diff --git a/launcher/config-domain-parsers.test.ts b/launcher/config-domain-parsers.test.ts
index 03037775..7480a8f3 100644
--- a/launcher/config-domain-parsers.test.ts
+++ b/launcher/config-domain-parsers.test.ts
@@ -106,6 +106,16 @@ test('parseLauncherMpvConfig reads launch mode preference', () => {
   assert.equal(parsed.aniskipButtonKey, 'F8');
 });
 
+test('parseLauncherMpvConfig ignores blank subminer binary paths', () => {
+  const parsed = parseLauncherMpvConfig({
+    mpv: {
+      subminerBinaryPath: '   ',
+    },
+  });
+
+  assert.equal(parsed.subminerBinaryPath, undefined);
+});
+
 test('parseLauncherMpvConfig ignores invalid launch mode values', () => {
   const parsed = parseLauncherMpvConfig({
     mpv: {
diff --git a/launcher/config/mpv-config.ts b/launcher/config/mpv-config.ts
index a57dd2ab..3a8b5cb0 100644
--- a/launcher/config/mpv-config.ts
+++ b/launcher/config/mpv-config.ts
@@ -37,8 +37,7 @@ export function parseLauncherMpvConfig(root: Record<string, unknown>): LauncherM
       typeof mpv.autoStartSubMiner === 'boolean' ? mpv.autoStartSubMiner : undefined,
     pauseUntilOverlayReady:
       typeof mpv.pauseUntilOverlayReady === 'boolean' ? mpv.pauseUntilOverlayReady : undefined,
-    subminerBinaryPath:
-      typeof mpv.subminerBinaryPath === 'string' ? mpv.subminerBinaryPath.trim() : undefined,
+    subminerBinaryPath: parseNonEmptyString(mpv.subminerBinaryPath),
     aniskipEnabled: typeof mpv.aniskipEnabled === 'boolean' ? mpv.aniskipEnabled : undefined,
     aniskipButtonKey: parseNonEmptyString(mpv.aniskipButtonKey),
   };
diff --git a/launcher/mpv.test.ts b/launcher/mpv.test.ts
index c5da5507..61339175 100644
--- a/launcher/mpv.test.ts
+++ b/launcher/mpv.test.ts
@@ -697,6 +697,47 @@ test('startOverlay borrows an already-running background app instead of owning i
   }
 });
 
+test('startOverlay keeps lifecycle ownership for its already-managed app', async () => {
+  const { dir, socketPath } = createTempSocketPath();
+  const appPath = path.join(dir, 'fake-subminer.sh');
+  const appInvocationsPath = path.join(dir, 'app-invocations.log');
+  fs.writeFileSync(
+    appPath,
+    [
+      '#!/bin/sh',
+      `printf '%s\\n' "$@" >> ${JSON.stringify(appInvocationsPath)}`,
+      'if [ "$1" = "--app-ping" ]; then exit 0; fi',
+      'exit 0',
+      '',
+    ].join('\n'),
+  );
+  fs.chmodSync(appPath, 0o755);
+  fs.writeFileSync(socketPath, '');
+  const originalCreateConnection = net.createConnection;
+  try {
+    state.appPath = appPath;
+    state.overlayManagedByLauncher = true;
+    net.createConnection = (() => {
+      const socket = new EventEmitter() as net.Socket;
+      socket.destroy = (() => socket) as net.Socket['destroy'];
+      socket.setTimeout = (() => socket) as net.Socket['setTimeout'];
+      setTimeout(() => socket.emit('connect'), 10);
+      return socket;
+    }) as typeof net.createConnection;
+
+    await startOverlay(appPath, makeArgs(), socketPath);
+
+    assert.equal(state.overlayManagedByLauncher, true);
+    assert.equal(state.appPath, appPath);
+  } finally {
+    net.createConnection = originalCreateConnection;
+    state.overlayProc = null;
+    state.overlayManagedByLauncher = false;
+    state.appPath = '';
+    fs.rmSync(dir, { recursive: true, force: true });
+  }
+});
+
 test('cleanupPlaybackSession stops launcher-managed overlay app and mpv-owned children', async () => {
   const { dir } = createTempSocketPath();
   const appPath = path.join(dir, 'fake-subminer.sh');
diff --git a/launcher/mpv.ts b/launcher/mpv.ts
index 10280ccc..f8298bfc 100644
--- a/launcher/mpv.ts
+++ b/launcher/mpv.ts
@@ -1016,7 +1016,7 @@ export async function startOverlay(
     env: buildAppEnv(process.env, target.env),
   });
   attachAppProcessLogging(state.overlayProc);
-  if (appAlreadyRunning) {
+  if (appAlreadyRunning && !(state.overlayManagedByLauncher && state.appPath === appPath)) {
     log(
       'debug',
       args.logLevel,
diff --git a/src/config/config.test.ts b/src/config/config.test.ts
index d35e966f..7ef2ae34 100644
--- a/src/config/config.test.ts
+++ b/src/config/config.test.ts
@@ -2096,10 +2096,19 @@ test('migrates legacy ankiConnect n+1 color value to subtitleStyle', () => {
     subtitleStyle: { nPlusOneColor?: string; knownWordColor?: string };
   };
   assert.equal(parsed.subtitleStyle.nPlusOneColor, '#c6a0f6');
-  assert.equal(config.subtitleStyle.knownWordColor, '#a6da95');
   assert.equal(Object.hasOwn(parsed.ankiConnect.nPlusOne ?? {}, 'nPlusOne'), false);
 });
 
