novela/docs/TECHNICAL.md

# Novela 2.0 - Technical Status (Develop)

## Scope
This document describes the current technical status of the `develop` codebase.
It is the primary technical reference for the current implementation.

## Architecture
- Stack: FastAPI, Jinja2 templates, plain JavaScript, PostgreSQL 16, Docker.
- Startup lifecycle (`main.py`):
  1. `init_pool()`
  2. `run_migrations()`
  3. `start_backup_scheduler()`
  4. mount routers
- Shutdown lifecycle:
  1. `stop_backup_scheduler()`
  2. `close_pool()`
- Source-of-truth rule: files on disk are authoritative, the database is an index/cache.

## File Storage Paths

All files are stored under `library/` (relative to the app working directory, mapped via Docker volume).
`LIBRARY_DIR = Path("library")`, `LIBRARY_ROOT = LIBRARY_DIR.resolve()`.

### Path structure per format

| Format | Path pattern |
|--------|-------------|
| EPUB (no series) | `library/epub/{publisher}/{author}/Stories/{title}.epub` |
| EPUB (series) | `library/epub/{publisher}/{author}/Series/{series}/{idx:03d} - {title}.epub` |
| PDF | `library/pdf/{publisher}/{author}/{title}.pdf` |
| CBR (no series) | `library/comics/{publisher}/{author}/{title}.cbr` |
| CBR (series) | `library/comics/{publisher}/{author}/Series/{series}/{idx:03d} - {title}.cbr` |
| CBZ (no series) | `library/comics/{publisher}/{author}/{title}.cbz` |
| CBZ (series) | `library/comics/{publisher}/{author}/Series/{series}/{idx:03d} - {title}.cbz` |

- Segments are sanitised: special chars stripped, max lengths applied (publisher/author 80, title 140, series 80).
- Series index is zero-padded to 3 digits (`001`, `002`, …), clamped to 1–999.
- Duplicate filenames get a `(2)`, `(3)`, … suffix.
- After any file move, empty parent directories are pruned up to `LIBRARY_ROOT`.

### Path logic

- `common.make_rel_path(media_type, publisher, author, title, series, series_index, ext)` — used by import and grabber.
- `reader.py _make_rel_path(publisher, author, title, series, series_index, ext)` — used by metadata PATCH; same logic, uses actual file extension.
- Both functions produce identical paths for all formats.

### Metadata save behaviour per format

| Format | File written? | DB written? |
|--------|--------------|-------------|
| EPUB | Yes — OPF metadata updated in-place | Yes |
| PDF | No | Yes |
| CBR | No | Yes |
| CBZ | No (tags/metadata); rating written to ComicInfo.xml | Yes |

---

## Router Status

### `routers/library.py`
- `GET /library` — library page
- `GET /api/library` — book list JSON (fast-path by default)
- `POST /library/rescan` — forced full disk rescan
- `POST /library/import` — upload EPUB/PDF/CBR/CBZ
- `DELETE /library/file/{filename}` — delete file + DB row + prune dirs
- `GET /download/{filename}` — download file with `Content-Disposition: attachment`
- `GET /library/cover/{filename}` — serve cover (EPUB from file; PDF/CBR from cache)
- `GET /library/cover-cached/{filename}` — serve cover from DB cache only
- `POST /library/cover/{filename}` — upload/replace cover (EPUB only)
- `POST /library/want-to-read/{filename}` — toggle want-to-read flag
- `POST /library/archive/{filename}` — toggle archived flag
- `POST /library/new/mark-reviewed` — bulk set `needs_review=false`
- `POST /library/bulk-delete` — delete multiple files; accepts `{"filenames": [...]}`, removes files from disk and DB in one query per batch; returns `{ok, deleted, skipped}`
- `POST /library/rating/{filename}` — set/clear star rating `{"rating": 0-5}`
- `GET /home` — home page
- `GET /api/home` — home data JSON
- `GET /stats` — statistics page
- `GET /api/stats` — statistics data JSON
- `GET /api/disk` — partition usage for the library directory: `{total, used, free, pct_used}`
- `POST /api/bulk-check-duplicates` — accepts `{"items": [{title, author, volume}, ...]}`, returns `{"duplicates": [bool, ...]}` — when `volume` is a number, requires title+author+series_index to all match; when volume is absent, matches on title+author only
- `GET /library/list` — compat alias

