diff --git a/static/player/episodes/nav.ts b/static/player/episodes/nav.ts
index 1c5d7a3a..08de9835 100644
--- a/static/player/episodes/nav.ts
+++ b/static/player/episodes/nav.ts
@@ -1,153 +1,472 @@
-import type { SkipSegment } from "../types";
-
 import { hydrateAlternateMode, updateModeButtons } from "../mode";
 import { markEpisodeTransition } from "../progress";
 import { updateQualityOptions } from "../quality";
 import { resolveActiveSegments, renderSegments } from "../skip/segments";
+import { streamUrlForMode } from "../source";
 import { state, showEndState, hideEndState } from "../state";
 import { safeLocalStorage } from "../storage";
 import { updateSubtitleOptions } from "../subtitles";
+import { isRecord, parseModeSources, parseSegments } from "../validate";
 import { loadVideoSource } from "../video";
 import { completeAnime } from "./complete";
-import { updateOverlay, isAutoplayEnabled, switchEpisodeRange } from "./ui";
+import {
+  isAutoplayEnabled,
+  switchEpisodeRange,
+  updateEpisodeHighlight,
+  updateEpisodeNavigation,
+  updateOverlay,
+} from "./ui";
 
-/**
- * Handles video end: either marks complete or loads next episode. Fetches episode data from API,
- * updates player state and URL.
- */
-export const goToNextEpisode = async (): Promise<void> => {
-  const currentEp = Number.parseInt(state.episode.current, 10);
-  if (!currentEp) {
+type EpisodePayload = {
+  episodeTitle: string;
+  initialMode: string;
+  modeSources: ReturnType<typeof parseModeSources>;
+  modeSwitchedFrom: string;
+  segments: ReturnType<typeof parseSegments>;
+  startTimeSeconds: number;
+};
+
+type TransitionHistory = "none" | "push" | "replace";
+
+type TransitionOptions = {
+  autoplay?: boolean;
+  fallbackHref?: string;
+  history?: TransitionHistory;
+  restoreFocus?: boolean;
+};
+
+type ActiveTransition = {
+  autoplay: boolean;
+  controller: AbortController;
+  fallbackHref: string;
+  id: number;
+  startedAt: number;
+};
+
+type EpisodeTransitionProfile = {
+  aborted: number;
+  fallback: number;
+  lastMediaReadyMs: number;
+  lastPayloadMs: number;
+  lastTotalMs: number;
+  stale: number;
+  succeeded: number;
+};
+
+declare global {
+  interface Window {
+    __malEpisodeTransitionProfile?: EpisodeTransitionProfile;
+  }
+}
+
+const profile = (): EpisodeTransitionProfile => {
+  window.__malEpisodeTransitionProfile ??= {
+    aborted: 0,
+    fallback: 0,
+    lastMediaReadyMs: 0,
+    lastPayloadMs: 0,
+    lastTotalMs: 0,
+    stale: 0,
+    succeeded: 0,
+  };
+  return window.__malEpisodeTransitionProfile;
+};
+
+const measure = (name: string, startedAt: number, duration: number): void => {
+  try {
+    performance.measure(name, { start: startedAt, duration });
+  } catch (error) {
+    console.debug("failed to measure episode transition:", error);
+  }
+};
+
+let activeTransition: ActiveTransition | null = null;
+let modeHydrationController: AbortController | null = null;
+let transitionID = 0;
+
+const episodeHref = (episode: number): string => {
+  const url = new URL(window.location.href);
+  url.searchParams.set("ep", String(episode));
+  return url.toString();
+};
+
+const fallbackToEpisodeNavigation = (href: string, autoplay: boolean): void => {
+  profile().fallback += 1;
+  if (autoplay) {
+    sessionStorage.setItem("mal:autoplay-next", "true");
+  }
+  window.location.href = href;
+};
+
+const parseEpisodePayload = (value: unknown): EpisodePayload | null => {
+  if (!isRecord(value)) {
+    return null;
+  }
+  const modeSources = parseModeSources(value.mode_sources);
+  if (Object.keys(modeSources).length === 0) {
+    return null;
+  }
+  const parsedStartTime = Number(value.start_time_seconds);
+  return {
+    episodeTitle: typeof value.episode_title === "string" ? value.episode_title : "",
+    initialMode: typeof value.initial_mode === "string" ? value.initial_mode : "",
+    modeSources,
+    modeSwitchedFrom: typeof value.mode_switched_from === "string" ? value.mode_switched_from : "",
+    segments: parseSegments(value.segments),
+    startTimeSeconds: Number.isFinite(parsedStartTime) && parsedStartTime > 0 ? parsedStartTime : 0,
+  };
+};
+
+const selectedMode = (payload: EpisodePayload, requestedMode: string): string | null => {
+  if (payload.modeSources[requestedMode]?.token) {
+    return requestedMode;
+  }
+  if (payload.modeSources[payload.initialMode]?.token) {
+    return payload.initialMode;
