fix: handle lightweight tags in get_tag tool

Lightweight tags point directly to commits, not tag objects. The get_tag
tool previously always called the Git Tag API which returns 404 for
lightweight tags since their SHA references a commit, not a tag object.

Now checks ref.Object.Type: if "commit" (lightweight), resolves the
commit directly and returns a tag-like structure for consistency. If
"tag" (annotated), proceeds with the existing tag object fetch.

Author: djdam

pkg/github/repositories.go

@@ -1592,7 +1592,58 @@ func GetTag(t translations.TranslationHelperFunc) inventory.ServerTool {
 				return ghErrors.NewGitHubAPIStatusErrorResponse(ctx, "failed to get tag reference", resp, body), nil, nil
 			}
 
-			// Then get the tag object
+			// Handle both annotated and lightweight tags.
+			// Annotated tags have ref.Object.Type == "tag" and point to a tag object.
+			// Lightweight tags have ref.Object.Type == "commit" and point directly to a commit.
+			if ref.Object.Type != nil && *ref.Object.Type == "commit" {
+				// Lightweight tag — resolve the commit directly
+				commit, resp, err := client.Git.GetCommit(ctx, owner, repo, *ref.Object.SHA)
+				if err != nil {
+					return ghErrors.NewGitHubAPIErrorResponse(ctx,
+						"failed to get commit for lightweight tag",
+						resp,
+						err,
+					), nil, nil
+				}
+				defer func() { _ = resp.Body.Close() }()
+
+				if resp.StatusCode != http.StatusOK {
+					body, err := io.ReadAll(resp.Body)
+					if err != nil {
+						return nil, nil, fmt.Errorf("failed to read response body: %w", err)
+					}
+					return ghErrors.NewGitHubAPIStatusErrorResponse(ctx, "failed to get commit for lightweight tag", resp, body), nil, nil
+				}
+
+				// Return a tag-like structure for consistency
+				lightweightTag := &github.Tag{
+					SHA: ref.Object.SHA,
+					Tag: github.Ptr(tag),
+					Object: &github.GitObject{
+						Type: github.Ptr("commit"),
+						SHA:  ref.Object.SHA,
+					},
+				}
+				if commit.Message != nil {
+					lightweightTag.Message = commit.Message
+				}
+				if commit.Author != nil {
+					lightweightTag.Tagger = &github.CommitAuthor{
+						Name:  commit.Author.Name,
+						Email: commit.Author.Email,
+						Date:  commit.Author.Date,
+					}
+				}
+
+				r, err := json.Marshal(lightweightTag)
+				if err != nil {
+					return nil, nil, fmt.Errorf("failed to marshal response: %w", err)
+				}
+
+				return utils.NewToolResultText(string(r)), nil, nil
+			}
+
+			// Annotated tag — fetch the tag object
 			tagObj, resp, err := client.Git.GetTag(ctx, owner, repo, *ref.Object.SHA)
 			if err != nil {
 				return ghErrors.NewGitHubAPIErrorResponse(ctx,

pkg/github/repositories_test.go

@@ -2840,7 +2840,16 @@ func Test_GetTag(t *testing.T) {
 	mockTagRef := &github.Reference{
 		Ref: github.Ptr("refs/tags/v1.0.0"),
 		Object: &github.GitObject{
-			SHA: github.Ptr("v1.0.0-tag-sha"),
+			SHA:  github.Ptr("v1.0.0-tag-sha"),
+			Type: github.Ptr("tag"),
+		},
+	}
+
+	mockLightweightTagRef := &github.Reference{
+		Ref: github.Ptr("refs/tags/v2.0.0"),
+		Object: &github.GitObject{
+			SHA:  github.Ptr("lightweight-commit-sha"),
+			Type: github.Ptr("commit"),
 		},
 	}
 
@@ -2854,6 +2863,15 @@ func Test_GetTag(t *testing.T) {
 		},
 	}
 
+	mockCommit := &github.Commit{
+		SHA:     github.Ptr("lightweight-commit-sha"),
+		Message: github.Ptr("Initial commit"),
+		Author: &github.CommitAuthor{
+			Name:  github.Ptr("Test User"),
+			Email: github.Ptr("test@example.com"),
+		},
+	}
+
 	tests := []struct {
 		name           string
 		mockedClient   *http.Client
@@ -2892,6 +2910,44 @@ func Test_GetTag(t *testing.T) {
 			expectError: false,
 			expectedTag: mockTagObj,
 		},
+		{
+			name: "successful lightweight tag retrieval",
+			mockedClient: NewMockedHTTPClient(
+				WithRequestMatchHandler(
+					GetReposGitRefByOwnerByRepoByRef,
+					expectPath(
+						t,
+						"/repos/owner/repo/git/ref/tags/v2.0.0",
+					).andThen(
+						mockResponse(t, http.StatusOK, mockLightweightTagRef),
+					),
+				),
+				WithRequestMatchHandler(
+					GetReposGitCommitsByOwnerByRepoByCommitSHA,
+					expectPath(
+						t,
+						"/repos/owner/repo/git/commits/lightweight-commit-sha",
+					).andThen(
+						mockResponse(t, http.StatusOK, mockCommit),
+					),
+				),
+			),
+			requestArgs: map[string]any{
+				"owner": "owner",
+				"repo":  "repo",
+				"tag":   "v2.0.0",
+			},
+			expectError: false,
+			expectedTag: &github.Tag{
+				SHA:     github.Ptr("lightweight-commit-sha"),
+				Tag:     github.Ptr("v2.0.0"),
+				Message: github.Ptr("Initial commit"),
+				Object: &github.GitObject{
+					Type: github.Ptr("commit"),
+					SHA:  github.Ptr("lightweight-commit-sha"),
+				},
+			},
+		},
 		{
 			name: "tag reference not found",
 			mockedClient: NewMockedHTTPClient(