Preserve the full error chain in network failure reasons and the CLI fallback so curl error codes and detailed TLS, DNS, and connection failures remain visible. Keep the concise two-line CLI presentation and typed readiness timeout handling.
Test TLS failures across all fetch transports, network error classifications, and CLI connection failures. Validated with cargo fmt --all, workspace Clippy with all targets and features, and cargo nextest run --no-fail-fast (18444 passed).
Refs #701