Gemini 3 tool calls auto-injected with signature validator on replay

Patch Changes

• f62ffe0: fix(google): auto-inject skip_thought_signature_validator for Gemini 3 tool-call replays without a signature

  Gemini 3 models reject requests when an assistant functionCall part lacks a thoughtSignature with HTTP 400 "Function call is missing a thought_signature in functionCall parts." This is easy to hit when application code persists/serializes messages and drops providerOptions.google.thoughtSignature (custom DB schemas, useChat server routes that rebuild messages, synthetic tool-call injection).

  The provider now detects this case (Gemini 3 model + missing signature under google, googleVertex, and vertex namespaces) and injects the documented skip_thought_signature_validator sentinel into the outbound functionCall, plus surfaces a one-shot warning per request listing the affected tool names so the developer can find and fix the upstream serialization. Non-Gemini-3 models are unaffected, and real signatures take precedence when present.