diff --git a/server/index.js b/server/index.js
index 0766706..a00a8bf 100755
--- a/server/index.js
+++ b/server/index.js
@@ -63,6 +63,11 @@ import {
     spawnOmp,
     abortOmpSession,
 } from './omp-cli.js';
+import {
+    spawnOmo,
+    abortOmoSession,
+} from './omo-cli.js';
+import { findLiveTmuxSpawnBlock } from './modules/providers/services/live-spawn-guard.service.js';
 import {
     stripAnsiSequences,
     normalizeDetectedUrl,
@@ -170,14 +175,11 @@ const wss = createWebSocketServer(server, {
             opencode: spawnOpenCode,
             gjc: spawnGjc,
             omp: spawnOmp,
-            // omo is intentionally NOT registered. Its transcripts are indexed
-            // like any other session, so a session that is currently live in a
-            // tmux pane can also be opened here; spawning would start a second
-            // headless omo on the same --session-id and both processes would
-            // append to one transcript. Observed: a full turn landed in a live
-            // session that the running agent never saw. Live sessions must go
-            // through the tmux relay. Re-enable only behind a guard that
-            // refuses to spawn when the session is live.
+            // Safe to register because findLiveTmuxSpawnBlock below refuses to
+            // spawn on a session that is currently live in a tmux pane (#44):
+            // a second headless omo on the same --session-id would otherwise
+            // append to one transcript the live agent never sees.
+            omo: spawnOmo,
         },
         abortFns: {
             claude: abortClaudeSDKSession,
@@ -186,9 +188,13 @@ const wss = createWebSocketServer(server, {
             opencode: abortOpenCodeSession,
             gjc: abortGjcSession,
             omp: abortOmpSession,
+            omo: abortOmoSession,
         },
         resolveToolApproval: resolveProviderToolApproval,
         getPendingApprovalsForSession: getPendingProviderApprovalsForSession,
+        // #44 guard: chat.send refuses to fork a session that a live tmux pane
+        // owns, for every provider that resumes by provider-native session id.
+        findLiveTmuxSpawnBlock,
     },
     shell: {
         resolveProviderSessionId: (sessionId, provider) => {
diff --git a/server/modules/providers/services/live-spawn-guard.service.ts b/server/modules/providers/services/live-spawn-guard.service.ts
new file mode 100644
index 0000000..1ae0f6f
--- /dev/null
+++ b/server/modules/providers/services/live-spawn-guard.service.ts
@@ -0,0 +1,57 @@
+import {
+  getExternalCliSessionsDetailedFresh,
+  type ExternalCliSession,
+  type ExternalLocalCliKind,
+} from '@/modules/providers/services/external-cli-sessions.service.js';
+import type { LLMProvider } from '@/shared/types.js';
+
+/**
+ * Providers whose transcripts are indexed as ordinary sessions even while a
+ * CLI is attached to them in a tmux pane. For these, `chat.send` spawning a
+ * headless resume would put a SECOND writer on the same transcript: the user
+ * sees a reply, the live agent never sees the message, and the JSONL
+ * interleaves two processes (#44).
+ *
+ * gjc is deliberately absent: its live sessions are reached through the SDK
+ * connect lane (`connectGjcSdkSession`), which attaches to the running agent
+ * instead of forking a new one, so the duplicate-writer failure cannot occur.
+ */
+const GUARDED_PROVIDERS: ReadonlySet<string> = new Set<ExternalLocalCliKind>([
+  'claude', 'codex', 'cursor', 'opencode', 'omp', 'omo',
+]);
+
+export type LiveTmuxSpawnBlock = { tmuxName: string };
+
+/** Pure matcher, exported for tests. */
+export function findLiveTmuxPaneForSession(
+  provider: LLMProvider | string,
+  providerSessionId: string,
+  sessions: readonly ExternalCliSession[],
+): LiveTmuxSpawnBlock | null {
+  if (!GUARDED_PROVIDERS.has(provider)) return null;
+  const owner = sessions.find((session) => (
+    session.kind === provider && session.providerSessionId === providerSessionId
+  ));
+  return owner ? { tmuxName: owner.tmuxName } : null;
+}
+
+/**
+ * Returns the live tmux owner of a provider-native session id, or null when
+ * spawning is safe. Fail-open on unavailable or failed discovery evidence:
+ * a false block would break the core chat path outright, while a false allow
+ * merely restores the pre-guard behavior — and when tmux is not running at
+ * all, no pane can own the transcript anyway.
