fix(failover): classify INTERNAL 500 responses as retryable timeouts (#68238)

* Agents: treat Google INTERNAL 500 as timeout failover

(cherry picked from commit c2538523a22d39b65c6b4056ab4857ee84f06887)

* test(failover): narrow INTERNAL timeout patterns

* fix: document INTERNAL timeout retry guard

* fix: ignore plain status prose in server error classification

* fix(failover): preserve mixed server-error retry signals

* test(failover): dedupe internal status samples

* fix(failover): retry status prose with code 500

* fix: classify INTERNAL 500 responses as retryable timeouts

* fix: classify INTERNAL 500 responses as retryable timeouts

---------

Co-authored-by: Kosbling <github@kosbling.com>
Co-authored-by: Openbling <github@openbling.ai>

CHANGELOG.md

@@ -34,6 +34,7 @@ Docs: https://docs.openclaw.ai
 - Feishu/card actions: resolve card-action chat type from the Feishu chat API when stored context is missing, preferring `chat_mode` over `chat_type`, so DM-originated card actions no longer bypass `dmPolicy` by falling through to the group handling path. (#68201)
 - Cron/isolated-agent: preserve `trusted: false` on isolated cron awareness events mirrored into the main session, and forward the optional `trusted` flag through the gateway cron wrapper so explicit trust downgrades survive session-key scoping. (#68210)
 - Agents/fallback: recognize bare leading ZenMux `402 ...` quota-refresh errors without misclassifying plain numeric `402 ...` text, and keep the embedded fallback regression coverage stable. (#47579) Thanks @bwjoke.
+- Failover/google: only treat `INTERNAL` status payloads as retryable timeouts when they also carry a `500` code, so malformed non-500 payloads do not enter the retry path. (#68238) Thanks @altaywtf and @Openbling.
 
 ## 2026.4.15