Smartstack: shipper queue

[timbeccue]

Summary

This is PR 4 of 8 completing the v1 banzai implementation of Smartstacking at site.

PR1 (#469): combine math
PR2 (#470): JPEG utilities
PR3 (#471): DB updates
PR4 (#473): shipper contract      <-- you are here
PR5 (#474): smartstack data products
PR6 (#475): stack worker polling
PR7 (#476): e2e tests, compose cleanup
PR8 (#477): logging

PR1 combine math ───────┐
PR2 JPEG utilities ─────┤
PR3 DB updates ─────────┼──> PR5 data products --> PR6 stack workers --> PR7 E2E --> PR8 logs/docs
PR4 shipper contract ───┘

PRs 1–4 provide the independent foundations for combining images, rendering JPEGs, storing stack state, and shipper integration (this PR). PR5 builds the products, PR6 adds the polling worker, and PR7–8 add end-to-end proof, logging, and final documentation.

What changes here

Added methods to post data to the shipper queue. In the case of smartstack previews, this includes passing in a subset of the fits header so that the ingester has the metadata it needs without the inclusion of a fits file.

Publishing contract

post_to_shipper_queue() publishes UTF-8, plain-text JSON:

Field	Final product	Preview
fits	e45 FITS path	null
small_thumbnail	JPEG path	JPEG path
large_thumbnail	JPEG path	JPEG path
instrument_enqueue_timestamp	Passed through	Passed through
thumbnail_metadata	Omitted by the current final caller	Included when supplied

The publisher also:

• Declares the durable fanout exchange, queue, and binding before publishing.
• Uses publisher confirms so broker rejection or acknowledgement timeout reaches PR6’s retry path.
• Applies bounded five-second connection and confirmation timeouts.
• Publishes and declares through the same channel.

New settings provide these defaults:

• SHIPPER_EXCHANGE=ship_files
• SHIPPER_QUEUE_NAME=ship
• SMARTSTACK_PREVIEWS=true

Scope

This PR defines and tests the publishing boundary only. It does not create products or decide when to preview, finalize, or retry; those responsibilities belong to PR5 and PR6.

Focused tests cover the durable binding, plain-text JSON bodies for previews and finals, optional thumbnail metadata, publisher confirms, and timeout options.