+  }
+  return Object.keys(payload.modeSources).find((mode) => payload.modeSources[mode]?.token) ?? null;
+};
+
+const updateHistory = (episode: number, mode: TransitionHistory): void => {
+  if (mode === "none") {
     return;
   }
+  const href = episodeHref(episode);
+  if (mode === "replace") {
+    history.replaceState(null, "", href);
+    return;
+  }
+  history.pushState(null, "", href);
+};
 
-  const navigateToEpisode = (episode: number): void => {
-    const url = new URL(window.location.href);
-    url.searchParams.set("ep", String(episode));
-    window.location.href = url.toString();
+const showLoader = (): void => {
+  const loading = state.elements.container.querySelector("[data-loading]") as HTMLElement | null;
+  if (loading) {
+    loading.style.display = "flex";
+  }
+};
+
+const finishTransition = (transition: ActiveTransition): void => {
+  if (activeTransition?.id !== transition.id) {
+    return;
+  }
+  const elapsed = performance.now() - transition.startedAt;
+  const metrics = profile();
+  metrics.lastMediaReadyMs = elapsed;
+  metrics.lastTotalMs = elapsed;
+  metrics.succeeded += 1;
+  measure("episode_transition_media_ready_ms", transition.startedAt, elapsed);
+  measure("episode_transition_total_ms", transition.startedAt, elapsed);
+  state.episode.transitionEpisode = null;
+  activeTransition = null;
+  transition.controller.abort();
+};
+
+const monitorMediaReady = (transition: ActiveTransition): void => {
+  const { signal } = transition.controller;
+  let retried = false;
+
+  const onLoadedMetadata = (): void => {
+    finishTransition(transition);
+  };
+  const onError = (): void => {
+    if (signal.aborted || activeTransition?.id !== transition.id) {
+      return;
+    }
+    if (retried) {
+      fallbackToEpisodeNavigation(transition.fallbackHref, transition.autoplay);
+      return;
+    }
+    retried = true;
+    fetch(
+      `/api/watch/episode/${state.episode.malID}/${encodeURIComponent(state.episode.current)}?mode=${encodeURIComponent(state.playback.currentMode)}`,
+      { signal },
+    )
+      .then((response) => {
+        if (!response.ok) {
+          throw new Error(`episode source refresh failed with status ${response.status}`);
+        }
+        return response.json();
+      })
+      .then((value: unknown) => {
+        if (signal.aborted || activeTransition?.id !== transition.id) {
+          return;
+        }
+        const payload = parseEpisodePayload(value);
+        const mode = payload ? selectedMode(payload, state.playback.currentMode) : null;
+        if (!payload || !mode) {
+          throw new Error("episode source refresh returned no playable source");
+        }
+        state.playback.modeSources = payload.modeSources;
+        state.playback.currentMode = mode;
+        const source = payload.modeSources[mode];
+        const preferredQuality = safeLocalStorage.getItem("mal:preferred-quality") || "best";
+        loadVideoSource(
+          streamUrlForMode(mode, preferredQuality),
+          source.type,
+          payload.startTimeSeconds,
+          false,
+        );
+      })
+      .catch((error: unknown) => {
+        if (error instanceof DOMException && error.name === "AbortError") {
+          return;
+        }
+        console.error("failed to refresh episode source:", error);
+        fallbackToEpisodeNavigation(transition.fallbackHref, transition.autoplay);
+      });
   };
 
-  const fallbackToEpisodeNavigation = (episode: number): void => {
-    sessionStorage.setItem("mal:autoplay-next", "true");
-    navigateToEpisode(episode);
-  };
+  state.elements.video.addEventListener("loadedmetadata", onLoadedMetadata, { signal });
+  state.elements.video.addEventListener("error", onError, { signal });
+};
 
-  // final episode: trigger completion flow or just stop if airing
-  if (state.episode.total > 0 && currentEp >= state.episode.total) {
+const hydrateEpisodeModes = (): void => {
+  modeHydrationController?.abort();
+  const controller = new AbortController();
+  modeHydrationController = controller;
+  hydrateAlternateMode(controller.signal)
+    .catch((error: unknown) => {
+      if (error instanceof DOMException && error.name === "AbortError") {
+        return;
+      }
+      console.error("failed to hydrate alternate mode after episode change:", error);
+    })
+    .finally(() => {
+      if (modeHydrationController === controller) {
