docs/link/v8.md

Protocol 8 — Client assets over the bridge

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. Supersedes the manual half of: ../website/UOFIDDLER.md, ../website/CLILOCS.md §Converting, ../website/SPAWN_ATLAS.md §Artwork and §Configuring the tree.

Two features on this platform read data that only exists inside a UO client, and today both reach the site by hand: the operator installs UOFiddler, converts Cliloc.enu on their own desktop, exports sprites one at a time from a GUI, hand-writes a slug→filename JSON map, and copies the result to the server. A third — the spawn atlas — avoids UOFiddler but pays a different price: the website must be able to read the shard's ServUO tree directly, over a bind mount or a shared volume.

This protocol deletes all three arrangements. The shard already has everything, and the bridge already goes to the website.

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1. The premise, which turns out to be free

A ServUO shard cannot boot without a UO client installation. It reads maps, statics, tiledata and multis out of .mul/.uop files, and Config/DataPath.cfg is where an operator declares where those live — required on Linux, auto-detected from the registry on Windows. At runtime the resolved directories sit in Server.Core.DataDirectories, a public static the plugin can read on any shard, with no new configuration and nothing for an operator to set up.

So the files the operator has been converting on their desktop are already on the shard host, in a directory the shard already knows the path of, in a process the bridge already runs inside.

Everything below follows from that.

1.1 What was measured, not assumed

Against this machine's ServUO 57.4 tree (C:\Users\colby\Desktop\ServUO) and client (D:\Games\Electronic Arts\Ultima Online Classic, 3.5 GB), loading ServUO's own Ultima.dll — the assembly overlay/Scripts/Scripts.csproj:39 already carries a <ProjectReference> to:

Call	Result
Art.GetStatic(0…16383)	16,384 decoded, 0 errors
Art.GetStatic(16384…65535)	32,766 decoded, 1 empty, 16,385 clean out-of-range errors
Art.GetLand(0…16383)	16,384 decoded, 0 errors
Animations.GetAnimation(0…2047, 0, 1)	1,144 bodies with a decodable first frame, 904 empty, 0 errors
Hues.GetHue(33)	loads
Bitmap.Save(…, Png)	852-byte PNG from one creature frame
Gumps.GetGump(2)	hard crash — AccessViolationException, process exit 0xC0000005
new StringList("enu", "Cliloc.enu")	throws — Non-negative number required

Two of those rows are load-bearing and are dealt with in §4 and §9. The rest say the same thing: most of the extraction this protocol needs is already implemented, already compiled, and already referenced by the plugin's own build.

Depth, for §11's sizing: body 400 (human male) has 35 actions × 5 directions = 1,050 frames. One body. §5.1 cuts that by exactly 5×.

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2. Architecture: the shard extracts, the sidecar forwards, the website decides

UO client files (operator's own, on the shard host)
   │  read by the plugin, off the Core thread
   ▼
ServUO shard (servuo-plugins/)     ← decodes; resolves body ids; hashes
   │  loopback JSON, request/reply, one batch outstanding at a time
   ▼
uo-link sidecar (link/)            ← forwards bytes; decides nothing
   │  REST, bearer-token auth, X-UOLink-Version: 8
   ▼
website (module-uo/)               ← stores, names, gates, serves

This is deliberately the only arrangement that keeps the bridge's standing rules intact:

• The sidecar stays a dumb forwarder. It moves opaque assets and decides nothing about them — no audience, no projection, no capability advertisement. Putting the decoders in Rust would have meant the sidecar deciding what an asset is, on top of re-deriving in Rust what is already compiled next door in C#.
• Access control stays on the website, which has the auth machinery and the admin forms.
• The shard is still never network-reachable. Nothing here opens a port; the plugin answers requests on the connection it already dialled out on.

