fix(executor): properly handle thinking application errors

internal/thinking/errors.go

@@ -1,6 +1,8 @@
 // Package thinking provides unified thinking configuration processing logic.
 package thinking
 
+import "net/http"
+
 // ErrorCode represents the type of thinking configuration error.
 type ErrorCode string
 
@@ -69,3 +71,8 @@ func NewThinkingErrorWithModel(code ErrorCode, message, model string) *ThinkingE
 		Model:   model,
 	}
 }
+
+// StatusCode implements a portable status code interface for HTTP handlers.
+func (e *ThinkingError) StatusCode() int {
+	return http.StatusBadRequest
+}

internal/thinking/provider/geminicli/apply.go

@@ -55,6 +55,9 @@ func (a *Applier) Apply(body []byte, config thinking.ThinkingConfig, modelInfo *
 	if config.Mode == thinking.ModeAuto {
 		return a.applyBudgetFormat(body, config)
 	}
+	if config.Mode == thinking.ModeBudget {
+		return a.applyBudgetFormat(body, config)
+	}
 
 	// For non-auto modes, choose format based on model capabilities
 	support := modelInfo.Thinking