fix(tools): reject empty repo/name identifier at tool layer (#37)

An empty required repo identifier built a trailing-empty path segment
(`/api/v1/repos/{owner}/`) and leaked gitea's bare 404. parseArgs now
validates, via reflection, that `repo`/`name` string args are non-empty and
returns a typed ErrValidation naming the field. Optional identifiers (e.g.
code_search's owner-wide fan-out `repo`) opt out with `,omitempty`. `owner` is
already enforced by the allowlist check.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tools/validate_test.go

@@ -0,0 +1,32 @@
+package tools_test
+
+import (
+	"context"
+	"encoding/json"
+	"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"
+)
+
+// #37: an empty required repo identifier must fail fast at the tool layer with a
+// typed ErrValidation naming the field, rather than building a trailing-empty
+// path segment (`/api/v1/repos/{owner}/`) that leaks gitea's bare 404.
+func TestEmptyRepoRejectedAsValidation(t *testing.T) {
+	c := gitea.NewClient("http://unused", "")
+	a := allowlist.New([]string{"mathias"})
+
+	_, err := tools.NewRepoGet(c, a).Call(context.Background(), json.RawMessage(`{"owner":"mathias","repo":""}`))
+	require.Error(t, err)
+	assert.ErrorIs(t, err, gitea.ErrValidation)
+	assert.Contains(t, err.Error(), "repo")
+
+	// same for an empty `name` on a create tool (name = required new-repo name)
+	_, err = tools.NewRepoCreate(c, a).Call(context.Background(), json.RawMessage(`{"owner":"mathias","name":""}`))
+	require.Error(t, err)
+	assert.ErrorIs(t, err, gitea.ErrValidation)
+	assert.Contains(t, err.Error(), "name")
+}