fix: Address PR review feedback for usePrevious implementation

- Update usePrevious hook to use useEffect pattern instead of mutating
  refs during render (addresses Concurrent Mode compatibility)
- Add wasManuallyDismissed flag to properly track dismissal of all error
  types (machineError, machineErrorMessage, and pyodideError)
- Add proper eslint-disable comment with explanation for ref access
- Update handlePopoverOpenChange to handle dismissal of all error types

These changes address all feedback from PR review #54

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/AppHeader.tsx

@@ -66,6 +66,7 @@ export function AppHeader() {
   const [dismissedErrorCode, setDismissedErrorCode] = useState<number | null>(
     null,
   );
+  const [wasManuallyDismissed, setWasManuallyDismissed] = useState(false);
 
   // Track previous values for comparison
   const prevMachineError = usePrevious(machineError);
@@ -99,7 +100,7 @@ export function AppHeader() {
     const hadAnyError =
       prevErrorMessage || prevPyodideError || hasError(prevMachineError);
 
-    // Auto-open popover when new error appears
+    // Auto-open popover when new error appears (but not if user manually dismissed)
     const isNewMachineError =
       hasError(machineError) &&
       machineError !== prevMachineError &&
@@ -108,7 +109,10 @@ export function AppHeader() {
       machineErrorMessage && machineErrorMessage !== prevErrorMessage;
     const isNewPyodideError = pyodideError && pyodideError !== prevPyodideError;
 
-    if (isNewMachineError || isNewErrorMessage || isNewPyodideError) {
+    if (
+      !wasManuallyDismissed &&
+      (isNewMachineError || isNewErrorMessage || isNewPyodideError)
+    ) {
       setErrorPopoverOpen(true);
     }
 
@@ -116,12 +120,14 @@ export function AppHeader() {
     if (!hasAnyError && hadAnyError) {
       setErrorPopoverOpen(false);
       setDismissedErrorCode(null); // Reset dismissed tracking
+      setWasManuallyDismissed(false); // Reset manual dismissal flag
     }
   }, [
     machineError,
     machineErrorMessage,
     pyodideError,
     dismissedErrorCode,
+    wasManuallyDismissed,
     prevMachineError,
     prevErrorMessage,
     prevPyodideError,
@@ -132,10 +138,17 @@ export function AppHeader() {
   const handlePopoverOpenChange = (open: boolean) => {
     setErrorPopoverOpen(open);
 
-    // If user manually closes it, remember the current error code to prevent reopening
-    if (!open && hasError(machineError)) {
+    // If user manually closes it while any error is present, remember this to prevent reopening
+    if (
+      !open &&
+      (hasError(machineError) || machineErrorMessage || pyodideError)
+    ) {
+      setWasManuallyDismissed(true);
+      // Also track the specific machine error code if present
+      if (hasError(machineError)) {
         setDismissedErrorCode(machineError);
       }
+    }
   };
 
   return (

src/hooks/usePrevious.ts

@@ -4,28 +4,23 @@
  * Returns the previous value of a state or prop
  * Useful for comparing current vs previous values in effects
  *
- * Note: This uses ref access during render, which is safe for this specific use case.
- * The pattern is recommended by React for tracking previous values.
+ * This implementation updates the ref in an effect instead of during render,
+ * which is compatible with React Concurrent Mode and Strict Mode.
+ *
+ * Note: The ref read on return is safe because it's only returning the previous value
+ * (from the last render), not the current value being passed in. This is the standard
+ * pattern for usePrevious hooks.
  */
 
-import { useRef } from "react";
+import { useEffect, useRef } from "react";
 
-/* eslint-disable react-hooks/refs */
 export function usePrevious<T>(value: T): T | undefined {
-  const ref = useRef<{ value: T; prev: T | undefined }>({
-    value,
-    prev: undefined,
-  });
+  const ref = useRef<T>();
 
-  const current = ref.current.value;
+  useEffect(() => {
+    ref.current = value;
+  }, [value]);
 
-  if (value !== current) {
-    ref.current = {
-      value,
-      prev: current,
-    };
-  }
-
-  return ref.current.prev;
+  // eslint-disable-next-line react-hooks/refs
+  return ref.current;
 }
-/* eslint-enable react-hooks/refs */