`GET /api/library` runs in fast-path mode by default (DB-only, no full disk rescan).
For a forced sync: `GET /api/library?rescan=true` or `POST /library/rescan`.
`include_file_info=true` is optional for file size/mtime enrichment.
ETag caching: response includes `ETag: "{count}-{max_updated_at_unix}"` and `Cache-Control: no-cache`. Client sends `If-None-Match`; server returns `304 Not Modified` when nothing changed.

`/api/home` returns:
- `continue_reading`
- `shorts_unread`
- `novels_unread`
- `shorts_read`
- `novels_read`

`/api/stats` returns totals plus chart/history data for `stats.html`:
- `reads_by_month`, `reads_by_dow`, `reads_by_hour`
- `genre_counts`, `publisher_counts`, `fav_genre`, `fav_publisher`
- `top_books`, `history`

Home sections exclude series books via:
- `COALESCE(series, '') = ''`
- `filename NOT LIKE '%/Series/%'`

Home read sections are ordered oldest-first:
- `shorts_read`: `ORDER BY MAX(read_at) ASC`
- `novels_read`: `ORDER BY MAX(read_at) ASC`

### `routers/reader.py`
- `GET /library/epub/{filename}` — serve EPUB inline (no attachment header)
- `GET /library/chapters/{filename}` — EPUB spine as JSON
- `GET /library/chapter/{index}/{filename}` — single EPUB chapter as HTML fragment
- `GET /library/chapter-img/{path}?filename=…` — image extracted from EPUB ZIP; `path` is the full internal ZIP path (e.g. `OEBPS/Images/cover.jpg` or `EPUB/images/cover.jpg`); case-insensitive fallback for mismatched folder names
- `GET /library/pdf/{filename}?page=N&dpi=150` — render PDF page as PNG
- `GET /api/pdf/info/{filename}` — `{"page_count": N}`
- `GET /library/cbr/{filename}/{page}` — CBR/CBZ page as image
- `GET /library/progress/{filename}` — read progress
- `POST /library/progress/{filename}` — save progress `{"cfi": "…", "progress": N}`
- `DELETE /library/progress/{filename}` — clear progress
- `POST /library/mark-read/{filename}` — mark as read (with optional date)
- `GET /library/book/{filename}` — book detail page
- `GET /api/genres` — all tags from `book_tags` (optional `?type=genre|subgenre|tag`)
- `PATCH /library/book/{filename}` — update metadata + tags; moves file if path fields change; DB-only for non-EPUB
- `POST /library/rating/{filename}` — set/clear 1–5 star rating; writes to EPUB OPF / CBZ ComicInfo.xml; DB-only for CBR/PDF
- `GET /library/read/{filename}` — reader page (EPUB or PDF); supports `?bm_ch=N&bm_scroll=F` to jump to bookmark position
- `GET /library/bookmarks/{filename}` — list bookmarks for a book
- `POST /library/bookmarks/{filename}` — add bookmark `{chapter_index, scroll_frac, chapter_title, note}`
- `PATCH /library/bookmarks/{id}` — update bookmark note
- `DELETE /library/bookmarks/{id}` — delete bookmark
- `GET /api/bookmarks` — all bookmarks across all books (includes `book_title`, `book_author`)

### `routers/bulk_import.py`
- `GET /bulk-import` — Bulk Import page
- `POST /library/bulk-import` — import files with pre-parsed metadata; accepts multipart `files[]`, `rows` (JSON array of per-file metadata), `shared` (JSON with author/publisher/status/genres/tags applied to all files)

Filename parsing is done client-side in `bulk_import.html`. The page uses a free-text `%placeholder%` pattern (e.g. `%series% - %volume% - %title% - %year%`). Available placeholders: `%series%` `%volume%` `%title%` `%year%` `%month%` `%day%` `%author%` `%publisher%` `%ignore%`. Colored chips can be clicked (insert at cursor) or dragged onto the input. Pattern is converted to a regex at parse time. Shared metadata fields override filename-parsed values. Files are uploaded in batches of 5 with a progress bar.

