# DiscDrop — Implementation Plan

A self-hosted, single-user app to follow MusicBrainz artists and track their **release groups** (not individual releases, to avoid duplicate vinyl/CD editions). Shows a combined web feed plus an RSS feed of new release groups, ordered by first-release-date.

> Tagline: _Drop the needle on every new release from the artists you follow._

---

## 1. Overview & Goals

| Aspect | Decision |
|---|---|
| Language / framework | Java 17 + Quarkus 3.x |
| Frontend | Server-rendered Qute templates + **htmx** + **daisyUI** (Tailwind) |
| Persistence | **Embedded H2 (file-based)** via Quarkus Hibernate ORM + Panache |
| MBZ access | **Quarkus REST Client (MicroProfile) + JSON** (no external Java library) |
| RSS | Single global RSS 2.0 feed of all followed artists |
| Users | Single-user, local/self-hosted (no auth layer in v1) |
| MBZ identity | `User-Agent: DiscDrop/1.0 (david.alvarez.81@gmail.com)` |
| Build / run | Maven (`./mvnw quarkus:dev`) |

### Functional requirements covered
1. Modern, adaptive UI with daisyUI theme switching.
2. Logo + favicon reflecting the app's purpose (vinyl "drop").
3. One combined feed of all followed artists.
4. Artist search autocomplete showing **disambiguation** + **area name**.
5. Centered, responsive header: logo, app name, search box, settings, theme switcher.
6. Feed rows: artist name, release title, release type, release date, MBZ link; ordered by first-release-date; "load more" pagination.
7. Follow artists from search results.
8. Unfollow already-tracked artists (search shows "unfollow" when tracked).
9. Follow/unfollow updates the feed in place (htmx) and clears the search box.
10. Click-outside closes the autocomplete dropdown.
11. Track **release groups**, not releases.
12. Separate **Artists page**: unfollow + per-artist primary-type monitoring toggles.
13. **Settings**: default primary type for new artists (default `album`) + sync schedule (6/12/24 h); closes on click-outside.

---

## 2. Architecture

```
┌──────────────── Browser (htmx + daisyUI) ────────────────┐
│  Header: logo · DiscDrop · search · settings · theme     │
│  Feed (Qute fragments swapped by htmx)                   │
│  /artists page · /rss feed                               │
└───────────────────────────┬──────────────────────────────┘
                            │ HTTP (HTML fragments / RSS / JSON)
┌─────────────── Quarkus App (DiscDrop) ───────────────────┐
│  Resources (Qute controllers)                            │
│   ├─ PageResource      GET /  (index + feed fragment)    │
│   ├─ SearchResource    GET /search/artists?q= (fragment) │
│   ├─ ArtistResource    POST/DELETE follow · GET /artists │
│   ├─ SettingsResource  GET/POST /settings (fragment)     │
│   └─ RssResource       GET /rss                          │
│  Services                                                │
│   ├─ FeedService       builds ordered feed page          │
│   ├─ ArtistService     follow/unfollow, settings         │
│   ├─ SyncService       refresh release groups            │
│   └─ SettingsService   app-wide settings                 │
│  MusicBrainzClient (REST Client, JSON, rate-limited)     │
│  Panache repositories (FollowedArtist, ReleaseGroup, …)  │
└───────────────┬───────────────────────┬──────────────────┘
        H2 file DB                    MusicBrainz API
        (discdrop.mv.db)              https://musicbrainz.org/ws/2/
                                      (1 req/sec, User-Agent)
```

**Request flow examples**
- Search typing → `GET /search/artists?q=…` → `MusicBrainzClient.searchArtists()` → Qute fragment (dropdown rows).
- Follow click → `POST /artists/follow` → persist `FollowedArtist` (+ default type settings) → enqueue immediate sync for that artist → return **updated feed fragment** + empty search fragment.
- Scheduled sync → for each followed artist, page through `release-group?artist=…&type=…` → upsert `ReleaseGroup` rows.

---

## 3. Data Model

Panache entities backed by H2. Keep it small; no premature normalization.

