feat: allow relative target paths for git mounts

- Remove absolute path requirement from target_path validation
- Resolve relative paths against working_directory at instance startup
- Fall back to /home/user if no working_directory is configured
- Update frontend to allow relative target paths
- Update spec to document relative path support
- Update tests to allow relative paths and test path traversal rejection

apps/api/src/api/config_profiles.py

@@ -82,8 +82,6 @@ class GitMountItem(BaseModel):
     @field_validator("target_path")
     @classmethod
     def validate_target_path(cls, v: str) -> str:
-        if not v.startswith("/"):
-            raise ValueError("target_path must be absolute (start with /)")
         if ".." in v:
             raise ValueError("target_path cannot contain path traversal (..)")
         return v

apps/api/src/api/tool_instances.py

@@ -61,6 +61,7 @@ async def _resolve_git_mounts(
     session: AsyncSession,
     resolved: ResolvedProfile,
     instance_dir: str | None = None,
+    working_directory: str | None = None,
 ) -> list[dict]:
     """Convert git mounts from resolved profile to Docker volume mounts.
     
@@ -74,7 +75,7 @@ async def _resolve_git_mounts(
     # Process all git mounts concurrently
     tasks = []
     for git_mount in resolved.git_mounts:
-        tasks.append(_resolve_single_git_mount(session, git_mount, instance_dir))
+        tasks.append(_resolve_single_git_mount(session, git_mount, instance_dir, working_directory))
     
     results = await asyncio.gather(*tasks, return_exceptions=True)
     
@@ -93,6 +94,7 @@ async def _resolve_single_git_mount(
     session: AsyncSession,
     git_mount: dict,
     instance_dir: str | None = None,
+    working_directory: str | None = None,
 ) -> list[dict]:
     """Resolve a single git mount to volume mount entries.
     
@@ -108,6 +110,12 @@ async def _resolve_single_git_mount(
         logger.warning("Invalid git mount skipped: missing remote_url or target_path")
         return []
     
+    # Resolve relative target paths against working directory
+    if target_path and not target_path.startswith("/"):
+        base = working_directory or "/home/user"
+        target_path = os.path.join(base, target_path)
+        logger.info("Resolved relative target path to %s", target_path)
+    
     if not instance_dir:
         logger.warning("Git mount skipped: no instance_dir provided for cloning")
         return []
@@ -918,7 +926,7 @@ async def start_instance(
             # Profile mounts are added to extra volumes
             extra_volumes.extend(profile_mounts)
             # Git repository mounts are resolved and added
-            git_mount_volumes = await _resolve_git_mounts(session, resolved, instance_dir)
+            git_mount_volumes = await _resolve_git_mounts(session, resolved, instance_dir, working_directory)
             extra_volumes.extend(git_mount_volumes)
             # Profile runtime hints override tool config values
             if profile_hints.get("start_command"):