Slice 9: git_checkout and create_branch (menu + MCP)

git boundary Checkout/CreateBranch; service GitCheckout/GitCreateBranch (activity detail names the branch; gitAction takes an ok-detail). HTTP /api/repo/git ops checkout + create-branch (branch field). MCP tools git_checkout and create_branch. <repo-menu> gains Switch branch… and New branch… (prompt for name). Service test covers create+switch and existing-branch failure. Checkout is not destructive - git refuses if it would overwrite changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/service/service.go

@@ -162,7 +162,7 @@ func (s *Service) MergeAndCleanup(ctx context.Context, actor activity.Actor, rep
 // gitAction runs one mutating git op through the boundary, records the outcome
 // on the activity feed, and refreshes the repo in the index on success. Callers
 // are responsible for §1.4 confirmation of destructive ops (e.g. discard).
-func (s *Service) gitAction(ctx context.Context, actor activity.Actor, repoPath, kind string, run func(dir string) (string, error)) (string, error) {
+func (s *Service) gitAction(ctx context.Context, actor activity.Actor, repoPath, kind, okDetail string, run func(dir string) (string, error)) (string, error) {
 	base, ok := s.index.Get(filepath.Clean(repoPath))
 	if !ok {
 		return "", fmt.Errorf("unknown repository %q", repoPath)
@@ -172,7 +172,10 @@ func (s *Service) gitAction(ctx context.Context, actor activity.Actor, repoPath,
 		s.feed.Record(actor, kind, base.Path, "failed: "+err.Error())
 		return "", err
 	}
-	s.feed.Record(actor, kind, base.Path, "ok")
+	if okDetail == "" {
+		okDetail = "ok"
+	}
+	s.feed.Record(actor, kind, base.Path, okDetail)
 	if s.refresh != nil {
 		s.refresh(ctx, base.Path)
 	}
@@ -182,19 +185,19 @@ func (s *Service) gitAction(ctx context.Context, actor activity.Actor, repoPath,
 // GitFetch, GitPull, GitPush, GitCommit, GitDiscard are the mutating commands
 // the right-click menu (and, later, MCP) invoke.
 func (s *Service) GitFetch(ctx context.Context, actor activity.Actor, repoPath string) (string, error) {
-	return s.gitAction(ctx, actor, repoPath, "git-fetch", func(d string) (string, error) {
+	return s.gitAction(ctx, actor, repoPath, "git-fetch", "ok", func(d string) (string, error) {
 		return "", s.git.Fetch(ctx, d)
 	})
 }
 
 func (s *Service) GitPull(ctx context.Context, actor activity.Actor, repoPath string) (string, error) {
-	return s.gitAction(ctx, actor, repoPath, "git-pull", func(d string) (string, error) {
+	return s.gitAction(ctx, actor, repoPath, "git-pull", "ok", func(d string) (string, error) {
 		return s.git.Pull(ctx, d)
 	})
 }
 
 func (s *Service) GitPush(ctx context.Context, actor activity.Actor, repoPath string) (string, error) {
-	return s.gitAction(ctx, actor, repoPath, "git-push", func(d string) (string, error) {
+	return s.gitAction(ctx, actor, repoPath, "git-push", "ok", func(d string) (string, error) {
 		return s.git.Push(ctx, d)
 	})
 }
@@ -203,18 +206,38 @@ func (s *Service) GitCommit(ctx context.Context, actor activity.Actor, repoPath,
 	if strings.TrimSpace(message) == "" {
 		return "", fmt.Errorf("a commit message is required")
 	}
-	return s.gitAction(ctx, actor, repoPath, "git-commit", func(d string) (string, error) {
+	return s.gitAction(ctx, actor, repoPath, "git-commit", "ok", func(d string) (string, error) {
 		return s.git.Commit(ctx, d, message)
 	})
 }
 
 // GitDiscard is DESTRUCTIVE (§1.4) — the caller must confirm with the user first.
 func (s *Service) GitDiscard(ctx context.Context, actor activity.Actor, repoPath string) (string, error) {
-	return s.gitAction(ctx, actor, repoPath, "git-discard", func(d string) (string, error) {
+	return s.gitAction(ctx, actor, repoPath, "git-discard", "ok", func(d string) (string, error) {
 		return s.git.DiscardAll(ctx, d)
 	})
 }
 
+// GitCheckout switches to an existing branch.
+func (s *Service) GitCheckout(ctx context.Context, actor activity.Actor, repoPath, branch string) (string, error) {
+	if strings.TrimSpace(branch) == "" {
+		return "", fmt.Errorf("a branch name is required")
+	}
+	return s.gitAction(ctx, actor, repoPath, "git-checkout", "switched to "+branch, func(d string) (string, error) {
+		return s.git.Checkout(ctx, d, branch)
+	})
+}
+
+// GitCreateBranch creates a new branch from HEAD and switches to it.
+func (s *Service) GitCreateBranch(ctx context.Context, actor activity.Actor, repoPath, name string) (string, error) {
+	if strings.TrimSpace(name) == "" {
+		return "", fmt.Errorf("a branch name is required")
+	}
+	return s.gitAction(ctx, actor, repoPath, "git-create-branch", "created "+name, func(d string) (string, error) {
+		return s.git.CreateBranch(ctx, d, name)
+	})
+}
+
 // resolveForge maps a repo path to (owner, repo) on the configured forge host via
 // its git remotes, preferring "origin".
 func (s *Service) resolveForge(ctx context.Context, repoPath string) (owner, repo string, err error) {

internal/service/service_test.go

@@ -65,6 +65,24 @@ func TestGitActions(t *testing.T) {
 		t.Fatalf("a.txt = %q, want restored to \"one\"", got)
 	}
 
+	// Create a branch (switches to it), then switch back to main.
+	if _, err := svc.GitCreateBranch(ctx, activity.ActorUser, repoPath, "feature-x"); err != nil {
+		t.Fatalf("GitCreateBranch: %v", err)
+	}
+	if st, _ := svc.GetRepo(repoPath); st.Branch != "feature-x" {
+		t.Fatalf("branch = %q, want feature-x", st.Branch)
+	}
+	if _, err := svc.GitCheckout(ctx, activity.ActorUser, repoPath, "main"); err != nil {
+		t.Fatalf("GitCheckout: %v", err)
+	}
+	if st, _ := svc.GetRepo(repoPath); st.Branch != "main" {
+		t.Fatalf("branch = %q, want main", st.Branch)
+	}
+	// Creating an existing branch fails.
+	if _, err := svc.GitCreateBranch(ctx, activity.ActorUser, repoPath, "feature-x"); err == nil {
+		t.Fatalf("expected error creating an existing branch")
+	}
+
 	// The feed recorded the successful actions.
 	kinds := map[string]bool{}
 	for _, e := range feed.Events(0) {