### `FollowedArtist`
| field | type | notes |
|---|---|---|
| id | Long (auto) | PK |
| mbid | String (UUID) | unique; MBZ artist MBID |
| name | String | display name |
| sortName | String | |
| disambiguation | String | e.g. "90s US grunge band" |
| areaName | String | from `area.name` |
| type | String | Person / Group / … |
| country | String | |
| followedAt | Instant | |
| lastSyncedAt | Instant | nullable |

### `ArtistTypeSetting`
Per-artist toggle for each **primary type** (requirement 12).
| field | type | notes |
|---|---|---|
| id | Long | PK |
| artist | FollowedArtist | FK |
| primaryType | String | `album` / `single` / `ep` / `broadcast` / `other` |
| enabled | boolean | |

Primary types come from the MBZ spec: `album, single, ep, broadcast, other`.
On follow, seed one row per primary type with `enabled` derived from the **default primary types** setting (`album` enabled by default).

### `ReleaseGroup`
Cached release groups (one row per MBZ release group per artist).
| field | type | notes |
|---|---|---|
| id | Long | PK |
| mbid | String (UUID) | unique |
| artist | FollowedArtist | FK |
| title | String | |
| firstReleaseDate | LocalDate | sortable; may be null/partial |
| firstReleaseDateRaw | String | preserve "2024-03" / "2024" granularity |
| primaryType | String | album / single / ep / … |
| secondaryTypes | String | comma-joined (live, compilation, …) |
| mbzUrl | String | `https://musicbrainz.org/release-group/{mbid}` |
| discoveredAt | Instant | when first seen by sync |

Unique on `mbid`. Index on `(firstReleaseDate DESC)` for feed ordering.

> **Cover art** needs no stored field — the front-cover URL is deterministic from the MBID: `https://coverartarchive.org/release-group/{mbid}/front` (Cover Art Archive, an MBZ-affiliated service). See §4.5.

### `AppSetting`
Key/value for global settings (requirement 13).
| key | example value | notes |
|---|---|---|
| `defaultPrimaryTypes` | `album` | comma-list applied to new artists |
| `syncScheduleHours` | `6` | one of `6`, `12`, `24` |
| `theme` | `dark` | optional server-side mirror of client theme |

---

## 4. MusicBrainz Integration

### 4.1 Endpoints used (all `fmt=json`)

| Purpose | Method + URL |
|---|---|
| Artist search (autocomplete) | `GET /ws/2/artist?query={q}&limit=10&fmt=json` |
| Browse release groups by artist | `GET /ws/2/release-group?artist={mbid}&type={types}&limit=100&offset={n}&inc=artist-credits&fmt=json&release-group-status=website-default` |
| (Optional) Artist lookup on follow | `GET /ws/2/artist/{mbid}?inc=aliases&fmt=json` |

Notes:
- `type` accepts primary types joined by `|` (e.g. `album|ep`); maps directly to each artist's enabled `ArtistTypeSetting` rows.
- `release-group-status=website-default` excludes groups that contain only promotional/bootleg/pseudo-release editions — keeps the feed clean. Default on; can later expose `all`.
- Release-group JSON fields we use: `id`, `title`, `first-release-date`, `primary-type`, `secondary-types[]`, `artist-credit[]` (for display name fallback).
- Artist search JSON fields we use: `id`, `name`, `disambiguation`, `area.name`, `type`, `country`, `score`.

### 4.2 REST Client definition (sketch)

The `User-Agent` is **not** hardcoded in the interface — it is supplied at runtime by a `ClientHeadersFactory` that reads `discdrop.mbz.user-agent` from `application.properties` (see §10). This keeps MBZ contact info out of source so it can be overridden per environment (dev vs. prod, different maintainer email) without recompiling.

```java
@ApplicationScoped
@RegisterRestClient(configKey = "musicbrainz")
@RegisterClientHeaders(MusicBrainzHeadersFactory.class)
public interface MusicBrainzClient {
    @GET @Path("/artist")
    ArtistSearchResult searchArtists(@QueryParam("query") String q,
                                     @QueryParam("limit") int limit,
                                     @QueryParam("fmt") String fmt);

    @GET @Path("/release-group")
    ReleaseGroupBrowseResult browseReleaseGroups(@QueryParam("artist") String mbid,
                                                 @QueryParam("type") String types,
                                                 @QueryParam("limit") int limit,
                                                 @QueryParam("offset") int offset,
                                                 @QueryParam("inc") String inc,
                                                 @QueryParam("fmt") String fmt,
                                                 @QueryParam("release-group-status") String status);
}
```

```java
@ApplicationScoped
public class MusicBrainzHeadersFactory implements ClientHeadersFactory {
    @ConfigProperty(name = "discdrop.mbz.user-agent")
    String userAgent;

    @Override
    public MultivaluedMap<String, String> update(MultivaluedMap<String, String> incoming,
                                                 MultivaluedMap<String, String> outgoing) {
        outgoing.putSingle("User-Agent", userAgent);
        return outgoing;
    }
}
```

Base URI and other REST Client settings are externalized via `quarkus.rest-client."musicbrainz".*` keys in `application.properties` (see §10).