+        modeHydrationController = null;
+      }
+    });
+};
+
+const commitEpisode = (
+  episode: number,
+  payload: EpisodePayload,
+  mode: string,
+  transition: ActiveTransition,
+  options: TransitionOptions,
+): void => {
+  state.playback.modeSources = payload.modeSources;
+  state.playback.currentMode = mode;
+  state.playback.modeSwitchedFrom = payload.modeSwitchedFrom;
+  state.playback.startTimeSeconds = payload.startTimeSeconds;
+  state.playback.pendingSeekTime = null;
+  state.episode.current = String(episode);
+  state.episode.endedProgressSaved = false;
+  state.episode.completionSent = false;
+  state.episode.completionAttempts = 0;
+  state.subtitles.activeCues = [];
+  state.skip.parsedSegments = payload.segments;
+
+  state.elements.container.dataset.currentEpisode = state.episode.current;
+  state.elements.container.dataset.startTimeSeconds = String(payload.startTimeSeconds);
+  hideEndState();
+
+  const preferredQuality = safeLocalStorage.getItem("mal:preferred-quality") || "best";
+  const source = payload.modeSources[mode];
+  monitorMediaReady(transition);
+  loadVideoSource(
+    streamUrlForMode(mode, preferredQuality),
+    source.type,
+    payload.startTimeSeconds,
+    false,
+  );
+
+  updateSubtitleOptions();
+  updateQualityOptions();
+  updateModeButtons();
+  updateOverlay(state.episode.current, payload.episodeTitle);
+  resolveActiveSegments();
+  renderSegments();
+  switchEpisodeRange(Math.floor((episode - 1) / 100));
+  updateEpisodeHighlight(episode, options.restoreFocus ?? false);
+  updateEpisodeNavigation(episode);
+  updateHistory(episode, options.history ?? "push");
+
+  if (payload.modeSwitchedFrom === "dub" && mode === "sub") {
+    window.showToast?.({
+      message: `Episode ${episode} is only available in sub, switched from dub.`,
+    });
+  }
+  hydrateEpisodeModes();
+};
+
+export const transitionToEpisode = async (
+  episode: number,
+  options: TransitionOptions = {},
+): Promise<boolean> => {
+  if (
+    !Number.isInteger(episode) ||
+    episode < 1 ||
+    (state.episode.total > 0 && episode > state.episode.total) ||
+    episode === Number.parseInt(state.episode.current, 10) ||
+    episode === state.episode.transitionEpisode
+  ) {
+    return false;
+  }
+
+  if (activeTransition) {
+    activeTransition.controller.abort();
+    profile().aborted += 1;
+  }
+  modeHydrationController?.abort();
+  modeHydrationController = null;
+  const transition: ActiveTransition = {
+    autoplay: options.autoplay ?? false,
+    controller: new AbortController(),
+    fallbackHref: options.fallbackHref ?? episodeHref(episode),
+    id: ++transitionID,
+    startedAt: performance.now(),
+  };
+  activeTransition = transition;
+  markEpisodeTransition(episode);
+  showLoader();
+
+  try {
+    const requestedMode = state.playback.currentMode;
+    const response = await fetch(
+      `/api/watch/episode/${state.episode.malID}/${episode}?mode=${encodeURIComponent(requestedMode)}`,
+      { signal: transition.controller.signal },
+    );
+    if (!response.ok) {
+      throw new Error(`episode transition failed with status ${response.status}`);
+    }
+    const payload = parseEpisodePayload(await response.json());
+    if (!payload) {
+      throw new Error("episode transition returned no playable source");
+    }
+    if (activeTransition?.id !== transition.id) {
+      profile().stale += 1;
+      return false;
+    }
+    const mode = selectedMode(payload, requestedMode);
+    if (!mode) {
+      throw new Error("episode transition returned no playable mode");
+    }
+    const payloadElapsed = performance.now() - transition.startedAt;
+    profile().lastPayloadMs = payloadElapsed;
+    measure("episode_transition_payload_ms", transition.startedAt, payloadElapsed);
+    commitEpisode(episode, payload, mode, transition, options);
+    return true;
+  } catch (error: unknown) {
+    if (error instanceof DOMException && error.name === "AbortError") {
+      return false;
+    }
+    if (activeTransition?.id !== transition.id) {
+      profile().stale += 1;
+      return false;
+    }
+    console.error("failed to transition episode:", error);
+    fallbackToEpisodeNavigation(transition.fallbackHref, options.autoplay ?? false);
+    return false;
+  }
+};
+
+const episodeFromLink = (anchor: HTMLAnchorElement): { episode: number; href: string } | null => {