+ */
+export async function findLiveTmuxSpawnBlock(
+  provider: LLMProvider | string,
+  providerSessionId: string | null | undefined,
+): Promise<LiveTmuxSpawnBlock | null> {
+  if (!providerSessionId || !GUARDED_PROVIDERS.has(provider)) return null;
+  try {
+    const detailed = await getExternalCliSessionsDetailedFresh();
+    if (!detailed.ok) return null;
+    return findLiveTmuxPaneForSession(provider, providerSessionId, detailed.sessions);
+  } catch {
+    return null;
+  }
+}
diff --git a/server/modules/providers/services/provider-capabilities.service.ts b/server/modules/providers/services/provider-capabilities.service.ts
index 5992bcc..17a6d3e 100644
--- a/server/modules/providers/services/provider-capabilities.service.ts
+++ b/server/modules/providers/services/provider-capabilities.service.ts
@@ -113,10 +113,10 @@ const PROVIDER_CAPABILITIES: Record<LLMProvider, ProviderCapabilities> = {
     provider: 'omo',
     permissionModes: ['default'],
     defaultPermissionMode: 'default',
-    // omo is discovery, transcript, and tmux relay only. `server/omo-cli.ts`
-    // implements the send runtime, but it is deliberately not registered in
-    // `spawnFns` (see the comment there): spawning would put a second headless
-    // omo on a session that may already be live in a tmux pane.
+    // The omo send runtime is registered behind the live-pane spawn guard
+    // (#44, `live-spawn-guard.service.ts`); like Oh My Pi, the runtime also
+    // forwards @<path> images and SIGTERM aborts, but this matrix mirrors the
+    // omp posture and keeps both UI controls hidden until verified end to end.
     supportsImages: false,
     supportsAbort: false,
     // omo's TUI renders "↑↓ navigate • enter select • esc close" and has no
diff --git a/server/modules/providers/tests/live-spawn-guard.test.ts b/server/modules/providers/tests/live-spawn-guard.test.ts
new file mode 100644
index 0000000..d656f3e
--- /dev/null
+++ b/server/modules/providers/tests/live-spawn-guard.test.ts
@@ -0,0 +1,60 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import type { ExternalCliSession } from '@/modules/providers/services/external-cli-sessions.service.js';
+import { findLiveTmuxPaneForSession } from '@/modules/providers/services/live-spawn-guard.service.js';
+
+const tmux = {
+  socketPath: '/tmp/tmux-1000/default',
+  sessionId: '$1',
+  windowId: '@1',
+  paneId: '%1',
+};
+
+function session(overrides: Partial<ExternalCliSession>): ExternalCliSession {
+  return { tmuxName: 'work', tmux, kind: 'omo', ...overrides };
+}
+
+// #44 regression lock: a chat.send to a session whose transcript is owned by a
+// live tmux pane must be refused — a second headless resume would interleave
+// two writers in one JSONL and the live agent would never see the message.
+test('a live pane owning the exact provider session blocks the spawn', () => {
+  const sessions = [
+    session({ kind: 'omo', providerSessionId: 'S-1', tmuxName: 'omo-pane' }),
+    session({ kind: 'omp', providerSessionId: 'S-2', tmuxName: 'omp-pane' }),
+  ];
+
+  assert.deepEqual(findLiveTmuxPaneForSession('omo', 'S-1', sessions), { tmuxName: 'omo-pane' });
+  assert.deepEqual(findLiveTmuxPaneForSession('omp', 'S-2', sessions), { tmuxName: 'omp-pane' });
+});
+
+test('a different provider, different id, or unresolved pane never blocks', () => {
+  const sessions = [
+    session({ kind: 'omo', providerSessionId: 'S-1' }),
+    // A pane whose native id inference has not resolved yet cannot claim ownership.
+    session({ kind: 'omo', providerSessionId: undefined }),
+  ];
+
+  // Same id under a different provider is a different session space.