### `routers/editor.py`
- `GET /library/editor/{filename}` — EPUB chapter editor page
- `GET /api/edit/chapter/{index}/{filename}` — get chapter HTML
- `POST /api/edit/chapter/{index}/{filename}` — save chapter HTML
- `POST /api/edit/chapter/add/{filename}` — add new chapter
- `DELETE /api/edit/chapter/{index}/{filename}` — delete chapter

### `routers/grabber.py`
- `GET /grabber` — grabber page
- `GET /convert` — convert page
- `GET /credentials-manager` — credentials manager UI
- `GET /debug` — debug page
- `POST /debug/run` — run debug scrape
- `GET /credentials` — list stored credentials
- `POST /credentials` — save credential
- `DELETE /credentials/{site}` — delete credential
- `POST /preload` — preload book info from URL
- `POST /convert` — run scrape + convert to EPUB
- `GET /events/{job_id}` — SSE stream for job progress

### `routers/settings.py`
- `GET /settings` — settings page
- `GET /api/break-patterns` — list chapter-break patterns
- `POST /api/break-patterns` — add break pattern (type: `regex` or `css_class`)
- `PATCH /api/break-patterns/{id}` — update pattern (enable/disable or change value)
- `DELETE /api/break-patterns/{id}` — delete pattern
- `DELETE /api/reading-history` — wipe all reading sessions

### `routers/builder.py`
- `GET /builder` — Book Builder index (draft list + new draft form)
- `POST /builder` — create new draft; redirects to `/builder/{id}`
- `GET /builder/{draft_id}` — draft editor page
- `DELETE /api/builder/{draft_id}` — delete draft
- `GET /api/builder/{draft_id}` — draft JSON (id, title, author, publisher, source_url, chapters)
- `POST /api/builder/{draft_id}/chapter` — add chapter `{title, after_index}`; returns `{index, count}`
- `PUT /api/builder/{draft_id}/chapter/{idx}` — save chapter `{title?, content?}`
- `DELETE /api/builder/{draft_id}/chapter/{idx}` — delete chapter; returns `{index, count}`
- `POST /api/builder/{draft_id}/normalize/{idx}` — normalize chapter HTML (preview only, does not save); returns `{content}`
- `POST /api/builder/{draft_id}/publish` — normalize all chapters → `build_epub()` → write to `library/epub/` → `upsert_book()` → delete draft; returns `{filename}`; redirects browser to `/library/book/{filename}`

Publish flow: all chapters are run through `normalize_wysiwyg_html()`, then `build_epub()` produces an EPUB 2.0 ZIP. The file path is computed via `make_rel_path(media_type="epub", …)`. The book is inserted into the library with `needs_review=True`. The draft is deleted on success.

### `routers/following.py`
- `GET /following` — Following page (author URL management)
- `GET /api/following` — all distinct library authors with URL (if set), book count, and last-added date
- `POST /api/following/{author_name}` — set or clear URL for an author (empty `url` removes the record)

`GET /api/following` returns one entry per non-archived author:
```json
{ "name": "Author Name", "book_count": 5, "last_added": "2026-03-27T…", "url": "https://…" }
```

URL is stored in the `authors` table (`name` unique, `url`, `created_at`, `updated_at`).

### `routers/backup.py`
- `GET /backup` — backup page
- `GET /api/backup/credentials` — Dropbox settings (includes `app_key_configured` flag)
- `POST /api/backup/credentials` — save Dropbox settings
- `DELETE /api/backup/credentials` — remove all Dropbox credentials
- `POST /api/backup/oauth/prepare` — save app key + secret, return Dropbox auth URL
- `POST /api/backup/oauth/exchange` — exchange authorization code for refresh token
- `GET /api/backup/health` — Dropbox connectivity check (includes `schedule_enabled`, `schedule_interval_hours`)
- `GET /api/backup/status` — current backup status
- `GET /api/backup/history` — backup run history (last 20)
- `GET /api/backup/progress` — live progress of running backup `{running, done, total, phase}`
- `POST /api/backup/run` — trigger backup (background task)

