feat: loosen multi_true gate to qualifier-scoped correctness

store/prompts/question_gen/gate_multi_true.md

@@ -16,10 +16,17 @@ You are checking whether a multiple-choice question has **more than one plausibl
 
 ## Instructions
 
-1. Read the source material and the question carefully.
-2. For each option, assess whether it could be considered a correct or plausible answer given the source.
-3. If exactly ONE option is clearly correct → verdict "pass".
-4. If TWO or more options are plausibly correct → verdict "fail".
+1. Read the source material and the question carefully. Note the question's
+   explicit qualifiers (subject, timing, manner, object).
+2. For each option, assess whether it is **fully correct under the question's
+   qualifiers** — not merely whether it has some partial or local support in
+   the source.
+3. A good hard-negative distractor MAY have partial/local evidence in the video
+   yet be FALSE under the question's constraints. Such an option is NOT a
+   second correct answer — do NOT fail the question for it.
+4. Verdict "fail" ONLY IF two or more options are each fully correct under the
+   question's qualifiers (a genuine ambiguity).
+5. Otherwise verdict "pass".
 
 ## Response Format (strict JSON)