docs(link): name it the Asset Bridge, and make libgdiplus a stated requirement

The work has a name now — the Asset Bridge — for commits, PR titles, branches
(feat/asset-bridge-p<n>) and conversation. Protocol number stays 8 and the file
stays docs/link/v8.md.

§4.4 closes the last real open question rather than deferring it to phase 0, and
takes all three answers instead of choosing one. ServUO targets net48, so a Linux
host runs it under Mono, and Mono's System.Drawing is a thin layer over
libgdiplus — which §4.2 put in the decode path, not just the encode. So on Linux
it is a hard prerequisite for art. Cliloc and atlas import are unaffected; neither
touches pixels. Windows hosts need nothing at all.

It is now written down as: a SHARD_PREREQS.md entry, a doctor check in the
installer, and a named NO_IMAGING status when it is missing, in the same family
as the cliloc reader's COMPRESSED — never a stack trace, never a 500. Install
routes per distro are in the section, apt-get install libgdiplus being the
normal one.

One fact recorded because depending on something unmaintained should be a
conscious act: github.com/mono/libgdiplus was ARCHIVED in March 2025 and is
read-only. Distributions still package and patch it, so installing it today is
supported and ordinary — but it is the strongest long-term argument for moving
extraction off System.Drawing eventually, and phase 4's UOP reader is written
without it so that door stays open.

§17 restructured: three settled items kept because each changes numbers
elsewhere, and one genuinely open question (the default audience) that does not
block starting.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016wDDVXWMDz82WqE1i969r4

link/v8.md

@@ -1,7 +1,13 @@
-# Protocol 8 — Client assets over the bridge
+# Asset Bridge (Protocol 8) — client assets without UOFiddler
+
+**Call it the Asset Bridge.** That is the name for this work everywhere — commits, PR titles,
+branches (`feat/asset-bridge-p<n>`), and conversation. The protocol number is **8** and this file is
+`docs/link/v8.md`.
 
 **Status:** Design of record. Approved in principle 2026-09-09 (architecture, asset scope,
-built-in cliloc decoder, atlas cleanup); §17 lists what is still open.
+built-in cliloc decoder, atlas cleanup); refined 2026-09-10 (one direction not five, ServUO's own
+decoders, the UOP reader for player bodies, the libgdiplus requirement). §17 lists what is still
+open.
 **Supersedes the manual half of:** [`../website/UOFIDDLER.md`](../website/UOFIDDLER.md),
 [`../website/CLILOCS.md`](../website/CLILOCS.md) §Converting,
 [`../website/SPAWN_ATLAS.md`](../website/SPAWN_ATLAS.md) §Artwork and §Configuring the tree.
@@ -181,8 +187,8 @@ Three costs come with it, all known and none of them blocking:
    not merely accepted: §4.3 adds a decoder for it**, because it is the player character and the
    scope says player models.
 2. **`System.Drawing` is a hard dependency, in the decode and not just the encode.** `Frame`
-   writes ARGB1555 straight through a `LockBits` pointer, so a Linux/Mono shard needs libgdiplus
+   writes ARGB1555 straight through a `LockBits` pointer, so a Linux shard needs **libgdiplus** to
-   to read a sprite at all. See §17.
+   read a sprite at all. That is a stated prerequisite — §4.4.
 3. **We inherit whatever `Ultima` a given ServUO vendors**, which can change under a shard upgrade.
    `EXTRACTOR_VERSION` (§7) is the mitigation: it already counts as drift, so a shard whose library
    changed re-derives on the next import.
@@ -217,6 +223,47 @@ silently puts a spider on the gargoyle page, and no error is raised anywhere. A
 correct behaviour; a plausible wrong picture is the failure this protocol most needs to avoid,
 because nothing downstream can detect it.
 
