feat(tools): file_write_branch

Add BranchExists/CreateBranch/UpsertFile gitea client methods and the
file_write_branch MCP tool. Branch is auto-created from base (or repo
default_branch) when it doesn't exist; file is upserted via PUT contents.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/tools/file_write_branch.go

@@ -0,0 +1,107 @@
+package tools
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+
+	"gitea.d-ma.be/mathias/gitea-mcp/internal/allowlist"
+	"gitea.d-ma.be/mathias/gitea-mcp/internal/gitea"
+	"gitea.d-ma.be/mathias/gitea-mcp/internal/registry"
+)
+
+type FileWriteBranch struct {
+	c *gitea.Client
+	a *allowlist.Allowlist
+}
+
+func NewFileWriteBranch(c *gitea.Client, a *allowlist.Allowlist) *FileWriteBranch {
+	return &FileWriteBranch{c: c, a: a}
+}
+
+func (t *FileWriteBranch) Descriptor() registry.ToolDescriptor {
+	return registry.ToolDescriptor{
+		Name:        "file_write_branch",
+		Description: "Create or update a file on a feature branch. Branch is created from base if it doesn't exist.",
+		InputSchema: json.RawMessage(`{
+			"type":"object",
+			"properties":{
+				"owner":{"type":"string"},
+				"name":{"type":"string"},
+				"path":{"type":"string"},
+				"content":{"type":"string"},
+				"branch":{"type":"string"},
+				"base":{"type":"string"},
+				"message":{"type":"string"},
+				"sha":{"type":"string"}
+			},
+			"required":["owner","name","path","content","branch","message"]
+		}`),
+	}
+}
+
+type fileWriteBranchArgs struct {
+	Owner   string `json:"owner"`
+	Name    string `json:"name"`
+	Path    string `json:"path"`
+	Content string `json:"content"`
+	Branch  string `json:"branch"`
+	Base    string `json:"base"`
+	Message string `json:"message"`
+	Sha     string `json:"sha"`
+}
+
+func (t *FileWriteBranch) Call(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
+	var args fileWriteBranchArgs
+	if err := parseArgs(raw, &args); err != nil {
+		return nil, err
+	}
+	if err := t.a.Check(args.Owner); err != nil {
+		return nil, err
+	}
+	if args.Branch == "" {
+		return nil, fmt.Errorf("branch is required: %w", gitea.ErrValidation)
+	}
+	if args.Message == "" {
+		return nil, fmt.Errorf("message is required: %w", gitea.ErrValidation)
+	}
+
+	// Resolve base default if branch needs to be created
+	exists, err := t.c.BranchExists(ctx, args.Owner, args.Name, args.Branch)
+	if err != nil {
+		return nil, err
+	}
+	if !exists {
+		base := args.Base
+		if base == "" {
+			repo, err := t.c.GetRepo(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
+		}
+	}
+
+	encoded := base64.StdEncoding.EncodeToString([]byte(args.Content))
+	result, err := t.c.UpsertFile(ctx, args.Owner, args.Name, args.Path, gitea.UpsertFileArgs{
+		Branch:  args.Branch,
+		Content: encoded,
+		Message: args.Message,
+		Sha:     args.Sha,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return textOK(map[string]any{
+		"path":       result.Content.Path,
+		"sha":        result.Content.Sha,
+		"branch":     args.Branch,
+		"commit_sha": result.Commit.Sha,
+		"html_url":   result.Content.HTMLURL,
+	})
+}