2.1 Why not the sidecar, and why not the operator's desktop

A Rust extractor in the sidecar would need ports of: the Mythic cliloc decompressor, FileIndex (including UOP), the ARGB1555 run-length frame decoder, Body.def/Bodyconv.def translation, Hues.mul, and a PNG encoder — weeks of work to re-derive what §1.1 shows already runs. It also cannot do §8: resolving a creature slug to a body id requires being inside ServUO.

Automating on the operator's desktop (shipping the converter with the installer) removes UOFiddler but keeps a manual step and still cannot do §8. It was considered and rejected.

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3. The transport, and the three traps in it

3.1 Assets go over the request/reply path, never the event path

link/sidecar/src/app.rs:122 persists every non-pong event into the SQLite store and broadcasts it to every WebSocket subscriber. An asset stream on that path would grow the sidecar's store without bound and fan megabytes out to every connected client, forever.

rpc.rs's try_route consumes a correlated reply and continues before either of those happens. So an asset batch is a reply, not an event. This is not a new mechanism — it is the one char.request, account.roster and vendor.snapshot already use.

3.2 One batch outstanding, always

BridgeLink.Emit() enqueues onto a bounded drop-oldest queue (Bridge.QueueCap, default 10,000). It counts lines, not bytes — a design that is correct for live events and dangerous for bulk transfer, because 10,000 queued 200 KB replies is 2 GB of shard memory.

The rule that makes this safe is flow control, not a bigger queue: the website requests batch n+1 only after batch n has arrived. Queue depth stays at approximately one. A dropped or lost reply simply times out and the batch is re-requested, which is safe because reading a client file is idempotent and has no world side effects.

3.3 The size ceilings are already fixed, and one of them is missing

Limit	Value	Where
Sidecar waits for a shard reply	10 s	rpc.rs REPLY_TIMEOUT
Website waits for the sidecar	12 s	module-uo/server/utils/uoLinkClient.js TIMEOUT_MS
Sidecar → shard line	1 MiB	BridgeLink.cs:283
Shard → sidecar line	none	shard.rs uses read_line unbounded

The first two bound a batch: it must decode, encode, serialise and cross the wire inside ten seconds. The last is a gap this protocol must close — an unbounded read_line facing a component that is now deliberately sending large lines is a memory-exhaustion shape we would be inventing ourselves. Protocol 8 adds an explicit inbound line cap to the sidecar, set above the largest legal batch and rejecting rather than buffering past it.

Batches are therefore sized by bytes, not by count, with the emitter cutting a batch short when it would exceed the cap. Base64 costs 33%; the budget must be stated in encoded bytes.

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4. The decoders: whose code, and the crash that decides it

§1.1 found that Gumps.GetGump(2) does not fail — it corrupts the process. An AccessViolationException from unsafe pointer code is a corrupted-state exception; on .NET Framework 4.8 it is not catchable by an ordinary try/catch. In-process, on a live shard, that is a shard crash with players on it.

Art and animation probed clean across ~66,000 and ~2,000 ids respectively. That is reassuring and it is not a guarantee: the inputs we have not tested are exactly the ones that matter — a shard's own patched or custom client files, which is the population this feature exists to serve.

Two ways to hold this safely:

A1 — call ServUO's vendored Ultima, isolate the fault. Fastest to build, and proven for the kinds we need. Requires running the decode where a fault costs one batch rather than the shard: a short-lived child process. That means a binary to deploy, which the overlay (deployed as source, compiled by ServUO at boot) has no mechanism for.

A2 — own bounds-checked decoders in the overlay. Roughly 600–900 lines of ordinary safe C#: FileIndex (~150), the RLE frame decoder (~60, and it is the same loop, writing to a ushort[] instead of through a LockBits pointer), the static-art decoder, Body.def/Bodyconv.def, hue application, and a minimal PNG writer over System.IO.Compression.DeflateStream (~80).

