# Architecture Three pages, one shared core, a handful of single-purpose build plugins. No framework, no state library — each page is one TypeScript module wiring DOM to the shared code. ## Pages | dir | page | entry | |---|---|---| | `/` | home: cards, share dialog | `home/main.ts` | | `send/` | file/snippet → fountain-coded QR stream on a canvas | `send/main.ts` | | `receive/` | camera → WASM QR decode in workers → fountain decoder → file | `receive/main.ts`, `receive/worker.ts` | The send page carries two non-entry modules: `send/qr-frame.ts`, the one QR generation path (pinned mask, version locking) shared by the live stream and the exporter so the two cannot drift apart, and `send/export.ts`, the animation exporter — the stream rendered into a looping APNG or a PNG-sequence ZIP, DOM-free so the whole pipeline is Node-tested (`tests/animation-export.test.ts` pins its frames pixel-for-pixel to the rasterizer, and its size forecast samples a real frame rather than modeling one). ## Shared modules (`shared/`) - `fountain.ts` — LT encoder/decoder, deterministic soliton distribution (see [Protocol](protocol.md)). - `protocol.ts` — frame header pack/parse, file container, SHA-256 verification, stream identity. - `frame-capacity.ts` — QR capacity math: payload size → block length / count limits. - `qr-raster.ts` — QR module matrix → RGBA raster. - `png.ts` — bilevel (1 bit per pixel, 2-entry palette) PNG primitives: chunk writer, CRC-32, scanline packing with an integer upscale baked in, deflate via the same `CompressionStream` the container uses. Palette rather than grayscale is deliberate — ffmpeg's APNG decoder refuses 1-bit grayscale, which would strand the export for the video pipelines it targets. - `apng.ts` — APNG assembly over `png.ts`: `acTL`/`fcTL`/`fdAT`, exact rational frame delays, infinite loop. - `zip.ts` — store-mode ZIP writer for the PNG-sequence export; structure only, the PNGs are already deflated. - `display.ts` — QR display-size fitting against the viewport. - `platform.ts` — `isIOS`/`isAndroid` sniffs and camera capability probing (torch, continuous focus, max fps). Policy: probe wherever probeable; sniff only for unprobeable behavior. - `worker-pool.ts` — decode worker pool; busy workers drop frames, the fountain absorbs it. - `no-signal.ts` — pure timing policy for the "Nothing happening?" hint (short first delay, longer after dismissal). - `progress.ts` — frames-collected progress estimation and fountain-overhead model. - `send-settings.ts` — canonical tx settings lists; the sender's dropdowns and the no-signal advice both render from it. - `snippet.ts` — text-snippet container type. - `dialog.ts` — geometric backdrop-click close for `