Route delivery receipts through proxy Queue instead of direct HTTP

[vrknetha]

Problem

Currently, when Alice's connector processes Bob's message, it POSTs the delivery receipt directly to Bob's proxy via HTTP. This has issues:

• Alice's connector needs to know Bob's proxy URL and authenticate to it
• If Bob's proxy is temporarily unavailable, the receipt is lost (fire-and-forget)
• Receipts never reach Bob's connector (see Delivery receipts are stored but never consumed by sender #165)

Current Flow

Alice's connector → HTTP POST → Bob's proxy → stores in DO → nobody reads it

Proposed Flow

Alice's connector → HTTP POST → Alice's proxy → Queue → Bob's proxy DO → WebSocket → Bob's connector

Why route through Alice's proxy?

• Connector stays dumb — only talks to its own proxy (WebSocket + HTTP)
• Connector doesn't need to know about Cloudflare Queues
• Proxy is the only component touching CF infrastructure
• Alice's proxy validates the receipt, publishes to Queue
• Bob's proxy consumes from Queue, stores in DO, pushes to Bob's connector via WebSocket (Delivery receipts are stored but never consumed by sender #165)

Architecture

• Alice's connector POSTs receipt to Alice's proxy (new endpoint or existing receipt path)
• Alice's proxy validates + publishes to receipt Queue
• Bob's proxy has Queue consumer → routes to Bob's DO
• Bob's DO stores receipt + pushes via WebSocket if connector is connected
• If connector is offline, receipt is stored in DO for delivery on reconnect

Benefits

• Decouples receipt delivery from connector-to-proxy connectivity
• Receipts are durable (Queue retries on failure)
• Solves Delivery receipts are stored but never consumed by sender #165 naturally — receipts flow all the way to sender's connector
• Dead letter receipts (dead_lettered status) follow the same path — sender's agent can act on failures
• Connector interface unchanged — still just HTTP POST to its own proxy

Dependencies

• Delivery receipts are stored but never consumed by sender #165 (push receipts to connector via WebSocket)

Impact

• Free plan: 10K Queue ops/day (receipts are low volume)
• No connector changes needed