404-Layers/CLAUDE.md

# SP-404MK2 layers

A combo trainer for the Roland SP-404MK2, wrapped as a sideloaded Android APK.

**Phase 1 (current):** the original single-file web app, wrapped in Capacitor as-is.
**Phase 2 (next):** port to React + TypeScript via Vite — data and pure logic with
tests first, then UI, then multitouch input.

## Layout

```
reference/     The original working web app. FROZEN — this is the spec.
               Never edit it. Behaviour, data and styling are all defined here.
native/        Native-only additions (native.css, native.js). Not in reference.
scripts/       install-android-toolchain.sh, sync-www.sh
www/           GENERATED by sync-www.sh. Never edit by hand, never committed.
android/       Generated by `npx cap add android`. A few files are hand-edited
               (see "Hand-edited native files" below).
```

## Commands

| Command | What it does |
|---|---|
| `npm run sync:www` | Rebuild `www/` from `reference/` + `native/` |
| `npm run sync` | The above, then `npx cap sync android` |
| `npm run apk` | Sync, then `./gradlew assembleDebug` |
| `npm run install:apk` | `adb install -r` the debug APK |
| `npm run run:android` | Build + install in one go — the usual loop |
| `npm run logcat` | Tail Capacitor + web console output from the device |

APK lands at `android/app/build/outputs/apk/debug/app-debug.apk`.

The Gradle build needs these in the environment (persisted to `~/.zshrc` by the
install script):

```
JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
ANDROID_HOME=$HOME/Android/Sdk
```

## Driving the device

**Launch through `scripts/device.sh`, never a bare `am start`.** TCL denies the
WebView renderer in the window just after `adb install -r`, and the app then
comes up blank with no crash, no JS error and an empty `document.title`. The
failure is sticky for the life of the process, so the app must be force-stopped
and started again — which is exactly what the helper retries.

Keep the phone unlocked while working. That is not what causes the denial (see
Device notes), but nothing on screen can be verified through a lockscreen and
`input keyevent` will not reach the app.

`scripts/device.sh` handles this so it cannot be forgotten:

| Command | What it does |
|---|---|
| `npm run device:keep-awake` | Stay awake while charging. Do this at the start of a session. |
| `npm run device:launch` | Check awake/unlocked, force-stop, start, wait for the page to actually parse |
| `npm run device:awake` | Just the check — prints a loud warning if locked |
| `npm run device:sleep-normal` | Revert the stay-awake setting when finished |

`device:launch` waits for the page, not merely for the activity: the activity
starts fine even when the renderer was denied. On failure it prints the
`AppBootManager` denial lines rather than leaving a blank window to puzzle over.

It also reads the pid *after* starting the app. `adb install -r` kills the
running process, so a pid captured earlier points at a dead process and the
devtools socket lookup fails while the app itself is healthy — that produced one
false "page never loaded" during Phase 1.

To attach Chrome DevTools by hand: `chrome://inspect`, or
`adb forward tcp:9333 localabstract:webview_devtools_remote_$(adb shell pidof dev.ncode.sp404layers)`
and open `http://127.0.0.1:9333/json`.

## Toolchain (verified, do not bump blind)

Pinned against Capacitor 8.5.2's `capacitor/build.gradle`:
`compileSdk 36`, `targetSdk 36`, `minSdk 24`, Java 21.

- JDK **21** — required by Capacitor 8; `openjdk-21-jdk` from apt
- cmdline-tools **15859902**
- build-tools **36.1.0** — pairs with compileSdk 36
- platforms **android-35**, **android-36**

`sdkmanager` prints a deprecation warning pointing at the newer `android` CLI.
It still works, and it writes the `licenses/` directory that Gradle checks. The
replacement downloads itself on first run and gates on an interactive ToS, which
is worse in an idempotent install script. Revisit if it actually breaks.

## Decisions

**`reference/` is never edited.** It is the Phase 2 spec, so it has to stay
byte-for-byte comparable. Everything native-specific is either an additive file
or one of three removals applied by `sync-www.sh`, which asserts each anchor
exists and fails loudly if the reference ever changes shape.

The three removals:
1. **Service worker registration** — would cache `index.html` and serve a stale
   app after an APK update. Assets are already local, so it buys nothing.
2. **Web manifest link** — the APK's own manifest governs the app.
3. Nothing else. `native.css` and `native.js` are *injected*, not substituted.

