Add Hedera charge intent by tomrowbo · Pull Request #251 · tempoxyz/mpp-specs

tomrowbo · 2026-04-28T18:19:54Z

Summary

Native charge intent for Hedera (draft-hedera-charge-00). One-time payments via native Hedera TransferTransaction with Attribution memo (challenge-bound, Tempo-compatible byte layout).

Session intent is in a separate PR per reviewer request.

Highlights

Push mode (type="hash"): client broadcasts native TransferTransaction, server verifies via Mirror Node REST API
Pull mode (type="transaction"): client signs + serializes, server broadcasts
Attribution memo: same 32-byte layout as Tempo (TAG + VERSION + SERVER_ID + CLIENT_ID + NONCE) — ensures cross-ecosystem compatibility
Splits: atomic multi-recipient (up to 9) via Hedera's native multi-party transfers
Fee delegation: documented as future extension (Hedera natively supports feePayerAccountId)

Reference implementation

npm: mppx-hedera (v0.2.2)
GitHub: tomrowbo/mppx-hedera
Tests: 300+ tests including real Hedera E2E (testnet + mainnet)
Agent Kit plugin: hak-mppx-hedera-plugin (v1.1.2) for Hedera Agent Kit

Hedera ecosystem support

Lindsay Walker (Hedera AI PM) and the Hedera AI Studio team are aware of this work and actively engaged — they are reviewing the Agent Kit plugin (hashgraph/hedera-agent-kit-js#760) and have provided feedback on the implementation. Happy to connect them for long-term maintenance questions.

Checklist

Follows STYLE.md conventions (RFC 2119 keywords, 72-char lines, IETF structure)
Uses method template structure (request schema, credential schema, verification, settlement, security, IANA)
Cross-references core spec (draft-httpauth-payment-00) and charge intent (draft-payment-intent-charge-00)
Security considerations address: replay protection, transport security, client verification, front-running
CI fixed (duplicate anchor resolved)
Split into charge-only per reviewer request (session in separate PR)

First native Machine Payments Protocol method for Hedera. Charge intent (draft-hedera-charge-00): - Native Hedera TransferTransaction with Attribution memo - Push mode (type="hash") + pull mode (type="transaction") - Challenge-bound replay protection (same 32-byte memo as Tempo) - Verification via Mirror Node REST API - Splits (atomic multi-recipient, up to 9) Session intent (draft-hedera-session-00): - HederaStreamChannel.sol escrow (ERC-20 payment channels) - EIP-712 cumulative voucher signatures - Open, voucher, topUp, close, requestClose, withdraw - SSE transport for metered streaming (LLM token billing) - 15-minute close grace period Reference implementation: https://github.com/tomrowbo/mppx-hedera npm: mppx-hedera@0.2.1 Deployed contracts (both Sourcify-verified): Testnet: 0x401b6dc30221823361E4876f5C502e37249D84C3 (296) Mainnet: 0x401b6dc30221823361E4876f5C502e37249D84C3 (295)

brendanjryan · 2026-05-11T03:09:10Z

Hi! Are you actively pushing this forward?

If so, can you fix CI and ensure your spec is clean before review?

Renamed subsection "Encoding" to "Memo Encoding" with explicit anchor {#memo-encoding} to avoid collision with top-level "Encoding Conventions" section {#encoding}. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tomrowbo · 2026-05-11T09:02:10Z

Hi! Are you actively pushing this forward?

If so, can you fix CI and ensure your spec is clean before review?

Hey! Yes, actively pushing. Just fixed the CI — was a duplicate section anchor. Should be green now. Let me know if there's anything else needed on the spec.

github-actions · 2026-05-11T15:42:13Z

Spec Preview

Spec	Changed	Artifacts
`draft-card-charge-00`	-	HTML · TXT · XML · PDF
`draft-evm-charge-00`	-	HTML · TXT · XML · PDF
`draft-hedera-charge-00`	New	HTML · TXT · XML · PDF
`draft-httpauth-payment-00`	-	HTML · TXT · XML · PDF
`draft-lightning-charge-00`	-	HTML · TXT · XML · PDF
`draft-lightning-session-00`	-	HTML · TXT · XML · PDF
`draft-payment-discovery-00`	-	HTML · TXT · XML · PDF
`draft-payment-intent-charge-00`	-	HTML · TXT · XML · PDF
`draft-payment-transport-mcp-00`	-	HTML · TXT · XML · PDF
`draft-solana-charge-00`	-	HTML · TXT · XML · PDF
`draft-stellar-charge-00`	-	HTML · TXT · XML · PDF
`draft-stripe-charge-00`	-	HTML · TXT · XML · PDF
`draft-tempo-charge-00`	-	HTML · TXT · XML · PDF
`draft-tempo-session-00`	-	HTML · TXT · XML · PDF

