ui: the chat comeback — side-based authorship, restored quotes, tucked whys

Blockquotes: the callout override had displaced Streamdown's own styled
blockquote component, so plain quotes rendered as bare unstyled text
since that commit. The pass-through branch now restores Streamdown's
verbatim classes (border-l-4, muted italic).

Explanations tucked for ALL questions (owner): the prediction's Why /
Hide-why toggle is universal — every quiz answered card sits its
explanation behind the same collapsed button. Same pattern, one law.

The thinking row's rhythm: my-1 -> my-3. The 4px margin hugged the
options on non-graded answered cards (owner report); 12px matches the
card's mt-2/mt-3 spacing grammar everywhere the row renders.

Side-based authorship (owner round, 2026-10-07): the document shape
blurred user into agent — three left-rail idioms (user text, user
thinking, quoted prose) collided once quotes rendered. User rows go
RIGHT: 'You' messages and practice thinking cards hug the right edge at
85% width with the rail mirrored (border-r), text still reading
left-to-right. In-card thinking (inside the answered card, the agent's
context) stays left. Transcript thinking rows arrive EXPANDED — the
thinking was clearly sent. Cmd+T (toggle-user-thinking, chat scope,
cheat-sheet row) sets every user-thinking row to one state via a module
store: explicit sets stomp individual toggles, late mounts honor the
last set (the state initializer reads the store, so static render
reflects it too).

tests/keyboard-toggle-sidebar.test.ts

@@ -30,6 +30,12 @@ describe("kbdEventForAction — the one spelling for action events", () => {
 });
 
 describe("the ⌘B chain — keypress → binding → action → event", () => {
+	it("mod+t is the toggle-user-thinking action (owner round, 2026-10-07)", () => {
+		assert.equal(actionForBinding("mod+t"), "toggle-user-thinking");
+		assert.equal(bindingForAction("toggle-user-thinking"), "mod+t");
+		assert.equal(kbdEventForAction("toggle-user-thinking"), "lh:kbd-toggle-user-thinking");
+	});
+
 	it("mod+b is the toggle-sidebar action", () => {
 		assert.equal(actionForBinding("mod+b"), "toggle-sidebar");
 		assert.equal(bindingForAction("toggle-sidebar"), "mod+b");