diff --git a/changes/external-yomitan-profile.md b/changes/external-yomitan-profile.md
index d845814..d1c6971 100644
--- a/changes/external-yomitan-profile.md
+++ b/changes/external-yomitan-profile.md
@@ -1,6 +1,6 @@
-type: added
+type: changed
 area: config
 
 - Added `yomitan.externalProfilePath` to reuse another Electron app's Yomitan profile in read-only mode.
 - SubMiner now reuses external Yomitan dictionaries/settings without writing back to that profile.
-- Fixed default config bootstrap so `config.jsonc` is seeded even when the config directory already exists.
+- SubMiner now seeds `config.jsonc` even when the default config directory already exists.
diff --git a/src/core/services/yomitan-extension-loader.ts b/src/core/services/yomitan-extension-loader.ts
index 6679126..0161580 100644
--- a/src/core/services/yomitan-extension-loader.ts
+++ b/src/core/services/yomitan-extension-loader.ts
@@ -9,6 +9,10 @@ import {
   resolveExternalYomitanExtensionPath,
   resolveExistingYomitanExtensionPath,
 } from './yomitan-extension-paths';
+import {
+  clearYomitanExtensionRuntimeState,
+  clearYomitanParserRuntimeState,
+} from './yomitan-extension-runtime-state';
 
 const { session } = electron;
 const logger = createLogger('main:yomitan-extension-loader');
@@ -28,6 +32,22 @@ export interface YomitanExtensionLoaderDeps {
 export async function loadYomitanExtension(
   deps: YomitanExtensionLoaderDeps,
 ): Promise<Extension | null> {
+  const clearRuntimeState = () =>
+    clearYomitanExtensionRuntimeState({
+      getYomitanParserWindow: deps.getYomitanParserWindow,
+      setYomitanParserWindow: deps.setYomitanParserWindow,
+      setYomitanParserReadyPromise: deps.setYomitanParserReadyPromise,
+      setYomitanParserInitPromise: deps.setYomitanParserInitPromise,
+      setYomitanExtension: () => deps.setYomitanExtension(null),
+      setYomitanSession: () => deps.setYomitanSession(null),
+    });
+  const clearParserState = () =>
+    clearYomitanParserRuntimeState({
+      getYomitanParserWindow: deps.getYomitanParserWindow,
+      setYomitanParserWindow: deps.setYomitanParserWindow,
+      setYomitanParserReadyPromise: deps.setYomitanParserReadyPromise,
+      setYomitanParserInitPromise: deps.setYomitanParserInitPromise,
+    });
   const externalProfilePath = deps.externalProfilePath?.trim() ?? '';
   let extPath: string | null = null;
   let targetSession: Session = session.defaultSession;
@@ -38,8 +58,7 @@ export async function loadYomitanExtension(
     if (!extPath) {
       logger.error('External Yomitan extension not found in configured profile path');
       logger.error('Expected unpacked extension at:', path.join(resolvedProfilePath, 'extensions'));
-      deps.setYomitanExtension(null);
-      deps.setYomitanSession(null);
+      clearRuntimeState();
       return null;
     }
 
@@ -56,8 +75,7 @@ export async function loadYomitanExtension(
     if (!extPath) {
       logger.error('Yomitan extension not found in any search path');
       logger.error('Run `bun run build:yomitan` or install Yomitan to one of:', searchPaths);
-      deps.setYomitanExtension(null);
-      deps.setYomitanSession(null);
+      clearRuntimeState();
       return null;
     }
 
@@ -68,13 +86,7 @@ export async function loadYomitanExtension(
     extPath = extensionCopy.targetDir;
   }
 
-  const parserWindow = deps.getYomitanParserWindow();
-  if (parserWindow && !parserWindow.isDestroyed()) {
-    parserWindow.destroy();
-  }
-  deps.setYomitanParserWindow(null);
-  deps.setYomitanParserReadyPromise(null);
-  deps.setYomitanParserInitPromise(null);
+  clearParserState();
   deps.setYomitanSession(targetSession);
 
