fix(installer): include URL, API message, and rate-limit info in HTTP errors

Non-2xx responses previously yielded bare `HTTP 403`. Now surface the
request URL, GitHub's JSON error message (or body snippet), X-RateLimit-Reset
when quota is exhausted, and Retry-After. Turns a mystery 403 into
'rate limit exhausted; resets at 2026-04-15T18:00:00Z' — the difference
between 'try GITHUB_TOKEN' and a wild goose chase.

tools/installer/modules/registry-client.js

@@ -1,6 +1,37 @@
 const https = require('node:https');
 const yaml = require('yaml');
 
+/**
+ * Build a rich Error from a non-2xx response. Includes the URL, the GitHub
+ * JSON error message (or a truncated body snippet), rate-limit reset time,
+ * and Retry-After — anything present that would help a user recover.
+ */
+function buildHttpError(url, res, body) {
+  const parts = [`HTTP ${res.statusCode} ${url}`];
+
+  if (body) {
+    try {
+      const parsed = JSON.parse(body);
+      if (parsed.message) parts.push(parsed.message);
+      if (parsed.documentation_url) parts.push(`(see ${parsed.documentation_url})`);
+    } catch {
+      const snippet = body.slice(0, 200).trim();
+      if (snippet) parts.push(snippet);
+    }
+  }
+
+  const remaining = res.headers['x-ratelimit-remaining'];
+  const reset = res.headers['x-ratelimit-reset'];
+  if (remaining === '0' && reset) {
+    parts.push(`rate limit exhausted; resets at ${new Date(Number(reset) * 1000).toISOString()}`);
+  }
+
+  const retryAfter = res.headers['retry-after'];
+  if (retryAfter) parts.push(`retry after ${retryAfter}`);
+
+  return new Error(parts.join(' — '));
+}
+
 /**
  * Shared HTTP client for fetching registry data from GitHub.
  * Used by ExternalModuleManager, CommunityModuleManager, and CustomModuleManager.
@@ -29,12 +60,14 @@ class RegistryClient {
             }
             return this.fetch(res.headers.location, timeoutMs, maxRedirects - 1).then(resolve, reject);
           }
-          if (res.statusCode !== 200) {
-            return reject(new Error(`HTTP ${res.statusCode}`));
-          }
           let data = '';
           res.on('data', (chunk) => (data += chunk));
-          res.on('end', () => resolve(data));
+          res.on('end', () => {
+            if (res.statusCode !== 200) {
+              return reject(buildHttpError(url, res, data));
+            }
+            resolve(data);
+          });
         })
         .on('error', reject)
         .on('timeout', () => {
@@ -133,12 +166,14 @@ class RegistryClient {
             }
             return this._fetchWithHeaders(res.headers.location, headers, timeoutMs, maxRedirects - 1).then(resolve, reject);
           }
-          if (res.statusCode !== 200) {
-            return reject(new Error(`HTTP ${res.statusCode}`));
-          }
           let data = '';
           res.on('data', (chunk) => (data += chunk));
-          res.on('end', () => resolve(data));
+          res.on('end', () => {
+            if (res.statusCode !== 200) {
+              return reject(buildHttpError(url, res, data));
+            }
+            resolve(data);
+          });
         })
         .on('error', reject)
         .on('timeout', () => {