Make graceful close, servecontent, and HTTP/2 error responses trim-safe

[quinnj]

Two places where a natively built (juliac --trim=safe) server on HTTP.jl 2.9 hits dynamic dispatch. Both turned up while moving LeagueEasy onto registered HTTP.jl.

Graceful close(server)

HTTP/2 connections stored their shutdown notification as a closure in a Function-typed field. A trimmed app that called close(server) hit an unresolved call. HTTP's own trim workloads use forceclose, which skips this path, so the tests never caught it. The shutdown state is now a concrete struct. The client/server trim workload now closes its server gracefully.

servecontent response types

• Response's body keyword defaulted to the nobody vector, so inference couldn't fold the "no keyword body" check. Every keyword-built response picked up an extra Response{Vector{UInt8}} type.
• servecontent was also annotated ::Response.

Together, callers saw the abstract HTTP.Response, so reading or writing its body was dynamically dispatched. A natively built server failed to verify when serving a byte range.

The keyword now defaults to a private singleton, and the annotation is gone. servecontent over bytes now infers three concrete response types. An explicit body=HTTP.nobody keeps its meaning. The file-server trim workload now reads a servecontent range body.

HTTP/2 status responses

The HTTP/2 server built its 500 responses with a request= keyword typed as a union of request types. A union-typed keyword makes the keyword call dynamically dispatched. Older inference happened to resolve these calls. On Julia 1.14-dev, after the body-keyword change, they became 4 verifier errors per server specialization. The request is now set after construction.

Validation

• Trim workloads, Julia 1.13.1, before and after:
  • graceful close: 2 verifier errors → 0;
  • range body: 4 → 0.
    Both binaries run.
• Full Pkg.test() passes locally on Julia 1.13.1, including all 81 trim checks.
• Servo's trim workload serves a real server through Servo.httphandler, with buffered and streaming responses and a graceful close.
  • Against this branch, built with a 1.14-dev Julia that carries the upstream ScopedValues fix: 0 verifier errors, and the binary passes.
  • On stock 1.13.1: only the known upstream ScopedValues findings.
• Downstream: LeagueEasy's native server build verifies with 0 errors on registered 2.9.0, minus its graceful-close fallback, and a live SSE stream works in the native binary.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.80%. Comparing base (f9eaa66) to head (a582b01).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1399   +/-   ##
=======================================
  Coverage   90.80%   90.80%           
=======================================
  Files          31       31           
  Lines       12838    12841    +3     
=======================================
+ Hits        11657    11660    +3     
  Misses       1181     1181           

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