   try {
@@ -91,8 +103,7 @@ export async function loadYomitanExtension(
   } catch (err) {
     logger.error('Failed to load Yomitan extension:', (err as Error).message);
     logger.error('Full error:', err);
-    deps.setYomitanExtension(null);
-    deps.setYomitanSession(null);
+    clearRuntimeState();
     return null;
   }
 }
diff --git a/src/core/services/yomitan-extension-runtime-state.test.ts b/src/core/services/yomitan-extension-runtime-state.test.ts
new file mode 100644
index 0000000..886c49e
--- /dev/null
+++ b/src/core/services/yomitan-extension-runtime-state.test.ts
@@ -0,0 +1,45 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { clearYomitanParserRuntimeState } from './yomitan-extension-runtime-state';
+
+test('clearYomitanParserRuntimeState destroys parser window and clears parser promises', () => {
+  const calls: string[] = [];
+  const parserWindow = {
+    isDestroyed: () => false,
+    destroy: () => {
+      calls.push('destroy');
+    },
+  };
+
+  clearYomitanParserRuntimeState({
+    getYomitanParserWindow: () => parserWindow as never,
+    setYomitanParserWindow: (window) => calls.push(`window:${window === null ? 'null' : 'set'}`),
+    setYomitanParserReadyPromise: (promise) =>
+      calls.push(`ready:${promise === null ? 'null' : 'set'}`),
+    setYomitanParserInitPromise: (promise) =>
+      calls.push(`init:${promise === null ? 'null' : 'set'}`),
+  });
+
+  assert.deepEqual(calls, ['destroy', 'window:null', 'ready:null', 'init:null']);
+});
+
+test('clearYomitanParserRuntimeState skips destroy when parser window is already gone', () => {
+  const calls: string[] = [];
+  const parserWindow = {
+    isDestroyed: () => true,
+    destroy: () => {
+      calls.push('destroy');
+    },
+  };
+
+  clearYomitanParserRuntimeState({
+    getYomitanParserWindow: () => parserWindow as never,
+    setYomitanParserWindow: (window) => calls.push(`window:${window === null ? 'null' : 'set'}`),
+    setYomitanParserReadyPromise: (promise) =>
+      calls.push(`ready:${promise === null ? 'null' : 'set'}`),
+    setYomitanParserInitPromise: (promise) =>
+      calls.push(`init:${promise === null ? 'null' : 'set'}`),
+  });
+
+  assert.deepEqual(calls, ['window:null', 'ready:null', 'init:null']);
+});
diff --git a/src/core/services/yomitan-extension-runtime-state.ts b/src/core/services/yomitan-extension-runtime-state.ts
new file mode 100644
index 0000000..3106593
--- /dev/null
+++ b/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);
+}
diff --git a/src/main.ts b/src/main.ts
index 53024f2..f596490 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -374,12 +374,9 @@ import { createOverlayVisibilityRuntimeService } from './main/overlay-visibility
 import { createCharacterDictionaryRuntimeService } from './main/character-dictionary-runtime';
 import { createCharacterDictionaryAutoSyncRuntimeService } from './main/runtime/character-dictionary-auto-sync';
 import { notifyCharacterDictionaryAutoSyncStatus } from './main/runtime/character-dictionary-auto-sync-notifications';
-import {
-  getCharacterDictionaryDisabledReason,
-  isCharacterDictionaryRuntimeEnabled,
-} from './main/runtime/character-dictionary-availability';
 import { createCurrentMediaTokenizationGate } from './main/runtime/current-media-tokenization-gate';
 import { createStartupOsdSequencer } from './main/runtime/startup-osd-sequencer';
+import { createYomitanProfilePolicy } from './main/runtime/yomitan-profile-policy';
 import { formatSkippedYomitanWriteAction } from './main/runtime/yomitan-read-only-log';
 import {
   getPreferredYomitanAnkiServerUrl as getPreferredYomitanAnkiServerUrlRuntime,
@@ -1332,9 +1329,7 @@ const characterDictionaryAutoSyncRuntime = createCharacterDictionaryAutoSyncRunt
   getConfig: () => {
     const config = getResolvedConfig().anilist.characterDictionary;
     return {
-      enabled:
-        config.enabled &&
-        isCharacterDictionaryRuntimeEnabled(getConfiguredExternalYomitanProfilePath()),
+      enabled: config.enabled && yomitanProfilePolicy.isCharacterDictionaryEnabled(),
       maxLoaded: config.maxLoaded,
       profileScope: config.profileScope,
     };
@@ -1354,8 +1349,10 @@ const characterDictionaryAutoSyncRuntime = createCharacterDictionaryAutoSyncRunt
     });
   },
   importYomitanDictionary: async (zipPath) => {
-    if (isYomitanExternalReadOnlyMode()) {
-      logSkippedYomitanWrite(formatSkippedYomitanWriteAction('importYomitanDictionary', zipPath));
+    if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
+      yomitanProfilePolicy.logSkippedWrite(
+        formatSkippedYomitanWriteAction('importYomitanDictionary', zipPath),
+      );
       return false;
     }
     await ensureYomitanExtensionLoaded();
@@ -1365,8 +1362,8 @@ const characterDictionaryAutoSyncRuntime = createCharacterDictionaryAutoSyncRunt
     });
   },
   deleteYomitanDictionary: async (dictionaryTitle) => {
-    if (isYomitanExternalReadOnlyMode()) {
-      logSkippedYomitanWrite(
+    if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
+      yomitanProfilePolicy.logSkippedWrite(
         formatSkippedYomitanWriteAction('deleteYomitanDictionary', dictionaryTitle),
       );
       return false;
@@ -1378,8 +1375,8 @@ const characterDictionaryAutoSyncRuntime = createCharacterDictionaryAutoSyncRunt
     });
   },
   upsertYomitanDictionarySettings: async (dictionaryTitle, profileScope) => {
-    if (isYomitanExternalReadOnlyMode()) {
-      logSkippedYomitanWrite(
+    if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
+      yomitanProfilePolicy.logSkippedWrite(
         formatSkippedYomitanWriteAction('upsertYomitanDictionarySettings', dictionaryTitle),
       );
       return false;
@@ -2762,7 +2759,7 @@ const {
       );
     },
     scheduleCharacterDictionarySync: () => {
-      if (!isCharacterDictionaryEnabledForCurrentProcess()) {
+      if (!yomitanProfilePolicy.isCharacterDictionaryEnabled()) {
         return;
       }
       characterDictionaryAutoSyncRuntime.scheduleSync();
@@ -2844,7 +2841,7 @@ const {
         ),
       getCharacterDictionaryEnabled: () =>
         getResolvedConfig().anilist.characterDictionary.enabled &&
-        isCharacterDictionaryEnabledForCurrentProcess(),
+        yomitanProfilePolicy.isCharacterDictionaryEnabled(),
       getNameMatchEnabled: () => getResolvedConfig().subtitleStyle.nameMatchEnabled,
       getFrequencyDictionaryEnabled: () =>
         getRuntimeBooleanOption(
@@ -3018,7 +3015,7 @@ const enforceOverlayLayerOrder = createEnforceOverlayLayerOrderHandler(
 
