Add component improvement doc

common/COMPONENT_IMPROVEMENTS.md

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+# Suggested Improvements to common/components.py
+
+## Completed
+
+### Caching on template rendering
+- Added `functools.lru_cache` on `_render_cached()` wrapper around `render_to_string`
+- Cache key: `(template_path, json.dumps(context, sort_keys=True))` — deterministic and unique
+- `maxsize=4096` in production, disabled entirely in DEBUG mode (so template changes are reflected immediately)
+- Only caches `template` path calls; `tag_name` calls are already nanosecond string ops
+- Verified working: identical calls return identical output, different inputs produce separate cache entries
+
+## Pending
+
+### 1. Non-deterministic IDs
+`randomid()` uses `random.choices()` producing unique IDs every call. Breaks:
+- Caching (can't cache Popover output because IDs change between requests)
+- Page consistency (same content produces different HTML across requests)
+- Thread safety of the `random` module for ID generation
+
+**Fix**: Replace with `hashlib.sha1(content_hash.encode()).hexdigest()[:10]` based on deterministic content hash.
+
+### 2. Inconsistent return types
+`Div()`/`A()`/`Button()` return `str`, but `LinkedPurchase()`/`NameWithIcon()` return `SafeText`.
+Forces callers to remember `mark_safe()` wrapping.
+
+**Fix**: Standardize — all component functions should return the same type.
+
+### 3. Fragile A() URL resolution
+Tries `reverse(url)` first, then falls back to literal string. Uses `type(url) is str`
+instead of `isinstance()`. Intentional but error-prone — a string matching a URL name
+will be reversed, while one that doesn't pass through as-is.
+
+**Fix**: Add explicit parameter like `url_name="view_game"` vs `href="/literal/path"`.
+
+### 4. Toast XSS vulnerability
+Custom string escaping for Alpine.js interpolation:
+```python
+safe_message = message.replace("\\", "\\\\").replace("`", "\\`")
+```
+Doesn't protect against all injection vectors (e.g., `})` could close the
+Alpine expression early).
+
+**Fix**: Use proper HTML escaping + JSON serialization for safe template interpolation.
+
+### 5. No tests
+Zero test coverage for the entire component system.
+
+**Fix**: Add unit tests for each component function — basic rendering, edge cases,
+and cache hit/miss verification.
+
+### 6. Default mutable arguments
+`attributes: list[HTMLAttribute] = []` is a classic Python gotcha (though harmless
+here since the list is only read, never mutated in place).
+
+**Fix**: Use `attributes: list[HTMLAttribute] | None = None` and convert to `[]`
+inside the function body.