+  assert.equal(findLiveTmuxPaneForSession('omp', 'S-1', sessions), null);
+  assert.equal(findLiveTmuxPaneForSession('omo', 'S-other', sessions), null);
+  assert.equal(findLiveTmuxPaneForSession('omo', 'S-1', []), null);
+});
+
+test('every headless-resume provider is guarded; gjc and non-CLI lanes are not', () => {
+  for (const kind of ['claude', 'codex', 'cursor', 'opencode', 'omp', 'omo'] as const) {
+    const sessions = [session({ kind, providerSessionId: 'S-1', tmuxName: `${kind}-pane` })];
+    assert.deepEqual(
+      findLiveTmuxPaneForSession(kind, 'S-1', sessions),
+      { tmuxName: `${kind}-pane` },
+      kind,
+    );
+  }
+
+  // gjc reaches live sessions through the SDK connect lane, not a fork —
+  // its rows must never be blocked by this guard.
+  assert.equal(
+    findLiveTmuxPaneForSession('gjc', 'S-1', [session({ kind: 'omo', providerSessionId: 'S-1' })]),
+    null,
+  );
+});
diff --git a/server/modules/websocket/services/chat-websocket.service.ts b/server/modules/websocket/services/chat-websocket.service.ts
index f164f5a..955bf17 100644
--- a/server/modules/websocket/services/chat-websocket.service.ts
+++ b/server/modules/websocket/services/chat-websocket.service.ts
@@ -78,6 +78,17 @@ type ChatWebSocketDependencies = {
   ) => void;
   /** Provider-runtime approvals included in `chat_subscribed` after reconnect. */
   getPendingApprovalsForSession: (providerSessionId: string) => unknown[];
+  /**
+   * Live-pane spawn guard (#44): resolves the tmux session that currently
+   * owns a provider-native session id, or null when spawning is safe. When a
+   * transcript is live in a tmux pane, spawning a headless resume would put a
+   * second writer on the same JSONL and the live agent would never see the
+   * message, so `chat.send` must refuse instead.
+   */
+  findLiveTmuxSpawnBlock?: (
+    provider: LLMProvider,
+    providerSessionId: string | null | undefined,
+  ) => Promise<{ tmuxName: string } | null>;
   /** Optional non-chat protocol mounted on the authenticated /ws gateway. */
   handleDiscovery?: (ws: WebSocket, data: AnyRecord) => boolean;
 };
@@ -173,6 +184,23 @@ async function handleChatSend(
     return;
   }
 
+  if (session.provider_session_id && dependencies.findLiveTmuxSpawnBlock) {
+    const liveOwner = await dependencies.findLiveTmuxSpawnBlock(
+      provider,
+      session.provider_session_id,
+    );
+    if (liveOwner) {
+      sendProtocolError(
+        ws,
+        'SESSION_LIVE_IN_TMUX',
+        `This session is currently live in tmux session "${liveOwner.tmuxName}". `
+          + 'Send input through the live session view instead of starting a second process.',
+        sessionId,
+      );
+      return;
+    }
+  }
+
   const run = chatRunRegistry.startRun({
     appSessionId: sessionId,
     provider,
@@ -215,7 +243,7 @@ async function handleChatSend(
 
   try {
     const providerRun = spawnFn(command, runtimeOptions, run.writer);
-    if (provider === 'gjc' || provider === 'omp') {
+    if (provider === 'gjc' || provider === 'omp' || provider === 'omo') {
       const abortHandle = (providerRun as ProviderSpawnResult).abortHandle;
       if (abortHandle) {
         run.writer.setAbortHandle(abortHandle);
@@ -263,7 +291,7 @@ async function handleChatAbort(
   if (abortFn && abortSessionId) {
     success = Boolean(await abortFn(abortSessionId));
   }
-  if (!success && (run.provider === 'gjc' || run.provider === 'omp')) {
+  if (!success && (run.provider === 'gjc' || run.provider === 'omp' || run.provider === 'omo')) {
     sendProtocolError(ws, 'ABORT_FAILED', `Session "${sessionId}" could not be aborted.`, sessionId);
     return;
   }