test: add comprehensive tests for config profile git mounts

- Add git mount merge function tests
- Add profile resolution tests with git mounts
- Add integration tests for CRUD with git mounts
- Add glob expansion tests (patterns, limits, repo boundary)
- Add branch checkout tests (success and failure)
- Add error handling tests for missing repos/invalid UUIDs

All 52 tests pass.

apps/api/tests/unit/test_git_mount_resolution.py

@@ -0,0 +1,139 @@
+"""Unit tests for git mount resolution in tool instances."""
+
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from src.api.tool_instances import (
+    _checkout_branch,
+    _expand_glob_source,
+    _resolve_single_git_mount,
+)
+from src.services.config_profile_resolver import ResolvedProfile
+
+
+class TestExpandGlobSource:
+    """Unit tests for glob pattern expansion."""
+
+    def test_no_glob_single_file(self, tmp_path: Path) -> None:
+        """Test non-glob path returns single file."""
+        test_file = tmp_path / "test.txt"
+        test_file.write_text("content")
+        
+        result = _expand_glob_source(str(test_file), str(tmp_path))
+        assert len(result) == 1
+        assert result[0] == str(test_file)
+
+    def test_no_glob_missing_file(self, tmp_path: Path) -> None:
+        """Test non-glob missing file returns empty list."""
+        missing_file = tmp_path / "missing.txt"
+        
+        result = _expand_glob_source(str(missing_file), str(tmp_path))
+        assert len(result) == 0
+
+    def test_glob_pattern(self, tmp_path: Path) -> None:
+        """Test glob pattern matches files."""
+        (tmp_path / "file1.txt").write_text("content1")
+        (tmp_path / "file2.txt").write_text("content2")
+        (tmp_path / "other.py").write_text("code")
+        
+        result = _expand_glob_source(str(tmp_path / "*.txt"), str(tmp_path))
+        assert len(result) == 2
+        assert all(f.endswith(".txt") for f in result)
+
+    def test_glob_recursive(self, tmp_path: Path) -> None:
+        """Test recursive glob pattern."""
+        subdir = tmp_path / "subdir"
+        subdir.mkdir()
+        (subdir / "nested.txt").write_text("content")
+        
+        result = _expand_glob_source(str(tmp_path / "**" / "*.txt"), str(tmp_path))
+        assert len(result) == 1
+        assert "nested.txt" in result[0]
+
+    def test_glob_limit_enforced(self, tmp_path: Path) -> None:
+        """Test that glob matches are limited to prevent abuse."""
+        # Create more than 100 files
+        for i in range(105):
+            (tmp_path / f"file{i}.txt").write_text("content")
+        
+        result = _expand_glob_source(str(tmp_path / "*.txt"), str(tmp_path))
+        assert len(result) == 100  # MAX_GLOB_MATCHES limit
+
+    def test_glob_escapes_repo(self, tmp_path: Path) -> None:
+        """Test that glob results outside repo are filtered."""
+        other_dir = tmp_path.parent / "other"
+        other_dir.mkdir(exist_ok=True)
+        (other_dir / "outside.txt").write_text("content")
+        
+        result = _expand_glob_source(str(tmp_path.parent / "*" / "*.txt"), str(tmp_path))
+        # Should only include files within tmp_path, not other_dir
+        assert all(r.startswith(str(tmp_path)) for r in result)
+
+
+class TestCheckoutBranch:
+    """Unit tests for branch checkout."""
+
+    def test_checkout_existing_branch(self, tmp_path: Path) -> None:
+        """Test checking out an existing branch."""
+        # Initialize git repo
+        os.system(f"cd {tmp_path} && git init && git config user.email 'test@test.com' && git config user.name 'Test'")
+        (tmp_path / "file.txt").write_text("content")
+        os.system(f"cd {tmp_path} && git add . && git commit -m 'initial'")
+        os.system(f"cd {tmp_path} && git branch feature")
+        
+        _checkout_branch(str(tmp_path), "feature")
+        
+        # Verify we're on feature branch
+        result = os.popen(f"cd {tmp_path} && git branch --show-current").read().strip()
+        assert result == "feature"
+
+    def test_checkout_nonexistent_branch(self, tmp_path: Path) -> None:
+        """Test checking out a non-existent branch raises error."""
+        os.system(f"cd {tmp_path} && git init && git config user.email 'test@test.com' && git config user.name 'Test'")
+        (tmp_path / "file.txt").write_text("content")
+        os.system(f"cd {tmp_path} && git add . && git commit -m 'initial'")
+        
+        with pytest.raises(RuntimeError, match="Failed to checkout branch"):
+            _checkout_branch(str(tmp_path), "nonexistent")
+
+
+class TestResolveSingleGitMount:
+    """Unit tests for resolving a single git mount."""
+
+    @pytest.mark.asyncio
+    async def test_resolve_missing_repo(self, db_session) -> None:
+        """Test that missing repo returns empty list."""
+        git_mount = {
+            "repo_id": "12345678-1234-1234-1234-123456789abc",
+            "source_path": ".",
+            "target_path": "/app",
+        }
+        
+        result = await _resolve_single_git_mount(db_session, git_mount)
+        assert result == []
+
+    @pytest.mark.asyncio
+    async def test_resolve_missing_target_path(self, db_session) -> None:
+        """Test that missing target path returns empty list."""
+        git_mount = {
+            "repo_id": "12345678-1234-1234-1234-123456789abc",
+            "source_path": ".",
+        }
+        
+        result = await _resolve_single_git_mount(db_session, git_mount)
+        assert result == []
+
+    @pytest.mark.asyncio
+    async def test_resolve_invalid_repo_id(self, db_session) -> None:
+        """Test that invalid repo_id returns empty list."""
+        git_mount = {
+            "repo_id": "not-a-uuid",
+            "source_path": ".",
+            "target_path": "/app",
+        }
+        
+        result = await _resolve_single_git_mount(db_session, git_mount)
+        assert result == []