A2 is recommended, for four reasons that compound:

1. It removes the crash class, rather than containing it.
2. It removes System.Drawing entirely. ServUO's Frame decoder writes ARGB1555 straight into a Bitmap via LockBits, so System.Drawing is in the decode, not just the encode — a Linux/Mono shard needs libgdiplus even to read a sprite. Writing our own pixels and our own PNG makes the feature portable by construction.
3. It removes the UOP gap. ServUO's vendored Animations reads legacy anim*.mul only. This client has a full 195 MB anim.mul so most bodies resolve — but gargoyle bodies 666/667 returned nothing, because gargoyles live in AnimationFrame*.uop. A player race missing from an asset store built for "player models and everything" is not a caveat, it is a defect.
4. We are already in this business. §9 writes a cliloc decompressor from scratch regardless.

A2 also ends the dependency on whatever version of Ultima a given ServUO happens to vendor, which is the kind of thing that silently changes under a shard upgrade.

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5. Addressing: one key for every asset

Every asset the bridge can serve is named by a single string key, and the key is the cache key, the hash key, the filename stem and the manifest row id:

static/3922                     one item graphic
static/3922/h33                 the same graphic, hue 33 applied
land/3                          one land tile
body/34/a0                      creature body 34, action 0, first frame
body/400/a0/f0..f9              human male, action 0, all ten frames
cliloc/enu                      the whole converted string table (not an image)
tree/Spawns/Trammel.xml         a ServUO tree file (§10)

Three properties this shape buys:

• Hue is part of the key, not a transform. itemId and hue are already on the wire together (BridgeMarket.cs:582, BridgeProfile.cs:314), so a marketplace listing already knows the exact key for its own picture. Applying hues website-side would mean shipping Hues.mul semantics into Node for no gain.
• Depth is expressible without being mandatory. body/400/a0 and body/400/a0/f0..f9 are the same addressing scheme at two depths, which is what lets §11 bulk-import thumbnails and fetch full animations on demand without a second protocol.
• Nothing in the key is client-version-specific, so a client patch changes an asset's bytes, not its name — which is what makes §7's delta work.

5.1 There is no direction segment, because only one direction is wanted

Bodies are stored in five directions and the client mirrors three of them to reach eight. Only one is needed here — the one facing the viewer — so direction is fixed by the extractor and is not part of the key. Leaving it in would advertise a choice nobody is going to make and would five-fold every count in §11 for nothing.

The front-facing index is 0. This was determined by rendering all five for a human, a wolf and a dragon rather than from a table, because the answer is not obvious and the small-thumbnail version of the same test suggested the opposite:

Index	View
0	Head-on, facing the viewer — face, chest and front legs visible
1	Front three-quarter
2	Full side profile
3	Rear three-quarter
4	Directly away — back of the head, and a quadruped's tail toward the camera

One caveat the render made obvious, and it is the reason this is written down rather than assumed: index 0 is the least legible view for four-legged and long-bodied creatures. A wolf seen head-on is a dark blob; the same wolf at index 2 is unmistakably a wolf, and at index 1 is the view UOFiddler's own thumbnail list picks. For a bestiary tile that matters. The extractor therefore takes the index as a configuration value defaulting to 0, so changing the catalogue's mind later is a setting and a re-import, not a protocol change.

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6. The manifest, and what the two buttons actually do

Two stages, which is where Import and Update come from.

Stage 1 — the source gate. The shard reports a manifest of the client files themselves: size, mtime and content hash of Cliloc.enu, anim*.idx/anim*.mul, art.mul/artidx.mul, Body.def, Bodyconv.def, Hues.mul. Unchanged since the last import, and nothing else happens. This is the same hash gate the spawn atlas and the cliloc table already use, and for the same reason: the normal case is a restart that changed nothing, and it must cost nothing.

anim.mul is 195 MB and art.mul is 148 MB, so the gate is (size, mtime) first, content hash only when those differ — a full hash of 343 MB on every status poll would make the admin panel feel broken.

Stage 2 — the asset manifest. For the working set (§11), the shard streams [{ key, sha256, bytes }] — no pixels. The website diffs that against what it holds and requests only the keys whose hash changed.

