Support container CLI argument prefixes

[Gordon Lam (yeelam-gordon)]

Motivation

Dev Containers can substitute a Docker-compatible executable such as wslc, but app-owned WSLC Sessions require --session <name> before ordinary Docker-shaped commands. The CLI therefore needs a small transport mechanism for placing provider-specific arguments immediately after the configured Docker executable.

Minimal design

• Add one hidden internal --docker-path-args option containing a JSON string array.
• Do not add devcontainer.json schema or public configuration surface.
• Keep the optional field inert when absent.
• Centralize prefix insertion across non-PTY and PTY execution.
• Leave ordinary Docker and Podman behavior unchanged.
• Leave standalone Compose unchanged.
• Preserve the prefix for V2 Compose and variant/version probes.

Why not environment variables

A provider may not expose an environment-variable mechanism, while explicit argv is auditable at process boundaries and keeps the transport contract visible to the embedding caller.

Scope

This change defines only a CLI transport contract. It contains no WSLC-specific behavior or UI.

Tests run

• npm run type-check
• Focused dockerUtils tests covering prefix ordering, Compose, and parsing
• npm run lint
• compile-prod

Design considerations and risks

The option is hidden and internal rather than a public compatibility promise. Parsing is strict so malformed input fails explicitly. Upstream consumers must package a matching CLI revision before relying on the argument contract.