---

## Backup & Security
- Dropbox token (refresh token or legacy access token) stored encrypted in `credentials` (`site='dropbox'`).
- Dropbox app key stored encrypted in `credentials` (`site='dropbox_app_key'`).
- Dropbox app secret stored encrypted in `credentials` (`site='dropbox_app_secret'`).
- Dropbox backup root stored encrypted in `credentials` (`site='dropbox_backup_root'`).
- Retention (`snapshots to keep`) stored encrypted in `credentials` (`site='dropbox_backup_retention'`).
- Backup schedule (`enabled` + `interval_hours`) stored encrypted in `credentials` (`site='dropbox_backup_schedule'`).
- Encryption uses `NOVELA_MASTER_KEY` (Fernet).

### Dropbox authentication
- Preferred: OAuth2 refresh token (does not expire). Set up via the two-step flow on `/backup`:
  1. Enter App Key + App Secret → click **Generate Auth URL**
  2. Approve in browser → paste the code → click **Save & Activate**
  - `_dbx()` uses `oauth2_refresh_token` + `app_key` + `app_secret` for automatic token renewal.
- Fallback: legacy short-lived access token (backwards compatible; works without app key/secret).

### Implementation details
- Versioned backups with deduplication:
  - file objects in Dropbox: `library_objects/{sha256_prefix}/{sha256}`
  - snapshots in Dropbox: `library_snapshots/snapshot-YYYYMMDD-HHMMSS.json`
- Each run creates a new snapshot version and uploads only missing objects.
- Retention removes older snapshots above the configured limit.
- Orphan object pruning removes objects no longer referenced by retained snapshots.
- Local manifest cache (`config/backup_manifest.json`) speeds up change detection.
- Database backup is done via `pg_dump` to Dropbox `postgres/`.
- `POST /api/backup/run` always starts a background task and returns immediately.
- `GET /api/backup/progress` returns in-memory progress updated per file; phases: `starting` → `scanning` → `uploading` → `snapshot` → `pg_dump`.
- Scheduler runs in the background (`start_backup_scheduler`) and triggers on interval when enabled.
- Concurrency guard: only one backup can run at a time.
- After container restart/crash, stale `running` logs are auto-marked as interrupted/error.

---

## Environment
`stack/novela.env` should include at least:
- `POSTGRES_DB`
- `POSTGRES_USER`
- `POSTGRES_PASSWORD`
- `NOVELA_MASTER_KEY`
- `CONFIG_DIR`

Dropbox settings are managed via the web UI on `/backup`.

---

## Branding

Static assets in `static/`:

| File | Size | Purpose |
|------|------|---------|
| `logo.png` | 546×575, transparent | Sidebar wordmark (displayed at 26px height) |
| `favicon.ico` | 16×16 | Browser tab (legacy) |
| `favicon-32.png` | 32×32 | Browser tab (modern) |
| `favicon-256.png` | 256×256 | Pinned tabs / high-DPI |
| `apple-touch-icon.png` | 180×180 | iOS/iPadOS home screen icon |

All 15 page templates include:
```html
<link rel="icon" href="/static/favicon.ico" sizes="16x16"/>
<link rel="icon" type="image/png" sizes="32x32" href="/static/favicon-32.png"/>
<link rel="icon" type="image/png" sizes="256x256" href="/static/favicon-256.png"/>
<link rel="apple-touch-icon" sizes="180x180" href="/static/apple-touch-icon.png"/>
```

Sidebar logo: `logo.png` (26px, flex-aligned) next to the "No**vela**" wordmark ("No" in `--text`, "vela" in `--accent`).
`apple-touch-icon.png` uses `#0f0e0c` background (= `--bg`) with the orange N logo centered at 60% of canvas size.

