Scope and design

Closes #187. Prerequisite for observability epic #173 / integrated qualification #178.

Replace the scheduling-sensitive 1ms whole-command timeout fixture with a deterministic, serial and restored test-only RoundTripper at the actual Client.Do boundary. Preserve live_transport_failure; require a live request context, exact synthetic GET target, exactly one attempt and http_attempted true. Cover transport-returned cancellation separately. Configuration-read cancellation/deadline during CLI startup requires configuration_error, http_attempted false and zero attempts.

No production, API, cache, MCP, Admin, configuration or observability behavior changes. The different actual pre-dispatch context cancellation false-positive diagnostic is #189; it remains an explicit O5 prerequisite and is not certified or fixed here.

Risk and recovery

Test-only process-global seams require serial ownership and cleanup; existing entrypoint tests are serial and already own cliRoute similarly. Normal real-loopback live-sync and offline/provider-selection controls remain. Revert this commit to restore prior test behavior; no migration, data repair or service restart is involved. Synthetic .invalid coordinates and fake credentials only; no external network or raw sensitive diagnostic output.

UX assessment

No new user-visible resource, lifecycle, action or remediation; existing CLI diagnostics are under test. MCP/Admin changes are not required. Whole-feature cross-surface qualification remains #178, including #188/#189 disposition.

Verification

Head: 8f6a387062944410b9c1acda4a96dfd8c6a7908c.
Base: f38d6c7ba52b058a4d2e243e50e4ca4f732a6829.

Author passed:

• Four focused transport/startup controls, count200.
• Full existing startup/live-provider scenario family under race, count10.
• Entire cmd/gitcode-mcp package under race, count1.
• Entire cmd/gitcode-mcp package shuffled, count5.
• go test ./... -count=1; go vet ./...; product-doc and whitespace gates.

Required exact-head CI: https://github.com/urandon/gitcode-mcp/actions/runs/38140667475 — success (attempt1, push ci.yml, all steps). Independent review evidence is linked in #187 comments. Live E2E, release and installed-service changes were not attempted. Merge requires no blocking discussion, matching canonical refs/SHA, clear independent review and green required CI; closure additionally requires resulting-main CI success.