diff --git a/apps/mobile/src/components/MediaVideoPlayer.tsx b/apps/mobile/src/components/MediaVideoPlayer.tsx
index bc5bd51888d9..09bb94bfb5de 100644
--- a/apps/mobile/src/components/MediaVideoPlayer.tsx
+++ b/apps/mobile/src/components/MediaVideoPlayer.tsx
@@ -115,6 +115,7 @@ interface MediaVideoPlayerProps {
   readonly thumbnailKey: string;
   readonly thumbnailVisible?: boolean;
   readonly unavailable?: boolean;
+  readonly unavailableDetail?: string;
   readonly expanded?: boolean;
   readonly autoPlay?: boolean;
   readonly paused?: boolean;
@@ -126,6 +127,9 @@ function MediaVideoPlayerContent(props: MediaVideoPlayerProps) {
   const [playbackUri, setPlaybackUri] = useState<string | null>(props.expanded ? props.uri : null);
   // Keep an opened player mounted while signing or reconnecting temporarily has no usable URL.
   if (playbackUri === null && props.expanded && props.uri !== null) setPlaybackUri(props.uri);
+  const unavailableText = props.unavailableDetail
+    ? `Video unavailable. ${props.unavailableDetail}`
+    : "Video unavailable";
 
   return (
     <View
@@ -144,7 +148,9 @@ function MediaVideoPlayerContent(props: MediaVideoPlayerProps) {
         <MediaActionsMenu media={mediaActions} inModal={props.expanded} style={{ flex: 1 }}>
           <Pressable
             accessibilityRole="button"
-            accessibilityLabel={`Play ${props.name}`}
+            accessibilityLabel={
+              props.unavailable ? `${props.name}. ${unavailableText}` : `Play ${props.name}`
+            }
             accessibilityHint={
               mediaActions.actions.length > 0 ? "Touch and hold for media actions" : undefined
             }
@@ -163,7 +169,7 @@ function MediaVideoPlayerContent(props: MediaVideoPlayerProps) {
               />
             ) : null}
             {props.unavailable ? (
-              <AppText className="text-sm text-white/80">Video unavailable</AppText>
+              <AppText className="text-center text-sm text-white/80">{unavailableText}</AppText>
             ) : props.uri === null ? (
               <AppActivityIndicator color="#ffffff" accessibilityLabel="Loading video" />
             ) : (
diff --git a/apps/mobile/src/features/threads/ThreadMarkdownVideo.tsx b/apps/mobile/src/features/threads/ThreadMarkdownVideo.tsx
index e01f6ae3b2aa..7e03a69dbeb5 100644
--- a/apps/mobile/src/features/threads/ThreadMarkdownVideo.tsx
+++ b/apps/mobile/src/features/threads/ThreadMarkdownVideo.tsx
@@ -1,3 +1,4 @@
+import { MISSING_FILE_ACCESS_MESSAGE } from "@t3tools/client-runtime/state/assets";
 import { createContext, useContext } from "react";
 import { MediaVideoPlayer } from "../../components/MediaVideoPlayer";
 import { useAssetUrlState, useRefreshAssetUrl } from "../../state/assets";
@@ -39,6 +40,11 @@ export function ThreadMarkdownVideo(props: {
       thumbnailKey={thumbnailKey}
       thumbnailVisible={visible}
       unavailable={"resource" in source && asset._tag === "Failure"}
+      unavailableDetail={
+        "resource" in source && asset._tag === "Failure" && asset.reason === "missing-file-access"
+          ? MISSING_FILE_ACCESS_MESSAGE
+          : undefined
+      }
       actionsSource={source.actionsSource}
     />
   );
diff --git a/apps/web/src/components/ChatMarkdown.assets.browser.test.tsx b/apps/web/src/components/ChatMarkdown.assets.browser.test.tsx
index 6e6d5fc368f4..daf0d97aab9a 100644
--- a/apps/web/src/components/ChatMarkdown.assets.browser.test.tsx
+++ b/apps/web/src/components/ChatMarkdown.assets.browser.test.tsx
@@ -1,3 +1,4 @@
+import { MISSING_FILE_ACCESS_MESSAGE } from "@t3tools/client-runtime/state/assets";
 import { EnvironmentId, ThreadId } from "@t3tools/contracts";
 import { AsyncResult } from "effect/reactivity";
 import { act } from "react";
@@ -5,6 +6,7 @@ import { createRoot, type Root } from "react-dom/client";
 import { afterEach, beforeEach, expect, it, vi } from "vite-plus/test";
 
 const mint = vi.hoisted(() => vi.fn());
+const deniedEnvironmentId = vi.hoisted(() => "denied-environment");
 // Atoms derived from the server config run in the real registry over a missing config.
 vi.mock(import("../state/server"), async (original) => {
   const actual = await original();
@@ -25,6 +27,16 @@ vi.mock(import("../state/session"), async (original) => ({
   useEnvironmentScope: () => false,
   readPreparedConnection: (() => ({ httpBaseUrl: "https://host.test" })) as never,
 }));
+vi.mock(import("../state/filesystem"), async (original) => {
+  const actual = await original();
+  return {
+    ...actual,
+    useFilesystemReadAccess: ((environmentId: EnvironmentId | null) =>
+      environmentId === deniedEnvironmentId
+        ? { canReadFiles: false, isPending: false, error: null }
+        : actual.useFilesystemReadAccess(environmentId)) as never,
+  };
+});
 
 import ChatMarkdown from "./ChatMarkdown";
 
