', 'palette');
+    expect(conflicts).toHaveLength(0);
+  });
+
+  it('finds multiple conflicts', () => {
+    state.setChord('search', 'Ctrl+K');
+    state.setChord('reload', 'Ctrl+K');
+    const conflicts = state.findConflicts('Ctrl+K', 'settings');
+    expect(conflicts).toHaveLength(3); // palette, search, reload
+  });
+});
+
+describe('capture mode', () => {
+  it('chordFromEvent records full chord for capture', () => {
+    // Simulate user pressing Ctrl+Shift+X in capture mode
+    const chord = chordFromEvent({
+      ctrlKey: true, metaKey: false, shiftKey: true, altKey: false, key: 'x',
+    });
+    expect(chord).toBe('Ctrl+Shift+X');
+  });
+});
diff --git a/ui-electrobun/tests/unit/workspace-store.test.ts b/ui-electrobun/tests/unit/workspace-store.test.ts
index be80662..eef562c 100644
--- a/ui-electrobun/tests/unit/workspace-store.test.ts
+++ b/ui-electrobun/tests/unit/workspace-store.test.ts
@@ -220,18 +220,20 @@ describe('workspace store — derived state', () => {
   });
 
   it('mountedGroupIds only includes active + previous', () => {
-    ws.addGroup('G1');
-    ws.addGroup('G2');
-    const g1Id = ws.getGroups()[1].id;
-    const g2Id = ws.getGroups()[2].id;
+    // Use deterministic IDs to avoid Date.now() collisions
+    const state = createWorkspaceState();
+    // Manually push groups with known IDs
+    const groups = state.getGroups();
+    groups.push({ id: 'grp-aaa', name: 'G1', icon: '2', position: 1 });
+    groups.push({ id: 'grp-bbb', name: 'G2', icon: '3', position: 2 });
 
-    ws.setActiveGroup(g1Id);
-    ws.setActiveGroup(g2Id);
-    const mounted = ws.getMountedGroupIds();
+    state.setActiveGroup('grp-aaa');
+    state.setActiveGroup('grp-bbb');
+    const mounted = state.getMountedGroupIds();
     expect(mounted.size).toBe(2);
-    expect(mounted.has(g2Id)).toBe(true);   // active
-    expect(mounted.has(g1Id)).toBe(true);   // previous
-    expect(mounted.has('dev')).toBe(false);  // two switches ago — not mounted
+    expect(mounted.has('grp-bbb')).toBe(true);   // active
+    expect(mounted.has('grp-aaa')).toBe(true);   // previous
+    expect(mounted.has('dev')).toBe(false);        // two switches ago — not mounted
   });
 });