fix(daemon): normalize cumulative ACP message chunks (#3333)

* fix(daemon): normalize cumulative acp message chunks

- apps/daemon/src/acp.ts
- apps/daemon/tests/acp.test.ts
- apps/web/src/providers/daemon.ts
- apps/web/src/components/DesignSystemFlow.tsx

Convert cumulative ACP message snapshots into suffix deltas and keep temporary browser debug instrumentation for trace verification.

* chore(web): remove temporary stream debug hooks

- apps/web/src/providers/daemon.ts
- apps/web/src/components/DesignSystemFlow.tsx

Remove the browser debug accumulator after validating the ACP duplication trace.

apps/daemon/src/acp.ts

@@ -457,6 +457,7 @@ export function attachAcpSession({
   let emittedThinkingStart = false;
   let emittedFirstTokenStatus = false;
   let emittedTextChunk = false;
+  let emittedTextBuffer = '';
   let finished = false;
   let fatal = false;
   let aborted = false;
@@ -618,16 +619,22 @@ export function attachAcpSession({
       if (update.sessionUpdate === 'agent_message_chunk') {
         const text = asObject(update.content)?.text;
         if (typeof text === 'string' && text.length > 0) {
-          emittedTextChunk = true;
-          if (!emittedFirstTokenStatus) {
-            emittedFirstTokenStatus = true;
-            send('agent', {
-              type: 'status',
-              label: 'streaming',
-              ttftMs: Date.now() - runStartedAt,
-            });
+          const delta = text.startsWith(emittedTextBuffer)
+            ? text.slice(emittedTextBuffer.length)
+            : text;
+          if (delta.length > 0) {
+            emittedTextChunk = true;
+            emittedTextBuffer += delta;
+            if (!emittedFirstTokenStatus) {
+              emittedFirstTokenStatus = true;
+              send('agent', {
+                type: 'status',
+                label: 'streaming',
+                ttftMs: Date.now() - runStartedAt,
+              });
+            }
+            send('agent', { type: 'text_delta', delta });
           }
-          send('agent', { type: 'text_delta', delta: text });
         }
         return;
       }

apps/daemon/tests/acp.test.ts

@@ -237,6 +237,74 @@ test('attachAcpSession includes image attachments as ACP resource links', () =>
   });
 });
 
+test('attachAcpSession converts cumulative ACP message snapshots into deltas', () => {
+  const child = new FakeAcpChild();
+  const events: Array<{ event: string; payload: unknown }> = [];
+
+  attachAcpSession({
+    child: child as never,
+    prompt: 'describe the project',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: (event, payload) => events.push({ event, payload }),
+  });
+
+  writeAcpResult(child, 1, {});
+  writeAcpResult(child, 2, { sessionId: 'session-1' });
+  writeAcpUpdate(child, {
+    sessionUpdate: 'agent_message_chunk',
+    content: { text: 'Agent Haven' },
+  });
+  writeAcpUpdate(child, {
+    sessionUpdate: 'agent_message_chunk',
+    content: { text: 'Agent Haven — managed AI agents' },
+  });
+  writeAcpUpdate(child, {
+    sessionUpdate: 'agent_message_chunk',
+    content: { text: 'Agent Haven — managed AI agents' },
+  });
+  writeAcpResult(child, 3, { usage: { inputTokens: 1, outputTokens: 2 } });
+
+  const textDeltas = events
+    .filter((entry) => entry.event === 'agent' && (entry.payload as { type?: unknown }).type === 'text_delta')
+    .map((entry) => (entry.payload as { delta?: unknown }).delta);
+
+  assert.deepEqual(textDeltas, ['Agent Haven', ' — managed AI agents']);
+});
+
+test('attachAcpSession keeps incremental ACP message chunks unchanged', () => {
+  const child = new FakeAcpChild();
+  const events: Array<{ event: string; payload: unknown }> = [];
+
+  attachAcpSession({
+    child: child as never,
+    prompt: 'describe the project',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: (event, payload) => events.push({ event, payload }),
+  });
+
+  writeAcpResult(child, 1, {});
+  writeAcpResult(child, 2, { sessionId: 'session-1' });
+  writeAcpUpdate(child, {
+    sessionUpdate: 'agent_message_chunk',
+    content: { text: 'Agent Haven' },
+  });
+  writeAcpUpdate(child, {
+    sessionUpdate: 'agent_message_chunk',
+    content: { text: ' — managed AI agents' },
+  });
+  writeAcpResult(child, 3, { usage: { inputTokens: 1, outputTokens: 2 } });
+
+  const textDeltas = events
+    .filter((entry) => entry.event === 'agent' && (entry.payload as { type?: unknown }).type === 'text_delta')
+    .map((entry) => (entry.payload as { delta?: unknown }).delta);
+
+  assert.deepEqual(textDeltas, ['Agent Haven', ' — managed AI agents']);
+});
+
 test('attachAcpSession exposes abort and sends session cancel after session creation', () => {
   const child = new FakeAcpChild();
   const writes: string[] = [];
@@ -328,6 +396,10 @@ function writeAcpResult(child: FakeAcpChild, id: number, result: unknown): void
   child.stdout.write(`${JSON.stringify({ id, result })}\n`);
 }
 
+function writeAcpUpdate(child: FakeAcpChild, update: unknown): void {
+  child.stdout.write(`${JSON.stringify({ method: 'session/update', params: { update } })}\n`);
+}
+
 function agentModelStatuses(events: Array<{ event: string; payload: unknown }>): unknown[] {
   return events
     .filter((entry) => {