Fix Moonpay buy tracking race condition

[Jon-edge]

CHANGELOG

Does this branch warrant an entry to the CHANGELOG?

• Yes

Dependencies

None

Description

Fixes the P1 Moonpay Buy_Success PostHog tracking bug where incorrect values were intermittently reported. The root cause was identified as the RampDeeplinkManager using a single-listener slot that got silently overwritten when a new quote was initiated before the previous transaction's deeplink arrived. This root cause is not confirmed, these changes are a theory, with handling and canary reporting to ensure we at least don't further pollute our tracking with inflated buy volume and report if the regression persists.

Commit 1: Fix deeplink handler overwrite race condition

Replace the single listener field in RampDeeplinkManager with a token-keyed Map. Each register() call now returns a unique token for targeted cleanup, preventing one handler from overwriting another. handleDeeplink() matches the most recently registered listener for the given providerId + direction.

Updates all callers (webViewUtils, moonpayRampPlugin, revolutRampPlugin, paybisRampPlugin) to use the token-based API.

Commit 2: Add Moonpay buy tracking verification via transactions API

When the Moonpay buy deeplink fires, query Moonpay's GET /v1/transactions/:id API to verify the actual transaction amounts:

• API succeeds: Log Buy_Success with API-verified values and include both closure + API values as diagnostic properties. If they differ, also log a Buy_Tracking_Mismatch event.
• API fails: Skip Buy_Success entirely (unverifiable) and log Buy_Tracking_Mismatch with the closure values and failure reason.

If the deeplink manager fix works correctly, Buy_Tracking_Mismatch should never appear in PostHog. If it does, we know there's another issue — but the Buy_Success data stays clean.

Requirements

If you have made any visual changes to the GUI. Make sure you have:

• Tested on iOS device
• Tested on Android device
• Tested on small-screen device (iPod Touch)
• Tested on large-screen device (tablet)

No visual changes in this PR.

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Note

Medium Risk
Touches shared deeplink/webview flow across multiple ramp providers and changes analytics emission behavior for Moonpay, so regressions could impact ramp completion handling or tracking accuracy.

Overview
Prevents ramp deeplink callbacks from being silently overwritten by replacing the single RampDeeplinkManager listener with a tokenized Map, updating ramp plugins and webViewUtils to store per-quote tokens and reliably unregister on close/errors.

For Moonpay buys, adds a verification step that fetches GET /v1/transactions/:id and logs Buy_Success using API-verified fiat/crypto amounts (with diagnostic fields), otherwise emits a new Buy_Tracking_Mismatch event when verification fails or values differ. Updates CHANGELOG.md accordingly.

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