Fix: Update SendGrid webhook when client_id changes

[dahagag]

Problem

When a domain is re-registered or configuration changes generate a new client_id, inbound emails are rejected with unregistered_client errors. This happens because the SendGrid webhook URL still points to the old client ID, while the server expects the new one.

Root Cause

SetupSendgridMailbox._run() would exit early when it found an existing SendGrid mailbox, without checking if the webhook URL matched the current client_id. This caused a silent mismatch between:

• What SendGrid knows (old webhook URL with stale client_id)
• What the server expects (new client_id)

Impact

Production domains lose all inbound email after re-registration until manual SendGrid reconfiguration.

Solution

Modified SetupSendgridMailbox._run() to:

1. GET existing SendGrid mailbox configuration
2. Compare current webhook URL with expected URL (containing current client_id)
3. PATCH the webhook if URLs mismatch, preserving spam_check and send_raw settings
4. Skip update only when URL is already correct

Changes

• Added http_patch import to sendgrid.py
• Updated SetupSendgridMailbox._run() with URL comparison and PATCH logic
• Updated test_skips_request_when_domain_already_exists to include JSON response in mock
• Added test_updates_webhook_when_url_mismatches to verify PATCH behavior

Testing

✅ All SendGrid service tests pass
✅ Code formatted with yapf (column_limit=120)
✅ Validated with production domain reproduction (lokole-repro-20260601.lokole.ca)

Before Fix

if get_response.ok:
    self.log_debug('Mailbox %s already exists', domain)
    break  # ❌ Exits without checking URL

After Fix

if get_response.ok:
    existing_config = get_response.json()
    expected_url = INBOX_URL.format(client_id)
    current_url = existing_config.get('url', '')
    
    if current_url != expected_url:
        # ✅ Updates webhook with correct client_id
        http_patch(...)

Deployment Notes

After merge and PyPI release, this fix will automatically apply when SetupSendgridMailbox runs (typically during client registration or periodic sync). Affected domains will see log messages: "Updating stale webhook for {domain}".