Harden Yomitan runtime state and profile policy handling

- Centralize external-profile read-only behavior in a shared Yomitan profile policy
- Clear parser/extension runtime state via dedicated helpers on load failures and reloads
- Prevent opening Yomitan settings when the Yomitan session is unavailable
- Add focused runtime-policy and state-clearing regression tests

src/core/services/yomitan-extension-runtime-state.ts

@@ -0,0 +1,34 @@
+type ParserWindowLike = {
+  isDestroyed?: () => boolean;
+  destroy?: () => void;
+} | null;
+
+export interface YomitanParserRuntimeStateDeps {
+  getYomitanParserWindow: () => ParserWindowLike;
+  setYomitanParserWindow: (window: null) => void;
+  setYomitanParserReadyPromise: (promise: Promise<void> | null) => void;
+  setYomitanParserInitPromise: (promise: Promise<boolean> | null) => void;
+}
+
+export interface YomitanExtensionRuntimeStateDeps extends YomitanParserRuntimeStateDeps {
+  setYomitanExtension: (extension: null) => void;
+  setYomitanSession: (session: null) => void;
+}
+
+export function clearYomitanParserRuntimeState(deps: YomitanParserRuntimeStateDeps): void {
+  const parserWindow = deps.getYomitanParserWindow();
+  if (parserWindow && !parserWindow.isDestroyed?.()) {
+    parserWindow.destroy?.();
+  }
+  deps.setYomitanParserWindow(null);
+  deps.setYomitanParserReadyPromise(null);
+  deps.setYomitanParserInitPromise(null);
+}
+
+export function clearYomitanExtensionRuntimeState(
+  deps: YomitanExtensionRuntimeStateDeps,
+): void {
+  clearYomitanParserRuntimeState(deps);
+  deps.setYomitanExtension(null);
+  deps.setYomitanSession(null);
+}