diff --git a/check.sh b/check.sh
index f6355fa..391c571 100755
--- a/check.sh
+++ b/check.sh
@@ -43,7 +43,8 @@ fi
 
 # A collapsed disclosure is valid supporting content, but provenance inside one
 # is not visible by default. Remove only collapsed details subtrees; an open
-# disclosure remains visible unless one of its ancestors is collapsed.
+# disclosure remains visible unless one of its ancestors is collapsed. Media
+# fallback subtrees are likewise hidden when the browser supports the element.
 VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
   awk '
     {
@@ -54,7 +55,11 @@ VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
           tag=tag char
           if (char == ">") {
             lower=tolower(tag)
-            if (lower ~ /^<details([[:space:]>])/) {
+            if (lower ~ /^<(video|audio)([[:space:]>])/) media_depth++
+            else if (lower ~ /^<\/(video|audio)([[:space:]>])/) {
+              if (media_depth > 0) media_depth--
+            }
+            else if (lower ~ /^<details([[:space:]>])/) {
               attributes=lower
               gsub(/"[^"]*"/, "", attributes)
               parent_hidden=(details_depth > 0 && hidden[details_depth])
@@ -67,7 +72,7 @@ VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
                 details_depth--
               }
             }
-            else if (!hidden[details_depth]) printf "%s", tag
+            else if (!hidden[details_depth] && media_depth == 0) printf "%s", tag
             in_tag=0
             tag=""
           }
@@ -76,11 +81,13 @@ VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
           in_tag=1
           tag=char
         }
-        else if (!hidden[details_depth]) printf "%s", char
+        else if (!hidden[details_depth] && media_depth == 0) printf "%s", char
       }
     }
   ')
 
+hidden_content_guidance='move ## Tracking and ## Attribution outside collapsed <details> or <video>/<audio> fallback content'
+
 # ---- branch form ----
 # <role>/bug-<id>/<kebab>
 if echo "${BRANCH}" | grep -qE "^(dev|ux|ops|security|perf|architect|support)/bug-[a-z0-9]+/[a-z0-9][a-z0-9-]*$"; then
@@ -119,7 +126,7 @@ if [ "${BRANCH_KIND}" = "role-bug" ]; then
     in_section { print }
   ')
   if [ -z "${tracking}" ]; then
-    echo "FAIL[check-naming]: PR body must contain a non-empty ## Tracking section"
+    echo "FAIL[check-naming]: PR body must contain a non-empty ## Tracking section visible by default; ${hidden_content_guidance}"
     FAILED=1
   else
     if ! printf '%s\n' "${tracking}" | grep -qE "(^|[[:space:]>])Fixes[[:space:]]+${BRANCH_BUG}([^a-z0-9]|$)"; then
@@ -145,7 +152,7 @@ if [ "${BRANCH_KIND}" != "invalid" ]; then
   ')
   watermark_re='Authored-By: .+ \(.+\) <a href="mailto:noreply@[[:alnum:].-]+"[^>]*>noreply@[[:alnum:].-]+</a>'
   if ! printf '%s\n' "${attribution}" | grep -qE "${watermark_re}"; then
-    echo "FAIL[check-naming]: ## Attribution must contain an Authored-By product/model watermark"
+    echo "FAIL[check-naming]: visible ## Attribution must contain an Authored-By product/model watermark; ${hidden_content_guidance}"
     FAILED=1
   fi
 
diff --git a/tests/bin/curl b/tests/bin/curl
index 3832ec0..afb5208 100755
--- a/tests/bin/curl
+++ b/tests/bin/curl
@@ -68,6 +68,10 @@ printf '%s\n' "${PR_BODY}" | awk '
       print line
       next
     }
+    if (lower ~ /^[ ]{0,3}<\/?(video|audio)([[:blank:]>])/) {
+      print line
+      next
+    }
     if (line ~ /^## Tracking[[:space:]]*$/) print "<h2>Tracking</h2>"
     else if (line ~ /^## Attribution[[:space:]]*$/) print "<h2>Attribution</h2>"
     else if (line ~ /^- Fixes[[:space:]]/) print "<li>" substr(line, 3) "</li>"
diff --git a/tests/run b/tests/run
index c6bce89..cbd31a0 100755
--- a/tests/run
+++ b/tests/run
@@ -188,6 +188,12 @@ check_contract "open details inside collapsed details remain hidden" \
 check_contract "open text in another details attribute remains collapsed" \
   $'<details title="x open y"><summary>Release notes</summary>\n\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</details>' \
   "$BASE" "$GOOD_HEAD" "PR body must contain a non-empty ## Tracking section"
+check_contract "video fallback cannot hide provenance" \
+  $'<video controls>\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</video>' \
+  "$BASE" "$GOOD_HEAD" "move ## Tracking and ## Attribution outside collapsed <details> or <video>/<audio> fallback content"
+check_contract "audio fallback cannot hide provenance" \
+  $'<audio controls>\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</audio>' \
+  "$BASE" "$GOOD_HEAD" "move ## Tracking and ## Attribution outside collapsed <details> or <video>/<audio> fallback content"
 check_contract_pass "unrelated collapsed details remain available" \
   $'<details><summary>Logs</summary>\n\nSupporting output\n</details>\n\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>' \
   "$BASE" "$GOOD_HEAD"