diff --git a/crates/x-media/src/lib.rs b/crates/x-media/src/lib.rs
index 97b0b4c..6aa432d 100644
--- a/crates/x-media/src/lib.rs
+++ b/crates/x-media/src/lib.rs
@@ -7,3 +7,23 @@ pub mod site;
 /// destructors), and without a marker the only safe assumption about the OS
 /// temp directory is "not mine".
 pub const TEMP_FILE_PREFIX: &str = "tgxmb-";
+
+/// True when `path` is a file inside a temp directory this project created: the
+/// directory's name carries [`TEMP_FILE_PREFIX`] and it sits directly under the
+/// OS temp directory (`tempfile`'s default location). The prefix lives on the
+/// directory, not the file, so checking the file name is not enough; requiring
+/// the parent to be the temp root stops an upstream-supplied bare path that
+/// merely contains a `tgxmb-` component from passing.
+pub fn is_own_temp_file(path: &std::path::Path) -> bool {
+    let Some(dir) = path.parent().and_then(|dir| dir.canonicalize().ok()) else {
+        return false;
+    };
+    let Ok(root) = std::env::temp_dir().canonicalize() else {
+        return false;
+    };
+    dir.parent() == Some(root.as_path())
+        && dir
+            .file_name()
+            .and_then(|name| name.to_str())
+            .is_some_and(|name| name.starts_with(TEMP_FILE_PREFIX))
+}
diff --git a/crates/xmedia-bot/src/handlers/urls.rs b/crates/xmedia-bot/src/handlers/urls.rs
index 0f42d5e..9eb2671 100644
--- a/crates/xmedia-bot/src/handlers/urls.rs
+++ b/crates/xmedia-bot/src/handlers/urls.rs
@@ -186,10 +186,7 @@ pub(super) fn media_to_payload(media: &Media, sensitive: bool) -> Option<MediaIt
     let url = media.url();
     // Only adapter-produced temp files may be non-HTTP. A bare path from an
     // upstream JSON field must never reach InputFile::file().
-    let is_local_temp = std::path::Path::new(url)
-        .file_name()
-        .and_then(|name| name.to_str())
-        .is_some_and(|name| name.starts_with(x_media::TEMP_FILE_PREFIX));
+    let is_local_temp = x_media::is_own_temp_file(std::path::Path::new(url));
     if !url.starts_with("http://") && !url.starts_with("https://") && !is_local_temp {
         log::warn!("dropping media with a non-URL upstream path");
         return None;
@@ -832,6 +829,46 @@ mod tests {
         assert!(media_to_payload(&media, false).is_none());
     }
 
+    /// Adapter output (bsky remux, pixiv ugoira) lives at `tgxmb-XXXX/video.mp4`
+    /// under the OS temp dir: the prefix is on the directory, so it must pass.
+    #[test]
+    fn media_to_payload_accepts_an_adapter_temp_video() {
+        let dir = tempfile::Builder::new()
+            .prefix(x_media::TEMP_FILE_PREFIX)
+            .tempdir()
+            .unwrap();
+        let path = dir.path().join("video.mp4");
+        std::fs::write(&path, b"mp4").unwrap();
+        let media = Media::Video {
+            url: path.to_string_lossy().into_owned(),
+            thumbnail_url: String::new(),
+        };
+        assert!(matches!(
+            media_to_payload(&media, false),
+            Some(MediaItemPayload::Video {
+                media: MediaRef::Source(_),
+                ..
+            })
+        ));
+    }
+
+    /// A `tgxmb-` directory outside the OS temp dir is an upstream-chosen path,
+    /// not one of ours, and must still be dropped.
+    #[test]
+    fn media_to_payload_rejects_a_tgxmb_dir_outside_the_temp_root() {
+        let dir = tempfile::Builder::new()
+            .prefix(x_media::TEMP_FILE_PREFIX)
+            .tempdir_in(std::env::current_dir().unwrap())
+            .unwrap();
+        let path = dir.path().join("video.mp4");
+        std::fs::write(&path, b"mp4").unwrap();
+        let media = Media::Video {
+            url: path.to_string_lossy().into_owned(),
+            thumbnail_url: String::new(),
+        };
+        assert!(media_to_payload(&media, false).is_none());
+    }
+
     /// The caption-quote threshold matches the post's text inside the caption,
     /// so a long-text cache hit is quoted and a short-text one is not.
     #[tokio::test]