• Update = stage 1, then stage 2, then fetch the diff.
• Import = the same path with the diff skipped and every key fetched.
• A key that has vanished from the manifest is staged for review, never applied silently — the same rule, and the same reasoning, as a vanished cliloc source or a disappearing atlas facet. An unmounted volume and a deliberate client downgrade look identical from here.

Clilocs are the exception and stay a whole-table replace whenever the file hash changes: the measured cost is 663 ms for 67,496 rows, so per-entry deltas would be complexity bought for nothing.

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7. The parser version applies here too

spawnAtlasSource.js carries PARSER_VERSION (currently 5) and the cliloc source carries its own, both counted as drift so that a corrected parse reaches an install whose files never change. The asset pipeline inherits the rule and needs it more, not less: a fixed hue application or a corrected frame offset changes the bytes we derive from files that are byte-identical.

EXTRACTOR_VERSION lives in the plugin, because the plugin is what derives the bytes, and it is folded into stage 1's gate. Bumping it makes every asset drift, which is correct.

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8. Body ids: the part only the shard can do

The atlas knows creatures by slug, derived from type names in Spawns/*.xml. The client knows them by body id. Nothing in the ServUO tree declares the mapping as data — today an operator bridges it by grepping Scripts/Mobiles/Normal/<Name>.cs for Body =, which appears variously as a decimal, as hex (0xD1), as Utility.RandomList(35, 36), and as an m_IDs[] table.

Inside ServUO the problem does not exist. BridgeWorld.cs:350 already does exactly the required thing for a different feature:

var type = ScriptCompiler.FindTypeByName(name, true);
var creature = Activator.CreateInstance(type) as BaseCreature;

Construct, read creature.Body.BodyID, Delete(). Authoritative, no source parsing, and correct for custom creatures a grep would never find.

This pass must run on the Core thread — it constructs and deletes mobiles, which is world mutation — while the decode in §4 must run off it. That split is the one genuinely new threading shape in this protocol, and it is why slug→body resolution is its own request kind with its own (small) batch size rather than a step inside asset extraction.

Constructing arbitrary creature types has side effects: constructors pack items, set skills, start timers. The mitigations are per-type try/catch, immediate Delete(), small batches, and the fact that the whole pass is admin-triggered rather than something that runs at boot.

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9. The cliloc decompressor is ours now

Every modern client ships Cliloc.* in the Mythic compressed container — this machine's Cliloc.enu is 4,989,921 bytes beginning E8 79 67 8E, high byte 0x8E. ServUO's bundled Ultima.StringList implements only the plain layout and throws on it (§1.1), which is also why the shard's own VendorSearch.GetItemName is already inert.

UOFiddler is released under the Beerware licence, so porting its decompressor into our GPL-3.0-or-later tree is clean. It lands in the overlay as ordinary C#, alongside §4's decoders, and from that point:

• No operator installs UOFiddler.
• No operator runs dotnet build on a converter.
• No operator copies a 5 MB file to a server.
• website/server/tools/cliloc-export/ is retired, and UOFIDDLER.md is deleted rather than rewritten.

What survives untouched is the custom/ overlay mechanism. Shard-added items carry cliloc ids no client table has, and ServUO has no server-side notion of a custom cliloc — that is a real gap in the game, not an artefact of the manual pipeline, and CLILOCS.md's reasoning for it stands. The base table now arrives over the bridge; overlays still come from a directory the site reads. Measured on the live shard: 16,434 cliloc ids referenced by the script tree, 37 absent from stock.

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10. The atlas stops needing a shared filesystem

Today SPAWN_ATLAS.md requires the website to read the ServUO tree — "same host, a bind mount, or a shared volume". That is the one place the platform's own rule (only the sidecar bridges the shard) is broken, and it is broken by the component that faces the internet.

