docs: cover CAP-84 muxed contract addresses in the agent skill.

skills/java-stellar-sdk/SKILL.md

@@ -72,7 +72,9 @@ These are the things that most often trip people up with *this* SDK:
 - **Amounts and balances are `BigDecimal`.** `new BigDecimal("10.5")`, never `double`/`float`.
 - **`G...` and `M...` both work as a destination.** Address strings accept plain ed25519
   accounts and SEP-23 muxed accounts; use `MuxedAccount` to build/parse `M...` (see
-  `references/sep.md`).
+  `references/sep.md`). Contracts have a muxed form too, `W...` (CAP-84, Protocol 30): a valid
+  SAC `transfer`/`mint` destination, but never a signer or storage owner (see
+  `references/xdr_scval.md`).
 - **Clients are `Closeable`.** `Server.close()`; wrap `SorobanServer`/`ContractClient` in
   try-with-resources. `SSEStream` from `.stream(...)` must also be closed to stop it.
 - **SDK exceptions are unchecked.** Everything extends `RuntimeException`

skills/java-stellar-sdk/references/sep.md

@@ -8,7 +8,7 @@ across top-level classes rather than a single `sep` package.
 | SEP-02 | Federation | `org.stellar.sdk.federation.Federation` |
 | SEP-05 | Key derivation (BIP-39 seed) | `KeyPair.fromBip39Seed(byte[], int)` |
 | SEP-10 | Web authentication | `org.stellar.sdk.Sep10Challenge` |
-| SEP-23 | Muxed accounts | `org.stellar.sdk.MuxedAccount` |
+| SEP-23 | Muxed addresses (`M...`, `W...`) | `org.stellar.sdk.MuxedAccount`; `Address` |
 | SEP-29 | Memo-required check | submission helpers / `AccountRequiresMemoException` |
 | SEP-35 | Operation IDs (TOID) | `org.stellar.sdk.TOID` |
 | SEP-45 | Soroban web auth | `org.stellar.sdk.Sep45Challenge` |
@@ -81,6 +81,9 @@ String mAddress = muxed.getAddress();           // M...
 MuxedAccount parsed = new MuxedAccount("M...");  // parse an existing M-address
 ```
 
+SEP-23 also defines the muxed contract strkey (`W...`, CAP-84), a contract plus a 64-bit ID.
+It has no `MuxedAccount` counterpart; see "Addresses" in `xdr_scval.md`.
+
 ## SEP-35: TOID (total order ID)
 
 ```java

skills/java-stellar-sdk/references/troubleshooting.md

@@ -93,3 +93,9 @@ Operation-level codes you'll hit often:
   `assembled.signAuthEntries(theirKeyPair)` before `signAndSubmit(...)`.
 - **Transaction still pending** → `getTransaction` returns status `NOT_FOUND` until it is in a
   ledger; poll with `pollTransaction` or a loop. See `soroban.md`.
+- **Address cannot authorize** → `IllegalArgumentException` from `Auth`; only `G...` and `C...`
+  addresses sign Soroban authorization entries, never a muxed (`M...`/`W...`), claimable balance
+  or liquidity pool address. Sign for the base address.
+- **Muxed address in contract storage** → `IllegalArgumentException` from `getContractData`; the
+  owner must be a `C...` and the key cannot contain an `M...`/`W...`. Use the base address (see
+  "Addresses" in `xdr_scval.md`).

skills/java-stellar-sdk/references/xdr_scval.md

@@ -22,7 +22,7 @@ Scv.toTimePoint(BigInteger.valueOf(1700000000)); Scv.toDuration(BigInteger.value
 Scv.toBytes(new byte[] {1, 2});
 Scv.toString("hello");  Scv.toSymbol("increment");
 Scv.toExecutableTag("v1");             // CAP-85 tag; byte[] overload for a binary tag
-Scv.toAddress("G...");                 // account or contract ("C...") address
+Scv.toAddress("G...");                 // G/C/M/W... address, see "Addresses"
 Scv.toVec(List.of(Scv.toUint32(1L), Scv.toUint32(2L)));
 Scv.toMap(Map.of(Scv.toSymbol("k"), Scv.toUint32(1L)));
 ```
@@ -50,8 +50,20 @@ import org.stellar.sdk.xdr.SCVal;
 Address addr = new Address("G...");      // account or "C..." contract
 SCVal scVal = addr.toSCVal();            // SCVal for contract args
 Address back = Address.fromSCVal(scVal);
+back.getAddressType();                   // ACCOUNT, CONTRACT, MUXED_ACCOUNT, ...
+
+new Address("M...");                     // muxed account (SEP-23)
+new Address("W...");                     // muxed contract (CAP-84, Protocol 30)
+Address.fromMuxedContract(raw);          // raw: 32-byte contract ID + 8-byte big-endian ID
+new Address("B...");                     // claimable balance, e.g. in events
+new Address("L...");                     // liquidity pool, e.g. in events
 ```
 
+`M...` and `W...` are payment destinations only, such as the `to` of a Stellar Asset Contract
+`transfer`; the balance goes to the base `G...`/`C...`. They cannot authorize or key contract
+storage, and the SDK rejects them there (`Auth`, `SorobanServer.getContractData`, the balance
+helpers), so use the base address.
+
 ## Transaction XDR
 
 ```java