t523: feat(paypal): PayPal PPCP integration review compliance

[superdav42]

Summary

PayPal reviewed our PPCP integration and provided specific feedback requiring changes before partnership approval. This task covers the 5 code changes needed in this repo.

Changes Required

1. Disconnect disclaimer — Update confirm dialog to use PayPal's required wording: "Disconnecting your PayPal account will prevent you from offering PayPal services and products on your website. Do you wish to continue?"

2. Onboarding failure UI — Display PayPal's required error messages when payments_receivable or email_confirmed is false after OAuth onboarding.

3. Block checkout for invalid merchant status — Remove paypal-rest from active gateways when merchant can't receive payments.

4. Add payee.merchant_id to orders — Include payee.merchant_id in purchase_units when using OAuth mode.

5. Log PayPal-Debug-Id headers — Capture and log the PayPal-Debug-Id response header from API calls for review submission.

Files Affected

• inc/gateways/class-paypal-rest-gateway.php
• inc/gateways/class-paypal-oauth-handler.php

Acceptance Criteria

• Disconnect dialog shows PayPal's exact required disclaimer text
• Settings page shows error banner when payments_receivable=false
• Settings page shows error banner when email_confirmed=false
• PayPal gateway hidden from checkout when merchant status is invalid
• Orders include payee.merchant_id in purchase_units when merchant_id is set
• PayPal-Debug-Id logged from every API response
• All existing PayPal tests still pass

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aidevops.sh v3.5.541 plugin for OpenCode v1.3.12 with claude-opus-4-6 spent 22m and 617 tokens on this as a headless worker.

[superdav42]

DISPATCH_CLAIM nonce=2c48c18d5924ab6ec66b161dd6cf2dcf runner=superdav42 ts=2026-04-01T02:26:05Z max_age_s=120

[superdav42]

Reopening — issue was closed as 'completed' at 02:32 UTC but no PR was merged for t523. The dispatch claim at 02:26 UTC suggests a worker was dispatched but the worktree (/home/dave/Git/ultimate-multisite-feature-725-paypal-ppcp-compliance) has 0 commits ahead of main. The task is not implemented. Relabelling to status:available for re-dispatch.

[superdav42]

Worker dispatched (PID 836096) to worktree feature/725-paypal-ppcp-compliance. Implementing PayPal PPCP review compliance items: disconnect disclaimer, onboarding failure UI, merchant status validation, payee field, debug ID logging.

[superdav42]

Worker dispatch blocked — Anthropic account rate-limited until ~05:08 UTC. Will retry when cooldown expires. Issue remains status:queued.