**Haptics needs no reference change.** `buzz()` is a `const` and cannot be
reassigned, but it calls `navigator.vibrate`, which can be overridden. `native.js`
redefines that to dispatch to `@capacitor/haptics`: scalar → `impact`, array →
`notification({type:"SUCCESS"})`, `>15` → `notification({type:"ERROR"})`.

**Storage mirrors rather than migrates.** `localStorage` stays the synchronous
source of truth so `load()`/`save()` keep their signatures. `save()` is wrapped
to mirror into `@capacitor/preferences` (SharedPreferences), which survives a
"clear app data" wipe. On boot, if `localStorage` is empty but Preferences is
not, it restores and re-renders. A full async port was rejected as a refactor of
code about to be rewritten in React anyway.

**Back button** is owned by `native.js`: sheet open → close it; otherwise not on
Explore → go to Explore; otherwise exit. Registering a listener suppresses
Capacitor's default history navigation.

**System bars: let Capacitor do it, by dropping `viewport-fit=cover`.** The app
renders between the status and gesture bars, always.

Capacitor 8 ships a `SystemBars` plugin that owns inset handling from a listener
on the **decor view**. Its behaviour hinges on the viewport meta tag:

- **with `viewport-fit=cover`** (what `reference/` has), `shouldPassthroughInsets`
  becomes true once `onPageCommitVisible` has checked the tag and called
  `requestApplyInsets()`. Decor padding drops to 0, the WebView grows from 735 to
  820, and the page must place itself from injected CSS variables.
- **without it**, the plugin pads the decor view instead. The WebView is 735px
  and already sits between the bars; `env(safe-area-inset-*)` and the
  reference's `--sab` are 0, and `.bnav` and `.sheet` are correct as written.

So `sync-www.sh` strips `viewport-fit=cover` from the generated `www/` (patch 5).
No native→web handshake exists, so there is nothing to race and no launch-time
layout jump. Verified identical across cold launch, resume and in-place reload:
`h=735 padTop=8px overflowBy=0`.

**This costs no space.** 820 − 45 − 114 and 735 − 8 − 66 both leave 661px, because
the bars take the same room whether the WebView is padded or draws underneath.
Reclaiming that 85px would mean *hiding* the bars, which is a different choice.

An earlier version did the opposite: `MainActivity` installed its own
`OnApplyWindowInsetsListener` on the WebView and pushed `--ins-t/r/b/l` through
`window.__applyInsets()`, with a 25 × 200ms retry. That was written without
realising Capacitor already had a plugin for this. The two listeners were on
different views, so they stacked rather than replaced each other, and the app
drew under the bars at random depending on which fired last. `MainActivity` is
now empty and bar styling is configured in `capacitor.config.json`
(`SystemBars.style: DARK`).

**No community plugins.** Only first-party: `@capacitor/core`, `/cli`,
`/android`, `/haptics`, `/preferences`, `/app`.

**Debug signing.** The debug keystore is stable per-machine, so Phase 2's APK
installs over Phase 1's without an uninstall and drill progress survives.
`appId` is `dev.ncode.sp404layers` and must not change for the same reason.

## Phase 2: the React port

Stack: **Vite + React + TypeScript + Vitest**. No router, no state library, no UI
kit — the app is four tabs and a reducer, and none of those earn their keep.

| Command | What it does |
|---|---|
| `npm test` | Run the domain suite once |
| `npm run test:watch` | Watch mode |
| `npm run typecheck` | `tsc --noEmit` |
| `npm run extract:data` | Regenerate the combo table from `reference/` |

```
src/domain/
  types.ts     hand-written: RawEntry, Entry, ContextCode, GroupId
  raw.ts       GENERATED — the 159-row combo table
  labels.ts    GENERATED — control labels, groups, contexts
  entries.ts   derives Entry[] from RAW
  layers.ts    which combos exist for a context + held modifiers
  drill.ts     decks, Leitner boxes, answer checking, card selection
  format.ts    ids to printed words, and the "SHIFT + PAD 1" lines
  search.ts    the Find tab's matcher
  storage.ts   the persisted blob, backup parsing, defaults
```

**Two strings are load-bearing for migration** and must not be changed casually:
`Entry.id` (below) and `STORAGE_KEY`, still `sp404mk2-layers-v1`. Together they
mean the boxes already on the phone are picked up by the React app rather than
orphaned. `storage.test.ts` parses a payload copied verbatim out of
`CapacitorStorage.xml` on the device, so a change that would break that fails.