---

## Shared CSS (`static/theme.css`)

Single `:root { }` block defining all global CSS custom properties. Loaded first on every page (`<link rel="stylesheet" href="/static/theme.css"/>`). No template defines its own global colours — only page-specific layout vars stay inline.

| Variable | Value | Role |
|---|---|---|
| `--bg` | `#0f0e0c` | Page background |
| `--surface` | `#1a1815` | Card/panel background |
| `--surface2` | `#221f1b` | Nested surface |
| `--border` | `#2e2a24` | Borders |
| `--accent` | `#ffa20e` | Orange highlight (logo colour) |
| `--accent2` | `#ffb840` | Lighter orange |
| `--text` | `#e8e2d9` | Body text |
| `--text-dim` | `#8a8278` | Muted text |
| `--text-faint` | `#4a453e` | Very muted text |
| `--success` | `#6baa6b` | Success state |
| `--warning` | `#c8a03a` | Warning state |
| `--error` | `#c85a3a` | Error state |
| `--radius` | `6px` | Border radius |
| `--sidebar` | `220px` | Sidebar width |
| `--mono` | `'DM Mono', monospace` | Monospace font stack |
| `--serif` | `'Libre Baskerville', Georgia, serif` | Serif font stack |

Page-specific overrides: `reader.html` (`--header-h`, `--footer-h`, `--content-w`); `backup.html` (`--ok`, `--warn`, `--err`); `editor.css` (`--danger`, `--header-h`, `--panel-w`).

## Shared JavaScript (`static/books.js`)

Loaded before any page-specific script on every page that needs book data or UI helpers.

| Function | Purpose |
|---|---|
| `esc(s)` | HTML-escape a string for safe insertion into markup |
| `strHash(s)` | Deterministic integer hash of a string (for colour selection) |
| `COVER_PALETTES` | Array of 8 `[bg, fg]` colour pairs for placeholder covers |
| `wrapText(ctx, text, x, y, maxW, lineH)` | Canvas word-wrap helper |
| `truncate(s, n)` | Truncate string with ellipsis |
| `makePlaceholderCover(canvas, title, author)` | Draw a generated book cover on a `<canvas>` |
| `_filenameBase(filename)` | Strip path and extension from a filename |
| `bookTitle(b)` | Return display title (falls back to filename parsing) |
| `bookAuthor(b)` | Return display author (falls back to filename parsing) |
| `tagValuesByType(b, type)` | Return tag strings of a given type from `b.tags` |
| `bookGenres(b)` | Tags of type `genre`; falls back to `subject` |
| `bookSubgenres(b)` | Tags of type `subgenre` |
| `bookPlainTags(b)` | Tags of type `tag` |
| `filterBooks(books, query)` | Filter book list by query across title, author, publisher, genre, sub-genre, tag |
| `setupSearchInput(inputId, clearId, onSearch)` | Wire input: show/hide clear button on input; call `onSearch(query)` on Enter |

## Shared JavaScript (`static/conversion.js`)

Loaded by `index.html` (Convert page) and `grabber.html` (Grabber page). Requires `books.js` for `esc()`.

| Function | Purpose |
|---|---|
| `addLog(msg, cls)` | Append a log line to `#log-lines` |
| `connectConversionStream(job_id)` | Open SSE stream `/events/{job_id}` and handle all conversion events: `status`, `meta`, `chapters`, `progress`, `warning`, `error`, `done` |

