feat(git): add git_current_branch, git_default_branch, and git_remote tools

[cblecker]

Description

Add three new tools to the Git MCP server for querying branch and remote information:

• git_current_branch — Returns the name of the currently checked out branch, or the short commit SHA with a "HEAD detached" indicator when HEAD is detached.
• git_default_branch — Determines the default branch for a remote, returning in remote/branch format (e.g. origin/main). Uses git ls-remote --symref (parsed via regex) to query the remote directly, with fallback to rev-parse for local ref resolution, then common branch name detection (main/master). Accepts an optional remote parameter (defaults to "origin").
• git_remote — Lists all configured remotes with their fetch and push URLs (wraps git remote -v).

Server Details

• Server: git
• Changes to: tools (three new tools added)

Motivation and Context

LLMs working with repositories frequently need to know the current branch, the default/mainline branch, and what remotes are configured. Currently this requires parsing git_status output or listing all branches, which is inefficient. These dedicated tools provide direct, unambiguous answers.

The remote/branch format for git_default_branch (e.g. origin/main) is more useful than a bare branch name, as it unambiguously identifies the remote tracking ref and can be used directly in git commands like git diff origin/main.

How Has This Been Tested?

• All 44 tests pass (35 existing + 9 new), confirming no regressions
• New tests cover:
  • test_git_current_branch — normal branch detection
  • test_git_current_branch_detached_head — detached HEAD state
  • test_git_default_branch_fallback_local — fallback to local main/master
  • test_git_default_branch_with_remote — ls-remote detection with bare remote
  • test_git_default_branch_custom_remote — non-"origin" remote parameter
  • test_git_default_branch_undetectable — raises ValueError when undetectable
  • test_git_default_branch_revparse_fallback — rev-parse path when ls-remote fails
  • test_git_remote_no_remotes — empty output for repos with no remotes
  • test_git_remote_with_remote — remote name and URL appear in output

Breaking Changes

None. Three new tools are added; existing tools are unchanged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options