Fix ⌘B: dispatch/listen event-name mismatch; thinking pill → "Thinking (⇧⇥)"

Root cause (interlude, owner 2026-09-25): keyboard-shortcuts dispatches
registry actions on the lh:kbd-<action> convention, but the sidebar's
listener sat on the pre-convention name "lh:toggle-sidebar" — a name
nothing ever dispatches, so ⌘B silently did nothing while its tooltip
and cheat-sheet row kept claiming the binding. A sweep of every lh:
listener confirmed the sidebar was the lone stray (chat-renamed and
graph-revision are deliberate non-kbd events).

Fix, structural: kbdEventForAction(action) exported from
src/core/keyboard.ts — the ONE spelling — and both sides compose
through it (dispatcher's default branch, sidebar's toggle listener);
keyboard-shortcuts re-exports the helper so the contract pin can assert
no second spelling exists. The mismatch is now impossible by
construction.

Thinking pill: label trimmed to "Thinking" with its real shortcut via
the registry-composition path — "Thinking (⇧⇥)" (cycle-thinking,
rebind-live like every Hint suffix).

Pins (tests/keyboard-toggle-sidebar.test.ts): the full chain — mod+b →
actionForBinding → toggle-sidebar → kbdEventForAction →
lh:kbd-toggle-sidebar; formatBinding("shift+tab") → ⇧⇥; the
dispatcher-imports-the-same-helper contract.

Live-verified on :3001: ⌘B visually toggles on home, /chat/[id], and
/chat/new (sidebar 0↔288px, hamburger slot 0↔36); with the rebind
lh:keymap {"toggle-sidebar":"mod+j"}: ⌘J toggles and ⌘B is inert
(rebind-live); thinking pill renders "Thinking (⇧⇥)"; keymap restored,
sidebar left open.

tests/keyboard-toggle-sidebar.test.ts

@@ -0,0 +1,51 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import {
+	actionForBinding,
+	bindingForAction,
+	formatBinding,
+	kbdEventForAction,
+} from "../src/core/keyboard.ts";
+import { kbdEventForAction as kbdEventForActionFromUi } from "../components/keyboard-shortcuts.tsx";
+
+/**
+ * The ⌘B sidebar bug interlude (owner, 2026-09-25): ⌘B did nothing because
+ * the sidebar listened on the pre-convention "lh:toggle-sidebar" while the
+ * dispatcher sent "lh:kbd-toggle-sidebar". The fix is structural — both
+ * sides compose the event name through the ONE helper — and these pins
+ * hold the chain together: the registry maps the keypress to the action,
+ * the helper spells the event, and the UI dispatcher imports the same
+ * helper (not its own copy).
+ */
+
+describe("kbdEventForAction — the one spelling for action events", () => {
+	it("dispatch and listen names are the helper's output", () => {
+		assert.equal(kbdEventForAction("toggle-sidebar"), "lh:kbd-toggle-sidebar");
+		assert.equal(kbdEventForAction("sessions-search"), "lh:kbd-sessions-search");
+	});
+
+	it("the dispatcher imports the same helper (no second spelling exists)", () => {
+		assert.equal(kbdEventForActionFromUi, kbdEventForAction);
+	});
+});
+
+describe("the ⌘B chain — keypress → binding → action → event", () => {
+	it("mod+b is the toggle-sidebar action", () => {
+		assert.equal(actionForBinding("mod+b"), "toggle-sidebar");
+		assert.equal(bindingForAction("toggle-sidebar"), "mod+b");
+		assert.equal(formatBinding("mod+b"), "⌘B");
+	});
+
+	it("the event the chain ends in is the one the sidebar answers on", () => {
+		const action = actionForBinding("mod+b");
+		assert.equal(action, "toggle-sidebar");
+		assert.equal(kbdEventForAction(action), "lh:kbd-toggle-sidebar");
+	});
+});
+
+describe("the thinking pill suffix — ⇧⇥ via the registry", () => {
+	it("shift+tab formats as ⇧⇥ and maps to cycle-thinking", () => {
+		assert.equal(actionForBinding("shift+tab"), "cycle-thinking");
+		assert.equal(formatBinding("shift+tab"), "⇧⇥");
+	});
+});