+test('legacy migration failures are logged and rethrown', () => {
+  const source = fs.readFileSync(path.join(process.cwd(), 'src/config/service.ts'), 'utf-8');
+  const catchBlock = source.match(/catch\s*\(error\)\s*\{(?<body>[\s\S]*?)\n    \}/)?.groups?.body;
+
+  assert.ok(catchBlock);
+  assert.match(catchBlock, /legacy config migration failed/);
+  assert.match(catchBlock, /console\.error/);
+  assert.match(catchBlock, /throw error;/);
+});
+
 test('migrates legacy ankiConnect nPlusOne known-word settings to knownWords', () => {
   const dir = makeTempDir();
   const configPath = path.join(dir, 'config.jsonc');
diff --git a/src/config/definitions/domain-registry.test.ts b/src/config/definitions/domain-registry.test.ts
index 7a2abd47..fbf0e947 100644
--- a/src/config/definitions/domain-registry.test.ts
+++ b/src/config/definitions/domain-registry.test.ts
@@ -132,7 +132,7 @@ test('n+1 annotation color has one public config path', () => {
   const leaves = collectConfigLeafPaths(DEFAULT_CONFIG);
 
   assert.ok(leaves.includes('subtitleStyle.nPlusOneColor'));
-  assert.ok(!leaves.includes('ankiConnect.nPlusOne.nPlusOne'));
+  assert.ok(!leaves.includes('ankiConnect.nPlusOne.color'));
 });
 
 test('every DEFAULT_CONFIG leaf is in CONFIG_OPTION_REGISTRY or UNDOCUMENTED_LEAVES', () => {
diff --git a/src/config/service.ts b/src/config/service.ts
index 2719d8ea..aa1ac28e 100644
--- a/src/config/service.ts
+++ b/src/config/service.ts
@@ -151,8 +151,9 @@ export class ConfigService {
       }
       fs.writeFileSync(configPath, content, 'utf-8');
       return rawConfig;
-    } catch {
-      return config;
+    } catch (error) {
+      console.error(`[ConfigService] legacy config migration failed for ${configPath}:`, error);
+      throw error;
     }
   }
 }
diff --git a/src/main.ts b/src/main.ts
index ecf6817c..3978fa2f 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -4251,6 +4251,7 @@ const {
         appState.currentSubText = '';
         appState.currentSubAssText = '';
         appState.currentSubtitleData = null;
+        broadcastToOverlayWindows('subtitle:set', { text: '', tokens: null });
       }
       autoplayReadyGate.invalidatePendingAutoplayReadyFallbacks();
       currentMediaTokenizationGate.updateCurrentMediaPath(path);
diff --git a/src/main/main-wiring.test.ts b/src/main/main-wiring.test.ts
index 03edb3a6..50812fbd 100644
--- a/src/main/main-wiring.test.ts
+++ b/src/main/main-wiring.test.ts
@@ -21,6 +21,23 @@ test('manual watched session action starts immersion tracker before marking watc
   );
 });
 
