fix: ACP assistant messageIds are UUIDs, not a counter

The ACP schema (agent-client-protocol 0.9.0, ContentChunk.messageId) says
"Both clients and agents MUST use UUID format for message IDs". The
ported allocator emitted hermes-assistant-N strings, which a strict
client may reject or fail to group. A fresh uuid4 per message keeps the
grouping semantics and can never collide with an earlier turn's id, so
the counter/prefix state is gone.

Tests trimmed to three invariants: chunks share one UUID until the None
flush sentinel (empty deltas ignored), thought + text share an id, and
the no-allocator shape stays unchanged.

acp_adapter/events.py

@@ -8,6 +8,7 @@ thread-safely onto the loop.
 
 import asyncio
 import logging
+import uuid
 from collections import deque
 from typing import Any, Callable, Deque, Dict
 
@@ -135,25 +136,21 @@ class AssistantMessageIdAllocator:
     that replaces "the current assistant message" on each chunk collapses
     separate autonomous turns into one bubble.
 
-    One allocator lives per ACP session so the sequence is monotonic across
-    turns — two different turns must never reuse an id. A contiguous run of
-    deltas shares ``current()``; ``close()`` marks the message finished so the
-    next delta allocates a fresh id. Ported from
-    PrimeIntellect-ai/prime-agent#1781 (``prime-agent-assistant-N``).
+    One allocator lives per ACP session; a contiguous run of deltas shares
+    ``current()`` and ``close()`` marks the message finished so the next delta
+    allocates a fresh id. Ids are UUID4 strings because the ACP schema requires
+    UUID-format message ids, and a fresh UUID can never collide with an earlier
+    turn's id.
     """
 
-    def __init__(self, prefix: str = "hermes-assistant") -> None:
-        self._prefix = prefix
-        self._sequence = 0
+    def __init__(self) -> None:
         self._active: str | None = None
         self._last: str | None = None
 
     def current(self) -> str:
         """Return the active message id, allocating one if none is open."""
         if self._active is None:
-            self._sequence += 1
-            self._active = f"{self._prefix}-{self._sequence}"
-            self._last = self._active
+            self._active = self._last = str(uuid.uuid4())
         return self._active
 
     def last(self) -> str | None:

tests/acp_adapter/test_events.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import gc
+import uuid
 import warnings
 from concurrent.futures import Future
 from unittest.mock import AsyncMock, MagicMock, patch
@@ -268,12 +269,9 @@ class TestSendUpdate:
 
 
 class TestAssistantMessageIds:
-    """Assistant messageId grouping — ported from prime-agent#1781."""
+    """Streamed chunks carry a per-message ACP messageId; the None flush sentinel starts a new one."""
 
-    def _sent_updates(self, mock_rcts):
-        return [call.args[0] for call in mock_rcts.call_args_list]
-
-    def test_deltas_share_one_id_until_flush(self, mock_conn, event_loop_fixture):
+    def test_deltas_share_one_uuid_until_flush(self, mock_conn, event_loop_fixture):
         from acp_adapter.events import AssistantMessageIdAllocator
 
         ids = AssistantMessageIdAllocator()
@@ -282,11 +280,14 @@ class TestAssistantMessageIds:
         with patch("acp_adapter.events._send_update",
                    side_effect=lambda c, s, l, u: sent.append(u)):
             cb("Hello ")
+            cb("")  # empty delta is ignored, not a flush
             cb("world")
             cb(None)  # flush sentinel — closes the message
             cb("next turn")
-        assert sent[0].message_id == sent[1].message_id == "hermes-assistant-1"
-        assert sent[2].message_id == "hermes-assistant-2"
+        assert sent[0].message_id == sent[1].message_id
+        assert sent[2].message_id != sent[0].message_id
+        # ACP requires UUID-format message ids.
+        assert uuid.UUID(sent[0].message_id) and uuid.UUID(sent[2].message_id)
 
     def test_thought_chunks_carry_id(self, mock_conn, event_loop_fixture):
         from acp_adapter.events import AssistantMessageIdAllocator
@@ -309,29 +310,3 @@ class TestAssistantMessageIds:
                    side_effect=lambda c, s, l, u: sent.append(u)):
             cb("text")
         assert sent[0].message_id is None
-
-    def test_ids_monotonic_never_reused(self):
-        from acp_adapter.events import AssistantMessageIdAllocator
-
-        ids = AssistantMessageIdAllocator()
-        seen = set()
-        for _ in range(5):
-            i = ids.current()
-            assert i not in seen
-            seen.add(i)
-            ids.close()
-        assert ids.last() == "hermes-assistant-5"
-
-    def test_empty_string_does_not_close_message(self, mock_conn, event_loop_fixture):
-        """Only the None sentinel ends a message; '' deltas are ignored."""
-        from acp_adapter.events import AssistantMessageIdAllocator
-
-        ids = AssistantMessageIdAllocator()
-        cb = make_message_cb(mock_conn, "s", event_loop_fixture, ids)
-        sent = []
-        with patch("acp_adapter.events._send_update",
-                   side_effect=lambda c, s, l, u: sent.append(u)):
-            cb("a")
-            cb("")
-            cb("b")
-        assert sent[0].message_id == sent[1].message_id