AgentSetAppearance sends 218 VisualParams (viewers send 253) — positional mismatch deforms the avatar body on OpenSim

[sharpdaddy59]

Summary

AppearanceManager.MakeAppearancePacket() hard-caps the VisualParam block
count at 218 (251 with a Physics wearable):

// LibreMetaverse/Appearance/AppearanceManager.cs (master @ 9455bdb, line 2490)
var nrParams = wearingPhysics ? 251 : 218;
set.VisualParam = new AgentSetAppearancePacket.VisualParamBlock[nrParams];

Modern viewers (tested against Firestorm) send 253 VisualParam blocks.
The array is positional — the receiver maps values onto its ordered param
table by index — so a library-driven client that sets its appearance on an
OpenSim region deforms the avatar: the first ~23 values line up, then the
membership of the library's VisualParams.Params enumeration diverges from
the viewer's ordering and every subsequent value lands on the wrong
slider (torso/leg/height params get unrelated values → grossly deformed,
"squashed" body). OpenSim persists the received array, so the corruption
also survives to subsequent sessions.

Reproduction

1. Dress an avatar with a viewer (Firestorm) on an OpenSim grid
   (0.9.3.0 standalone in our case) and log out. The grid's avatars.db
VisualParams row now holds 253 comma-separated values.
2. Log the same avatar in with a LibreMetaverse 3.1.3 client with
   Settings.Agent.SendAppearance enabled (default) and let the CSB
   pipeline run to completion (all wearables download, bake succeeds,
   AppearanceSet fires with Success = true).
3. Observe in any viewer: the avatar's body is deformed. Inspect the
   persisted VisualParams row: now 218 values.

Direct comparison of the persisted arrays (same avatar, same wearables):

viewer  count=253: ... 63, 165, 88, 132,   0, 136,  81,  85, 103, 136 ...
                                     ^ index 23
library count=218: ... 63, 165, 88,   0, 132,   0,  63,  63,   0,   0 ...

Identical through index 22, then the library's sequence contains an entry
the viewer's ordering doesn't have (or vice versa) and everything shifts.
The values the library computes are correct — the height-related params
it looks up by ID for AgentData.Size produce the right avatar height —
only the positional serialization is wrong.

Expected

The VisualParam array should match the current viewer wire format: 253
entries, same param membership and ordering, so index N means the same
slider to every receiver.

Suggested fix

Bring VisualParams.Params (and the nrParams cap) up to date with the
current avatar_lad param set used by SL/Firestorm-era viewers (253 params,
Bakes-on-Mesh era), and derive the block count from the table rather than
the hardcoded 218/251. The special-casing on wearingPhysics suggests the
table already contains more params than are sent — the cap, not the table,
may be the immediate problem, but membership/order needs to match too
(the divergence starts at index ~23, well before the physics params).

Workaround we're using

Send appearance packets ourselves: let the CSB pipeline bake, then rebuild
the packet via the (public) MakeAppearancePacket() and replace
pkt.VisualParam with the 253-value array the grid has persisted from a
viewer session before sending. This renders correctly everywhere and
round-trips through OpenSim persistence.

Happy to provide logs or test on a branch.

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Environment: LibreMetaverse 3.1.3 (NuGet, repo commit 70877a6), .NET 10,
OpenSim 0.9.3.0 standalone, observed with Firestorm viewers.