fix: coinbase popup polling fallback, retry reset, and animated alerts

[broody]

Summary

Three fixes for the Coinbase payment popup flow, plus a UX polish.

1. Fallback polling prevents stuck 'Complete in Popup'

Problem: If the BroadcastChannel signal from the popup was lost (e.g. browser restrictions, timing), the keychain would stay stuck on 'Complete in Popup' forever.

Fix: Start a slow 5s fallback poll as soon as the popup opens. This detects payment completion on the backend even without the popup signal. When polling_success arrives from the popup, the poll upgrades to 1s fast poll with a 15s timeout (same as before).

2. Terminal ref set on polling_success (race condition fix)

Problem: After successful payment, the popup closes after 1.5s. The popup-close watcher would detect this and set popupClosed=true before the backend confirmation poll completed, causing the UI to show 'Payment Window Closed' instead of progressing.

Fix: Set terminalReachedRef.current = true immediately on polling_success, not just when the backend confirms Completed.

3. Retry clears cancelled state in popup

Problem: After cancelling a payment and retrying within the same popup, the 'Payment Cancelled' alert stayed visible because pending_payment_auth, payment_authorized, and apple_pay_button_pressed events only set committed=true without clearing failed and error.

Fix: Clear failed and error on all active-payment events.

4. Animated status bar alerts

Problem: Status bar alerts popped in abruptly and shifted the Coinbase iframe down.

Fix: Status bar now overlays the top of the iframe with a translate-y slide-down animation (300ms ease-out). The iframe always fills the full screen.

Polling Strategy

Popup opens → 5s fallback poll (backend)
                    ↓ (if BroadcastChannel polling_success received)
              1s fast poll (15s timeout)
                    ↓ (on Completed/Failed)
              Stop all polls → navigate

[vercel]

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Project	Deployment	Actions	Updated (UTC)
controller-example-next	Ready	Preview	Feb 27, 2026 6:52pm
keychain	Ready	Preview	Feb 27, 2026 6:52pm
keychain-storybook	Ready	Preview	Feb 27, 2026 6:52pm

[claude]

Claude finished @broody's task —— View job

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Documentation Analysis

• Analyze PR changes for user-facing impact
• Determine documentation requirements

Result

No documentation updates needed.

This PR contains internal reliability improvements and UX polish for the Coinbase payment popup flow:

1. Fallback polling mechanism - Internal reliability improvement to prevent stuck states
2. Race condition fix - Internal timing fix for proper state transitions
3. Retry state clearing - Internal bug fix for popup state management
4. Animated status alerts - Visual polish (CSS transitions)

Why no docs changes:

• No API changes - developers using @cartridge/controller or @cartridge/keychain see no difference in how they integrate
• No new features or configuration options exposed
• No behavioral changes that require developer action
• Changes are entirely within the keychain's internal payment flow implementation

These improvements make the payment experience more reliable for end users, but the developer-facing integration remains unchanged.

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