diff --git a/apps/daemon/src/acp.ts b/apps/daemon/src/acp.ts
index 77df76bf0..705de8c72 100644
--- a/apps/daemon/src/acp.ts
+++ b/apps/daemon/src/acp.ts
@@ -288,34 +288,155 @@ function currentModelFromSessionResult(result: JsonObject): string | null {
 
 export function createJsonLineStream(onMessage: (message: unknown, rawLine: string) => void) {
   let buffer = '';
+  let pendingJson = '';
+  let pendingJsonLineCount = 0;
+
+  const emit = (candidate: string): boolean => {
+    try {
+      onMessage(JSON.parse(candidate), candidate);
+      return true;
+    } catch {
+      return false;
+    }
+  };
+
+  const startPendingJson = (line: string) => {
+    pendingJson = line;
+    pendingJsonLineCount = 1;
+  };
+
+  const resetPendingJson = () => {
+    pendingJson = '';
+    pendingJsonLineCount = 0;
+  };
+
+  const handleLine = (line: string) => {
+    const trimmed = line.trim();
+    if (!trimmed) return;
+    if (pendingJson) {
+      const nextCandidate = `${pendingJson}\n${trimmed}`;
+      if (emit(nextCandidate)) {
+        resetPendingJson();
+        return;
+      }
+      pendingJsonLineCount += 1;
+      if (
+        pendingJsonLineCount === 2 &&
+        pendingJson !== '{' &&
+        pendingJson !== '[' &&
+        emit(trimmed)
+      ) {
+        resetPendingJson();
+        return;
+      }
+      const state = classifyJsonCandidate(nextCandidate);
+      if (
+        state === 'incomplete' &&
+        nextCandidate.length <= 128_000 &&
+        pendingJsonLineCount <= 256
+      ) {
+        pendingJson = nextCandidate;
+        return;
+      }
+      resetPendingJson();
+      handleLine(trimmed);
+      return;
+    }
+    if (emit(trimmed)) return;
+    // ACP is line-delimited JSON-RPC, but a few bridges have emitted
+    // pretty-printed JSON during startup. Keep a bounded aggregate so an
+    // otherwise valid multiline initialize response does not get discarded
+    // line-by-line and leave the session stuck in spawn pending.
+    if (trimmed.startsWith('{') || trimmed.startsWith('[')) {
+      startPendingJson(trimmed);
+    }
+  };
+
   return {
     feed(chunk: string) {
       buffer += chunk;
       const lines = buffer.split('\n');
       buffer = lines.pop() || '';
       for (const line of lines) {
-        const trimmed = line.trim();
-        if (!trimmed) continue;
-        try {
-          onMessage(JSON.parse(trimmed), trimmed);
-        } catch {
-          // Ignore non-JSON log lines on stdout.
-        }
+        handleLine(line);
       }
     },
     flush() {
       const trimmed = buffer.trim();
       buffer = '';
-      if (!trimmed) return;
-      try {
-        onMessage(JSON.parse(trimmed), trimmed);
-      } catch {
-        // Ignore trailing non-JSON log lines on stdout.
+      if (trimmed) {
+        handleLine(trimmed);
       }
+      if (pendingJson && emit(pendingJson)) {
+        pendingJson = '';
+      }
+      // Ignore trailing non-JSON log lines on stdout.
     },
   };
 }
 
+function classifyJsonCandidate(value: string): 'complete' | 'incomplete' | 'invalid' {
+  const stack: string[] = [];
+  let started = false;
+  let complete = false;
+  let inString = false;
+  let escaping = false;
+
+  for (const char of value) {
+    if (!started) {
+      if (/\s/.test(char)) continue;
+      if (char === '{') {
+        started = true;
+        stack.push('}');
+        continue;
+      }
+      if (char === '[') {
+        started = true;
+        stack.push(']');
+        continue;
+      }
+      return 'invalid';
+    }
+
+    if (complete) {
+      if (/\s/.test(char)) continue;
+      return 'invalid';
+    }
+
+    if (inString) {
+      if (escaping) {
+        escaping = false;
+      } else if (char === '\\') {
+        escaping = true;
+      } else if (char === '"') {
+        inString = false;
+      }
+      continue;
+    }
+
+    if (char === '"') {
+      inString = true;
+      continue;
+    }
+    if (char === '{') {
+      stack.push('}');
+      continue;
+    }
+    if (char === '[') {
+      stack.push(']');
+      continue;
+    }
+    if (char === '}' || char === ']') {
+      if (stack.pop() !== char) return 'invalid';
+      if (stack.length === 0) complete = true;
+    }
+  }
+
+  if (!started) return 'invalid';
+  if (inString || escaping || stack.length > 0) return 'incomplete';
+  return complete ? 'complete' : 'invalid';
+}
+
 export async function detectAcpModels({
   bin,
   args,
diff --git a/apps/daemon/tests/acp.test.ts b/apps/daemon/tests/acp.test.ts
index c528980c7..2359b8a56 100644
--- a/apps/daemon/tests/acp.test.ts
+++ b/apps/daemon/tests/acp.test.ts
@@ -383,6 +383,58 @@ test('attachAcpSession.abort during startup ends stdin without sending session/c
   assert.equal(cancelRequests.length, 0);
 });
 
+test('attachAcpSession accepts pretty-printed ACP startup responses', () => {
+  const child = new FakeAcpChild();
+  const writes: string[] = [];
+  const events: Array<{ event: string; payload: unknown }> = [];
+  child.stdin.on('data', (chunk) => writes.push(String(chunk)));
+
+  attachAcpSession({
+    child: child as never,
+    prompt: 'hello',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: (event, payload) => events.push({ event, payload }),
+  });
+
+  child.stdout.write('{\n  "id": 1,\n  "result":\n  {}\n}\n');
+  child.stdout.write('{\n  "id": 2,\n  "result":\n  {\n    "sessionId": "session-1"\n  }\n}\n');
+
+  const methods = parseRpcWrites(writes)
+    .map((entry) => entry.method)
+    .filter(Boolean);
+  assert.deepEqual(methods, ['initialize', 'session/new', 'session/prompt']);
+  assert.equal(events.some((entry) => entry.event === 'error'), false);
+});
+
+test('attachAcpSession recovers when bracket-prefixed logs precede JSON frames', () => {
+  const child = new FakeAcpChild();
+  const writes: string[] = [];
+  const events: Array<{ event: string; payload: unknown }> = [];
+  child.stdin.on('data', (chunk) => writes.push(String(chunk)));
+
+  attachAcpSession({
+    child: child as never,
+    prompt: 'hello',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: (event, payload) => events.push({ event, payload }),
+  });
+
+  child.stdout.write('[vela] starting OpenCode bridge\n');
+  child.stdout.write(`${JSON.stringify({ id: 1, result: {} })}\n`);
+  child.stdout.write('{not json but looks like an object log\n');
+  child.stdout.write(`${JSON.stringify({ id: 2, result: { sessionId: 'session-1' } })}\n`);
+
+  const methods = parseRpcWrites(writes)
+    .map((entry) => entry.method)
+    .filter(Boolean);
+  assert.deepEqual(methods, ['initialize', 'session/new', 'session/prompt']);
+  assert.equal(events.some((entry) => entry.event === 'error'), false);
+});
+
 function parseRpcWrites(writes: string[]): Array<Record<string, unknown>> {
   return writes
     .join('')