fix: skip retries on 4xx client errors

Client errors (400, 404, 405, etc.) will never succeed on retry.
Only retry on transient failures like 5xx server errors and network
errors. This avoids tripling wasted API calls on permanent failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: madisonrickert

src/toggl-api.ts

@@ -67,7 +67,12 @@ export class TogglAPI {
               `Server response: ${text}`
             );
           }
-          throw new Error(`Toggl API error (${response.status}): ${text}`);
+          const err = new Error(`Toggl API error (${response.status}): ${text}`);
+          // Only retry on server errors (5xx); client errors (4xx) won't succeed on retry
+          if (response.status >= 400 && response.status < 500) {
+            throw Object.assign(err, { noRetry: true });
+          }
+          throw err;
         }
 
         // Handle 204 No Content
@@ -76,9 +81,9 @@ export class TogglAPI {
         }
 
         return await response.json() as T;
-      } catch (error) {
-        if (i === retries - 1) throw error;
-        // Exponential backoff
+      } catch (error: any) {
+        if (error?.noRetry || i === retries - 1) throw error;
+        // Exponential backoff for transient/network errors
         await new Promise(resolve => setTimeout(resolve, (i + 1) * 1000));
       }
     }