Handle case when session started with Docker Desktop proxy available, and the Desktop is stopped

[gtardif]

• detect if proxy is not avaiable anymore in the middle of a session and fallback to no proxy.
• improve error message if using the gateway but no auth token is available

Signed-off-by: Guillaume Tardif guillaume.tardif@gmail.com

[docker-agent]

Assessment: 🟢 APPROVE

PR: Handle case when session started with Docker Desktop proxy available, and Desktop is stopped

The implementation looks correct. The fallbackTransport correctly handles the proxy-unavailable scenario:

• Atomic state management: atomic.Bool for proxyDisabled is the right tool — no locks needed for this flag.
• Request retry logic: Correctly distinguishes retryable requests (Body == nil || GetBody != nil) from non-retryable consumed-body requests.
• DisableCompression plumbing: The type-switch in httpclient/client.go correctly handles both *http.Transport and the new fallbackTransport via the interface{ DisableCompression() } duck-typing approach.
• Independent transport clones: proxyTransport and transport (direct) are independent clones of http.DefaultTransport, so DisableCompression() mutations are safe.
• Error message improvement: Centralising NoDesktopTokenErrorMessage in base.go is a clean refactor.

The isProxySocketError pattern matching was examined — while "dial unix" is broad, in practice this transport is only used for outbound LLM API HTTP calls through the Desktop proxy socket, so false positives from unrelated Unix sockets (e.g., /var/run/docker.sock) are not a realistic concern in this context.