fix(demo): format session cumulative amount and split channel open UX

[coffeexcoin]

Summary

• Format the session cumulative amount display using token decimals (formatUnits with USDC 6 decimals) and prefix with $ — shows $0.001 instead of raw 1000
• Add onChannelOpened callback to abstractSession client options, called after the on-chain channel open but before voucher signing — supports deferring the voucher via a returned Promise
• Rework the demo session UI to require two discrete button presses for stream initiation: "Open Channel" (approve + open tx) then "Sign Voucher", instead of firing both signatures in a single click
• Subsequent voucher requests remain single-click

Test plan

• Verify cumulative amount displays as $0.001, $0.002, etc. after each session request
• Verify first session request pauses after channel open and shows "Sign Voucher" button
• Verify clicking "Sign Voucher" completes the request and shows the response
• Verify subsequent requests use a single "Send Voucher" button without pause
• Verify Reset returns to initial state

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🦋 Changeset detected

Latest commit: 2c0a0ba

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@abstract-foundation/mpp	Patch

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Project	Deployment	Actions	Updated (UTC)
mpp-abstract-mpp-demo	Ready	Preview, Comment	Mar 25, 2026 11:18pm

[cursor]

PR Summary

Medium Risk
Changes the session client’s channel-open flow by inserting an awaited callback before the first voucher is signed, which can affect request timing and error handling if misused. Demo changes are low risk but exercise this new async path.

Overview
Session client enhancement: abstractSession now accepts an optional onChannelOpened(channelId) callback that runs after the on-chain open completes but before the opening voucher is signed; returning a Promise pauses voucher signing until it resolves.

Demo UX updates: The session demo is reworked into explicit phases so the first interaction becomes two steps ("Open Channel" then "Sign Voucher"), while later payments remain single-click; it also formats the displayed cumulative amount using formatUnits with USDC_DECIMALS and updates the session client wrapper to pass the new option.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

UI freezes on retry after failed voucher signing

Medium Severity

handleOpenChannel assumes onChannelOpened will always fire, but the callback only runs for new channels (inside if (!entry) in session.ts). If the first request opens a channel on-chain and the user then rejects the voucher signature, the channel entry persists in the client's internal channels map while state.channelOpen stays false. On retry, handleOpenChannel fires mppx.fetch again, which takes the "voucher for existing channel" path — onChannelOpened is never called, so the phase never transitions from 'opening' to 'awaitingVoucher', and no handler ever processes the resolved response. The UI gets permanently stuck on the "Opening channel…" spinner.

Additional Locations (1)

• packages/mpp/src/client/session.ts#L263-L276