feat: cmd+shift+bracket aliases for tab cycling

Add the browser-convention Cmd+Shift+] / Cmd+Shift+[ as extraBindings
on tab.next/tab.prev, alongside the existing Ctrl+Tab defaults -- the
same always-on alias mechanism palette.open already uses.
keyFromEventCode grows BracketLeft/BracketRight support (shift-
independent, like every key it maps). No collisions: checked against
RESERVED_COMBOS, all command bindings, and the native menu.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FJ8wStsHyu7XPLTspNjMnQ

Author: alicoding

frontend/src/shared/commands.test.ts

@@ -47,6 +47,21 @@ describe('dispatchCommandForEvent with extraBindings', () => {
     expect(dispatchCommandForEvent(event({ code: 'KeyP', metaKey: true }), overrides)).toBe(true)
   })
 
+  it('tab.next/tab.prev carry the browser-convention bracket aliases', () => {
+    expect(findCommand('tab.next')?.extraBindings).toEqual([{ mods: ['cmd', 'shift'], key: ']' }])
+    expect(findCommand('tab.prev')?.extraBindings).toEqual([{ mods: ['cmd', 'shift'], key: '[' }])
+  })
+
+  it('Cmd+Shift+] and Cmd+Shift+[ dispatch (tab cycling via the aliases)', () => {
+    expect(dispatchCommandForEvent(event({ code: 'BracketRight', metaKey: true, shiftKey: true }), {})).toBe(true)
+    expect(dispatchCommandForEvent(event({ code: 'BracketLeft', metaKey: true, shiftKey: true }), {})).toBe(true)
+  })
+
+  it('bare Cmd+] stays unbound -- the aliases require Shift, exact-mods matching', () => {
+    expect(dispatchCommandForEvent(event({ code: 'BracketRight', metaKey: true }), {})).toBe(false)
+    expect(dispatchCommandForEvent(event({ code: 'BracketLeft', metaKey: true }), {})).toBe(false)
+  })
+
   it('a command with no extraBindings is unaffected (backward-compatible)', () => {
     // tab.close has no extras -- only its own Cmd+W default dispatches
     // it, same behavior as before this feature existed.

frontend/src/shared/commands.ts

@@ -100,12 +100,21 @@ export const COMMANDS: Command[] = [
     id: 'tab.next',
     label: 'Next tab',
     defaultBinding: { mods: ['ctrl'], key: 'Tab' },
+    // ⌘⇧] -- the browser convention (Safari/Chrome "Show Next Tab")
+    // for the identical action, alongside Ctrl+Tab the same way
+    // palette.open carries its ⌘//⌘? aliases. Checked against
+    // RESERVED_COMBOS (shared/keybinding.ts), every other command's
+    // bindings here, and the native menu (no bracket accelerators):
+    // no collision.
+    extraBindings: [{ mods: ['cmd', 'shift'], key: ']' }],
     run: () => cycleWorkTab(1),
   },
   {
     id: 'tab.prev',
     label: 'Previous tab',
     defaultBinding: { mods: ['ctrl', 'shift'], key: 'Tab' },
+    // ⌘⇧[ -- same browser convention as tab.next's ⌘⇧] above.
+    extraBindings: [{ mods: ['cmd', 'shift'], key: '[' }],
     run: () => cycleWorkTab(-1),
   },
   {

frontend/src/shared/keybinding.test.ts

@@ -45,6 +45,11 @@ describe('keyFromEventCode', () => {
   // physical key, shift-independent like every other key here -- Shift
   // held or not is captured separately as a mod (modsFromEvent), not a
   // second key value.
+  it('maps the bracket codes to literal brackets (tab.next/prev ⌘⇧]/⌘⇧[ aliases)', () => {
+    expect(keyFromEventCode('BracketLeft')).toBe('[')
+    expect(keyFromEventCode('BracketRight')).toBe(']')
+  })
+
   it('maps the Slash code to a literal forward slash', () => {
     expect(keyFromEventCode('Slash')).toBe('/')
   })

frontend/src/shared/keybinding.ts

@@ -24,6 +24,12 @@ export function keyFromEventCode(code: string): string | null {
   // Shift MOD is what distinguishes ⌘/ from ⌘? at the KeyCombo level
   // (modsFromEvent below), not a second key value here.
   if (code === 'Slash') return '/'
+  // Bracket keys exist for tab.next/tab.prev's ⌘⇧]/⌘⇧[ extra bindings
+  // (shared/commands.ts) -- the browser convention for cycling tabs.
+  // Shift-independent like every other key here: the '{'/'}' glyphs are
+  // the same physical keys, distinguished only by the Shift mod.
+  if (code === 'BracketLeft') return '['
+  if (code === 'BracketRight') return ']'
   return null
 }