+  if (anchor.target && anchor.target !== "_self") {
+    return null;
+  }
+  const url = new URL(anchor.href, window.location.href);
+  const parts = url.pathname.split("/").filter(Boolean);
+  const episode = Number.parseInt(anchor.dataset.episodeId ?? url.searchParams.get("ep") ?? "", 10);
+  if (
+    url.origin !== window.location.origin ||
+    parts[0] !== "anime" ||
+    parts[2] !== "watch" ||
+    Number.parseInt(parts[1] ?? "", 10) !== state.episode.malID ||
+    !Number.isInteger(episode) ||
+    episode < 1
+  ) {
+    return null;
+  }
+  return { episode, href: url.toString() };
+};
+
+export const handleEpisodeNavigationClick = (event: MouseEvent): boolean => {
+  if (event.button !== 0 || event.metaKey || event.ctrlKey || event.shiftKey || event.altKey) {
+    return false;
+  }
+  const target = event.target;
+  if (!(target instanceof Element)) {
+    return false;
+  }
+  const anchor = target.closest("a[data-episode-id]");
+  if (!(anchor instanceof HTMLAnchorElement)) {
+    return false;
+  }
+  const destination = episodeFromLink(anchor);
+  if (!destination || destination.episode === Number.parseInt(state.episode.current, 10)) {
+    return false;
+  }
+  event.preventDefault();
+  void transitionToEpisode(destination.episode, {
+    fallbackHref: destination.href,
+    history: "push",
+    restoreFocus: true,
+  });
+  return true;
+};
+
+export const setupEpisodeNavigation = (signal: AbortSignal): void => {
+  const root = document.querySelector("[data-episode-navigation]");
+  root?.addEventListener(
+    "click",
+    (event) => {
+      if (event instanceof MouseEvent) {
+        handleEpisodeNavigationClick(event);
+      }
+    },
+    { signal },
+  );
+
+  window.addEventListener(
+    "popstate",
+    () => {
+      const url = new URL(window.location.href);
+      const episode = Number.parseInt(url.searchParams.get("ep") ?? "1", 10);
+      if (!episode || episode === Number.parseInt(state.episode.current, 10)) {
+        return;
+      }
+      void transitionToEpisode(episode, { fallbackHref: url.toString(), history: "none" });
+    },
+    { signal },
+  );
+
+  signal.addEventListener(
+    "abort",
+    () => {
+      activeTransition?.controller.abort();
+      activeTransition = null;
+      modeHydrationController?.abort();
+      modeHydrationController = null;
+    },
+    { once: true },
+  );
+};
+
+/** Handles video end: completes the series or advances when autoplay is enabled. */
+export const goToNextEpisode = async (): Promise<void> => {
+  const currentEpisode = Number.parseInt(state.episode.current, 10);
+  if (!currentEpisode) {
+    return;
+  }
+  if (state.episode.total > 0 && currentEpisode >= state.episode.total) {
     if (!state.episode.isAiring) {
-      completeAnime(currentEp).catch((error) => {
+      completeAnime(currentEpisode).catch((error: unknown) => {
         console.error("failed to complete final episode:", error);
       });
     }
     showEndState();
     return;
   }
-
-  // skip if autoplay disabled
   if (!isAutoplayEnabled()) {
     showEndState();
     return;
   }
-
-  const nextEp = currentEp + 1;
-  markEpisodeTransition(nextEp);
-
-  try {
-    const res = await fetch(
-      `/api/watch/episode/${state.episode.malID}/${nextEp}?mode=${encodeURIComponent(state.playback.currentMode)}`,
-    );
-    if (!res.ok) {
-      // fallback: full page navigation
-      fallbackToEpisodeNavigation(nextEp);
-      return;
-    }
-
-    const data = await res.json();
-
-    // update state with new episode data
-    state.playback.modeSources = data.mode_sources ?? {};
-
-    const backendMode = typeof data.initial_mode === "string" ? data.initial_mode : "";
-    const fallback = state.playback.modeSources[backendMode]?.token
-      ? backendMode
-      : state.playback.availableModes.find((m) => state.playback.modeSources[m]?.token);
-    if (!fallback) {
-      fallbackToEpisodeNavigation(nextEp);
-      return;
-    }
-
-    state.episode.current = String(nextEp);
-    state.playback.currentMode = fallback;
-    state.episode.endedProgressSaved = false;
-
-    hideEndState();
-
-    if (data.mode_switched_from === "dub" && fallback === "sub") {
-      window.showToast?.({
-        message: `Episode ${nextEp} is only available in sub, switched from dub.`,
-      });
-    }
-    // The progress reset is sent asynchronously, so do not trust the fetch to observe it first.