+test('media path changes clear rendered subtitle state', () => {
+  const source = readMainSource();
+  const actionBlock = source.match(
+    /updateCurrentMediaPath:\s*\(path\)\s*=>\s*\{(?<body>[\s\S]*?)autoplayReadyGate\.invalidatePendingAutoplayReadyFallbacks\(\);/,
+  )?.groups?.body;
+
+  assert.ok(actionBlock);
+  assert.match(actionBlock, /appState\.currentSubText = '';/);
+  assert.match(actionBlock, /appState\.currentSubAssText = '';/);
+  assert.match(actionBlock, /appState\.currentSubtitleData = null;/);
+  assert.match(actionBlock, /broadcastToOverlayWindows\('subtitle:set',/);
+  assert.ok(
+    actionBlock.indexOf('appState.currentSubtitleData = null;') <
+      actionBlock.indexOf("broadcastToOverlayWindows('subtitle:set'"),
+  );
+});
+
 test('main process uses one shared mpv plugin runtime config helper', () => {
   const source = readMainSource();
   assert.match(source, /function getMpvPluginRuntimeConfig\(\)/);
diff --git a/src/main/runtime/autoplay-subtitle-primer.test.ts b/src/main/runtime/autoplay-subtitle-primer.test.ts
index dcd706c1..0219c2b1 100644
--- a/src/main/runtime/autoplay-subtitle-primer.test.ts
+++ b/src/main/runtime/autoplay-subtitle-primer.test.ts
@@ -30,6 +30,13 @@ test('selectAutoplayStartupCue returns the next imminent cue before playback sta
   );
 });
 
+test('selectAutoplayStartupCue clamps negative current time to startup', () => {
+  assert.deepEqual(
+    selectAutoplayStartupCue([{ startTime: 0, endTime: 1, text: 'startup' }], -0.5, 0),
+    { startTime: 0, endTime: 1, text: 'startup' },
+  );
+});
+
 test('selectAutoplayStartupCue does not reveal far future subtitle text', () => {
   assert.equal(
     selectAutoplayStartupCue([{ startTime: 12, endTime: 15, text: 'later' }], 0, 2),
diff --git a/src/main/runtime/autoplay-subtitle-primer.ts b/src/main/runtime/autoplay-subtitle-primer.ts
index fbc93314..2f96256b 100644
--- a/src/main/runtime/autoplay-subtitle-primer.ts
+++ b/src/main/runtime/autoplay-subtitle-primer.ts
@@ -5,7 +5,7 @@ export function selectAutoplayStartupCue(
   currentTimeSeconds: number,
   lookaheadSeconds: number,
 ): SubtitleCue | null {
-  const currentTime = Number.isFinite(currentTimeSeconds) ? currentTimeSeconds : 0;
+  const currentTime = Math.max(0, Number.isFinite(currentTimeSeconds) ? currentTimeSeconds : 0);
   const lookahead = Math.max(0, Number.isFinite(lookaheadSeconds) ? lookaheadSeconds : 0);
   const latestStartTime = currentTime + lookahead;
 
diff --git a/src/renderer/modals/session-help-sections.ts b/src/renderer/modals/session-help-sections.ts
index b1c68e73..be9806ea 100644
--- a/src/renderer/modals/session-help-sections.ts
+++ b/src/renderer/modals/session-help-sections.ts
@@ -68,10 +68,13 @@ function normalizeKeyToken(token: string): string {
 }
 
 function formatKeybinding(rawBinding: string): string {
-  const parts = rawBinding.split('+');
+  const parts = rawBinding
+    .split('+')
+    .map((part) => part.trim())
+    .filter(Boolean);
   const key = parts.pop();
   if (!key) return rawBinding;
-  const normalized = [...parts, normalizeKeyToken(key)];
+  const normalized = [...parts.map(normalizeKeyToken), normalizeKeyToken(key)];
   return normalized.join(' + ');
 }
 
diff --git a/src/renderer/modals/session-help.test.ts b/src/renderer/modals/session-help.test.ts
index e9f9e632..ebad232f 100644
--- a/src/renderer/modals/session-help.test.ts
+++ b/src/renderer/modals/session-help.test.ts
@@ -33,6 +33,10 @@ test('session help formats bracket keybindings as physical keys', () => {
   assert.equal(formatSessionHelpKeybinding('Shift+BracketLeft'), 'Shift + [');
 });
 
+test('session help normalizes configured modifier aliases', () => {
+  assert.equal(formatSessionHelpKeybinding('CommandOrControl+KeyS'), 'Cmd/Ctrl + S');
+});
+
 test('session help imports browser-safe special command constants', () => {
   const source = fs.readFileSync(
     path.join(process.cwd(), 'src', 'renderer', 'modals', 'session-help-sections.ts'),
diff --git a/src/renderer/subtitle-render.test.ts b/src/renderer/subtitle-render.test.ts
index 5ce78dc8..98f0a638 100644
--- a/src/renderer/subtitle-render.test.ts
+++ b/src/renderer/subtitle-render.test.ts
@@ -45,6 +45,12 @@ class FakeStyleDeclaration {
   setProperty(name: string, value: string) {
     this.values.set(name, value);
   }
+
+  removeProperty(name: string) {
+    const previous = this.values.get(name) ?? '';
+    this.values.delete(name);
+    return previous;
+  }
 }
 
 class FakeElement {
@@ -475,6 +481,57 @@ test('applySubtitleStyle applies primary and secondary css declaration objects',
   }
 });
 