### 4.3 Rate limiting (mandatory: ≤ 1 req/sec)

A single shared gate that **all** MBZ calls pass through:
- `MusicBrainzService` wraps the client with a synchronized `acquire()` that enforces ≥1000 ms between outgoing requests (track `lastCallMillis`).
- The background sync loop naturally spaces calls (one artist/page at a time).
- Live search also goes through `acquire()`; combined with 300 ms client-side debounce, this keeps us compliant even with fast typing.

### 4.4 DTOs (Jackson)
`ArtistSearchResult { count, artists[] }` → `ArtistDto { id, name, disambiguation, area { name }, type, country, score }`.
`ReleaseGroupBrowseResult { "release-group-count", "release-group-offset", "release-groups[] }` → `ReleaseGroupDto { id, title, first-release-date, primary-type, secondary-types[], artist-credit[] }`.

### 4.5 Cover Art Archive
Cover art comes from the **Cover Art Archive** (`https://coverartarchive.org`), the MBZ-affiliated image service hosted by the Internet Archive. No API key required.
- **Front cover by release-group MBID**: `https://coverartarchive.org/release-group/{mbid}/front` — responds with `307` redirect to the archived image (JPEG), or `404` if no art exists.
- This URL is **deterministic from the MBID**, so:
  - No extra HTTP calls during sync.
  - No `coverArtUrl` field on `ReleaseGroup` needed.
  - Templates render `<img src="https://coverartarchive.org/release-group/{mbid}/front" onerror="this.src='/img/no-cover.svg'">` — the browser follows the redirect, and a small JS `onerror` swaps to a local placeholder when a release group has no art (common for bootlegs/obscure releases).
- **Optional optimization (later)**: during sync, issue a `HEAD` per release group and store a `hasCoverArt` boolean to avoid any broken-image flashes. Defer this unless the `onerror` flicker is bothersome; it adds N calls per sync and is unnecessary for v1.
- Rate limits on `coverartarchive.org` are more lenient than the MBZ web service, and since we hit it client-side (browser `<img>`) or not at all, it never contends with our 1 req/sec MBZ gate.

---

## 5. Sync / Scheduler

- `SyncService` with a `@Scheduled` method. The cadence is read from `AppSetting.syncScheduleHours` and reconfigured at runtime (Quarkus supports programmatic scheduler via `Scheduler` / `ScheduledExecutor`, or simply restart after settings change for v1).
- Per run, iterate `FollowedArtist` rows; for each, build the `type=` filter from its enabled `ArtistTypeSetting` rows, page through release groups (offset increments by received count, up to `limit=100`), and upsert into `ReleaseGroup`.
- After an artist is processed, update `lastSyncedAt`.
- **Immediate sync on follow**: when a user follows an artist, trigger a one-off sync for that artist (async, fire-and-forget) so the feed populates without waiting for the next schedule.
- Honor rate limit between every MBZ call.

---

## 6. UI / UX

### 6.1 Layout & theming
- Single base template (`templates/index.html`) with a sticky **header** and the **feed** below.
- daisyUI via CDN for rapid dev (`daisyui` full CSS + Tailwind Play CDN); switch to a built/minified local Tailwind CSS for production.
- Theme switching: toggle `data-theme` on `<html>` (e.g. `light`/`dark` or a daisyUI pair like `nord`/`dim`). Persist in `localStorage` for instant restore; optionally mirror to `AppSetting.theme`. Small vanilla JS handler on the theme switcher button.

### 6.2 Header (centered, responsive, consistent gap)
A flex container, `justify-center`, `gap-4`, wrapping gracefully on narrow screens:
`[logo] [DiscDrop] [search box] [settings btn] [theme switcher]`

- **Logo**: small SVG (see §7).
- **App name**: "DiscDrop" wordmark.
- **Search box**: text input with autocomplete dropdown anchored below it.
- **Settings button**: opens a dropdown panel (§6.6).
- **Theme switcher**: icon button cycling/toggling themes.