-    state.playback.startTimeSeconds = 0;
-    state.elements.container.dataset.currentEpisode = state.episode.current;
-    state.elements.container.dataset.startTimeSeconds = String(state.playback.startTimeSeconds);
-
-    // load new video (keep preferences)
-    const preferredQuality = safeLocalStorage.getItem("mal:preferred-quality") || "best";
-    const source = state.playback.modeSources[fallback];
-    const nextSourceURL = `${state.playback.streamURL}?mode=${encodeURIComponent(fallback)}&token=${encodeURIComponent(source.token)}${source.type === "m3u8" ? "&hls=1" : ""}${preferredQuality !== "best" ? `&quality=${encodeURIComponent(preferredQuality)}` : ""}`;
-    loadVideoSource(nextSourceURL, source.type);
-    if (!state.elements.video.paused) {
-      state.elements.video.play().catch((error) => {
-        console.debug("failed to play video:", error);
-      });
-    }
-
-    state.playback.pendingSeekTime = null;
-    state.episode.completionSent = false;
-    state.episode.completionAttempts = 0;
-    state.subtitles.activeCues = [];
-
-    // update UI
-    updateSubtitleOptions();
-    updateQualityOptions();
-    updateModeButtons();
-    updateOverlay(state.episode.current, data.episode_title ?? "");
-    hydrateAlternateMode().catch((error) => {
-      console.error("failed to hydrate alternate mode after episode change:", error);
-    });
-
-    // update skip segments
-    if (data.segments?.length) {
-      state.skip.parsedSegments = data.segments
-        .map((s: SkipSegment) => ({ ...s, start: Number(s.start) || 0, end: Number(s.end) || 0 }))
-        .filter((s: SkipSegment) => s.end > s.start);
-      resolveActiveSegments();
-      renderSegments();
-    }
-
-    // highlight new episode in list/grid
-    state.elements.episodeList?.querySelectorAll("[data-episode-id]").forEach((el) => {
-      el.classList.remove("bg-accent/20");
-    });
-    const newListEl = state.elements.episodeList?.querySelector(`[data-episode-id="${nextEp}"]`);
-    newListEl?.classList.add("bg-accent/20");
-
-    if (state.elements.episodeGrid) {
-      state.elements.episodeGrid.querySelectorAll("[data-episode-id]").forEach((el) => {
-        el.classList.remove("bg-accent/20", "ring-2", "ring-accent", "text-accent");
-      });
-      switchEpisodeRange(Math.floor((nextEp - 1) / 100));
-      const newGridEl = state.elements.episodeGrid.querySelector(`[data-episode-id="${nextEp}"]`);
-      newGridEl?.classList.add("bg-accent/20", "ring-2", "ring-accent", "text-accent");
-    }
-
-    // update URL without reload
-    const url = new URL(window.location.href);
-    url.searchParams.set("ep", String(nextEp));
-    history.pushState(null, "", url.toString());
-  } catch (error) {
-    console.error("failed to update url:", error);
-    fallbackToEpisodeNavigation(nextEp);
-  }
+  const nextEpisode = currentEpisode + 1;
+  await transitionToEpisode(nextEpisode, {
+    autoplay: true,
+    fallbackHref: episodeHref(nextEpisode),
+    history: "push",
+  });
 };