Typography round 5 (owner): drop the message count + active-row weight; ISO dates

Three declutter moves, all trivially reversible:

- The meta line drops the message count (idle meta is now just how long
  ago). The count informed no decision — clutter. messageCount still
  rides the API payload, so this is a one-line flip in sessionMeta if
  it's ever wanted.
- The active row is marked by the background alone: weight was a second
  channel doing the same job, and the flip made selected titles jump.
- Dates beyond the week render ISO (YYYY-MM-DD, zero-padded) instead of
  M/D/YYYY — the US convention swapped for the international standard:
  unambiguous in any locale, sorts lexically. A user-locale setting can
  come later — it's a format-function swap.

Also dropped the row's vestigial text-sm: both lines carry explicit
sizes now (16px title, 11px meta).

Live: active weight 400 + bg-accent, metas '17m ago' /
'Waiting for your answer · 1d ago', no counts. Gates: typecheck, lint,
469/469.

components/sidebar.tsx

@@ -86,7 +86,11 @@ function SessionStatus({ busy }: { busy: boolean }) {
 
 /** Compact "how long ago": "just now", "5m ago", "3h ago", "2d ago",
  *  then a plain date. How long a session has been WAITING matters more
- *  than an absolute timestamp. Pure — exported for tests. */
+ *  than an absolute timestamp. Beyond a week the date renders ISO
+ *  (YYYY-MM-DD, zero-padded) — the international standard: unambiguous
+ *  in any locale and it sorts (owner, typography round 5; the old
+ *  M/D/YYYY was the US convention. A user-locale setting can come later
+ *  — trivial, a format function swap). Pure — exported for tests. */
 export function timeAgo(iso: string, now = new Date()): string {
 	const ms = now.getTime() - new Date(iso).getTime();
 	if (ms < 60_000) return "just now";
@@ -96,16 +100,21 @@ export function timeAgo(iso: string, now = new Date()): string {
 	if (h < 24) return `${h}h ago`;
 	const d = Math.floor(h / 24);
 	if (d < 7) return `${d}d ago`;
-	return new Date(iso).toLocaleDateString();
+	const date = new Date(iso);
+	const mm = String(date.getMonth() + 1).padStart(2, "0");
+	const dd = String(date.getDate()).padStart(2, "0");
+	return `${date.getFullYear()}-${mm}-${dd}`;
 }
 
-/** The row's second line: state replaces the message count when the state
- *  is the more useful fact (most resting sessions are awaiting an answer —
- *  that's what the learner scans for). */
+/** The row's second line: the state when a state exists (waiting/working),
+ *  otherwise just how long ago. The message count is DROPPED (owner,
+ *  typography round 5): it informed no decision — clutter. messageCount
+ *  still rides the API payload, so this is a one-line flip back if it's
+ *  ever wanted. */
 function sessionMeta(chat: ChatListItem): string {
 	if (chat.pendingQuestion) return `Waiting for your answer · ${timeAgo(chat.updatedAt)}`;
 	if (chat.busy) return "Teacher is working…";
-	return `${chat.messageCount} messages · ${new Date(chat.updatedAt).toLocaleDateString()}`;
+	return timeAgo(chat.updatedAt);
 }
 
 /**
@@ -127,8 +136,8 @@ export function SessionRow({
 			type="button"
 			onClick={onOpen}
 			className={cn(
-				"relative mb-0.5 flex w-full items-center gap-2 rounded-lg px-3 py-2 text-left text-sm transition-colors hover:bg-accent",
-				active && "bg-accent font-medium",
+				"relative mb-0.5 flex w-full items-center gap-2 rounded-lg px-3 py-2 text-left transition-colors hover:bg-accent",
+				active && "bg-accent",
 			)}
 		>
 			<SessionStatus busy={chat.busy} />

tests/render-sidebar.test.tsx

@@ -86,26 +86,30 @@ describe("SessionRow", () => {
 		const working = render(item({ busy: true }));
 		assert.ok(working.includes("Teacher is working…"), "working meta");
 
+		// Owner, typography round 5: the message count is dropped — it
+		// informed no decision. Idle meta is just how long ago.
 		const idle = render(item({ title: "Partial derivatives", messageCount: 7 }));
 		assert.ok(idle.includes("Partial derivatives"));
-		assert.match(idle, /7 messages · \d{1,2}\/\d{1,2}\/\d{4}/, "idle keeps the count");
+		assert.ok(!idle.includes("messages"), "the count is gone (flip-flop: one line in sessionMeta)");
+		assert.match(idle, /\d{4}-\d{2}-\d{2}/, "idle shows the ISO date");
 	});
 
-	it("active row is visually marked", () => {
+	it("active row is visually marked by the background alone (owner, round 5: no weight change)", () => {
 		const html = render(item({}), true);
-		assert.ok(html.includes("font-medium"), "active emphasis");
+		assert.ok(html.includes("bg-accent"), "active background");
+		assert.ok(!html.includes("font-medium"), "weight is not a second channel doing the same job");
 	});
 });
 
 describe("timeAgo", () => {
 	const now = new Date("2026-01-02T12:00:00.000Z");
 
-	it("just now / minutes / hours / days, then falls back to a date", () => {
+	it("just now / minutes / hours / days, then the ISO date (owner, round 5)", () => {
 		assert.equal(timeAgo("2026-01-02T11:59:30.000Z", now), "just now");
 		assert.equal(timeAgo("2026-01-02T11:55:00.000Z", now), "5m ago");
 		assert.equal(timeAgo("2026-01-02T09:00:00.000Z", now), "3h ago");
 		assert.equal(timeAgo("2025-12-31T12:00:00.000Z", now), "2d ago");
-		assert.match(timeAgo("2025-06-02T12:00:00.000Z", now), /\d/, "beyond a week: a date");
+		assert.equal(timeAgo("2025-06-02T12:00:00.000Z", now), "2025-06-02", "beyond a week: ISO — unambiguous, sortable");
 	});
 
 	it("negative drift (clock skew) reads as just now, never a future date", () => {