diff --git a/check.sh b/check.sh
index d6b1b75..f04b634 100755
--- a/check.sh
+++ b/check.sh
@@ -42,7 +42,8 @@ elif ! RENDERED_BODY=$(printf '%s' "${BODY}" |
 fi
 
 # A collapsed disclosure is valid supporting content, but provenance inside one
-# is not visible by default. Remove details subtrees before locating sections.
+# is not visible by default. Remove only collapsed details subtrees; an open
+# disclosure remains visible unless one of its ancestors is collapsed.
 VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
   awk '
     {
@@ -53,11 +54,18 @@ VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
           tag=tag char
           if (char == ">") {
             lower=tolower(tag)
-            if (lower ~ /^<details([[:space:]>])/) details_depth++
-            else if (lower ~ /^<\/details([[:space:]>])/) {
-              if (details_depth > 0) details_depth--
+            if (lower ~ /^<details([[:space:]>])/) {
+              parent_hidden=(details_depth > 0 && hidden[details_depth])
+              details_depth++
+              hidden[details_depth]=(parent_hidden || lower !~ /[[:space:]]open([[:space:]=>]|$)/)
             }
-            else if (details_depth == 0) printf "%s", tag
+            else if (lower ~ /^<\/details([[:space:]>])/) {
+              if (details_depth > 0) {
+                delete hidden[details_depth]
+                details_depth--
+              }
+            }
+            else if (!hidden[details_depth]) printf "%s", tag
             in_tag=0
             tag=""
           }
@@ -66,7 +74,7 @@ VISIBLE_BODY=$(printf '%s\n' "${RENDERED_BODY}" |
           in_tag=1
           tag=char
         }
-        else if (details_depth == 0) printf "%s", char
+        else if (!hidden[details_depth]) printf "%s", char
       }
     }
   ')
diff --git a/tests/bin/curl b/tests/bin/curl
index 63b420a..6ac3373 100755
--- a/tests/bin/curl
+++ b/tests/bin/curl
@@ -62,7 +62,8 @@ printf '%s\n' "${PR_BODY}" | awk '
       next
     }
     if (lower ~ /^[ ]{0,3}<details([[:blank:]>])/) {
-      print "<details>"
+      if (lower ~ /[[:blank:]]open([[:blank:]=>]|$)/) print "<details open=\"\">"
+      else print "<details>"
       next
     }
     if (line ~ /^## Tracking[[:space:]]*$/) print "<h2>Tracking</h2>"
diff --git a/tests/run b/tests/run
index 6ac70af..15246a2 100755
--- a/tests/run
+++ b/tests/run
@@ -179,6 +179,12 @@ check_contract_pass "fenced code examples remain available" \
 check_contract "details cannot collapse provenance" \
   $'<details><summary>Release notes</summary>\n\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</details>' \
   "$BASE" "$GOOD_HEAD" "PR body must contain a non-empty ## Tracking section"
+check_contract_pass "open details preserve visible provenance" \
+  $'<details open><summary>Release notes</summary>\n\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</details>' \
+  "$BASE" "$GOOD_HEAD"
+check_contract "open details inside collapsed details remain hidden" \
+  $'<details><summary>Release notes</summary>\n<details open><summary>Visible only after expansion</summary>\n\n## Tracking\n- Fixes bug-x7k2m9 — https://agenthub.fritzlab.net/bug-x7k2m9\n\n## Attribution\n- Authored-By: Codex (GPT-5) <noreply@openai.com>\n</details>\n</details>' \
+  "$BASE" "$GOOD_HEAD" "PR body must contain a non-empty ## Tracking section"
 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"