feat: support creating local branch during session creation

- Add new_branch field to CreateInstanceRequest
- Run git checkout -b after cloning when new_branch is provided
- Store new branch name in ToolInstance record

apps/api/src/api/tool_instances.py

@@ -2,6 +2,7 @@
 
 import logging
 import os
+import subprocess
 import uuid
 from datetime import datetime
 
@@ -61,6 +62,7 @@ class CreateInstanceRequest(BaseModel):
     display_name: str | None = Field(default=None, description="Optional display name for the instance")
     clone_mode: str = Field(default="mount", description="Repository access mode: 'mount' or 'clone'")
     branch: str | None = Field(default="main", description="Branch to clone (when clone_mode='clone')")
+    new_branch: str | None = Field(default=None, description="Create a new local branch after cloning")
 
 
 def _modify_compose_file(
@@ -256,6 +258,25 @@ async def create_instance(
         else:
             repo_path = repo.path
 
+        # Create new local branch if requested
+        if data.clone_mode == "clone" and data.new_branch:
+            try:
+                result = subprocess.run(
+                    ["git", "-C", repo_path, "checkout", "-b", data.new_branch],
+                    capture_output=True,
+                    text=True,
+                )
+                if result.returncode != 0:
+                    logger.error("Failed to create branch %s: %s", data.new_branch, result.stderr)
+                    raise RuntimeError(f"Failed to create branch: {result.stderr}")
+                logger.info("Created local branch %s in cloned repository", data.new_branch)
+            except Exception as exc:
+                logger.exception("Failed to create local branch: %s", exc)
+                raise HTTPException(
+                    status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+                    detail=f"Failed to create local branch: {exc}"
+                )
+
         # Handle based on definition type
         if tool_type.definition_type == "dockerfile":
             # Build image from Dockerfile
@@ -318,7 +339,7 @@ services:
             compose_path=compose_path,
             port=tool_port,
             clone_mode=data.clone_mode,
-            branch=data.branch if data.clone_mode == "clone" else None,
+            branch=data.new_branch if data.new_branch else (data.branch if data.clone_mode == "clone" else None),
         )
         session.add(instance)
         await session.commit()