+### 4.4 Requirement: a Linux shard host needs libgdiplus
+
+**Stated prerequisite, not a soft recommendation.** ServUO targets `net48`, so on Linux it runs under
+Mono, and Mono's `System.Drawing` is a thin layer over **libgdiplus**. §4.2 put `System.Drawing` in
+the decode path, so without that library a Linux shard cannot extract art at all — the cliloc table
+(§9) and the atlas files (§10) are unaffected, since neither touches pixels.
+
+**Windows shard hosts need nothing.** `System.Drawing` ships with .NET Framework. This is a
+Linux-only prerequisite and most shards will never read this section.
+
+| Host | Get it with |
+|---|---|
+| Debian / Ubuntu | `sudo apt-get install libgdiplus` — in Debian since bullseye (6.0.4) and bookworm/trixie (6.1), and in Ubuntu universe |
+| Fedora / RHEL | `sudo dnf install libgdiplus` (EPEL or the Mono repository) |
+| Docker | `RUN apt-get update && apt-get install -y libgdiplus` in the shard image |
+| Alpine, or a distro with no package | Build from source — see the repository below. This is the awkward case and is worth avoiding by choosing a Debian-based image |
+
+Upstream is <https://github.com/mono/libgdiplus>, with the Mono project's own page at
+<https://www.mono-project.com/docs/gui/libgdiplus/>.
+
+**One thing to know before depending on it: that repository was archived in March 2025 and is
+read-only.** Distributions still package and patch it, so `apt-get install libgdiplus` is a normal,
+supported thing to do today — but upstream is not maintained. It is the strongest long-term argument
+for eventually moving extraction off `System.Drawing`, and phase 4's UOP reader (§4.3) is written
+without it precisely so that door stays open. It does not change the decision now.
+
+**How its absence must present.** Never a stack trace and never a 500. Missing libgdiplus is a
+named, actionable outcome in the same family as the cliloc reader's `COMPRESSED`:
+
+```
+status: unavailable
+code:   NO_IMAGING
+reason: This shard host cannot render images — Mono's System.Drawing needs libgdiplus.
+        Install it (apt-get install libgdiplus) and re-run the import. Cliloc and
+        atlas import are unaffected.
+```
+
+The installer's `doctor` checks for it and reports it alongside its other host checks, so an
+operator learns about this while setting the shard up rather than from an empty bestiary weeks
+later.
+
 ---
 
 ## 5. Addressing: one key for every asset
@@ -556,8 +603,8 @@ disagree, so a split bump means the next bundle silently fails to compose.
 | `link/` | Six command families forwarded, the REST surface, **the inbound line cap (§3.3)**, `PROTOCOL_VERSION` |
 | `module-uo/` | Client calls, asset store, the atlas source backend (§10), cliloc ingest, admin surface |
 | `website/` | None expected — `ctx.uploads` already suffices (§12) |
-| `docs/` | This file; rewrite `CLILOCS.md` §Converting and `SPAWN_ATLAS.md` §Artwork + §Configuring; **delete `UOFIDDLER.md`** |
+| `docs/` | This file; rewrite `CLILOCS.md` §Converting and `SPAWN_ATLAS.md` §Artwork + §Configuring; **delete `UOFIDDLER.md`**; add the libgdiplus prerequisite to `SHARD_PREREQS.md` (§4.4) |
-| `installer/` | None expected; the bundle pairing already enforces §15 |
+| `installer/` | A `doctor` check for libgdiplus on Linux hosts (§4.4). Bundle pairing already enforces §15 |
 | `android-app/` | Consumes images by URL; no parity gate expected until a screen shows one |
 | `integration-kit/` | A chapter note only — this is UO-specific and teaches nothing about the module contract |
 
@@ -592,18 +639,19 @@ because §4.3's whole point is that this failure mode produces confident, wrong
 
 ---
 
-## 17. Decisions still open
+## 17. Decisions
+
+Items 1–3 are settled and recorded here because each one changes numbers elsewhere in the document.
+**Item 4 is the only thing still open, and it does not block starting.**
 
 1. **§4: settled 2026-09-10 — call ServUO's vendored `Ultima`,** with one exception added the same
    day: **§4.3's UOP animation decoder**, scoped to the player bodies the legacy path cannot reach
    and to nothing else (phase 4). The crash is confined to the `hasExtra: true` branch that only
    `Gumps` reaches, and nothing here calls `Gumps`.
-2. **§17.1's consequence: Linux/Mono shards.** §4.2 item 2 leaves `System.Drawing` in the decode
+2. **§4.4: settled 2026-09-10 — libgdiplus is a stated requirement** on Linux shard hosts, with
-   path, so a non-Windows shard needs **libgdiplus** installed or art extraction fails there. Three
+   all three answers taken rather than one: it goes in `SHARD_PREREQS.md`, the installer's `doctor`
-   ways to answer it, and this is the one real question left: document it as a prerequisite in
+   checks it, and its absence degrades to a named `NO_IMAGING` status instead of an error. Windows
-   `SHARD_PREREQS.md` and let it fail loudly; have the installer's `doctor` detect and report it;
+   hosts are unaffected.
-   or fall back to no-art on that platform with a status the panel explains. Phase 0 should
-   establish which failure it actually is before we pick.
 3. **§5.1/§5.2: direction — settled 2026-09-10.** Player character bodies use index 0, everything
    else index 1, direction is not in the key, and the player-body set is enumerated from
    `Race.AllRaces` rather than hardcoded. Nothing outstanding; recorded here because it changes