Allow to check out branches

The git server currently lacks branch switching capabilities, limiting both
LLMs and developers. This adds branch checkout so LLMs can
help developers add new functionality in a new feature branch.

src/git/src/mcp_server_git/server.py

@@ -44,6 +44,10 @@ class GitCreateBranch(BaseModel):
     branch_name: str
     base_branch: str | None = None
 
+class GitCheckout(BaseModel):
+    repo_path: str
+    branch_name: str
+
 class GitTools(str, Enum):
     STATUS = "git_status"
     DIFF_UNSTAGED = "git_diff_unstaged"
@@ -53,6 +57,7 @@ class GitTools(str, Enum):
     RESET = "git_reset"
     LOG = "git_log"
     CREATE_BRANCH = "git_create_branch"
+    CHECKOUT = "git_checkout"
 
 def git_status(repo: git.Repo) -> str:
     return repo.git.status()
@@ -96,6 +101,10 @@ def git_create_branch(repo: git.Repo, branch_name: str, base_branch: str | None
     repo.create_head(branch_name, base)
     return f"Created branch '{branch_name}' from '{base.name}'"
 
+def git_checkout(repo: git.Repo, branch_name: str) -> str:
+    repo.git.checkout(branch_name)
+    return f"Switched to branch '{branch_name}'"
+
 async def serve(repository: Path | None) -> None:
     logger = logging.getLogger(__name__)
 
@@ -152,6 +161,11 @@ async def serve(repository: Path | None) -> None:
                 description="Creates a new branch from an optional base branch",
                 inputSchema=GitCreateBranch.schema(),
             ),
+            Tool(
+                name=GitTools.CHECKOUT,
+                description="Switches branches",
+                inputSchema=GitCheckout.schema(),
+            ),
         ]
 
     async def list_repos() -> Sequence[str]:
@@ -249,6 +263,13 @@ async def serve(repository: Path | None) -> None:
                     text=result
                 )]
 
+            case GitTools.CHECKOUT:
+                result = git_checkout(repo, arguments["branch_name"])
+                return [TextContent(
+                    type="text",
+                    text=result
+                )]
+
             case _:
                 raise ValueError(f"Unknown tool: {name}")