refactoring: switched to gpt-5-nano for commit message generation

Remove commitMessageModel from persisted settings and defaults
Eliminate UI controls and state for commitMessageModel in GitSettings and config store
Update backend and persistence layers to stop reading or writing commitMessageModel

packages/desktop/src-tauri/src/commands/git.rs

@@ -15,6 +15,44 @@ use tokio::fs;
 use tokio::io::AsyncReadExt;
 use tokio::process::Command;
 
+fn extract_json_object(value: &str) -> Option<String> {
+    let trimmed = value.trim();
+    if trimmed.is_empty() {
+        return None;
+    }
+
+    let mut start = match trimmed.find('{') {
+        Some(index) => index,
+        None => return None,
+    };
+
+    while start < trimmed.len() {
+        let mut end = match trimmed[start..].find('}') {
+            Some(index) => start + index,
+            None => break,
+        };
+
+        loop {
+            let candidate = &trimmed[start..=end];
+            if serde_json::from_str::<Value>(candidate).is_ok() {
+                return Some(candidate.to_string());
+            }
+
+            end = match trimmed[end + 1..].find('}') {
+                Some(index) => end + 1 + index,
+                None => break,
+            };
+        }
+
+        start = match trimmed[start + 1..].find('{') {
+            Some(index) => start + 1 + index,
+            None => break,
+        };
+    }
+
+    None
+}
+
 const GIT_IDENTITY_STORAGE_FILE: &str = "git-identities.json";
 const GIT_FILE_DIFF_TIMEOUT_MS: u64 = 15_000;
 const GIT_LS_REMOTE_TIMEOUT_MS: u64 = 5_000;
@@ -2225,32 +2263,17 @@ Diff summary:
 {}"#,
         diff_summaries
     );
- 
-    let settings = state.settings().load().await.unwrap_or(serde_json::Value::Null);
-    let raw_model = settings.get("commitMessageModel")
-        .and_then(|v| v.as_str())
-        .unwrap_or("");
 
-    let model_candidate = raw_model
-        .split('/')
-        .last()
-        .unwrap_or(raw_model)
-        .trim();
-
-    let model = if model_candidate.is_empty() {
-        "big-pickle"
-    } else {
-        model_candidate
-    };
+    let model = "gpt-5-nano";
 
     // 3. Call API
     let client = Client::new();
     let res = client
-        .post("https://opencode.ai/zen/v1/chat/completions")
+        .post("https://opencode.ai/zen/v1/responses")
         .json(&serde_json::json!({
             "model": model,
-            "messages": [{ "role": "user", "content": prompt }],
-            "max_tokens": 3000,
+            "input": [{ "role": "user", "content": prompt }],
+            "max_output_tokens": 1000,
             "stream": false,
             "reasoning": {
                 "effort": "low"
@@ -2265,8 +2288,12 @@ Diff summary:
     }
 
     let body: serde_json::Value = res.json().await.map_err(|e| e.to_string())?;
-    let raw_content = body["choices"][0]["message"]["content"]
-        .as_str()
+    let raw_content = body["output"]
+        .as_array()
+        .and_then(|items| items.iter().find(|item| item["type"] == "message"))
+        .and_then(|item| item["content"].as_array())
+        .and_then(|content| content.iter().find(|entry| entry["type"] == "output_text"))
+        .and_then(|entry| entry["text"].as_str())
         .unwrap_or("")
         .trim();
 
@@ -2278,8 +2305,28 @@ Diff summary:
         .trim_end_matches("```")
         .trim();
 
-    let message: GeneratedCommitMessage =
-        serde_json::from_str(cleaned).map_err(|e| format!("Failed to parse AI response: {}", e))?;
+    let extracted = extract_json_object(cleaned);
 
-    Ok(CommitMessageResponse { message })
+    let mut last_error: Option<String> = None;
+
+    if let Some(candidate) = extracted.as_deref() {
+        if candidate.starts_with('{') || candidate.starts_with('[') {
+            match serde_json::from_str::<GeneratedCommitMessage>(candidate) {
+                Ok(message) => return Ok(CommitMessageResponse { message }),
+                Err(err) => last_error = Some(err.to_string()),
+            }
+        }
+    }
+
+    if cleaned.starts_with('{') || cleaned.starts_with('[') {
+        match serde_json::from_str::<GeneratedCommitMessage>(cleaned) {
+            Ok(message) => return Ok(CommitMessageResponse { message }),
+            Err(err) => last_error = Some(err.to_string()),
+        }
+    }
+
+    Err(format!(
+        "Failed to parse AI response: {}",
+        last_error.unwrap_or_else(|| "unknown error".to_string())
+    ))
 }

packages/desktop/src-tauri/src/commands/settings.rs

@@ -265,15 +265,6 @@ fn sanitize_settings_update(payload: &Value) -> Value {
                 result_obj.insert("defaultGitIdentityId".to_string(), json!(trimmed));
             }
         }
-        if let Some(Value::String(s)) = obj.get("commitMessageModel") {
-            let trimmed = s.trim();
-            if trimmed.is_empty() {
-                result_obj.insert("commitMessageModel".to_string(), Value::Null);
-            } else {
-                result_obj.insert("commitMessageModel".to_string(), json!(trimmed));
-            }
-        }
-
         // Boolean fields
         if let Some(Value::Bool(b)) = obj.get("gitmojiEnabled") {
             result_obj.insert("gitmojiEnabled".to_string(), json!(b));