fix: derive an SDK-conforming Antigravity conversation id

The Antigravity SDK now requires conversation_id to be at least 32
characters and match [a-zA-Z0-9-]. The wrapper built it as
"{session_id}_{agent_name}", which is too short and contains
underscores, so resuming a conversation raised a ValidationError.
Derive it from a hash of the session id and agent name instead, so it
stays deterministic (trajectories still resume) while always meeting
the constraints.

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 949741204

Author: GWeale

src/google/adk/labs/antigravity/_antigravity_agent.py

@@ -27,6 +27,7 @@
 
 from __future__ import annotations
 
+import hashlib
 import logging
 from typing import Any
 from typing import AsyncGenerator
@@ -54,6 +55,13 @@
 )
 
 
+def _derive_conversation_id(session_id: str, agent_name: str) -> str:
+  """Returns a deterministic conversation id (>=32 chars, [a-zA-Z0-9-])."""
+  # Hashing keeps the id stable across turns (so trajectories resume) while
+  # always satisfying the Antigravity SDK's length and character constraints.
+  return hashlib.sha256(f'{session_id}/{agent_name}'.encode()).hexdigest()
+
+
 class AntigravityAgent(BaseAgent):
   """Runs a Google Antigravity SDK agent as an ADK root agent.
 
@@ -114,7 +122,7 @@ async def _run_async_impl(
     # The SDK Agent's AsyncExitStack is single-use, so a new instance is needed
     # per turn; copying also avoids mutating the caller's config.
     config = self.config.model_copy(deep=True)
-    conversation_id = f'{ctx.session.id}_{self.name}'
+    conversation_id = _derive_conversation_id(ctx.session.id, self.name)
 
     # Resume only when a trajectory already exists; the harness errors if a
     # conversation_id is given with no matching file on disk.

tests/unittests/labs/antigravity/test_antigravity_agent.py

@@ -95,16 +95,19 @@ async def _receive_steps():
   conversation = MagicMock()
   conversation.send = AsyncMock()
   conversation.receive_steps = _receive_steps
+  conversation_id = _antigravity_agent._derive_conversation_id(
+      'sess_456', 'agy'
+  )
   active_agent = MagicMock()
   active_agent.conversation = conversation
-  active_agent.conversation_id = 'sess_456_agy'
+  active_agent.conversation_id = conversation_id
   active_agent.__aenter__ = AsyncMock(return_value=active_agent)
   active_agent.__aexit__ = AsyncMock(return_value=None)
 
   # A prior trajectory + resume index in save_dir triggers resume at index 1.
   save_dir = tmp_path
-  (save_dir / 'traj-sess_456_agy').write_bytes(b'data')
-  (save_dir / 'traj-sess_456_agy.resume').write_text('1')
+  (save_dir / f'traj-{conversation_id}').write_bytes(b'data')
+  (save_dir / f'traj-{conversation_id}.resume').write_text('1')
   agent = AntigravityAgent(
       name='agy', config=_make_config(save_dir=str(save_dir))
   )