Safeguard lab answer saving against blank overwrites (Firefox)

apps/api/routes.py

@@ -196,6 +196,11 @@ def save_lab_answers(lab_inst_id):
         lab_answers = LabAnswers(user_id=current_user.id, lab_id=lab_inst.lab_id)
         db.session.add(lab_answers)
 
+    current_app.logger.info(
+        f"Save lab_answers id={lab_answers.id} user={current_user.username} "
+        f"lab={lab_inst.lab_id} request-answers={content}"
+    )
+
     # Merge into the stored answers rather than replacing them: keep keys not
     # present in this payload, and don't let an empty incoming value wipe an
     # answer that was already saved (guards against a partial/early auto-save

apps/templates/pages/lab_instance_view.html

@@ -410,6 +410,16 @@ <h3 class="card-title">Lab Guide</h3>
         if (!answers || Object.keys(answers).length === 0) {
           return;
         }
+        // Never overwrite stored answers with an all-blank form. Firefox's
+        // form-state restoration re-blanks fields after load and fires change
+        // events; without this guard that would auto-save an empty payload and
+        // wipe the user's answers.
+        var hasValue = Object.keys(answers).some(function(k){
+          return answers[k] !== "" && answers[k] != null;
+        });
+        if (!hasValue) {
+          return;
+        }
         var request = $.ajax({
           url:  "/api/lab_answers/{{ lab['lab_instance_id'] }}",
           type: "POST",
@@ -441,6 +451,9 @@ <h3 class="card-title">Lab Guide</h3>
       $('.save-answers').click(function () {
 	saveAnswers();
       });
+      // stop Firefox from restoring/re-blanking these fields after load, which
+      // otherwise fights the answer loader and triggers empty auto-saves
+      $("#lab-guide input, #lab-guide textarea, #lab-guide select").attr('autocomplete', 'off');
       var timeoutSave;
       $("#lab-guide input, #lab-guide textarea, #lab-guide select").on('input propertychange change', function() {
           // don't auto-save until the initial load has settled, otherwise a

tests/js/labAnswers.test.js

@@ -147,11 +147,24 @@ const { $ } = env;
   eq('save: first radio not clobbered by later unchecked siblings', post.q_radio, 'A');
 }
 
-// === saveAnswers: empty / unchecked groups serialize as "" =================
+// === saveAnswers: a fully-blank form is NOT posted (never wipe answers) =====
+// Firefox re-blanks the guide inputs after load and fires change events; the
+// guard in saveAnswers must skip the POST entirely so an all-empty payload
+// can't overwrite previously saved answers.
 {
   env.setForm(FORM);
   const post = env.save();
-  eq('save: empty text',              post.q_text, '');
+  eq('save: blank form suppresses POST', post, undefined);
+}
+
+// === saveAnswers: blank fields still serialize as "" in a partial save ======
+// When at least one field has a value the POST goes through, and the empty
+// fields must still serialize as "" so they round-trip via applyAnswers.
+{
+  env.setForm(FORM);
+  $("input[name=q_text]").val('answered');
+  const post = env.save();
+  eq('save: partial POST happens',     post && post.q_text, 'answered');
   eq('save: unchecked checkbox group', post.q_cb, '');
   eq('save: no radio selected',        post.q_radio, '');
 }