The same transport closes it. spawnAtlasSource.js already labels every file it reads with a portable key:

Label	Count (stock 57.4)
Data/Regions.xml	1
Data/Locations/*.xml	6
Spawns/*.xml	13, ~10.5 MB
Config/ChampionSpawns.xml	1
Data/Decoration/**	tree

So the shard serves tree/<label> → bytes over the same batched request/reply path, and spawnAtlasSource.js gains a second backend behind its existing interface: filesystem (today, kept for same-host installs and for development) or sidecar (new, and the default once configured).

The parsers do not move. spawnAtlasParse.js is pure, fs-free and CI-covered without a ServUO tree, and every quirk it handles — the two respawn delay units, :OBJ= splitting, facet-name reconciliation, the XmlSpawner directive stripping — stays exactly where it is. The shard sends bytes; the website still decides what they mean. That is the same division as §2, and it keeps the sidecar a forwarder here too.

SERVUO_PATH and the spawn_atlas_servuo_path setting remain, and select the filesystem backend.

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11. What is bulk and what is on demand

The scope approved is creature art, item art, player models "and everything", against a future project. §1.1's measurements make the sizing question concrete:

Kind	Addressable	Bulk?
Item statics	~49,150	No — on demand, cached, keyed by itemId (+ hue)
Land tiles	16,384	No — on demand
Creature/player bodies, first frame	1,144	Yes — this is the catalogue
One body, every action, one direction	210 frames (body 400); 96–210 measured across six bodies	No — on demand, per body
All bodies, every action, one direction	~173,000 frames, ~170 MB	No — but no longer unthinkable
The same at five directions	~865,000 frames	Not built (§5.1)
Cliloc table	123,490 entries → 67,496 rows	Yes — whole-table replace
ServUO tree files (§10)	~21 files, ~10.6 MB	Yes

The working set is one thumbnail per body, plus the atlas's own creatures. 1,144 sprites at roughly a kilobyte each is under 2 MB — trivial to import, trivial to re-hash, and it is the set that makes a bestiary, a marketplace listing and a character sheet render.

Everything deeper is the same protocol at a deeper key (§5), fetched on demand and cached. That is what serves the future project without exporting 3.5 GB of someone else's copyrighted client into a database: a viewer that wants body 400's full walk cycle asks for body/400/a2/f0..f9 and gets it, once, and it is cached from then on.

Because §5.1 dropped four of the five directions, a complete one-direction animation set for every body is now ~173,000 frames rather than ~865,000 — around 170 MB. That is still not the default and still not something to import before anything asks for it, but it has moved from "never" to "a thing an operator could reasonably choose", and phase 5 should leave room for a bulk-fill-everything switch rather than assuming on-demand is the only mode.

Hued variants are on demand, always. static/3922/h33 is generated when something on the wire actually carries hue 33. The cross product of 49,150 statics and ~3,000 hues is not a set anyone enumerates.

Gump art is out of scope for Protocol 8 — see §4; it is the one kind whose vendored decoder demonstrably corrupts the process, and A2 would have to reimplement it against the UOP-with-extra- field layout that broke it. It is additive to add later under this same key scheme (gump/<id>), which is the point of §5.

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12. Where it lands on the website

Images are written by module-uo into the upload directory. ctx.uploads ({ upload, UPLOAD_DIR, MIME_EXT }) is already exposed to modules and MODULE_API.md:626 already names its consumer as "atlas art import", so no MODULE_API_VERSION bump is needed to store them.

• shard_spawn_creatures.art stops being NULL-by-default and starts being filled by the import.
• A new asset table carries key, sha256, bytes, width, height, imported_at — the manifest side of §6, and what makes an Update a diff rather than a re-download.
• The operator-supplied spawnAtlas.art.json map stays supported and continues to win over an imported asset. An operator who has drawn their own creature portraits must not have them overwritten by a sprite rip on the next Update.