 async function loadYomitanExtension(): Promise<Extension | null> {
   const extension = await yomitanExtensionRuntime.loadYomitanExtension();
-  if (extension && !isYomitanExternalReadOnlyMode()) {
+  if (extension && !yomitanProfilePolicy.isExternalReadOnlyMode()) {
     await syncYomitanDefaultProfileAnkiServer();
   }
   return extension;
@@ -3026,7 +3023,7 @@ async function loadYomitanExtension(): Promise<Extension | null> {
 
 async function ensureYomitanExtensionLoaded(): Promise<Extension | null> {
   const extension = await yomitanExtensionRuntime.ensureYomitanExtensionLoaded();
-  if (extension && !isYomitanExternalReadOnlyMode()) {
+  if (extension && !yomitanProfilePolicy.isExternalReadOnlyMode()) {
     await syncYomitanDefaultProfileAnkiServer();
   }
   return extension;
@@ -3038,28 +3035,6 @@ function getPreferredYomitanAnkiServerUrl(): string {
   return getPreferredYomitanAnkiServerUrlRuntime(getResolvedConfig().ankiConnect);
 }
 
-function getConfiguredExternalYomitanProfilePath(): string {
-  return configuredExternalYomitanProfilePath;
-}
-
-function isYomitanExternalReadOnlyMode(): boolean {
-  return getConfiguredExternalYomitanProfilePath().length > 0;
-}
-
-function isCharacterDictionaryEnabledForCurrentProcess(): boolean {
-  return isCharacterDictionaryRuntimeEnabled(getConfiguredExternalYomitanProfilePath());
-}
-
-function getCharacterDictionaryDisabledReasonForCurrentProcess(): string | null {
-  return getCharacterDictionaryDisabledReason(getConfiguredExternalYomitanProfilePath());
-}
-
-function logSkippedYomitanWrite(action: string): void {
-  logger.info(
-    `[yomitan] skipping ${action}: yomitan.externalProfilePath is configured; external profile mode is read-only`,
-  );
-}
-
 function getYomitanParserRuntimeDeps() {
   return {
     getYomitanExt: () => appState.yomitanExt,
@@ -3080,7 +3055,7 @@ function getYomitanParserRuntimeDeps() {
 }
 
 async function syncYomitanDefaultProfileAnkiServer(): Promise<void> {
-  if (isYomitanExternalReadOnlyMode()) {
+  if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
     return;
   }
 