**The combo table is never transcribed by hand.** `scripts/extract-reference-data.mjs`
lifts the literals out of `reference/index.html`, evaluating only pure-data
declarations in a `vm` with no DOM, and writes `raw.ts` and `labels.ts`. Re-run it
after any reference change; never edit those two files. Retyping 159 rows is
precisely where silent errors would creep in, and the extraction cross-checks:
159 entries, matching the count the Phase 1 app reported on the device.

**`Entry.id` keeps the reference's format verbatim** (`shift>p1@S#FIX VEL`) — built
from the *unsplit* context string and the target as authored. That string is the
key drill progress is stored under, so preserving it byte-for-byte means existing
boxes on the phone migrate to the React app instead of being orphaned.

**The domain layer is pure.** The reference mutated a module-level `store` and
called `Math.random()` inline; here boxes go in and new boxes come out, and the
random source is injected. That is what makes card selection testable at all.

Tests assert against numbers **observed on the device**, not just against the
code: 159 entries, sample-mode layer counts of 3 / 35 / 2 for no-modifier /
SHIFT / SHIFT+REVERSE, and a 16-card SHIFT+pads deck.

## Visual spec (settled — build Phase 2 against this)

The look is **Direction A, "manual"**, after Teenage Engineering's EP-133 manual,
with a dark counterpart. Canvas: https://claude.ai/artifact/4Jvjop1hEsJY2xzcpGrrgg
Working files: `design/canvas/*.dc.html` + `canvas.json` (the seeded payload is
gitignored and regenerates from them).

**`reference/` is now the behaviour and data spec only.** It no longer governs
appearance — this section and the canvas do. Combos, layer logic, Leitner
scheduling and the pointer model still come from the reference.

The language:

- Flat fills, no gradients, no blur. Depth is a **hard zero-blur offset shadow**:
  4px on the panel, 3px on cards and pickers.
- **2px `#111111` outlines** everywhere (dark mode: 2px `#000000`).
- **One accent, `#FF4A00`**, meaning exactly one thing: this control is live.
  Pad numerals stay grey so the accent is never ambiguous.
- Uppercase, technical labels; monospaced numerals and annotations.
- **No green or red.** Drill feedback is orange fill for correct, dashed outline
  for not-quite.
- The LCD is a **positive** display — `#C9D2C4` with dark text — in both modes.

Panel construction, drawn from the hardware rather than invented:

- The screen's circle sits **behind** the display, not around it: a 124px circle
  behind a 168×84 LCD shows only as two 20px caps above and below. The display
  names the layer and lists what is on it.
- The control block is grouped as the unit is silkscreened (`PATTERN SEQUENCER`,
  `SAMPLING`, `SAMPLE EDIT`, `BANK`), each group a hairline bracket caption over
  its row, 10px between the two blocks and 7px between groups.
- FX buttons are dark with orange text, as on the device.
- Key labels are **7px, no letter-spacing, 1px side padding**. A left-block
  button is 35.9px wide and only 27.9px of that is usable text width; at 8px with
  tracking `SAMPLE` measured ~27.8px and sat flush against the border.
  `RESAMPLE`, `REMAIN` and `REVERSE` are the only labels with no space in them,
  so they carry soft hyphens — everything else wraps at its space.
- `SHIFT` gets `flex: 1.25` in the six-button bank row, as the hardware widens it.

Vertical budget at the real 360×735, which nothing may exceed:

```
root   8 + 44 + 8 + 525 + 8 + 84 + 8 + 50            = 735
panel  8 + 36 + 8 + 124 + 10 + 134 + 10 + 187 + 8    = 525
pads   (187 - 15) / 4                                = 43px rows
```

**Typeface: Space Grotesk + Space Mono.** Space Grotesk for labels and headings,
Space Mono for numerals and technical annotations. Self-hosted as woff2 under
`public/fonts/` — the app must work with no network, as Barlow did. Martian Mono
was the alternate and was rejected on measurement: it is a wide mono, and key
labels already clear their buttons by only 2.3px at 7px.

**Accent: `#FF4A00`.** TE's orange, not the softer `#ff7a1a` Phase 1 used. It
holds against both the light body and the dark mode's near-black, which matters
because the accent has exactly one job — marking a control as live.

## Phase 2 must carry these UI changes

Phase 1 fixes a strip ergonomics problem in `native/native.{css,js}` rather than
in `reference/`, which stays frozen. The React port must reproduce these, since
they will not come along with the reference:

1. **The two chip rows sit flush on phones.** The reference spaces them with
   `#strip .chips + .chips { margin-top: 6px }`, but the `.lbl` heading between
   them is `display:none` on phones and still in the DOM, so the adjacent-sibling
   selector never matches. Measured gap: 0px. Both selected chips are also
   light-filled and left-aligned, so they visually merge into one shape.
2. **Both chip rows collapse into two pickers side by side on one 44px row.**
   Only one layer is ever active, so neither the mode nor the layer needs a
   scrolling row of its own. Each opens the existing sheet. The mode sheet shows
   `CTXHINT`, which the phone layout otherwise never displays; the layer sheet
   shows each layer's function count.

