feat(gitea): default-branch lru cache

Shared LRU avoids repeated Gitea calls for default-branch resolution;
the simple stdlib map alternative would race on concurrent access without
a mutex per entry, which is more code than the LRU.

go.mod

@@ -4,6 +4,7 @@ go 1.26.2
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/stretchr/testify v1.11.1 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

go.sum

@@ -1,5 +1,7 @@
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
+github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=

internal/gitea/client.go

@@ -6,12 +6,15 @@ import (
 	"io"
 	"net/http"
 	"time"
+
+	"github.com/hashicorp/golang-lru/v2/expirable"
 )
 
 type Client struct {
 	baseURL     string
 	token       string
 	hc          *http.Client
+	branchCache *expirable.LRU[string, string]
 }
 
 func NewClient(baseURL, token string) *Client {
@@ -19,9 +22,24 @@ func NewClient(baseURL, token string) *Client {
 		baseURL:     baseURL,
 		token:       token,
 		hc:          &http.Client{Timeout: 30 * time.Second},
+		branchCache: expirable.NewLRU[string, string](64, nil, 60*time.Second),
 	}
 }
 
+// DefaultBranch returns the default branch for a repo. Cached for 60s.
+func (c *Client) DefaultBranch(ctx context.Context, owner, name string) (string, error) {
+	key := owner + "/" + name
+	if v, ok := c.branchCache.Get(key); ok {
+		return v, nil
+	}
+	repo, err := c.GetRepo(ctx, owner, name)
+	if err != nil {
+		return "", err
+	}
+	c.branchCache.Add(key, repo.DefaultBranch)
+	return repo.DefaultBranch, nil
+}
+
 func (c *Client) doOnce(ctx context.Context, method, path string, body []byte) ([]byte, int, error) {
 	var reader io.Reader
 	if body != nil {

internal/gitea/repos_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"net/http"
 	"net/http/httptest"
+	"sync/atomic"
 	"testing"
 
 	"gitea.d-ma.be/mathias/gitea-mcp/internal/gitea"
@@ -45,3 +46,23 @@ func TestListRepos(t *testing.T) {
 	assert.Equal(t, "mathias/infra", repos[0].FullName)
 	assert.Equal(t, "main", repos[0].DefaultBranch)
 }
+
+func TestDefaultBranchCachesAcrossCalls(t *testing.T) {
+	var hits int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		atomic.AddInt32(&hits, 1)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"name":"infra","full_name":"o/infra","default_branch":"trunk"}`))
+	}))
+	defer srv.Close()
+
+	c := gitea.NewClient(srv.URL, "tok")
+
+	for i := 0; i < 5; i++ {
+		b, err := c.DefaultBranch(context.Background(), "o", "infra")
+		require.NoError(t, err)
+		assert.Equal(t, "trunk", b)
+	}
+
+	assert.Equal(t, int32(1), atomic.LoadInt32(&hits), "5 calls should cause exactly 1 server hit due to cache")
+}

internal/tools/file_read.go

@@ -57,11 +57,11 @@ func (t *FileRead) Call(ctx context.Context, raw json.RawMessage) (json.RawMessa
 
 	ref := args.Ref
 	if ref == "" {
-		repo, err := t.c.GetRepo(ctx, args.Owner, args.Name)
+		var err error
+		ref, err = t.c.DefaultBranch(ctx, args.Owner, args.Name)
 		if err != nil {
 			return nil, err
 		}
-		ref = repo.DefaultBranch
 	}
 
 	fc, err := t.c.GetFileContents(ctx, args.Owner, args.Name, args.Path, ref)

internal/tools/file_write_branch.go

@@ -75,11 +75,11 @@ func (t *FileWriteBranch) Call(ctx context.Context, raw json.RawMessage) (json.R
 	if !exists {
 		base := args.Base
 		if base == "" {
-			repo, err := t.c.GetRepo(ctx, args.Owner, args.Name)
+			var err error
+			base, err = t.c.DefaultBranch(ctx, args.Owner, args.Name)
 			if err != nil {
 				return nil, err
 			}
-			base = repo.DefaultBranch
 		}
 		if err := t.c.CreateBranch(ctx, args.Owner, args.Name, args.Branch, base); err != nil {
 			return nil, err

internal/tools/workflow_run_trigger.go

@@ -61,11 +61,11 @@ func (t *WorkflowRunTrigger) Call(ctx context.Context, raw json.RawMessage) (jso
 
 	ref := args.Ref
 	if ref == "" {
-		repo, err := t.c.GetRepo(ctx, args.Owner, args.Name)
+		var err error
+		ref, err = t.c.DefaultBranch(ctx, args.Owner, args.Name)
 		if err != nil {
 			return nil, err
 		}
-		ref = repo.DefaultBranch
 	}
 
 	result, err := t.c.DispatchWorkflow(ctx, args.Owner, args.Name, args.Workflow, gitea.DispatchWorkflowArgs{