@@ -3138,7 +3113,7 @@ function initializeOverlayRuntime(): void {
 }
 
 function openYomitanSettings(): boolean {
-  if (isYomitanExternalReadOnlyMode()) {
+  if (yomitanProfilePolicy.isExternalReadOnlyMode()) {
     const message =
       'Yomitan settings unavailable while using read-only external-profile mode.';
     logger.warn(
@@ -3557,7 +3532,7 @@ const createCliCommandContextHandler = createCliCommandContextFactory({
   getAnilistQueueStatus: () => anilistStateRuntime.getQueueStatusSnapshot(),
   processNextAnilistRetryUpdate: () => processNextAnilistRetryUpdate(),
   generateCharacterDictionary: async (targetPath?: string) => {
-    const disabledReason = getCharacterDictionaryDisabledReasonForCurrentProcess();
+    const disabledReason = yomitanProfilePolicy.getCharacterDictionaryDisabledReason();
     if (disabledReason) {
       throw new Error(disabledReason);
     }
@@ -3650,11 +3625,15 @@ const { ensureTray: ensureTrayHandler, destroyTray: destroyTrayHandler } =
     },
     buildMenuFromTemplate: (template) => Menu.buildFromTemplate(template),
   });
-const configuredExternalYomitanProfilePath = getResolvedConfig().yomitan.externalProfilePath.trim();
+const yomitanProfilePolicy = createYomitanProfilePolicy({
+  externalProfilePath: getResolvedConfig().yomitan.externalProfilePath,
+  logInfo: (message) => logger.info(message),
+});
+const configuredExternalYomitanProfilePath = yomitanProfilePolicy.externalProfilePath;
 const yomitanExtensionRuntime = createYomitanExtensionRuntime({
   loadYomitanExtensionCore,
   userDataPath: USER_DATA_PATH,
-  externalProfilePath: getConfiguredExternalYomitanProfilePath(),
+  externalProfilePath: configuredExternalYomitanProfilePath,
   getYomitanParserWindow: () => appState.yomitanParserWindow,
   setYomitanParserWindow: (window) => {
     appState.yomitanParserWindow = window as BrowserWindow | null;
diff --git a/src/main/runtime/yomitan-profile-policy.test.ts b/src/main/runtime/yomitan-profile-policy.test.ts
new file mode 100644
index 0000000..0d7be2c
--- /dev/null
+++ b/src/main/runtime/yomitan-profile-policy.test.ts
@@ -0,0 +1,36 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createYomitanProfilePolicy } from './yomitan-profile-policy';
+
+test('yomitan profile policy trims external profile path and marks read-only mode', () => {
+  const calls: string[] = [];
+  const policy = createYomitanProfilePolicy({
+    externalProfilePath: '  /tmp/gsm-profile  ',
+    logInfo: (message) => calls.push(message),
+  });
+
+  assert.equal(policy.externalProfilePath, '/tmp/gsm-profile');
+  assert.equal(policy.isExternalReadOnlyMode(), true);
+  assert.equal(policy.isCharacterDictionaryEnabled(), false);
+  assert.equal(
+    policy.getCharacterDictionaryDisabledReason(),
+    'Character dictionary is disabled while yomitan.externalProfilePath is configured.',
+  );
+
+  policy.logSkippedWrite('importYomitanDictionary(sample.zip)');
+  assert.deepEqual(calls, [
+    '[yomitan] skipping importYomitanDictionary(sample.zip): yomitan.externalProfilePath is configured; external profile mode is read-only',
+  ]);
+});
+
+test('yomitan profile policy keeps character dictionary enabled without external profile path', () => {
+  const policy = createYomitanProfilePolicy({
+    externalProfilePath: '   ',
+    logInfo: () => undefined,
+  });
+
+  assert.equal(policy.externalProfilePath, '');
+  assert.equal(policy.isExternalReadOnlyMode(), false);
+  assert.equal(policy.isCharacterDictionaryEnabled(), true);
+  assert.equal(policy.getCharacterDictionaryDisabledReason(), null);