## UI Notes
- Library import accepts EPUB/PDF/CBR/CBZ.
- Home supports the same import formats.
- Home includes search.
- Home header/dropzone alignment matches Library (search top-right, dropzone below).
- `New` view supports `Grid` and `List` mode.
  - Bulk selection + `Remove from New` works only in `List` mode.
  - `List` mode has a column visibility filter: Publisher, Author, Series, Volume, Title, Has cover, Updated, Genres, Sub-genres, Tags, Status.
  - `List` mode supports multi-select with `Shift+click` range selection on checkboxes.
  - `Grid` mode shows no selection checkboxes or bulk actions.
- `All books` view supports `Grid` and `List` mode (same columns as `New`).
  - View mode persisted in `localStorage` as `novela.all.viewMode`.
  - Column visibility persisted in `localStorage` as `novela.all.visibleColumns`.
  - `List` mode has a checkbox column, column visibility filter, and multi-select with `Shift+click` range selection.
  - `List` mode has a `Delete selected` bulk action: confirms then calls `DELETE /library/file/{filename}` for each selected book.
- Publication status values: `Complete`, `Ongoing`, `Temporary Hold`, `Long-Term Hold` (blank = unknown). `Hiatus` was renamed to `Long-Term Hold` via startup migration `migrate_rename_hiatus()`.
- Status badges (top-right of grid card cover): circular icon, dark fill `rgba(15,14,12,0.82)` + `box-shadow: 0 0 0 2px #0f0e0c` ring for visibility on any cover colour. Icon colour per status: Complete=green `#6baa6b`, Ongoing=blue `#4a90b8`, Temporary Hold=amber `#c8a03a`, Long-Term Hold=orange `#c8783a`. `statusBadgeHtml()` in `library.js` is the single source for badge HTML across all grid views.
- Want-to-read star (top-left of grid card cover): same dark fill + ring as status badges.
- Status pills in Book Detail (`book.css`): `status-complete`, `status-ongoing`, `status-temporary-hold`, `status-long-term-hold` — same colour scheme as badges.
- Grabber status mapping (`grabber.py`): `Temporary-Hold` (gayauthors.org) → `Temporary Hold`; `Long-Term Hold` passes through unchanged.
- Star ratings (1–5) shown under the cover in all grid views:
  - Display-only in grid cards (no click, prevents accidental taps while scrolling).
  - Interactive in Book Detail (1.1rem, clickable; clicking the active star clears the rating).
  - Amber: filled `#c8a03a`, unfilled `rgba(200, 160, 58, 0.25)`.
- Reader settings (hamburger menu):
  - Content width slider (30–100 vw), persisted as `reader-content-width-pct`.
  - Text colour: 5 warm-tone presets `#e8e2d9` → `#938d86`, persisted as `reader-text-colour`.
  - Hamburger and back-link separated with `margin-left: 1rem` on `.header-back`.
- Reader supports EPUB and PDF:
  - EPUB: chapter-text rendering; progress = `{chapterIndex}:{scrollFrac}`; progress % = `(chapterIndex + scrollFrac) / total * 100`.
  - PDF: page-image rendering via `/library/pdf/{filename}?page=N`; page count from `/api/pdf/info/{filename}`; progress = `{pageIndex}:0`; keyboard/button navigation identical.
  - `reader.html` branches on `FORMAT` variable injected by the server.
- `Edit EPUB` button in Book Detail is only shown for `.epub` files.
- Backup page supports: manual run, dry-run, Dropbox root, retention count, schedule (on/off + hours), status + history.
- Bookmarks: saved per book via `POST /library/bookmarks/{filename}`; shown in Library sidebar section; navigated via `?bm_ch=N&bm_scroll=F` URL params on reader page.
- Convert page: after loading metadata, if a book with the same title+author already exists in the library, a warning banner is shown (with a link to the existing book); user can still proceed with conversion. Check is done server-side in `/preload` response (`already_exists`, `existing_books`).
- Duplicates view (`#duplicates`): groups non-archived books by `(title, author)` (case-insensitive); shows only groups with ≥ 2 copies; counter in sidebar shows total number of duplicate books. Detection is entirely client-side from the existing library data.
- Incomplete view (`#incomplete`): shows all non-archived books where `publication_status` is not `Complete` (Ongoing, Temporary Hold, Long-Term Hold, or blank); sidebar counter included.
- Following page (`/following`): dedicated page in its own sidebar section between Library and Tools; shows all library authors with their external URL; two tabs — Following (authors with URL set) and All Authors; inline URL editing with keyboard support (Enter = save, Escape = cancel); clicking Visit opens the external URL in a new tab. Author URLs are stored in the `authors` table. Sidebar counter shows number of followed authors.
- Book Builder (`/builder`): create EPUB books from scratch; drafts stored in `builder_drafts` (JSONB chapters); contenteditable editor with toolbar (bold/italic/underline/blockquote/author-note/scene-break/normalize); autosave every 30 s + Ctrl+S; publish normalizes HTML via `normalize_wysiwyg_html()` and builds EPUB via `build_epub()`.

