feat: add issue_edit tool (#34)

Adds issue_edit, mapping to Gitea's PATCH /repos/{owner}/{repo}/issues/{index},
so an existing issue's title and/or body can be edited through the MCP surface.
Previously the only post-create mutation was issue_comment, which buries
backlinks in the thread instead of the canonical body.

Partial patch via pointer fields (omitempty): omitted fields are left
untouched, an explicit empty string clears a field. Body is sent verbatim —
no identity footer — so repeated edits are idempotent, matching the acceptance
criteria. Registered alongside the other issue tools for tool_search discovery.

Closes #34

internal/tools/issue_edit.go

@@ -0,0 +1,80 @@
+package tools
+
+import (
+	"context"
+	"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 IssueEdit struct {
+	c *gitea.Client
+	a *allowlist.Allowlist
+}
+
+func NewIssueEdit(c *gitea.Client, a *allowlist.Allowlist) *IssueEdit {
+	return &IssueEdit{c: c, a: a}
+}
+
+func (t *IssueEdit) Descriptor() registry.ToolDescriptor {
+	return registry.ToolDescriptor{
+		Name: "issue_edit",
+		Description: "Edit an existing issue's title and/or body. Only fields explicitly set are patched; " +
+			"omitted fields are left untouched. Body is replaced verbatim (no identity footer) so edits are idempotent. " +
+			"WARNING: body is a full replacement — to amend rather than clobber, read-modify-write " +
+			"(fetch with issue_get, edit the text, send it back).",
+		InputSchema: json.RawMessage(`{
+			"type":"object",
+			"properties":{
+				"owner":{"type":"string"},
+				"name":{"type":"string"},
+				"number":{"type":"integer","minimum":1},
+				"title":{"type":"string","description":"New title. Omit to leave unchanged."},
+				"body":{"type":"string","description":"New body, full replacement. Omit to leave unchanged."}
+			},
+			"required":["owner","name","number"]
+		}`),
+	}
+}
+
+type issueEditArgs struct {
+	Owner  string  `json:"owner"`
+	Name   string  `json:"name"`
+	Number int     `json:"number"`
+	Title  *string `json:"title,omitempty"`
+	Body   *string `json:"body,omitempty"`
+}
+
+func (t *IssueEdit) Call(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
+	var args issueEditArgs
+	if err := parseArgs(raw, &args); err != nil {
+		return nil, err
+	}
+	if err := t.a.Check(args.Owner); err != nil {
+		return nil, err
+	}
+	if args.Number < 1 {
+		return nil, fmt.Errorf("number is required: %w", gitea.ErrValidation)
+	}
+	if args.Title == nil && args.Body == nil {
+		return nil, fmt.Errorf("at least one of title or body must be set: %w", gitea.ErrValidation)
+	}
+
+	iss, err := t.c.EditIssue(ctx, args.Owner, args.Name, args.Number, gitea.EditIssueArgs{
+		Title: args.Title,
+		Body:  args.Body,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return textOK(map[string]any{
+		"number":   iss.Number,
+		"title":    iss.Title,
+		"html_url": iss.HTMLURL,
+		"state":    iss.State,
+	})
+}

internal/tools/issue_edit_test.go

@@ -0,0 +1,91 @@
+package tools_test
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"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/tools"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIssueEditTool(t *testing.T) {
+	var captured []byte
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, http.MethodPatch, r.Method)
+		assert.Equal(t, "/api/v1/repos/mathias/infra/issues/26", r.URL.Path)
+		var err error
+		captured, err = io.ReadAll(r.Body)
+		require.NoError(t, err)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"number":26,"title":"new","state":"open","html_url":"http://gitea.example.com/mathias/infra/issues/26"}`))
+	}))
+	defer srv.Close()
+
+	tool := tools.NewIssueEdit(gitea.NewClient(srv.URL, "tok"), allowlist.New([]string{"mathias"}))
+	out, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"mathias","name":"infra","number":26,"title":"new","body":"updated body"}`))
+	require.NoError(t, err)
+
+	var payload map[string]any
+	require.NoError(t, json.Unmarshal(captured, &payload))
+	assert.Equal(t, "new", payload["title"])
+	assert.Equal(t, "updated body", payload["body"])
+
+	assert.Contains(t, string(out), `"number":26`)
+}
+
+// Body must be sent verbatim — no identity footer appended (keeps edits idempotent).
+func TestIssueEditTool_BodyVerbatim(t *testing.T) {
+	var captured []byte
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var err error
+		captured, err = io.ReadAll(r.Body)
+		require.NoError(t, err)
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"number":26,"state":"open"}`))
+	}))
+	defer srv.Close()
+
+	tool := tools.NewIssueEdit(gitea.NewClient(srv.URL, "tok"), allowlist.New([]string{"mathias"}))
+	_, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"mathias","name":"infra","number":26,"body":"exact text"}`))
+	require.NoError(t, err)
+
+	var payload map[string]any
+	require.NoError(t, json.Unmarshal(captured, &payload))
+	assert.Equal(t, "exact text", payload["body"], "body must be unchanged — no footer")
+	_, hasTitle := payload["title"]
+	assert.False(t, hasTitle, "title must be omitted when not provided")
+}
+
+func TestIssueEditTool_RequiresAField(t *testing.T) {
+	tool := tools.NewIssueEdit(gitea.NewClient("http://unused", ""), allowlist.New([]string{"mathias"}))
+	_, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"mathias","name":"infra","number":26}`))
+	require.Error(t, err)
+	assert.ErrorIs(t, err, gitea.ErrValidation)
+}
+
+func TestIssueEditTool_NotFound(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		_, _ = w.Write([]byte(`{"message":"issue not found"}`))
+	}))
+	defer srv.Close()
+
+	tool := tools.NewIssueEdit(gitea.NewClient(srv.URL, "tok"), allowlist.New([]string{"mathias"}))
+	title := "x"
+	body, _ := json.Marshal(map[string]any{"owner": "mathias", "name": "infra", "number": 999, "title": title})
+	_, err := tool.Call(context.Background(), body)
+	require.Error(t, err)
+}
+
+func TestIssueEditAllowlistRejects(t *testing.T) {
+	tool := tools.NewIssueEdit(gitea.NewClient("http://unused", ""), allowlist.New([]string{"mathias"}))
+	_, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"evil","name":"x","number":1,"title":"y"}`))
+	require.Error(t, err)
+}