fix(providers): robust Gemini thought_signature detection and history mapping

Improves supportsThoughtSignature with providerType and model normalization.
Strengthens collapseToolCallsWithoutSig with TrimSpace and camelCase support
to handle 'Thinking=OFF' whitespace signatures and proxy key translations.

internal/providers/openai.go

@@ -259,8 +259,9 @@ func (p *OpenAIProvider) buildRequestBody(model string, req ChatRequest, stream
 	inputMessages := req.Messages
 
 	// Compute provider capability once: does this endpoint support Google's thought_signature?
-	// We check name, apiBase, and the model string (which covers OpenRouter/LiteLLM routing to Gemini).
-	supportsThoughtSignature := strings.Contains(strings.ToLower(p.name), "gemini") ||
+	// We check providerType, name, apiBase, and the model string (robust detection for proxies/OpenRouter).
+	supportsThoughtSignature := strings.Contains(strings.ToLower(p.providerType), "gemini") ||
+		strings.Contains(strings.ToLower(p.name), "gemini") ||
 		strings.Contains(strings.ToLower(p.apiBase), "generativelanguage") ||
 		strings.Contains(strings.ToLower(model), "gemini")
 

internal/providers/openai_gemini.go

@@ -17,7 +17,17 @@ func collapseToolCallsWithoutSig(msgs []Message) []Message {
 			continue
 		}
 		for _, tc := range m.ToolCalls {
-			if tc.Metadata["thought_signature"] == "" {
+			// If meta is nil or signature is empty/whitespace, collapse the whole message's tool cycle.
+			// Checks both snake_case and camelCase for cross-proxy reliability.
+			sig := ""
+			if tc.Metadata != nil {
+				sig = tc.Metadata["thought_signature"]
+				if sig == "" {
+					sig = tc.Metadata["thoughtSignature"]
+				}
+			}
+
+			if strings.TrimSpace(sig) == "" {
 				for _, tc2 := range m.ToolCalls {
 					collapseIDs[tc2.ID] = true
 				}