feat: enhance error handling in OAuth URL building and client creation; improve tool argument sanitization

src/app/mcp/manager.rs

@@ -13,8 +13,8 @@ const MCP_CALL_TIMEOUT_MS: u64 = 60_000;
 fn mcp_static_str(s: &str) -> &'static str {
     static CACHE: OnceLock<Mutex<Vec<&'static str>>> = OnceLock::new();
     let mut cache = CACHE.get_or_init(|| Mutex::new(Vec::new())).lock().unwrap();
-    if let Some(existing) = cache.iter().find(|e| **e == s) {
-        return *existing;
+    if let Some(&existing) = cache.iter().find(|e| **e == s) {
+        return existing;
     }
     let leaked: &'static str = Box::leak(s.to_string().into_boxed_str());
     cache.push(leaked);
@@ -163,7 +163,7 @@ fn call_via_stdio(
     let mut guard;
     let child: &mut StdioChild = if let Some(mtx) = existing_handle {
         guard = mtx.lock().map_err(|e| anyhow::anyhow!("MCP handle lock: {}", e))?;
-        &mut *guard
+        &mut guard
     } else {
         let mut fresh = spawn_stdio_child(command, extra_args)?;
         let result = fresh.call("tools/call", json!({