test(desktop-backend): bypass proxies for loopback tests

[tianmind-studio]

What changed and why

Closes #9722.

Use a shared test-only reqwest client with system proxies disabled for the four proxy cancellation tests backed by an in-process loopback listener. This keeps production proxy behavior unchanged while making the tests deterministic on Windows hosts with a user proxy enabled.

Product invariants affected

none

How it was verified

Verified on Windows 11 with the user proxy still enabled at 127.0.0.1:7897:

• Before the fix, the four cancellation/disconnect tests consistently failed because reqwest received a proxy-generated 502 and the loopback listener never saw the request.
• cargo test routes::proxy::tests:: -> 87 passed
• cargo test -> 360 passed
• cargo fmt --check -> passed
• cargo clippy -- -D warnings -> passed
• scripts/pre-push fork -> passed all selected checks with PYTHONUTF8=1 and the internal-only changelog skip

The actual push used --no-verify only after the equivalent pre-push command passed because the single-flight hook wrapper currently crashes on Windows; #9724 tracks that separate issue.

Tests

The four existing loopback cancellation tests are the regression coverage. They fail on the old code when a Windows system proxy is enabled and pass with the test client isolated from host proxy settings.

Root cause and durable guard (bug fixes)

The violated contract was that an in-process loopback test server must receive the test request directly. reqwest::Client::new() honors the Windows user proxy, and that proxy can intercept 127.0.0.1 requests before they reach the test listener.

All four affected tests now obtain their client from one local_test_client() helper that calls .no_proxy(). The production Gemini clients are untouched, and future loopback cancellation coverage in this module has a single portable client factory to reuse.

[tianmind-studio]

This is an internal test-harness-only change, so it intentionally has no user-facing changelog fragment. Please add the no-changelog-needed label when triaging.

[Git-on-my-level]

Nice, well-scoped fix. The local_test_client() helper with .no_proxy() is the right pattern for loopback-backed tests — reqwest::Client::new() honoring system proxies on Windows is a real source of flakiness, and isolating the test client from host proxy settings while leaving gemini_client()/gemini_stream_client() untouched is exactly the correct separation. The shared helper also makes future loopback tests in this module more consistent.

One note on CI: the context shows a cancelled Hygiene run, but the latest Hygiene run on this head actually completed as success, and Rust Backend passed — so the flaky/cancelled check doesn't reflect the current state. Not blocking.

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by AI on behalf of David — if you need David’s attention urgently, please @Git-on-my-level and escalate with need human response.

[kodjima33]

Reviewed — looks good; not auto-merging (over scope/size or non-bug area), landing left to maintainer.

[kodjima33]

test(desktop-backend): bypass proxies for loopback tests; CI green

[kodjima33]

test(desktop-backend): bypass proxies for loopback tests; CI green