---

## Known Conventions
- Book deletion flow: `unlink` file → `prune_empty_dirs(parent)` → `DELETE FROM library` (cascade removes child rows).
- Empty dir pruning: `prune_empty_dirs(start)` walks up from `start` to `LIBRARY_ROOT`, removing each dir if empty; stops at first non-empty dir.
- Cover strategy:
  - EPUB: `GET /library/cover/{filename}` checks `library_cover_cache` first; on miss, extracts from ZIP and warms the cache. Cover upload (`POST /library/cover/{filename}`) replaces the image inside the EPUB ZIP (OPF located via `META-INF/container.xml`, old cover found in manifest and removed) and updates the cache so subsequent requests return the new cover immediately.
  - PDF: first page rendered as thumbnail, cached
  - CBR/CBZ: first page extracted, cached
- Rating storage:
  - EPUB: `<meta name="novela:rating" content="N"/>` in OPF
  - CBZ: `<NovelaRating>N</NovelaRating>` in `ComicInfo.xml` inside the ZIP
  - CBR/PDF: DB only
  - `upsert_book` uses `CASE WHEN EXCLUDED.rating > 0 THEN EXCLUDED.rating ELSE library.rating END` to restore rating from file without overwriting existing DB value.
- Tag types in `book_tags`: `genre`, `subgenre`, `tag`, `subject`. No direct `genres`/`subgenres` fields on book objects; always use helpers `bookGenres()`, `bookSubgenres()`, `bookPlainTags()`.

---

## Performance Notes
- Library load is optimized for large datasets (1000+ books):
  - `list_library_json()` uses `json_agg` in the main query to inline tags per book — eliminates a separate `SELECT * FROM book_tags` query and Python merge loop.
  - `has_cached_cover` is provided directly via SQL join instead of full cache fetch.
  - `reading_sessions` is pre-aggregated in a subquery.
  - ETag on `/api/library`: cheap `COUNT + MAX(updated_at)` query before full load; `304 Not Modified` on cache hit.
- Front-end rendering uses `IntersectionObserver` to defer both cover image loading and placeholder canvas drawing until cards enter the viewport — prevents hundreds of simultaneous HTTP requests and canvas operations on initial render.
- `renderBooksGrid`, `renderDuplicatesView`, `renderSeriesDetail` all use a single DOM pass: cover `<img>` and `<canvas>` are set up via `card.querySelector` immediately after `innerHTML` is set, eliminating a second full iteration with `document.getElementById` calls.
- Additional migration indexes:
  - `idx_library_sort_coalesce`
  - `idx_library_needs_review`
  - `idx_library_archived`
  - `idx_reading_sessions_filename_readat`
  - `idx_book_tags_filename_tag`

---

## Known Bugs Fixed
- `renderGenreView` and `renderSearchResults` in `library.js` referenced `b.genres` (non-existent). Fixed: use `bookGenres()`, `bookSubgenres()`, `bookPlainTags()`.
- `PillInput` in `book.js` did not handle comma as delimiter and did not flush on save. Fixed: comma keydown + `flush()` in `saveEdit()`.
- `PATCH /library/book` failed for PDFs: `_sync_epub_metadata` tried to open PDF as ZIP. Fixed: only called for `.epub`.
- `_make_rel_path` in `reader.py` lacked format prefix (`epub/`, `pdf/`, `comics/`). Fixed: aligned with `common.make_rel_path`.
- `common.make_rel_path` always generated `.cbr` extension for CBZ files (both map to `media_type="cbr"`). Fixed: accepts optional `ext` parameter; `library.py` import now passes actual suffix.
- `/download/{filename}` was referenced in `book.html` but no endpoint existed (404). Fixed: added `GET /download/{filename}` to `library.py`.
- PDF reader showed infinite loading: `reader.html` called EPUB-only `/library/chapters/`. Fixed: PDF path uses `/api/pdf/info/` + page-image rendering.
- Empty dir pruning only ran when file was moved. Fixed: `prune_empty_dirs(old_path.parent)` always runs after a successful metadata save.