feat(anthropic): respect explicit thinking_budget from Anthropic routes

- Add explicit_budget parameter to _get_thinking_config
- Cap Claude thinking budget at 31999 when explicit budget provided
- Pass thinking_budget kwarg from Anthropic translator to provider

Author: FammasMaz

src/rotator_library/providers/antigravity_provider.py

@@ -1944,21 +1944,39 @@ def _close_tool_loop_for_thinking(
     # =========================================================================
 
     def _get_thinking_config(
-        self, reasoning_effort: Optional[str], model: str
+        self,
+        reasoning_effort: Optional[str],
+        model: str,
+        explicit_budget: Optional[int] = None,
     ) -> Optional[Dict[str, Any]]:
         """
         Map reasoning_effort to thinking configuration.
 
         - Gemini 2.5 & Claude: thinkingBudget (integer tokens)
         - Gemini 3 Pro: thinkingLevel (string: "low"/"high")
         - Gemini 3 Flash: thinkingLevel (string: "minimal"/"low"/"medium"/"high")
+
+        If explicit_budget is provided (from Anthropic route), it takes precedence
+        over reasoning_effort mapping. For Claude, explicit budget is capped at 31999.
         """
         internal = self._alias_to_internal(model)
         is_gemini_25 = "gemini-2.5" in model
         is_gemini_3 = internal.startswith("gemini-3-")
         is_gemini_3_flash = "gemini-3-flash" in model or "gemini-3-flash" in internal
         is_claude = self._is_claude(model)
 
+        if not (is_gemini_25 or is_gemini_3 or is_claude):
+            return None
+
+        # Handle explicit budget from Anthropic route (takes precedence)
+        if explicit_budget is not None and (is_gemini_25 or is_claude):
+            if explicit_budget <= 0:
+                return {"thinkingBudget": 0, "include_thoughts": False}
+            # Cap Claude budget at max allowed
+            if is_claude:
+                explicit_budget = min(explicit_budget, CLAUDE_FORCED_THINKING_BUDGET)
+            return {"thinkingBudget": explicit_budget, "include_thoughts": True}
+
         if not (is_gemini_25 or is_gemini_3 or is_claude):
             return None
 
@@ -3756,7 +3774,10 @@ async def acompletion(
             # Gemini 3 performs better with temperature=1 for tool use
             gen_config["temperature"] = 1.0
 
-        thinking_config = self._get_thinking_config(reasoning_effort, model)
+        explicit_thinking_budget = kwargs.get("thinking_budget")
+        thinking_config = self._get_thinking_config(
+            reasoning_effort, model, explicit_thinking_budget
+        )
         if thinking_config:
             gen_config.setdefault("thinkingConfig", {}).update(thinking_config)