vocab: stop re-teaching a word later in the same session (239 tags)

A word tagged VOCAB in one activity was tagged again in later activities of the
same session, so the learner got the same chip repeatedly — most visibly in the
pronunciation drills, which re-listed every word from the dialogue before them
(reported: book 7 session 1-2). Rule applied: drop a VOCAB whose word was
already tagged in an EARLIER activity of that session. Repeats INSIDE one
activity are kept — those teach distinct senses ('stuck to his finger' vs
'stuck the milk in the fridge', 'shop' as verb then noun). Also dropped chips
for plurals of already-known words in book 7 session 1-2, where the drill
teaches the singular/plural pair rather than new vocabulary. No session lost
all of its vocabulary (verified).

Co-authored-by: Cursor <cursoragent@cursor.com>

book-4-lesson-2.module

@@ -150,7 +150,6 @@ ID: l2-s4
 INTRO: Meet Sgt Paul Travis. He got a new stripe today, so he's in an excellent mood. Listen and read along as he gets ready for work.
 INSTRUCTION: Listen and read along.
 
-VOCAB: sergeant
 Narrator: He's a sergeant in the Army. {st-page_032_001.jpg}
 Narrator: He lives on an Army post. {st-page_032_001.jpg}
 Narrator: His name is Paul Travis. {st-page_032_001.jpg}
@@ -162,13 +161,10 @@ Narrator: Every morning, he gets up and showers. He shaves with his razor. {st-p
 VOCAB: uniform
 Narrator: Sgt Travis checks his uniform {st-page_032_003.jpg}
 
-VOCAB: cap
 Narrator: and his cap. {st-page_032_005.jpg}
 
-VOCAB: name tag
 Narrator: He puts his name tag on his uniform. {st-page_032_006.jpg}
 
-VOCAB: stripes
 Narrator: He looks at his stripes. {st-page_032_007.jpg}
 Narrator: Today he has a new stripe, and he's happy.