[jamie950315]

Summary

Treat the observed streamed Gemini rejection Request contains an invalid argument. as request-scoped when it reaches the gateway as a 5xx failure without authentication metadata.

Problem

An upstream Gemini stream can return HTTP 200, then emit an error containing only:

{"type":"error","error":{"message":"Request contains an invalid argument."}}

Cockpit reports this as a gateway 502. Because the envelope has no usable request-error code, the existing classifier treats it as an account failure and applies a model cooldown. Subsequent retries can exhaust the available routes and replace the original request error with No compatible account is available for this model.

Change

• Recognize the provider's exact rejection message, ignoring case and surrounding whitespace, on gateway 5xx failures without authentication metadata.
• Mark the failure request-scoped so account cooldown reporting skips it.
• Preserve the failed response's status and message; the caller still receives the upstream request failure.
• Keep authentication, quota, model-availability, and genuine server-failure handling unchanged. Broad errors merely mentioning an argument do not match.

This change is independent of the tool-identity fix in #2901, account-model routing in #2902, and the upstream Argon continuation repair in router-for-me/CLIProxyAPI#6935.

Validation

• cargo test --manifest-path src-tauri/Cargo.toml --lib upstream_errors::tests
• cargo test --manifest-path src-tauri/Cargo.toml --lib native_connection_failures_do_not_cool_accounts_or_shorten_existing_cooldown
• cargo test --manifest-path src-tauri/Cargo.toml --lib native_actual_upstream_failures_keep_auth_quota_and_server_cooldowns
• rustfmt --check --edition 2021 on the two changed Rust files
• git diff --check

Regression coverage includes streamed error observation, unchanged failure status/message, skipped account cooldowns, and preserved authentication/quota/server cooldown behavior. Tests use synthetic fixtures; no private request logs or credentials are included.