practice round: dead session starts, prompt laws, preamble, label unify

THE START BUG (owner report, reproduced live both kinds): new sessions
(?prompt flow — practice and teach alike) sat dead until a second
message, which then persisted WITHOUT the first. Root cause, proven
both directions: the submit POST rode the view's consumeAbort
controller; React StrictMode's simulated remount fires Diet A's
unmount cleanup (model.stop()) ~8ms in and killed the POST mid-flight;
the page's sentInitial guard had already flipped, so it never retried.
Teach was equally broken — only unnoticed, because every teach chat in
use predates the diet and practice starts are always fresh. Fix: the
submit law — POSTs are not abortable by view teardown (they are ~100ms
acks since Diet B and cannot starve the pool); after the ack, a
consumeAbort identity check guards the stream attach. Pinned with the
stop-mid-submit regression test. Live: StrictMode on, practice draft
POST 200/67ms, stream attached, message persisted, problem posed.

PRACTICE PROMPT (00-base): the opening rule — material arrives two
ways, both first-class (picked propositions primary; free-form —
topics, course material, files/PDFs — fully supported, never refused);
as soon as material exists the reply poses, at most one short line
before the problem call, no warm-up interview. Plus the hard law: no
problem is ever conversation — every problem through the tool (no
thinking field/no reveal/no verdict attaches to prose).

GRAPH-CONTEXT PREAMBLE: custom markers flatten to user-role on the
wire, so the old "Contextualization — the learner picked…" read like a
system broadcast in the learner's voice channel. Now the bracket
convention: "[Session context] — picked from the learner's knowledge
map…".

SIDEBAR: busy rows unify to "Working…" for both kinds (the spinner's
default label included); "Practicing…"/"Teacher is working…" retired.

Gates: 1490/1490, typecheck, lint. doctrine's stale doc pointer fixed.

tests/graph-context.test.ts

@@ -48,7 +48,7 @@ describe("newGraphContextMessage", () => {
 	it("frames the context for the model: propositions listed, chains appended", () => {
 		const m = newGraphContextMessage(PICKS, ["Modus ponens → Soundness"]);
 		assert.equal(m.customType, "graph-context");
-		assert.match(m.content, /Contextualization — the learner picked these propositions/);
+		assert.match(m.content, /\[Session context\] — picked from the learner's knowledge map/);
 		// IDS FIRST (owner round 9): every pick carries its id — the problem
 		// tool's target field references these; names alone no longer.
 		assert.ok(m.content.includes(`- [${PICKS[0]!.id}] Modus ponens: If P implies Q and P holds, Q holds.`));
@@ -69,7 +69,7 @@ describe("newGraphContextMessage", () => {
 		const wire = toLlmMessages([m as unknown as LhMessage] as never);
 		assert.equal(wire.length, 1);
 		assert.equal(wire[0]!.role, "user");
-		assert.ok(String((wire[0]!.content as { text?: string }[])[0]!.text).includes("Contextualization"));
+		assert.ok(String((wire[0]!.content as { text?: string }[])[0]!.text).includes("[Session context]"));
 	});
 
 	it("projectView: a user-side data part — never a text bubble", () => {