fix(github-client): distinguish API error from no-tags in fetchLatestSemverTag

Changed fetchLatestSemverTag to throw on API errors (401, 403, 404, 5xx,
etc.) and return null only when the repo genuinely has no semver tags.
Previously, both cases returned undefined, making them indistinguishable
to callers.

This enables callers to:
- Catch API errors and handle them appropriately via classifyError()
- Distinguish "repo has no tags" (null return) from network/auth failures

Updated all call sites (release-readiness-tool and changelog-draft-tool)
to check for null specifically, and updated tests to expect exceptions
for API errors.

Author: AlbinoGeek

src/server/changelog-draft-tool.ts

@@ -82,8 +82,8 @@ export function registerChangelogDraftTool(server: FastMCP): void {
         }
 
         if (!base) {
-          base = await fetchLatestSemverTag(owner, repo);
-          if (!base) {
+          const fetchedTag = await fetchLatestSemverTag(owner, repo);
+          if (fetchedTag === null) {
             return errorRespond(
               mkError(
                 "NOT_FOUND",
@@ -92,6 +92,7 @@ export function registerChangelogDraftTool(server: FastMCP): void {
               ),
             );
           }
+          base = fetchedTag;
         }
 
         const cmp = await octokit.repos.compareCommitsWithBasehead({

src/server/github-client.test.ts

@@ -219,15 +219,27 @@ describe("getOctokit", () => {
 
 describe("fetchLatestSemverTag", () => {
   test("returns a semver tag string for a repo that has releases", async () => {
-    const tag = await fetchLatestSemverTag("Rethunk-AI", "rethunk-github-mcp");
-    // If auth is absent the function returns undefined — acceptable
-    if (tag === undefined) return;
-    expect(tag).toMatch(/^v?\d+\.\d+\.\d+$/);
+    try {
+      const tag = await fetchLatestSemverTag("Rethunk-AI", "rethunk-github-mcp");
+      // If we get a result, it should match semver
+      if (tag !== null) {
+        expect(tag).toMatch(/^v?\d+\.\d+\.\d+$/);
+      }
+    } catch {
+      // If auth is absent the function will throw — skip gracefully
+      return;
+    }
   });
 
-  test("returns undefined for a nonexistent repo", async () => {
-    const tag = await fetchLatestSemverTag("Rethunk-AI", "repo-that-does-not-exist-xyzzy");
-    expect(tag).toBeUndefined();
+  test("throws on API errors like 404", async () => {
+    try {
+      await fetchLatestSemverTag("Rethunk-AI", "repo-that-does-not-exist-xyzzy");
+      // Should not reach here if API throws
+      expect(false).toBe(true);
+    } catch {
+      // Expected to throw on API errors or auth failure
+      return;
+    }
   });
 });
 

src/server/github-client.ts

@@ -226,18 +226,11 @@ export async function fetchPRMetadata(
 
 /**
  * Return the most recent semver tag (vX.Y.Z or X.Y.Z) in a repo.
- * Returns `undefined` when no matching tag exists or the request fails.
+ * Returns `null` when no matching tag exists. Throws on API errors.
  */
-export async function fetchLatestSemverTag(
-  owner: string,
-  repo: string,
-): Promise<string | undefined> {
-  try {
-    const octokit = getOctokit();
-    const res = await octokit.repos.listTags({ owner, repo, per_page: 20 });
-    const semverRe = /^v?\d+\.\d+\.\d+$/;
-    return res.data.filter((t) => semverRe.test(t.name))[0]?.name;
-  } catch {
-    return undefined;
-  }
+export async function fetchLatestSemverTag(owner: string, repo: string): Promise<string | null> {
+  const octokit = getOctokit();
+  const res = await octokit.repos.listTags({ owner, repo, per_page: 20 });
+  const semverRe = /^v?\d+\.\d+\.\d+$/;
+  return res.data.filter((t) => semverRe.test(t.name))[0]?.name ?? null;
 }

src/server/release-readiness-tool.ts

@@ -91,8 +91,8 @@ export function registerReleaseReadinessTool(server: FastMCP): void {
         }
 
         if (!base) {
-          base = await fetchLatestSemverTag(owner, repo);
-          if (!base) {
+          const fetchedTag = await fetchLatestSemverTag(owner, repo);
+          if (fetchedTag === null) {
             return errorRespond(
               mkError(
                 "NOT_FOUND",
@@ -103,6 +103,7 @@ export function registerReleaseReadinessTool(server: FastMCP): void {
               ),
             );
           }
+          base = fetchedTag;
         }
 
         const cmp = await octokit.repos.compareCommitsWithBasehead({