docs: document the foliate-js reader

Adds a reader section covering the vendored tree, the $foliate alias and the
traps around it, and refreshes the stale stack line, oklch claim and rough
edges. Records why CSP is not enabled in TODO.md.

AGENTS.md

@@ -9,13 +9,15 @@ a KOSync-compatible endpoint.
 
 ## Layout
 
-| Path | What |
+| Path                       | What                                                                                     |
-| --- | --- |
+| -------------------------- | ---------------------------------------------------------------------------------------- |
-| `backend/` | Litestar REST API + PostgreSQL. See `backend/AGENTS.md`. |
+| `backend/`                 | Litestar REST API + PostgreSQL. See `backend/AGENTS.md`.                                 |
-| `frontend/` | SvelteKit SSR web app. See `frontend/AGENTS.md`. |
+| `frontend/`                | SvelteKit SSR web app. See `frontend/AGENTS.md`.                                         |
-| `docker-compose.yml` | Production stack: `db` (postgres:17), `backend`, `frontend`. |
+| `frontend/src/lib/vendor/` | Vendored `foliate-js` (the EPUB engine), copied by `frontend/scripts/vendor-foliate.sh`. |
-| `docs/screenshots/` | Images used by `README.md`. |
+| `frontend/static/pdfjs/`   | Vendored pdf.js viewer, used by the PDF reader in an iframe.                             |
-| `shell.nix` | Root dev shell; composes the two sub-shells. |
+| `docker-compose.yml`       | Production stack: `db` (postgres:17), `backend`, `frontend`.                             |
+| `docs/screenshots/`        | Images used by `README.md`.                                                              |
+| `shell.nix`                | Root dev shell; composes the two sub-shells.                                             |
 
 ## Development environment
 

TODO.md

@@ -51,6 +51,29 @@ Worth adding at the same time:
 
 ## Frontend
 
+### No CSP, so scripted EPUBs run against the app origin
+
+EPUB files may contain JavaScript. foliate-js renders each section in an iframe from a
+**same-origin** `blob:` URL and cannot sandbox it — `allow-scripts` is required, and
+blob URLs inherit the embedder's origin — so script inside a book can reach `/api/*`
+with the session cookie attached. foliate's own README says not to use it without a
+Content Security Policy blocking scripts.
+
+The obvious policy is `kit.csp` in `svelte.config.js` with `script-src: ['self']`, and
+deliberately no `default-src` (it would also cover `style-src`/`img-src`/`font-src` and
+kill both the book's own blob: assets and the inline `<style id="chitai-theme">` that
+`hooks.server.ts` injects via `transformPageChunk`).
+
+**What blocks it:** `mode-watcher` renders its own inline `setInitialMode` script, which
+sets the dark class before first paint. SvelteKit only nonces the bootstrap script it
+injects itself, so that one is blocked and every page load flashes the light theme.
+Fixing it means pinning a SHA-256 of a third-party inline script whose contents change
+with the package version and the props passed — it would break silently on upgrade, and
+the symptom would be a theme flash rather than an error.
+
+Worth revisiting if `mode-watcher` gains a nonce prop, or if the theme class moves to a
+cookie so the server can set it without an inline script.
+
 ### Remove the epub.js locations-cache purge
 
 `frontend/src/lib/reader/legacy-cache.ts` — `purgeLegacyLocationCache`

frontend/AGENTS.md

@@ -4,13 +4,16 @@ SvelteKit web app for the eBook library. See the repo-root `AGENTS.md` for the o
 dev-environment setup.
 
 **Stack:** SvelteKit 2 with `adapter-node` · Svelte 5 (runes) · Tailwind v4 · Zod v4 ·
-`epubjs` · `mode-watcher` (dark mode) · `svelte-sonner` (toasts) · pnpm.
+vendored `foliate-js` (EPUB) · vendored `pdf.js` (PDF) · `mode-watcher` (dark mode) ·
+`svelte-sonner` (toasts) · pnpm.
 
 Two experimental flags are on in `svelte.config.js` and the codebase depends on both:
 `kit.experimental.remoteFunctions` and `compilerOptions.experimental.async` (`await` in components).
 
