Fix intermittent "connection was not ready" failures in proxy_trusted_server tests #1485

Description

Tests in crates/trusted-server-cli/tests/proxy_trusted_server.rs (added in #1251) fail intermittently in the cargo test (axum native) job of Run Tests. They fail at the shared send() helper (line 347):

should receive the actual Trusted Server response: hyper::Error(Canceled, "connection was not ready")

The failure is not in a test assertion: the request is never sent. It has hit two different tests in this file:

The PR #1435 job passed when re-run with no code change, and later main commits pass this job; the main run was not re-run. PR #1435 does not touch this file or the dev-proxy code.

Likely cause (not confirmed): both failing tests send a second request over the same hyper::client::conn::http1::SendRequest (lines 428/443 and 506/558). send() calls send_request without first awaiting SendRequest::ready(). If the HTTP/1 connection hasn't finished the previous exchange, or has been closed, hyper rejects the new request with Canceled: connection was not ready. authenticated_proxy_reaches_real_trace_actions_for_every_upstream_mode also sends two requests per connection (line 385) and has not been seen to fail, so reuse alone is not sufficient; the failure looks like a race between the previous exchange finishing and the next send_request.

Reproduction steps

1. Run cargo test --package trusted-server-cli --target <host-triple> --test proxy_trusted_server repeatedly, or let CI run it (it's part of ./scripts/test-cli.sh).
2. Occasionally a test that reuses one connection panics at line 347 with the error above.

Expected behavior

The proxy integration tests pass deterministically. A second request on a reused connection waits until the connection is ready, or the test opens a new connection per request.

Affected area

CI / Tooling

Version

main at d1bb3fa19; the test file was last changed in #1251 (3d54bbd59).

Done when

• send() awaits SendRequest::ready() before send_request (or each request uses its own connection), and a connection that closes early fails with a clear message rather than Canceled.
• proxy_trusted_server passes in a repeated local loop (for example 50 iterations) on Linux and macOS.