   This matters for the panel, not just for tidiness: `.pads` uses
   `minmax(34px, 1fr)` rows and on this device it sits exactly at that 34px
   floor, so the SP-404 illustration clips at the bottom if anything takes more
   room. Two rows cost 96px; one costs 44px, and the 52px goes to the panel.

   The layer list is read out of the reference's own chips at render time rather
   than recomputed, so the set, ordering and counts cannot drift from what
   `renderExplore()` decided. In React this becomes shared derived state
   instead.
3. **Chip targets go from 34.9px to 44px.** They scroll horizontally, so an
   undersized target turns a mis-hit into a scroll instead of a tap.
4. **Overflowing rows get a right-edge fade.** Scrollbars are hidden, and both
   rows overflow badly (703px and 952px of content in a 360px viewport) with
   nothing indicating more content. The fade is applied only to rows that
   actually overflow.

In React this should be real component state, not a post-render DOM patch:
Phase 1 has to re-apply the collapse after every `renderExplore()` because that
function rewrites `#strip` wholesale.

## Hand-edited native files

`cap sync` does not regenerate these — keep them when recreating `android/`:

- `android/app/src/main/AndroidManifest.xml` — `android:screenOrientation="portrait"`

That is the only one. `MainActivity.java` is deliberately an empty
`BridgeActivity`: everything it used to do is either configured in
`capacitor.config.json` or handled by Capacitor's own `SystemBars` plugin. If
you find yourself adding an inset listener there, read the system-bars decision
above first — that path has already been tried and reverted.

## Device notes (TCL 50 PRO NXTPAPER 5G, Android 16 / API 36)

**adb needs a udev rule.** The phone is USB `1bbb:0c01`. Ubuntu's
`android-sdk-platform-tools-common` matches vendor *and* product, and lists only
older TCL products, so nothing matched and the device node stayed `root:root`.
Fixed with a vendor-wide rule (product IDs change with USB mode):

```
echo 'SUBSYSTEM=="usb", ATTR{idVendor}=="1bbb", MODE="0660", GROUP="plugdev", TAG+="uaccess"' \
  | sudo tee /etc/udev/rules.d/51-android-tcl.rules
sudo udevadm control --reload-rules && sudo udevadm trigger
```

It lives in `/etc/udev` so apt upgrades don't overwrite it. The `uaccess` tag
grants the logged-in session access, so no logout is needed.

**A blank grey window means the renderer was denied — relaunch.** TCL's
`AppBootManagerService` sometimes refuses to let the app bind the WebView's
sandboxed renderer process:

```
W/AppBootManager: Type[TYPE_SERVICE];Result[false];
  Target[org.chromium.content.app.SandboxedProcessService0];
  Caller[dev.ncode.sp404layers];Reason[screen_on & caller care]
E/cr_ChildProcessConn: Failed to establish the service connection.
```

With no renderer the page never parses, so there is no crash, no JS error, an
empty `document.title`, and DevTools `Runtime.evaluate` hangs. The failure is
sticky for the life of the process — reopening from Recents keeps the grey
window. Only `am force-stop` plus a fresh start clears it.

**The trigger is the window just after `adb install -r` replaces the package.**
Every observed failure followed an install; an immediate relaunch with no
install has always succeeded on the first try. Do not trust the `Reason` string:
it reports the current screen state, and both `screen_off` and `screen_on` have
been seen denying, so screen state is not the cause. An earlier version of this
file claimed it was — that was wrong.

`scripts/device.sh launch` therefore retries the whole force-stop/start cycle up
to 3 times. This is an OEM policy, not an app bug, and it only bites when
launching over adb — tapping the icon is fine.

## Gotchas

- The reference's multitouch relies on `touch-action:none` on `.unit` plus
  per-`pointerId` tracking in a `Map`. This is the most delicate part to port in
  Phase 2 — read `exDown`/`exUp`/`drDown`/`drUp` before touching it.
- `store`, `st` and `SK` are `const`/`let` at classic-script top level: reachable
  by bare name from `native.js`, but absent from `window`. `save`/`render`/
  `closeSheet` are function declarations, so they *are* on `window` and can be
  wrapped.