-Tailwind v4 has **no config file** — the theme, oklch colour tokens and `@custom-variant dark` all
+Tailwind v4 has **no config file** — the theme, colour tokens (hex, not oklch) and
-live in `src/app.css`.
+`@custom-variant dark` all live in `src/app.css`. `dark` is the _only_ custom variant defined, so
+generated components that assume others — shadcn's slider ships `data-horizontal:` / `data-vertical:`
+classes — silently produce no styles. Use the `data-[orientation=…]` form instead.
 
 ## Talking to the backend
 
@@ -65,8 +68,12 @@ Svelte context with a module-level `Symbol` key and a `setXState` / `getXState`
 
 ```ts
 const LIBRARY_KEY = Symbol('LIBRARY');
-export function setLibraryState(libraries: Library[]) { return setContext(LIBRARY_KEY, new LibraryState(libraries)); }
+export function setLibraryState(libraries: Library[]) {
-export function getLibraryState() { return getContext<ReturnType<typeof setLibraryState>>(LIBRARY_KEY); }
+	return setContext(LIBRARY_KEY, new LibraryState(libraries));
+}
+export function getLibraryState() {
+	return getContext<ReturnType<typeof setLibraryState>>(LIBRARY_KEY);
+}
 ```
 
 Follow that pattern rather than introducing stores. `library.svelte.ts` is the reference — including
@@ -79,10 +86,56 @@ its optimistic-delete-with-rollback and toast handling. `bookCollection` / `book
   `@ieedan/shadcn-svelte-extras` (`jsrepo.json`). Treat as generated: add components with the CLIs
   rather than hand-writing them, and prefer wrapping over editing.
 - App components live in `forms/`, `layout/`, `view/` (browser, grid/list/table, filters, sort) and
-  `reader/` (epub reader + chapter sidebar).
+  `reader/` (see [The readers](#the-readers)).
 - `cn()` from `$lib/utils` merges Tailwind classes; the `WithElementRef` / `WithoutChild` helpers
   there are the shadcn prop-typing conventions.
 
+## The readers
+
+**PDF** is the pdf.js viewer vendored under `static/pdfjs/`, pointed at by an iframe. Untouched by
+the EPUB work; leave it alone unless the task is about PDFs.
+
+**EPUB** is built on `foliate-js`, copied verbatim into `src/lib/vendor/foliate-js/` by
+`scripts/vendor-foliate.sh` (pinned commit; see `src/lib/vendor/foliate-js/README.chitai.md`).
+Upstream has no npm release and recommends a submodule; this repo has none and already vendors
+pdf.js the same way, so it is copied instead. Only the import closure reachable from `view.js` is
+vendored, and **`pdf.js` in that directory is our stub, not upstream's** — the real one imports a
+bare `@pdfjs/pdf.min.mjs` that Rollup resolves at build time even though the path never runs.
+
+Layout:
+
+| Path                                       | What                                                                         |
+| ------------------------------------------ | ---------------------------------------------------------------------------- |
+| `lib/vendor/foliate-js/`                   | The engine. Do not edit — `vendor-foliate.sh` overwrites it.                 |
+| `lib/reader/foliate.ts`                    | Lazy loader for the custom elements. The only thing that imports `$foliate`. |
+| `lib/reader/settings.ts` · `stylesheet.ts` | Defaults/bounds, and the CSS injected into the book.                         |
+| `lib/reader/progress.ts`                   | Debounced progress writer with a `sendBeacon` flush.                         |
+| `lib/state/reader-settings.svelte.ts`      | Settings state, persisted to `localStorage`.                                 |
+| `components/reader/foliate-view.svelte`    | Wraps `<foliate-view>`; owns the imperative lifecycle.                       |
+| `components/reader/epub-reader.svelte`     | The shell: chrome, TOC, errors, progress.                                    |
+
+Things that will bite:
+
+- **`$foliate` is a Vite-only alias.** It is deliberately absent from `kit.alias` and tsconfig
+  `paths` so TypeScript cannot resolve it and falls back to the ambient declaration in
+  `lib/reader/foliate-js.d.ts`; `src/lib/vendor` is also in tsconfig `exclude`. Without both,
+  `checkJs` walks ~11k lines of untyped JS. The declaration file must **not** be named `foliate.d.ts`
+  — beside `foliate.ts`, TypeScript takes it for that file's emitted declaration and drops it.
+- **Never import the vendored code at module scope.** `view.js` calls `customElements.define` and
+  subclasses `HTMLElement` on import, so it must stay behind `loadFoliate()` inside `onMount`. SSR is
+  otherwise on for the reader route.
+- **Sections render in iframes, which swallow key events.** Keyboard handlers are bound per section
+  document on the `load` event, and modifier combinations are replayed onto the host window so app
+  shortcuts (the sidebar's ctrl+B) still work while reading.
+- **Renderer settings split two ways.** Flow, gap, margins, column count and line width are
+  _attributes_ set with `setAttribute` (there is no JS property API, no `margin` shorthand and no
+  `spread` — a spread is `max-column-count: 2`). Typography is CSS passed to `renderer.setStyles`,
+  which takes a `[before, after]` pair: the first is prepended to the section head so the book
+  overrides it, the second appended so it wins. User settings belong in the second, with
+  `!important`, or the book's own CSS beats them.
+- **Progress needs no locations pre-pass.** `relocate` carries both a CFI and an overall `fraction`,
+  which map straight onto `epub_cfi` and `percentage`.
+
 ## Routing
 
