feat: Add split tab keyboard shortcut (to mirror Superhuman)

[mickn]

Summary

• Adds Tab / Shift+Tab navigation for inbox split tabs only when Superhuman Keyboard Shortcuts are enabled.
• Leaves Gmail Keyboard Shortcuts mode on native Tab focus traversal; Gmail-style split cycling via ` / ~ is unchanged.
• Keeps keyboard-selected tabs visually identical to clicked tabs by avoiding an extra focus-ring border.
• Adds E2E coverage for Superhuman Tab cycling and for Gmail mode not switching tabs on Tab.

Test Plan

• npm run build
• npx playwright test tests/e2e/inbox-tabs.spec.ts --project=e2e
• npm run typecheck:web
• git diff --check

[greptile-apps]

Greptile Summary

This PR adds Tab / Shift+Tab keyboard navigation for inbox split tabs in Superhuman keyboard mode, mirroring Superhuman's section-cycling UX. It wires up ARIA roles (role="tablist", role="tab", aria-selected, data-split-tab-id) in SplitTabs.tsx to enable DOM targeting, implements focusSplitTab via requestAnimationFrame, and guards the shortcut behind isSuperhuman && !showSettings && mode === "normal".

• cycleSplit gains an options.focusTab flag so Gmail's `/~ cycling does not trigger focusSplitTab, preserving the existing Gmail keyboard flow.
• Three new E2E tests cover Superhuman Tab cycling, Gmail mode pass-through, and compose-mode non-interception, with a custom expectNoVisibleBoxShadow helper that handles multiple Chromium-normalised representations.

Confidence Score: 5/5

Safe to merge — the shortcut is narrowly gated and the prior concerns raised in review threads have been correctly addressed in this revision.

The Tab handler is guarded by three independent conditions (isSuperhuman, !showSettings, mode === normal), so it cannot fire in Gmail mode, settings, or while compose is open. The options.focusTab flag on cycleSplit correctly restricts focusSplitTab to the new Superhuman path and leaves the Gmail backtick/tilde flow untouched. E2E tests cover all three cases, and the expectNoVisibleBoxShadow helper is robust to Chromium-normalised computed values.

No files require special attention.

Important Files Changed

Filename	Overview
src/renderer/components/SplitTabs.tsx	Adds splitId, role=tab, aria-selected, and data-split-tab-id props to Tab buttons and wraps the container in role=tablist — clean ARIA/DOM hookup enabling both the keyboard shortcut and the E2E tests to target tabs by role/data attribute.
src/renderer/hooks/useKeyboardShortcuts.ts	Introduces focusSplitTab helper and a Tab/Shift+Tab case gated behind isSuperhuman && !showSettings && mode === normal. The options.focusTab flag on cycleSplit correctly prevents focusSplitTab from firing during Gmail backtick/tilde cycling, and the mode === normal guard prevents Tab from being swallowed when compose is open.
tests/e2e/inbox-tabs.spec.ts	Adds three well-structured E2E tests for Tab cycling in Superhuman mode, Gmail mode native Tab pass-through, and compose-mode non-interception. Uses Zustand store helpers to set bindings and inspect currentSplitId without relying on brittle UI coupling.

_{Reviews (8): Last reviewed commit: "Simplify focusSplitTab to a direct attri..." | Re-trigger Greptile}

[devin-ai-integration]

Devin Review found 1 potential issue.

View 4 additional findings in Devin Review.

[ankitvgupta]

nice, recommend using /reviewloop to handle the review comments, and consider the /review skill in gstack as well. will plan to get this in soon

[mickn]

nice, recommend using /reviewloop to handle the review comments, and consider the /review skill in gstack as well. will plan to get this in soon

all comments are addressed 👍