Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@packages/vscode-preview/src/main.tsx`:
- Around line 14-21: The click handler uses an unsafe cast (e.target as
HTMLElement) and calls .closest(), which can throw if target is null or not an
HTMLElement; update the listener callback to runtime-guard e.target (e.g., check
e.target !== null and use instanceof HTMLElement or 'closest' in target) to
narrow its type before calling .closest('a[href]'), remove the as-cast, and keep
the rest of the logic (anchor variable and the call to
ExtensionApi.openExternalUrl(href)) unchanged.

In `@packages/vscode/src/panel/activateMessenger.ts`:
- Around line 110-112: The call in messenger.onWebviewOpenExternalUrl currently
invokes vscode.env.openExternal without awaiting or handling errors; update the
handler to validate the URL scheme (e.g., allow only http/https) then await
vscode.env.openExternal(...) inside a try/catch and log or surface any error
(use the existing logger or vscode.window.showErrorMessage) so failures are not
silently ignored; reference the messenger.onWebviewOpenExternalUrl callback and
vscode.env.openExternal to locate and update the code.

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@packages/vscode-preview/src/interceptExternalLinks.spec.ts`:
- Around line 14-85: Add tests in interceptExternalLinks.spec.ts to assert that
interceptExternalLinks() registers both the required DOM listeners (spy on
window.addEventListener or document.addEventListener for the event types used by
interceptExternalLinks) and that the returned disposer removes them (spy on
removeEventListener and call the disposer then expect removeEventListener to
have been called with the same event names/handlers). Reference the
interceptExternalLinks function to locate where listeners are added and the
disposer it returns; ensure the test names describe registration and cleanup and
restore/clear the spies after each test.

In `@packages/vscode-preview/src/interceptExternalLinks.ts`:
- Around line 16-18: The code in interceptExternalLinks.ts uses unsafe casts
like (target as Element) and (e as MouseEvent); instead, change the
click/auxclick handler signature to accept a typed parameter (e: MouseEvent) and
use type-safe narrowing with "if (!target || !(target instanceof Element))
return" so you can call target.closest('a[href]') without casts, and remove the
remaining (e as MouseEvent) casts; update references to target and anchor
accordingly (the variables target and anchor and the handler function) so the
code relies on instanceof Element and the typed event parameter.

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@packages/vscode-preview/src/interceptExternalLinks.ts`:
- Around line 31-34: The auxclick listener currently uses the generic handler
which calls handleExternalLinkClick/openExternalUrl for any non-primary button;
update the auxclick path to only proceed for middle-button clicks by checking
MouseEvent.button === 1 before invoking handleExternalLinkClick/openExternalUrl
(either add that guard inside the existing handler function or register a
separate auxclick handler that performs the button === 1 check and then calls
handleExternalLinkClick).

---

Nitpick comments:
In `@packages/vscode-preview/src/vscode.ts`:
- Around line 57-59: Add a JSDoc block above the new public method
openExternalUrl on the exported ExtensionApi surface describing purpose,
expected URL shape (e.g., must be absolute http(s) URL), any safety constraints
(no data URLs, normalized/validated by the caller), and side-effects (sends a
WebviewMsgs.OpenExternalUrl notification via messenger.sendNotification to
HOST_EXTENSION). Mention parameters and return type (void) and any
errors/validation behavior so consumers know intent and constraints.

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@packages/vscode-preview/src/vscode.ts`:
- Around line 57-59: The public API method openExternalUrl currently lacks JSDoc
and an explicit return type; update the exported ExtensionApi's openExternalUrl
definition to add a JSDoc block describing the purpose and parameters and change
its signature to include an explicit return type `: void` (e.g.,
`openExternalUrl: (url: string): void => { ... }`) so the contract is clear for
consumers and matches project guidelines.