+test('applySubtitleStyle removes css declarations missing from later updates', () => {
+  const restoreDocument = installFakeDocument();
+  try {
+    const subtitleRoot = new FakeElement('div');
+    const subtitleContainer = new FakeElement('div');
+    const secondarySubRoot = new FakeElement('div');
+    const secondarySubContainer = new FakeElement('div');
+    const ctx = {
+      state: createRendererState(),
+      dom: {
+        subtitleRoot,
+        subtitleContainer,
+        secondarySubRoot,
+        secondarySubContainer,
+      },
+    } as never;
+
+    const renderer = createSubtitleRenderer(ctx);
+    renderer.applySubtitleStyle({
+      css: {
+        'font-size': '42px',
+        'text-wrap': 'balance',
+      },
+      secondary: {
+        css: {
+          'text-transform': 'uppercase',
+        },
+      },
+    } as never);
+    renderer.applySubtitleStyle({
+      css: {
+        'font-size': '44px',
+      },
+      secondary: {
+        css: {},
+      },
+    } as never);
+
+    const primaryValues = (subtitleRoot.style as unknown as { values?: Map<string, string> })
+      .values;
+    const secondaryValues = (secondarySubRoot.style as unknown as { values?: Map<string, string> })
+      .values;
+
+    assert.equal(primaryValues?.get('font-size'), '44px');
+    assert.equal(primaryValues?.has('text-wrap'), false);
+    assert.equal(secondaryValues?.has('text-transform'), false);
+  } finally {
+    restoreDocument();
+  }
+});
+
 test('annotated subtitle tokens inherit configured base subtitle typography', () => {
   const restoreDocument = installFakeDocument();
   try {
diff --git a/src/renderer/subtitle-render.ts b/src/renderer/subtitle-render.ts
index e7dbf2aa..0138c842 100644
--- a/src/renderer/subtitle-render.ts
+++ b/src/renderer/subtitle-render.ts
@@ -158,6 +158,49 @@ function applyInlineStyleDeclarations(
   }
 }
 
+const appliedCssKeys = new WeakMap<HTMLElement, Set<string>>();
+
+function inlineStyleDeclarationKeys(
+  declarations: Record<string, unknown>,
+  excludedKeys: ReadonlySet<string>,
+): Set<string> {
+  const keys = new Set<string>();
+  for (const [key, value] of Object.entries(declarations)) {
+    if (excludedKeys.has(key)) continue;
+    if (value === null || value === undefined || typeof value === 'object') continue;
+    keys.add(key);
+  }
+  return keys;
+}
+
+function clearInlineStyleDeclaration(target: HTMLElement, key: string): void {
+  if (key.includes('-')) {
+    target.style.removeProperty(key);
+    if (key === '--webkit-text-stroke') {
+      target.style.removeProperty('-webkit-text-stroke');
+    }
+    return;
+  }
+
+  (target.style as unknown as Record<string, string>)[key] = '';
+}
+
+function replaceInlineStyleDeclarations(
+  target: HTMLElement,
+  declarations: Record<string, unknown>,
+  excludedKeys: ReadonlySet<string> = new Set<string>(),
+): void {
+  const nextKeys = inlineStyleDeclarationKeys(declarations, excludedKeys);
+  const previousKeys = appliedCssKeys.get(target) ?? new Set<string>();
+  for (const key of previousKeys) {
+    if (!nextKeys.has(key)) {
+      clearInlineStyleDeclaration(target, key);
+    }
+  }
+  applyInlineStyleDeclarations(target, declarations, excludedKeys);
+  appliedCssKeys.set(target, nextKeys);
+}
+
 function normalizeCssDeclarationObject(value: unknown): Record<string, string> {
   if (!value || typeof value !== 'object' || Array.isArray(value)) {
     return {};
@@ -177,8 +220,8 @@ function applySubtitleCssDeclarations(
   container: HTMLElement,
   declarations: Record<string, string>,
 ): void {
-  applyInlineStyleDeclarations(root, declarations, CONTAINER_STYLE_KEYS);
-  applyInlineStyleDeclarations(
+  replaceInlineStyleDeclarations(root, declarations, CONTAINER_STYLE_KEYS);
+  replaceInlineStyleDeclarations(
     container,
     pickInlineStyleDeclarations(declarations, CONTAINER_STYLE_KEYS),
   );