Licensing is unchanged and the reasoning is unchanged: these are the operator's own client files, extracted on their own host, for their own shard. Nothing is committed, nothing ships in a repo, and nothing is redistributed. What changes is only that the extraction stopped requiring a GUI on a desktop.

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13. Visibility

New surfaces over shard data are admin-toggleable with an operator-set audience, and this is no exception. Asset serving is gated like every other shard read: a requireFeature gate, an audience, and 404-not-403 when the feature is off, so a disabled feature does not advertise itself.

The default is the least surprising one: assets are as public as the page that uses them. A bestiary that is already anonymous does not become staff-only because its pictures arrived over a new pipe.

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14. Routes and commands added

Loopback (shard ↔ sidecar), all request/reply:

Command	Reply	Purpose
assets.sources	assets.sources.ok	Stage 1: client file manifest + EXTRACTOR_VERSION
assets.manifest	assets.manifest.ok	Stage 2: [{key, sha256, bytes}], paged
assets.fetch	assets.fetch.ok	Content for an explicit key list, paged
assets.bodies	assets.bodies.ok	Slug → body id (§8, Core thread)
cliloc.table	cliloc.table.ok	The converted table, paged
tree.manifest / tree.fetch	.ok	§10, the ServUO tree files

Sidecar REST mirrors those one for one under /assets/*, /cliloc, /tree/*, carrying X-UOLink-Version: 8 and forwarding verbatim.

Website admin (Admin → Shard, admin-only): status, Import, Update, approve/reject for a vanished key, and the existing path settings. Every action to the admin activity log, as shard.assets.*.

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15. Cross-repo obligations

PROTOCOL_VERSION goes 7 → 8 in link/sidecar/src/main.rs, and in the same PR servuo-plugins/overlay.toml — the installer refuses to pair a sidecar and an overlay that disagree, so a split bump means the next bundle silently fails to compose.

Repo	Work
servuo-plugins/	The decoders (§4), the cliloc decompressor (§9), body resolution (§8), the request handlers, overlay.toml
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
installer/	None expected; the 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

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16. Phases

#	Scope	Repos
0	Spike: A2's decoders against this machine's client — statics, land, one body, the Mythic cliloc — proving output matches UOFiddler's byte for byte	servuo-plugins
1	The transport: assets.sources, flow control, the sidecar line cap, EXTRACTOR_VERSION, protocol bump	servuo-plugins, link
2	Clilocs end to end; retire the converter and UOFIDDLER.md §Part 1	all
3	Body resolution (§8) + the 1,144-body catalogue; shard_spawn_creatures.art filled	servuo-plugins, module-uo
4	Item statics and land on demand, hued keys, the cache	servuo-plugins, module-uo
5	Deep animation keys (body/<id>/a<n>/f<n>) for the future project, plus the bulk-fill switch	servuo-plugins, module-uo
6	The atlas over the sidecar (§10); shared-filesystem requirement retired	module-uo
7	Admin surface, Import/Update, approve/reject, activity log	module-uo
8	Docs pass across five repos; live walk on the real rig	docs

Phase 0 exists because §4 chose to own the decoders, and the honest way to hold that choice is to prove byte-identical output before building six phases on top of it.

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17. Decisions still open

1. §4: A2 (own decoders) versus A1 (vendored Ultima in a child process). A2 is recommended and the phase plan assumes it. It costs a spike and ~600–900 lines; it buys the crash class, the libgdiplus dependency, the UOP gap and the vendor-drift risk all going away at once.
2. §11: gump art deferred. Confirm that paperdoll and equipment gump art is genuinely out of scope for 8, given it is the one kind whose existing decoder crashes.
3. §5.1: direction is fixed at index 0 (head-on) and is not in the key — settled 2026-09-10. What is not settled is whether the catalogue should default to index 1 or 2 instead, since a head-on wolf is a dark blob and a side-on wolf is a wolf. It is a setting either way.
4. §13: the default audience for asset serving — inheriting the using page's audience is proposed; the operator sets the policy either way.