Browse preview release assets

brendanjryan · 2026-05-11T17:30:34Z

Thanks! Gave a brief skim

Two asks:

Can you split the charge and session proposal into two separate PRs? Charge is well defined and easy to review, but the session scope is much broader.
Has any other developer / representative of Hadera looked at this? Who would be the long-term maintainers of this spec?

brendanjryan · 2026-05-11T17:28:05Z

+
+Every Hedera charge transaction MUST include an Attribution
+memo in the transaction's native memo field. The memo
+provides challenge binding (replay protection) and server


brendanjryan · 2026-05-11T17:28:30Z

+  client is anonymous, all 10 bytes MUST be zero.
+
+NONCE (bytes 25-31)
+: The first 7 bytes of `keccak256(challengeId)`, where


Session spec moved to a dedicated PR per reviewer request. This PR now covers charge intent only. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tomrowbo · 2026-05-12T12:26:33Z

Done — split into two PRs:

Add Hedera charge intent #251 (this one): charge intent only
Add Hedera session intent #258: session intent

On the Hedera side: Lindsay Walker (Hedera AI PM) and the AI Studio team are actively engaged — they're reviewing the Agent Kit plugin integration (hashgraph/hedera-agent-kit-js#760) and have provided implementation feedback. Happy to connect them here for long-term maintenance questions if that would help.

walkerlj0 · 2026-05-12T13:54:56Z

Hello, I am the product manager of AI Studio at Hedera Hashgraph. We will maintain and make PRs to this if we make and changes and updates to our plugins. Please let us know if there is anything we ever need to do by raising an issue in the AI Studio JS SDK repo

brendanjryan · 2026-05-14T02:14:48Z

incredible -- thank you both! Doing a final review now

brendanjryan

one comment on co-authors but otherwise this looks great!

brendanjryan · 2026-05-14T02:15:29Z

+author:
+  - name: Tom Rowbotham
+    ins: T. Rowbotham
+    email: tom@xeno.money


can you add https://github.com/walkerlj0 as a co-author?

generally we want to have more than one author for proposals

brendanjryan · 2026-05-14T02:16:07Z

+This requests a transfer of 0.50 USDC on Hedera
+testnet (chain ID 296). Note that `decimals` is not
+present in the wire format; it is only used during
+request construction by the mppx schema transform.


brendanjryan · 2026-05-14T02:17:38Z

+## Mirror Node Lag {#mirror-node-lag}
+
+Hedera achieves consensus in approximately 3-5 seconds,
+but the Mirror Node REST API may take an additional 3-5


helpful context -- thank you!

brendanjryan · 2026-05-14T02:18:24Z

+
+# Acknowledgements
+
+The author thanks the Tempo team for the MPP attribution


tomrowbo · 2026-05-14T10:23:37Z

Added Lindsay as co-author — updated on both the charge (#251) and session (#258) PRs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tomrowbo added 2 commits April 28, 2026 19:19

fix: update contract address to 0x8Aaf...daE

e4c16ad

brendanjryan reviewed May 11, 2026

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refactor: split session into separate PR

a25d65c

Session spec moved to a dedicated PR per reviewer request. This PR now covers charge intent only. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tomrowbo changed the title ~~Add Hedera payment method: charge + session intents~~ Add Hedera charge intent May 12, 2026

tomrowbo mentioned this pull request May 12, 2026

Add Hedera session intent #258

Open

4 tasks

brendanjryan reviewed May 14, 2026

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tomrowbo force-pushed the add-hedera-method branch from 334f0ad to f8072fb Compare May 14, 2026 10:22

docs: add Lindsay Walker (Hedera) as co-author

b7a0d8b

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tomrowbo force-pushed the add-hedera-method branch from f8072fb to b7a0d8b Compare May 14, 2026 21:15

brendanjryan approved these changes May 14, 2026

View reviewed changes

brendanjryan merged commit 217dfdd into tempoxyz:main May 14, 2026
4 checks passed


		# Acknowledgements

		The author thanks the Tempo team for the MPP attribution

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Summary

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Reference implementation

Hedera ecosystem support

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