### 6.3 Search + autocomplete (requirements 4, 7, 8, 9, 10)
- Input wired with htmx: `hx-get="/search/artists?q=..."`, `hx-trigger="input changed delay:300ms, keyup changed"`, `hx-target="#search-dropdown"`, `hx-swap="innerHTML"`.
- Dropdown rows render: **name** · **disambiguation** (muted) · **area name** (badge). Each row carries a **Follow**/**Unfollow** button depending on whether the MBID is already in `FollowedArtist`.
- Follow/Unfollow buttons: `hx-post="/artists/follow"` / `hx-delete="/artists/{mbid}"` with:
  - `hx-target="#feed-list"` and `hx-swap="innerHTML"` (refresh feed), **and**
  - `hx-on::after-request="this.closest('form').reset(); document.querySelector('#search-dropdown').innerHTML='';"` (clear input + close dropdown) — satisfying requirement 9.
- **Click-outside to close** (requirement 10): a tiny JS helper listens for `document` clicks; if the target is outside `#search-wrap`, it empties `#search-dropdown`. (Same helper pattern reused for settings.)

### 6.4 Feed (requirements 3, 6, 11)
- Server renders the first page of release groups ordered by `firstReleaseDate DESC`.
- Each row: **cover art thumbnail** (see §4.5 — `<img src="https://coverartarchive.org/release-group/{mbid}/front" onerror="…no-cover placeholder…">`, sized ~64–96px, lazy-loaded), **artist name** (link to artist page section), **release title**, **release type** badge(s) (primary + secondary), **release date** (human-friendly, with raw granularity preserved), and an **external link** to `https://musicbrainz.org/release-group/{mbid}`.
- **Load more**: a button `hx-get="/feed?offset={N+page}" hx-target="this" hx-swap="outerHTML"` that appends the next page and re-emits itself with the new offset, until exhausted (then no button).

### 6.5 Artists page (requirement 12)
- Route `/artists` listing every `FollowedArtist` as a card/row with:
  - name + disambiguation + area,
  - **Unfollow** button (`hx-delete="/artists/{mbid}"`, target the row, swap `outerHTML` → removes row),
  - **primary-type toggles**: a set of daisyUI checkboxes/switches for `album, single, ep, broadcast, other`; each change `hx-post="/artists/{mbid}/types"` (persist + re-sync that artist) with `hx-swap="none"` and an out-of-band feed refresh.

### 6.6 Settings (requirement 13)
- Settings button opens a dropdown panel (anchored, same click-outside helper).
- Controls:
  - **Default primary types** for newly followed artists (checkbox set; default `album` checked) → `AppSetting.defaultPrimaryTypes`.
  - **Sync schedule**: radio/select among `6h / 12h / 24h` → `AppSetting.syncScheduleHours`.
- Save: `hx-post="/settings"` with `hx-swap="innerHTML"` on the panel (re-render + confirm). Click-outside closes (does not save unsaved changes in v1, or autosave on change — pick autosave-on-change to keep it simple).

---

## 7. Branding: Logo & Favicon

Concept: **a vinyl record dropping into a slot** — reinforces "DiscDrop".

**Logo SVG (inline, scales in header)**
- Outer black circle (vinyl) with 2–3 thin concentric groove rings.
- Colored center label (accent theme color) with a tiny spindle hole.
- A subtle downward chevron / motion line at the bottom-right indicating "drop".
- Wordmark "DiscDrop" next to it in the header.

**Favicon**
- Simplified 32×32 / SVG: just the vinyl circle + center label + a small downward arrow. Provide `favicon.svg` (modern browsers) plus a generated `favicon.ico`/`192.png` for broader support.

Assets live in `src/main/resources/static/img/` and are referenced from the base template (`<link rel="icon" ...>` and header `<img>`).

---

## 8. htmx Interaction Flows (summary)

| Action | Request | Targets / effects |
|---|---|---|
| Type in search | `GET /search/artists?q=` | swap `#search-dropdown` |
| Follow | `POST /artists/follow` | swap `#feed-list` + clear search + close dropdown |
| Unfollow (from search) | `DELETE /artists/{mbid}` | swap `#feed-list` + clear search + close dropdown |
| Unfollow (artists page) | `DELETE /artists/{mbid}` | remove row (`outerHTML`) + OOB feed refresh |
| Toggle artist type | `POST /artists/{mbid}/types` | OOB `#feed-list` refresh |
| Load more | `GET /feed?offset=` | append rows, replace button |
| Save settings | `POST /settings` | re-render panel |
| Theme switch | (client JS) | toggle `data-theme`, save `localStorage` |

Out-of-band swaps (`hx-swap-oob`) keep the feed consistent when follow/unfollow/type-toggle happens from anywhere but the feed itself.

