fix: align auth-by-message with 401 path, decode URLs before secret check

[aaronlab]

Summary

• error_classifier.py — auth retryable inconsistency: Message-only auth errors ("invalid api key", "unauthorized", etc.) are classified as retryable=True (line 707), while the HTTP 401 code path (line 432) correctly uses retryable=False + should_fallback=True. This mismatch causes 3 wasted retries with the same broken credential before fallback is attempted, while 401 errors immediately try fallback. The credential pool rotation also never fires because status_code is None for message-only errors, making the retries completely futile. Aligned to retryable=False, should_fallback=True.

• web_tools.py — URL-encoded secret bypass: The _PREFIX_RE check in web_extract_tool() runs against the raw URL string (line 1196). URL-encoded secrets like %73k-1234... (sk-1234...) bypass the filter because the regex expects literal ASCII characters. Added urllib.parse.unquote() before the check so percent-encoded variants are also caught.

Test plan

• Verify auth error from message-only path (no HTTP status) immediately attempts fallback
• Verify URL with literal sk-... is still blocked
• Verify URL with %73k-... (URL-encoded sk-) is now blocked
• Verify normal URLs without secrets still pass through

🤖 Generated with Claude Code

[teknium1]

Merged via PR #7094. Your commit was cherry-picked onto current main with your authorship preserved in git log. The error_classifier.py comment conflict was resolved (the code change for should_fallback=True had already landed via #7027, so we kept main's comment). The URL-decode fix for secret-prefix bypass is a great catch. Thanks!