docs: TV input design — keyboard/gamepad inside iframe apps, globally

evdev->uinput gamepad-as-keyboard daemon on kiosk nodes (works in any
iframe, any origin) + shell-side focus handoff via useControllerNav;
CDP/per-app injection rejected. Implementation order included.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/tv-input-iframe-apps.md

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+# TV input: keyboard/gamepad inside iframe apps — design
+
+**Goal (2026-07-23, user requirement):** on a TV/kiosk node, keyboard and
+gamepad control must work *inside iframe apps* (IndeeHub, Jellyfin, fedimint
+UI, AIUI…), easily and globally — no per-app hacks.
+
+## What already exists
+
+- `neode-ui/src/composables/useControllerNav.ts` — a complete spatial-nav
+  system for the shell: reads gamepads (`navigator.getGamepads`), moves focus
+  between `data-controller-container` regions, plays nav sounds. It stops at
+  iframe boundaries: nothing is forwarded into frames.
+- Keyboard focus DOES enter iframes natively (click/Tab into the frame), and a
+  focused iframe receives all keys — same- or cross-origin. The gap is
+  gamepad→app and deliberate focus handoff shell↔frame.
+- Kiosk Chromium is our process (archipelago-kiosk-launcher), X11, and the ISO
+  already ships `xdotool`. Most app iframes are **cross-origin**
+  (`http://host:port`), so shell-side script injection is impossible for them;
+  only the nginx-proxied `/app/...` ones are same-origin.
+
+## Recommended architecture — two layers, both global
+
+### Layer 1 (OS, kiosk nodes): gamepad → virtual keyboard, kernel-level
+
+A small host daemon (`archipelago-gamepad-keys`) on kiosk nodes:
+
+- reads game controllers via evdev (`/dev/input/event*`, capability
+  BTN_GAMEPAD), hotplug-aware (udev monitor or 5s rescan — same pattern as the
+  audio router);
+- emits a **uinput virtual keyboard**: D-pad/left-stick → arrow keys, A →
+  Enter, B → Escape, X → Space (play/pause), Y → `f` (fullscreen in most
+  players), shoulders → Tab / Shift+Tab, Start → Enter, Select → Escape;
+- ships exactly like the audio router: `image-recipe/configs/` script + unit,
+  spliced into the ISO, `include_str!` self-heal in `bootstrap.rs`, gated on
+  the kiosk being installed. The `archipelago` user is in `input` group OR the
+  unit runs as root (uinput needs it anyway — run as root, it's ~100 lines of
+  evdev→uinput with no network).
+
+Why this layer wins: the browser sees a real keyboard, so **every iframe —
+any origin, any app — just works** the way it does for a physical keyboard
+today. Video players, web games, AIUI: all of them already have keyboard
+bindings. Zero app cooperation, zero web-platform security fights.
+
+### Layer 2 (shell): deliberate focus handoff into/out of frames
+
+Small extension to `useControllerNav`:
+
+- When spatial nav selects an app-session container and the user presses
+  A/Enter: call `iframe.focus()` (works cross-origin) — keys (real or
+  virtual) now flow into the app.
+- A dedicated **exit chord** the daemon maps from the gamepad (e.g. Home
+  button → F12 or a rarely-used key): the shell listens with a *capturing*
+  window listener; on seeing it, `iframe.blur()` + return focus to the shell
+  nav. Keyboard users get the same via a documented chord (e.g. long
+  Escape / Ctrl+Escape — plain Escape stays with the app, players use it).
+- Same-origin frames (the `/app/...` proxied set) can additionally get the
+  full spatial-nav treatment by running the existing nav over
+  `iframe.contentDocument` — nice-to-have after the layers above land.
+
+### Optional layer 3 (per-app polish): postMessage contract
+
+For OUR app UIs only (AIUI, fedimint, launcher pages): a tiny
+`archipelago:input` postMessage contract for semantic actions (back, home,
+context-menu) where raw keys aren't expressive enough. Documented in the app
+packaging docs; never required for an app to be usable.
+
+## What NOT to do
+
+- ❌ CDP (`--remote-debugging-port` + Input.dispatchKeyEvent): works but adds
+  a privileged debug port to the kiosk and a daemon↔browser coupling; the
+  uinput route gets the same result at kernel level with no attack surface.
+- ❌ Per-app nav scripts injected into iframes: cross-origin makes this
+  impossible for most apps, and it's exactly the per-app hack the requirement
+  rules out.
+
+## Implementation order
+
+1. `archipelago-gamepad-keys` daemon (evdev→uinput, ~python3 stdlib or small
+   Rust bin) + unit + ISO splice + bootstrap self-heal. Test on Framework PT
+   with any USB/BT controller.
+2. `useControllerNav`: A-button → `iframe.focus()` on the focused app session;
+   exit-chord capture listener to reclaim focus.
+3. (Later) same-origin spatial nav inside `/app/...` frames; postMessage
+   contract for our own app UIs.