practice: the between-problems pause — conclude ends the turn, the learner's go-ahead paces the stream (round 16)

Owner ruling (2026-10-06): every concluded problem opens a pause. The
agent may speak its closing words about the learner's last thinking
after the conclude result, then ENDS ITS TURN — a system-prompt law
deliberately, per owner correction, NOT tool-level terminate. The next
problem is never posed until the learner explicitly moves on; the pause
is the session's teaching space (repairs, clarifications, follow-ups —
still surgical, never re-teaching).

The move-on signal is a first-class input: { type: "next" } appends a
practice-next marker (content = single-sourced NEXT_PROBLEM_TEXT — the
model's unambiguous go-ahead: pose per the selection rules or wrap if
the arc is complete). Honest 400s: practice sessions only, nothing
active (mid-problem input rides the dock), riding after any pending
dismissal synthesis exactly like text.

The fast path (owner approved: composer-band chip + Enter-on-empty):
- Composer.enterAction gains "next" — Enter on an EMPTY composer in
  the pause fires the signal; typing anything makes Enter a send again;
  busy (steer/stop) outranks the pause.
- The Next chip hovers at the composer band's top-right (pick-pill
  chrome register) whenever the pause is live and a problem has ever
  been posed; the placeholder becomes the hint ("Ask about this
  problem — or press Enter for the next one…", exact);
- the transcript renders the signal as a compact centered NEXT PROBLEM
  line (mono-caps chrome); session-core appends it optimistically.

CONCLUDE_ACK_TEXT rewritten to carry the law; doctrine §VIII gains the
pause law (owner-sanctioned edit #3); 00-base's conclude/dismissal
bullets rewritten + the between-problems section added.

tests/render-composer.test.tsx

@@ -75,8 +75,21 @@ describe("enterAction", () => {
 		assert.equal(enterAction({ busy: true, canSend: false }), "stop");
 	});
 
-	it("idle: send when there is text, nothing when there is not", () => {
+	it("idle: send when there is the text, nothing when there is not", () => {
 		assert.equal(enterAction({ busy: false, canSend: true }), "send");
 		assert.equal(enterAction({ busy: false, canSend: false }), "none");
 	});
+
+	it("the practice pause (owner round 16): Enter on an EMPTY composer fires the move-on signal", () => {
+		assert.equal(enterAction({ busy: false, canSend: false, nextProblem: true }), "next");
+	});
+
+	it("typing anything outranks the pause — text makes Enter a send again", () => {
+		assert.equal(enterAction({ busy: false, canSend: true, nextProblem: true }), "send");
+	});
+
+	it("busy outranks the pause — steering and Stop keep their lanes", () => {
+		assert.equal(enterAction({ busy: true, canSend: false, nextProblem: true }), "stop");
+		assert.equal(enterAction({ busy: true, canSend: true, nextProblem: true }), "send");
+	});
 });