@@ -68,3 +80,23 @@ it("opens host media through server authorization before the client grant loads"
     ),
   );
 });
+
+it("explains a host video the connection cannot read instead of offering a retry", async () => {
+  const container = document.body.appendChild(document.createElement("div"));
+  const root = createRoot(container);
+  roots.push(root);
+  await act(async () =>
+    root.render(
+      <ChatMarkdown
+        cwd="/repo"
+        threadRef={{
+          environmentId: EnvironmentId.make(deniedEnvironmentId),
+          threadId: ThreadId.make("media-thread"),
+        }}
+        text="![Demo](/tmp/demo.mp4)"
+      />,
+    ),
+  );
+  await vi.waitFor(() => expect(container.textContent).toContain(MISSING_FILE_ACCESS_MESSAGE));
+  expect(container.textContent).not.toContain("Retry video");
+});
diff --git a/apps/web/src/components/ChatMarkdown.tsx b/apps/web/src/components/ChatMarkdown.tsx
index a608ecb0298b..abee35edfbb2 100644
--- a/apps/web/src/components/ChatMarkdown.tsx
+++ b/apps/web/src/components/ChatMarkdown.tsx
@@ -1517,6 +1517,7 @@ function ChatMarkdownVideo(props: {
   readonly copyMarkdown: string | undefined;
   readonly originalUrl?: string | undefined;
   readonly sourceFailed?: boolean | undefined;
+  readonly unavailableDetail?: string | undefined;
   readonly style?: CSSProperties | undefined;
   readonly mediaIdentity?: string | undefined;
   readonly actionsSource?: MediaActionSource | undefined;
@@ -1527,6 +1528,7 @@ function ChatMarkdownVideo(props: {
       key={props.mediaIdentity ?? props.copyMarkdown ?? props.src}
       src={props.src}
       sourceFailed={props.sourceFailed}
+      unavailableDetail={props.unavailableDetail}
       label={props.alt}
       originalUrl={props.originalUrl}
       style={props.style}
@@ -1592,6 +1594,10 @@ export const ChatMarkdownAssetImage = memo(function ChatMarkdownAssetImage(props
       : undefined;
   const relativePath = reference?.kind === "file" ? reference.relativePath : undefined;
   const fallbackSrc = assetUrl._tag === "Failure" ? props.fallbackSrc : undefined;
+  const missingFileAccess =
+    assetUrl._tag === "Failure" &&
+    assetUrl.reason === "missing-file-access" &&
+    fallbackSrc === undefined;
   const src =
     assetUrl._tag === "Success"
       ? assetUrl.url + (props.srcFragment ?? "")
@@ -1633,12 +1639,14 @@ export const ChatMarkdownAssetImage = memo(function ChatMarkdownAssetImage(props
       <ChatMarkdownVideo
         src={src}
         sourceFailed={assetUrl._tag === "Failure" && fallbackSrc === undefined}
+        unavailableDetail={missingFileAccess ? MISSING_FILE_ACCESS_MESSAGE : undefined}
         alt={props.alt}
         copyMarkdown={props.copyMarkdown}
         originalUrl={props.originalUrl}
         style={props.style}
         mediaIdentity={JSON.stringify([props.environmentId, props.resource, props.srcFragment])}
-        onRetry={refreshAssetUrl}
+        // A retry signs a new URL; it cannot grant the file access this connection lacks.
+        onRetry={missingFileAccess ? undefined : refreshAssetUrl}
         actionsSource={actionsSource}
       />
     );
@@ -1649,13 +1657,7 @@ export const ChatMarkdownAssetImage = memo(function ChatMarkdownAssetImage(props
       key={JSON.stringify([props.environmentId, props.resource, props.srcFragment])}
       src={src}
       sourceFailed={assetUrl._tag === "Failure" && fallbackSrc === undefined}
-      unavailableDetail={
-        assetUrl._tag === "Failure" &&
-        assetUrl.reason === "missing-file-access" &&
-        fallbackSrc === undefined
-          ? MISSING_FILE_ACCESS_MESSAGE
-          : undefined
-      }
+      unavailableDetail={missingFileAccess ? MISSING_FILE_ACCESS_MESSAGE : undefined}
       alt={props.alt}
       copyMarkdown={props.copyMarkdown}
       standalone={props.standalone ?? true}
diff --git a/apps/web/src/components/media/MediaVideoPlayer.tsx b/apps/web/src/components/media/MediaVideoPlayer.tsx
index 1392b995c536..1e7863858ddd 100644
--- a/apps/web/src/components/media/MediaVideoPlayer.tsx
+++ b/apps/web/src/components/media/MediaVideoPlayer.tsx
@@ -13,6 +13,7 @@ interface MediaVideoPlayerProps {
   readonly src: string | null;
   readonly label: string;
   readonly sourceFailed?: boolean | undefined;
+  readonly unavailableDetail?: string | undefined;
   readonly originalUrl?: string | undefined;
   readonly revision?: string | null | undefined;
   readonly preload?: "visible" | "metadata" | undefined;
@@ -31,6 +32,7 @@ export function MediaVideoPlayer({
   src: latestSrc,
   label,
   sourceFailed = false,
+  unavailableDetail,
   originalUrl,
   revision = null,
   preload = "visible",
@@ -137,9 +139,9 @@ export function MediaVideoPlayer({
             stateClassName,
           )}
         >
-          <span className="inline-flex items-center gap-1.5">
+          <span data-thread-find-ignore className="inline-flex items-center gap-1.5">
             <TriangleAlertIcon aria-hidden className="size-3.5 shrink-0" />
-            Video unavailable{label ? ` · ${label}` : ""}
+            {["Video unavailable", label, unavailableDetail].filter(Boolean).join(" · ")}
           </span>
           <span className="flex flex-wrap items-center justify-center gap-2">
             {latestSrc !== null || onRetry ? (