fix: prevent local CLI-agent providers from deadlocking

[Traigor]

Summary

Fixes CLI-1890 by preventing local CLI-agent providers from deadlocking when child processes write large stdout/stderr output.

Changes

• Drain CLI-agent stdout and stderr concurrently while the child process runs.
• Bound captured diagnostics per stream while continuing to drain overflow.
• Include stdout_truncated and stderr_truncated in nonzero-exit diagnostics.
• Return a clear error when successful stdout is truncated before JSON parsing.
• Document Codex config propagation behavior and avoid unsupported temperature/token flags.
• Add regression coverage for large stdout, large stderr, bounded diagnostics, and Codex argv behavior.

Verification

• cargo check -p bitloops-inference
• cargo test -p bitloops-inference --lib provider::cli_agent -- --nocapture
• cargo test -p bitloops-inference --test protocol_loop codex_exec_runtime_returns_normalised_parsed_json -- --nocapture
• cargo test -p bitloops-inference --test protocol_loop claude_code_print_runtime_passes_prompt_model_and_schema -- --nocapture
• cargo test -p bitloops-inference