---

## 9. RSS Feed

- `GET /rss` returns **RSS 2.0** (`application/rss+xml`; Qute template generating XML, or a small builder).
- Single global feed: latest N (e.g. 50) release groups across all followed artists, ordered by `firstReleaseDate DESC`.
- Each `<item>`: title = `{artist} – {title}`; link = `https://musicbrainz.org/release-group/{mbid}`; pubDate = `firstReleaseDate`; description = type(s) + date; `<guid>` = the MBZ MBID (stable).
- **Cover art**: each item embeds the front cover via the [Media RSS](https://www.rssboard.org/media-rss) namespace (`xmlns:media="http://search.yahoo.com/mrss/"`):
  ```xml
  <media:content url="https://coverartarchive.org/release-group/{mbid}/front"
                 type="image/jpeg" medium="image" />
  ```
  Media RSS is preferred over a plain `<enclosure>` because `<enclosure>` requires a `length` (byte size) attribute we don't know without a HEAD probe, whereas `<media:content>` has no such requirement and is widely supported by modern RSS readers. Add `xmlns:media` to the `<rss>` root element.
- Channel metadata: "DiscDrop – New Releases", link to the app root.
- Discoverable via `<link rel="alternate" type="application/rss+xml" ...>` in the base template.

---

## 10. Project Structure

```
discdrop/
├── pom.xml
├── README.md
├── src/main/java/io/discdrop/
│   ├── DiscDropApp.java
│   ├── resource/
│   │   ├── PageResource.java          # GET / (index + feed fragment), GET /feed
│   │   ├── SearchResource.java        # GET /search/artists
│   │   ├── ArtistResource.java        # follow/unfollow, GET /artists, type toggles
│   │   ├── SettingsResource.java      # GET/POST /settings
│   │   └── RssResource.java           # GET /rss
│   ├── service/
│   │   ├── FeedService.java
│   │   ├── ArtistService.java
│   │   ├── SyncService.java
│   │   └── SettingsService.java
│   ├── mbz/
│   │   ├── MusicBrainzClient.java     # REST Client interface (no hardcoded User-Agent)
│   │   ├── MusicBrainzHeadersFactory.java  # injects discdrop.mbz.user-agent from config
│   │   ├── MusicBrainzService.java    # rate-limited wrapper
│   │   └── dto/{ArtistSearchResult,ArtistDto,ReleaseGroupBrowseResult,ReleaseGroupDto}.java
│   └── persistence/
│       ├── FollowedArtist.java
│       ├── ArtistTypeSetting.java
│       ├── ReleaseGroupEntity.java
│       └── AppSetting.java
├── src/main/resources/
│   ├── application.properties
│   ├── templates/
│   │   ├── index.html                 # base: header + feed
│   │   ├── artists.html
│   │   ├── rss.xml
│   │   └── fragments/
│   │       ├── feed-list.html
│   │       ├── feed-row.html
│   │       ├── search-dropdown.html
│   │       ├── settings-panel.html
│   │       └── artist-row.html
│   └── static/
│       ├── img/{logo.svg, favicon.svg, favicon.ico, no-cover.svg}
│       ├── css/  (daisyUI/Tailwind, dev via CDN or built)
│       └── js/app.js  (theme switch + click-outside helper)
```

### Key `application.properties`
```properties
quarkus.application.name=DiscDrop
quarkus.http.port=8080

# H2 file DB
quarkus.datasource.db-kind=h2
quarkus.datasource.jdbc.url=jdbc:h2:file:./data/discdrop;DB_CLOSE_DELAY=-1
quarkus.datasource.username=sa
quarkus.datasource.password=
quarkus.hibernate-orm.database.generation=update

# MusicBrainz REST client
quarkus.rest-client."musicbrainz".url=https://musicbrainz.org/ws/2
# User-Agent (MBZ requires a meaningful contact string) — override per environment, never hardcode in code
discdrop.mbz.user-agent=DiscDrop/1.0 (david.alvarez.81@gmail.com)
discdrop.mbz.rate-limit-ms=1000
discdrop.feed.page-size=25
discdrop.rss.item-count=50
```
On startup, validate that `discdrop.mbz.user-agent` is non-empty (fail fast with a clear `StartupException` rather than emitting anonymous requests MBZ may block).

### Maven dependencies (essentials)
- `quarkus-resteasy-reactive-qute`, `quarkus-rest-client-jackson`, `quarkus-hibernate-orm`, `quarkus-jdbc-h2`, `quarkus-panache`, `quarkus-scheduler`, `quarkus-resteasy-reactive-jackson`.

