SPIKE: Protocol 28 (CAP-0084)

[sisuresh]

Regenerates rs-stellar-xdr XDR for Protocol 28 / CAP-0084 (Muxed Contract Addresses).

Changes

• Regenerated from stellar-xdr#307 head `787382ef2099cca168ca1cb282730d6b7b9e2f16` (submodule + `xdr-version` pinned).
• Added `cap_0084_muxed_contract` feature token; bumped version `27.0.0` → `28.0.0`.
• Regenerated generated Rust + JSON schemas (`ScAddress::MuxedContract`, `MuxedContract` type, etc.).

Reviewer flag

• `ScAddress::MuxedContract` `Display` returns `Err` — muxed contract addresses have no strkey encoding yet (stellar-strkey ≤0.0.18). Needs a human decision on the strkey format. `FromStr` is correct by omission (no muxed-contract `Strkey` variant).

Deferred

• Re-pin to merged `main` SHA once stellar-xdr#307 merges, then cascade to downstreams.

Upstream

• SPIKE: Protocol 28 (CAP-0084) stellar-xdr#307

[sisuresh]

Protocol 28 · CAP-0084 (Muxed Contract Addresses) — SPIKE PR chain

Full cross-repo chain opened in this run (upstream → downstream):

• XDR source: SPIKE: Protocol 28 (CAP-0084) stellar-xdr#307
• Rust XDR anchor: SPIKE: Protocol 28 (CAP-0084) #552
• Host: SPIKE: Protocol 28 (CAP-0084) rs-soroban-env#1700
• SDK (Rust): SPIKE: Protocol 28 (CAP-0084) rs-soroban-sdk#1924
• Core: SPIKE: Protocol 28 (CAP-0084) stellar-core#5337
• Go SDK: SPIKE: Protocol 28 (CAP-0084) go-stellar-sdk#5961
• Horizon: SPIKE: Protocol 28 (CAP-0084) stellar-horizon#203
• RPC: SPIKE: Protocol 28 (CAP-0084) — muxed contract addresses stellar-rpc#837
• JS base: SPIKE: Protocol 28 (CAP-0084) js-stellar-base#981
• JS SDK: SPIKE: Protocol 28 (CAP-0084) js-stellar-sdk#1507
• JS xdr-json: SPIKE: Protocol 28 (CAP-0084) js-stellar-xdr-json#59
• Laboratory: SPIKE: Protocol 28 (CAP-0084) laboratory#2141
• Quickstart (docker): SPIKE: Protocol 28 (CAP-0084) quickstart#950

All draft/SPIKE, pinned to unmerged upstream heads; re-pin to merged SHAs as each lands.