feat: add action_type and focal_node_id to AI chat message API

- Add VALID_ACTION_TYPES literal and action_type/focal_node_id fields to
  AIChatMessageRequest schema
- Add tree_id field to AIChatStartRequest schema for editor-embedded sessions
- Update send_message() signature with action_type and focal_node_id params
- Update start_chat_session() signature with tree_id param
- Pass new params through endpoints to service functions
- All new params have defaults so existing behavior is unchanged

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/endpoints/ai_chat.py

@@ -95,6 +95,7 @@ async def create_session(
             user_id=current_user.id,
             account_id=current_user.account_id,
             db=db,
+            tree_id=data.tree_id,
         )
     except Exception as e:
         logger.exception("AI chat session start failed: %s", e)
@@ -168,7 +169,9 @@ async def post_message(
 
     try:
         ai_content, tree_update, new_phase, metadata = await send_message(
-            session, data.content, db
+            session, data.content, db,
+            action_type=data.action_type or "open_chat",
+            focal_node_id=data.focal_node_id,
         )
     except Exception as e:
         logger.exception("AI chat message failed: %s", e)

backend/app/core/ai_chat_service.py

@@ -391,6 +391,7 @@ async def start_chat_session(
     user_id: uuid.UUID,
     account_id: uuid.UUID,
     db: AsyncSession,
+    tree_id: str | None = None,
 ) -> tuple[AIChatSession, str]:
     """Create a chat session and return the AI's opening greeting.
 
@@ -400,6 +401,7 @@ async def start_chat_session(
         user_id=user_id,
         account_id=account_id,
         flow_type=flow_type,
+        tree_id=uuid.UUID(tree_id) if tree_id else None,
         expires_at=datetime.now(timezone.utc) + timedelta(hours=settings.AI_CONVERSATION_TTL_HOURS),
     )
     db.add(session)
@@ -443,6 +445,8 @@ async def send_message(
     session: AIChatSession,
     user_message: str,
     db: AsyncSession,
+    action_type: str = "open_chat",
+    focal_node_id: str | None = None,
 ) -> tuple[str, Optional[dict], Optional[str], Optional[dict]]:
     """Send a user message and get AI response.
 

backend/app/schemas/ai_chat.py

@@ -14,12 +14,35 @@ class AIChatStartRequest(BaseModel):
     flow_type: Literal["troubleshooting", "procedural"] = Field(
         ..., description="Type of flow to build"
     )
+    tree_id: Optional[str] = Field(
+        default=None,
+        description="ID of existing tree for editor-embedded sessions",
+    )
+
+
+VALID_ACTION_TYPES = Literal[
+    "generate_full",
+    "generate_branch",
+    "modify_node",
+    "add_steps",
+    "quick_action",
+    "open_chat",
+    "variable_inference",
+]
 
 
 class AIChatMessageRequest(BaseModel):
     """Send a user message in a chat session."""
 
     content: str = Field(..., min_length=1, max_length=5000)
+    action_type: Optional[VALID_ACTION_TYPES] = Field(
+        default="open_chat",
+        description="Type of AI action to perform",
+    )
+    focal_node_id: Optional[str] = Field(
+        default=None,
+        description="ID of the node/step being acted on",
+    )
 
 
 class AIChatImportRequest(BaseModel):