docs: sync mppx main updates

[brendanjryan]

Motivation

Keep MPP documentation aligned with public changes in the latest mppx main snapshot.

Summary

• document deferred EVM signing and the validation lifecycle
• document MCP multi-offer composition and sponsored key-authorization policy
• bind subscription documentation to Challenge IDs and remove the unneeded Stripe viem dependency
• update the mppx package snapshot and sync bookmark

Key design considerations

• keep direct signer configuration as the recommended default
• preserve HTTP-specific offer policy semantics while explaining MCP behavior

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
mpp	Ready	Preview	Sep 10, 2026 1:43pm UTC

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-10T13:29:37.895932Z	502f281	PR opened

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	mppx@​0.0.0-main-20260904175203 ⏵ 0.0.0-main-20260909172717			+1

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[socket-security]

All alerts resolved. Learn more about Socket for GitHub.

This PR previously contained dependency changes with security issues that have been resolved, removed, or ignored.

Ignoring alerts on:

• mppx@0.0.0-main-20260909172717

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[brendanjryan]

@SocketSecurity ignore npm/mppx@0.0.0-main-20260909172717