 Route groups carry the layout structure:
@@ -95,21 +148,26 @@ Route groups carry the layout structure:
 ## Conventions
 
 Prettier (`.prettierrc`): tabs, single quotes, no trailing commas, 100 columns, with the Svelte and
-Tailwind plugins. Run `pnpm check` (svelte-check) and `pnpm lint` before considering work done.
+Tailwind plugins. Run `pnpm check` (svelte-check) and `pnpm lint` before considering work done —
+but take a baseline first, because neither is clean (see below).
+
+`src/lib/vendor/` is excluded from Prettier, ESLint and svelte-check. Don't reformat vendored code.
 
 ## Known rough edges
 
 Observed in the current tree — don't mistake these for intentional patterns to copy:
 
 - `src/lib/schema/openapi/schema.d.ts` is **stale** — it predates the `BookProgress` rework and has
-  no `BookProgressRead`, so `book.progress` types as `{}`. This is the source of most of the ~104
+  no `BookProgressRead`, so `book.progress` types as `{}`. It is the source of most of the errors
-  errors `pnpm check` reports on a clean tree; regenerating it should clear them. Get a baseline
+  `pnpm check` reports; regenerating it should clear them. **Baseline as of 2026-08-11: 37 errors,
-  before assuming an error is yours.
+  1 warning, 11 files.** Get your own baseline before assuming an error is yours.
+- `pnpm lint` does not pass either — 131 pre-existing ESLint errors, 35 of them
+  `svelte/no-navigation-without-resolve` on plain `href`s, plus ~59 files Prettier would rewrite
+  (mostly vendored shadcn components). Check the files you touched, not the whole tree.
 - `src/routes/api/[...path]/+server.ts` — all four handlers are annotated `RequestHandler` while the
-  import of that type is commented out at line 4.
+  import of that type is commented out at line 4. It also buffers whole responses with
-- `src/app.d.ts` — `App.Locals["user"]` is typed from `lucide-svelte`'s `User` *icon* component
+  `arrayBuffer()` and forwards no `Range` header, so book downloads are not streamed.
+- `src/app.d.ts` — `App.Locals["user"]` is typed from `lucide-svelte`'s `User` _icon_ component
   rather than the `User` interface in `$lib/server/auth`.
-- Uncommitted work in progress (as of 2026-08-10): library icons, spanning
+- No CSP, which foliate's README asks for because EPUBs can carry scripts. See `TODO.md` for why it
-  `components/ui/icon-picker/`, the newly vendored `components/ui/popover/`,
+  is not enabled yet.
-  `forms/library-create-form.svelte`, `layout/library-switcher.svelte` and `schema/library.ts`.
-  Prefer not to refactor those files mid-flight.