fix(gemini): resolve 400 errors by refining safety settings and sanitizing stop sequences

- Exclude 'HARM_CATEGORY_CIVIC_INTEGRITY' when using v1 endpoint (v1beta only).
- Filter out empty strings from 'stop_sequences' which are rejected by Gemini.
- Update error probe to use non-streaming endpoint for better JSON error diagnostics.

src/providers/gemini.rs

@@ -531,15 +531,19 @@ impl GeminiProvider {
     }
 
     /// Default safety settings to avoid blocking responses.
-    fn get_safety_settings(&self) -> Vec<GeminiSafetySetting> {
-        let categories = vec![
+    fn get_safety_settings(&self, base_url: &str) -> Vec<GeminiSafetySetting> {
+        let mut categories = vec![
             "HARM_CATEGORY_HARASSMENT",
             "HARM_CATEGORY_HATE_SPEECH",
             "HARM_CATEGORY_SEXUALLY_EXPLICIT",
             "HARM_CATEGORY_DANGEROUS_CONTENT",
-            "HARM_CATEGORY_CIVIC_INTEGRITY",
         ];
 
+        // Civic integrity is only available in v1beta
+        if base_url.contains("v1beta") {
+            categories.push("HARM_CATEGORY_CIVIC_INTEGRITY");
+        }
+
         categories
             .into_iter()
             .map(|c| GeminiSafetySetting {
@@ -589,12 +593,21 @@ impl super::Provider for GeminiProvider {
             return Err(AppError::ProviderError("No valid messages to send".to_string()));
         }
 
+        let base_url = self.get_base_url(&model);
+
+        // Sanitize stop sequences: Gemini rejects empty strings
+        let stop_sequences = request.stop.map(|s| {
+            s.into_iter()
+                .filter(|seq| !seq.is_empty())
+                .collect::<Vec<_>>()
+        }).filter(|s| !s.is_empty());
+
         let generation_config = Some(GeminiGenerationConfig {
             temperature: request.temperature,
             top_p: request.top_p,
             top_k: request.top_k,
             max_output_tokens: request.max_tokens.map(|t| t.min(8192)),
-            stop_sequences: request.stop,
+            stop_sequences,
             candidate_count: request.n,
         });
 
@@ -604,10 +617,9 @@ impl super::Provider for GeminiProvider {
             generation_config,
             tools,
             tool_config,
-            safety_settings: Some(self.get_safety_settings()),
+            safety_settings: Some(self.get_safety_settings(&base_url)),
         };
 
-        let base_url = self.get_base_url(&model);
         let url = format!("{}/models/{}:generateContent", base_url, model);
         tracing::debug!("Calling Gemini API: {}", url);
 
@@ -729,12 +741,21 @@ impl super::Provider for GeminiProvider {
             return Err(AppError::ProviderError("No valid messages to send".to_string()));
         }
 
+        let base_url = self.get_base_url(&model);
+
+        // Sanitize stop sequences: Gemini rejects empty strings
+        let stop_sequences = request.stop.map(|s| {
+            s.into_iter()
+                .filter(|seq| !seq.is_empty())
+                .collect::<Vec<_>>()
+        }).filter(|s| !s.is_empty());
+
         let generation_config = Some(GeminiGenerationConfig {
             temperature: request.temperature,
             top_p: request.top_p,
             top_k: request.top_k,
             max_output_tokens: request.max_tokens.map(|t| t.min(8192)),
-            stop_sequences: request.stop,
+            stop_sequences,
             candidate_count: request.n,
         });
 
@@ -744,10 +765,9 @@ impl super::Provider for GeminiProvider {
             generation_config,
             tools,
             tool_config,
-            safety_settings: Some(self.get_safety_settings()),
+            safety_settings: Some(self.get_safety_settings(&base_url)),
         };
 
-        let base_url = self.get_base_url(&model);
         let url = format!(
             "{}/models/{}:streamGenerateContent?alt=sse",
             base_url, model,
@@ -757,7 +777,8 @@ impl super::Provider for GeminiProvider {
         // Capture a clone of the request to probe for errors (Gemini 400s are common)
         let probe_request = gemini_request.clone();
         let probe_client = self.client.clone();
-        let probe_url = url.clone();
+        // Use non-streaming URL for probing to get a valid JSON error body
+        let probe_url = format!("{}/models/{}:generateContent", base_url, model);
         let probe_api_key = self.api_key.clone();
 
         // Create the EventSource first (it doesn't send until polled)