---

## 11. Implementation Phases

### Phase 0 — Scaffold (0.5 day)
- `quarkus create app` (Java 17, Maven, REST + Qute + Hibernate + H2 + Scheduler + REST Client).
- Base template with daisyUI CDN, htmx CDN, logo/favicon placeholders, header layout.
- Verify `./mvnw quarkus:dev` boots and renders the header.

### Phase 1 — MBZ client + search (1 day)
- `MusicBrainzClient` + DTOs + rate-limited `MusicBrainzService`.
- `/search/artists` returning Qute dropdown fragment (name, disambiguation, area).
- Click-outside close helper.

### Phase 2 — Persistence + follow/unfollow (1 day)
- Panache entities + repositories; `SettingsService` defaults.
- Follow/unfollow endpoints; seed `ArtistTypeSetting` from default primary types.
- Immediate one-off sync on follow; feed fragment endpoint.
- Wire follow buttons in search dropdown; clear search + refresh feed via htmx.

### Phase 3 — Sync + feed (1 day)
- `SyncService` scheduler (configurable 6/12/24 h); paged release-group browse + upsert.
- Feed ordering by `firstReleaseDate DESC`, row fragment with **cover art thumbnail** (Cover Art Archive URL + `onerror` placeholder), **load more** pagination.
- MBZ external links on each row.

### Phase 4 — Artists page + type toggles (0.5 day)
- `/artists` page with unfollow + per-artist primary-type switches; OOB feed refresh on change.

### Phase 5 — Settings panel (0.5 day)
- Settings dropdown: default primary types + sync schedule; autosave-on-change; click-outside close.

### Phase 6 — RSS + branding polish (0.5 day)
- `/rss` RSS 2.0 with `<media:content>` cover art per item; `<link rel="alternate">` discovery.
- Finalize logo/favicon SVG + `no-cover.svg` placeholder; theme switcher; responsive pass.

### Phase 7 — Hardening (0.5 day)
- Error states (MBZ down / rate-limited / empty feed) with friendly UI.
- README with run + config instructions.
- Optional: replace daisyUI/Tailwind CDN with a built local CSS for production.

**Estimated total: ~5–6 days.**

---

## 12. Out of Scope (v1) / Future
- Multi-user / auth (currently single-user local).
- Cover-art `HEAD` probing during sync (to pre-flag missing art and avoid broken-image flashes); the `onerror` placeholder handles this client-side for v1.
- Secondary-type per-artist filters (only primary types are toggled per requirement 12; secondary types are shown as badges).
- Notifications (email/webhook) beyond RSS.
- Migration to PostgreSQL (entity model is portable; only datasource config changes).
- Replacing the daisyUI/Tailwind CDN with a production Tailwind build.

---

## 13. Key Design Decisions & Rationale
- **Release groups, not releases** (req 11): browse `release-group` with `inc=artist-credits`; one row per group, no duplicate vinyl/CD.
- **`release-group-status=website-default`**: filters promo/bootleg/pseudo-release-only groups → cleaner feed.
- **Server-side rate limiting shared by search + sync**: guarantees the 1 req/sec MBZ rule regardless of UI activity.
- **Quarkus REST Client + JSON** over the dead/GPL `musicbrainzws2-java` library: lighter, idiomatic, no licensing constraints.
- **Externalized `User-Agent` via `ClientHeadersFactory`**: the MBZ contact string lives in `application.properties` (`discdrop.mbz.user-agent`), not in code — so it can be overridden per environment and updated without a recompile. App fails fast at startup if the property is missing, to avoid sending anonymous requests MBZ may block.
- **H2 file-based**: zero-ops for a personal app; portable to Postgres later by changing datasource props.
- **htmx + Qute fragments**: the feed, search dropdown, and settings all swap HTML fragments — no SPA needed; matches requirements 9 and 10 (in-place updates, dropdown close).
- **Cover art via deterministic Cover Art Archive URLs**: `https://coverartarchive.org/release-group/{mbid}/front` needs no per-item API call or storage — the URL is derived from the MBID, fetched lazily by the browser `<img>`, with a JS `onerror` placeholder for release groups without art. Keeps sync fast and the data model lean.
- **Media RSS `<media:content>` over `<enclosure>`** for RSS images: avoids the mandatory `length` (byte-size) attribute that `<enclosure>` requires and that we'd need a HEAD probe to obtain.
- **Autosave settings on change**: avoids a "save" button and keeps the settings panel simple (closes on click-outside per req 13).