Verifiable, tamper-evident spend receipts alongside cost tracing

[joecattt]

Support pointed me here after a cold email (thanks, Daniel) — posting as an idea since I don't know if this fits the roadmap, not filing it as a formal ask.

Langfuse traces show what an agent did and what it cost, computed from token counts / provider pricing. What it doesn't do (and I don't think is meant to) is answer a narrower question: can that cost be proven against the provider's own record, in a form a third party — an auditor, a finance team, a client being billed for agent usage — can check without trusting Langfuse's database or the agent operator's word for it?

I built paymaster to explore that: a reference implementation for signed, tamper-evident AI-agent-spend receipts. Evidence-graded (it won't silently promote "we assume this cost $X" to "verified"), MIT licensed, MCP server included.

Not proposing you build this in — more flagging that "trace shows what happened" and "receipt proves what it cost, verifiably" feel like adjacent, complementary layers, and I'm curious whether anyone here has run into real demand for the second one. Happy to be told this is out of scope or already solved a different way.

[CodeCLS]

Thanks for the suggestion/sharing this with the community!