feat: decouple fee payment from sequence number management

[marcelosalloum]

What

• Replace single feePayer param with separate signer (source account) and feeBumpSigner (fee payer) on both Charge and Channel servers
• Rename push-mode credential type from "signature" to "hash" per MPP spec draft-stellar-charge-00
• Remove feePayerKey from schema and client progress events
• Replace closeKey with signer + feeBumpSigner on Channel server and standalone close() function
• Add resolveKeypair utility, exported from all server subpaths

Why

Servers commonly use a pool of accounts for sequence numbers and a single dedicated account to pay fees via FeeBumpTransaction. The old feePayer parameter conflated both roles, making it impossible to separate fee payment from transaction signing. This decoupling is standard practice in Stellar infrastructure (see x402 facilitator pattern).

The type: "signature" → type: "hash" rename aligns with MPP spec PR #199 which specifies type="hash" for push-mode credentials.

Breaking changes

Before	After
charge({ feePayer: kp })	charge({ signer: kp, feeBumpSigner?: kp2 })
channel({ closeKey: kp })	channel({ signer: kp, feeBumpSigner?: kp2 })
close({ closeKey: kp })	close({ signer: kp, feeBumpSigner?: kp2 })
type: "signature" (push mode)	type: "hash"
feePayerKey in schema/events	Removed

Example

// Before
stellar.charge({
  recipient: 'G...',
  currency: USDC_SAC_TESTNET,
  feePayer: Keypair.fromSecret('S...'),  // paid fees AND provided sequence number
})

// After — separate concerns
stellar.charge({
  recipient: 'G...',
  currency: USDC_SAC_TESTNET,
  signer: Keypair.fromSecret('S...'),         // source account (sequence number)
  feeBumpSigner: Keypair.fromSecret('S...'),  // pays all fees via FeeBumpTransaction
})

[Copilot]

Pull request overview

Decouples Stellar fee payment (fee-bump) from sequence-number management across the SDK’s Charge and Channel servers, aligns push-mode credential naming with the latest spec draft, and introduces a shared keypair resolution utility exported through public entrypoints.

Changes:

• Replace feePayer / closeKey with signer (source account) and optional feeBumpSigner (fee payer) on server APIs and channel close helpers.
• Rename push-mode credential payload type from "signature" to "hash" and remove feePayerKey from schema and client progress events.
• Add and export resolveKeypair(Keypair|string) across SDK/server entrypoints; update docs/examples accordingly.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk/src/signers.ts	Adds resolveKeypair helper for Keypair-or-secret-string normalization.
sdk/src/signers.test.ts	Unit tests for resolveKeypair.
sdk/src/server/index.ts	Re-exports resolveKeypair from the server entrypoint.
sdk/src/server/Charge.ts	Splits sponsorship signer vs fee-bump signer; updates push-mode to "hash"; removes feePayerKey; adds fee-bump wrapping.
sdk/src/server/Charge.test.ts	Updates parameter acceptance tests; updates hash-dedup tests for "hash" type.
sdk/src/integration.test.ts	Updates credential type validation to "hash".
sdk/src/index.ts	Re-exports resolveKeypair from the root SDK entrypoint.
sdk/src/client/Charge.ts	Removes feePayerKey progress/event plumbing; renames push credential payload to "hash".
sdk/src/channel/server/index.ts	Re-exports resolveKeypair from channel server entrypoint.
sdk/src/channel/server/Channel.ts	Replaces closeKey with signer and adds optional fee-bump wrapping for close/open + standalone close().
sdk/src/channel/server/Channel.test.ts	Updates tests for signer requirement and adds acceptance for feeBumpSigner.
sdk/src/Methods.ts	Updates credential schema discriminator to "hash" and removes feePayerKey from methodDetails schema.
sdk/src/Methods.test.ts	Updates schema tests for "hash" and removes feePayerKey assertion.
examples/channel-close.ts	Updates example to use signer instead of closeKey.
README.md	Updates public API docs/events and describes signer vs fee-bump signer roles.

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