Custom asset

[RemmyAcee]

Close: #35
Here's a summary of what was produced:

2026-06-sac-compatibility.md
— created from scratch since the file didn't exist yet. Contains:

Compatibility matrix (10 asset/flag combinations × 5 columns)
7 numbered findings (F-01 through F-07) covering: USDC/EURC safety, Protocol 22 trust() trustline elimination, AUTH_REQUIRED incompatibility, AUTH_CLAWBACK_ENABLED risk, AUTH_REVOCABLE monitoring, burn/mint edge cases, 64-bit amount limits
Issuer addresses table (USDC + EURC mainnet + testnet, verified against Circle)
Test results table (8 test cases with pass/fail)
stellar-custom-assets.mdx
— 637 lines, 10 sections:

SAC Overview — how stealth-sender uses the SAC (trust() → transfer() → announce() atomically), trustline mechanics and Protocol 22 behaviour
USDC Issuer Addresses — mainnet + testnet addresses for USDC and EURC, SAC contract address derivation via Asset.contractId()
Send USDC via agent — one-liner chat call + curl
Sender Flow (low-level) — SAC address derivation → stealth address generation → sender trustline + balance check → stealth-sender Soroban invocation with correct i128 USDC scaling (7 decimal places) → createAccount + send combined in one tx for fresh addresses
Recipient Flow — scanning for USDC, checking stealth address balances, auto-establishing destination trustline, signing withdrawals with the stealth scalar via signStellarTransaction
Path Payments — pathPaymentStrictReceive with a separate announcer.announce() call, path-finding via Horizon strictReceivePaths
Fees — complete cost table (classic ops vs Soroban, reserve cost), fee estimation via simulateTransaction
SAC Compatibility Matrix — faithfully reproduced from the audit, condensed to 5 columns
AUTH_REQUIRED / Clawback Warnings — why AUTH_REQUIRED breaks stealth flows, what clawback means in practice, checkAssetFlags() helper, agent warning messages
Testnet Example — complete copy-pasteable end-to-end flow: create two agents, fund via Friendbot, send 50 USDC, scan, withdraw
docs.json — guides/stellar-custom-assets added to navigation

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@RemmyAcee Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

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[RemmyAcee]

Done, Close: #57

[truthixify]

Clean merge. 822-line Stellar custom assets guide + 175-line SAC compatibility audit + the federation guide content + types reference all land cleanly. Substantial. Thanks @RemmyAcee.

This also supersedes #52 (federation) since the federation guide content is included here. Closing that one as superseded.