+});
diff --git a/src/main/runtime/yomitan-profile-policy.ts b/src/main/runtime/yomitan-profile-policy.ts
new file mode 100644
index 0000000..7958bfd
--- /dev/null
+++ b/src/main/runtime/yomitan-profile-policy.ts
@@ -0,0 +1,25 @@
+import {
+  getCharacterDictionaryDisabledReason,
+  isCharacterDictionaryRuntimeEnabled,
+} from './character-dictionary-availability';
+
+export function createYomitanProfilePolicy(options: {
+  externalProfilePath: string;
+  logInfo: (message: string) => void;
+}) {
+  const externalProfilePath = options.externalProfilePath.trim();
+
+  return {
+    externalProfilePath,
+    isExternalReadOnlyMode: (): boolean => externalProfilePath.length > 0,
+    isCharacterDictionaryEnabled: (): boolean =>
+      isCharacterDictionaryRuntimeEnabled(externalProfilePath),
+    getCharacterDictionaryDisabledReason: (): string | null =>
+      getCharacterDictionaryDisabledReason(externalProfilePath),
+    logSkippedWrite: (action: string): void => {
+      options.logInfo(
+        `[yomitan] skipping ${action}: yomitan.externalProfilePath is configured; external profile mode is read-only`,
+      );
+    },
+  };
+}
diff --git a/src/main/runtime/yomitan-settings-opener.ts b/src/main/runtime/yomitan-settings-opener.ts
index 6c59fb2..2695320 100644
--- a/src/main/runtime/yomitan-settings-opener.ts
+++ b/src/main/runtime/yomitan-settings-opener.ts
@@ -24,11 +24,16 @@ export function createOpenYomitanSettingsHandler(deps: {
         deps.logWarn('Unable to open Yomitan settings: extension failed to load.');
         return;
       }
+      const yomitanSession = deps.getYomitanSession?.() ?? null;
+      if (!yomitanSession) {
+        deps.logWarn('Unable to open Yomitan settings: Yomitan session is unavailable.');
+        return;
+      }
       deps.openYomitanSettingsWindow({
         yomitanExt: extension,
         getExistingWindow: deps.getExistingWindow,
         setWindow: deps.setWindow,
-        yomitanSession: deps.getYomitanSession?.() ?? null,
+        yomitanSession,
       });
     })().catch((error) => {
       deps.logError('Failed to open Yomitan settings window.', error);
diff --git a/src/main/runtime/yomitan-settings-runtime.test.ts b/src/main/runtime/yomitan-settings-runtime.test.ts
index a14e950..db93ac6 100644
--- a/src/main/runtime/yomitan-settings-runtime.test.ts
+++ b/src/main/runtime/yomitan-settings-runtime.test.ts
@@ -31,3 +31,28 @@ test('yomitan settings runtime composes opener with built deps', async () => {
   assert.deepEqual(existingWindow, { id: 'settings' });
   assert.deepEqual(calls, ['open-window:session']);
 });
+
+test('yomitan settings runtime warns and does not open when no yomitan session is available', async () => {
+  let existingWindow: { id: string } | null = null;
+  const calls: string[] = [];
+
+  const runtime = createYomitanSettingsRuntime({
+    ensureYomitanExtensionLoaded: async () => ({ id: 'ext' }),
+    openYomitanSettingsWindow: () => {
+      calls.push('open-window');
+    },
+    getExistingWindow: () => existingWindow as never,
+    setWindow: (window) => {
+      existingWindow = window as { id: string } | null;
+    },
+    getYomitanSession: () => null,
+    logWarn: (message) => calls.push(`warn:${message}`),
+    logError: (message) => calls.push(`error:${message}`),
+  });
+
+  runtime.openYomitanSettings();
+  await new Promise((resolve) => setTimeout(resolve, 0));
+
+  assert.equal(existingWindow, null);
+  assert.deepEqual(calls, ['warn:Unable to open Yomitan settings: Yomitan session is unavailable.']);
+});