Bounded work after the response on Fastly and Axum, drained on Axum SIGTERM #476

Summary

Bounded work after the response on Fastly and Axum, drained on Axum SIGTERM.

Behavior

A task registered during a request runs after the response is delivered, bounded in time.

Acceptance criteria

• On Fastly and Axum the task runs after delivery, and on Axum SIGTERM waits for registered tasks up to the grace
• Later, on Cloudflare the task runs after delivery, and Spin returns a capability error

Dependencies

Blocked by:

• PR feat: implement portable outbound HTTP and request lifecycle contracts #275 feat: implement portable outbound HTTP and request lifecycle contracts
• PR Add Axum production startup and bounded shutdown #406 Add Axum production startup and bounded shutdown

Blocks:

• EZI-1c After-response work on Cloudflare (waitUntil) (new in this plan)
• EZI-1s After-response capability error on Spin (new in this plan)
• R2 Integration-branch tag with the Fastly and Axum parts of EZI-1 (new in this plan)

Related

• Needed by Server-side identity on every adapter trusted-server#1558, server-side identity on every adapter. Planned in wave 3 (MVP: Fastly and Axum); priority P1, size M.
• Work in progress: Add Axum production startup and bounded shutdown #406 Add Axum production startup and bounded shutdown
• Requirement EZI-1 in the design.