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.

src/core/view.ts

@@ -401,6 +401,18 @@ function projectMarker(marker: LhMarkerMessage, out: LhViewMessage[]): void {
 			});
 			return;
 		}
+		case "practice-next": {
+			// The learner's explicit move-on signal (owner round 16): a compact
+			// centered system line — the mono-caps chrome register, not prose.
+			// The model reads the marker's content; the transcript never shows
+			// it (the label is chrome, single-sourced in the renderer).
+			out.push({
+				id: marker.id,
+				role: "user",
+				parts: [{ type: "data-practice-next", id: `pn_${marker.id}`, data: null }],
+			});
+			return;
+		}
 		case "problem-dismissed":
 			// UI-only (the ask-style dismissal): the synthesized conclude
 			// pair — which rides the NEXT input — carries the record's face.