fix(appcontainer): suppress empty console window for piped sandbox children

[caarlos0]

📖 Description

The Windows ProcessContainer backends (BaseContainer + AppContainer) launched
console-subsystem children (e.g. pwsh, cmd, rg, …)
without CREATE_NO_WINDOW. On a headless host with piped stdio Windows
allocates a new console that briefly flashes on screen, even though stdio is
redirected via pipes (STARTF_USESTDHANDLES).

This sets CREATE_NO_WINDOW on both spawn paths (base_container_runner and
appcontainer_runner, including BaseContainer's env-not-supported retry) when
stdio is piped:

let no_window_flag = if pipe_mode { CREATE_NO_WINDOW.0 } else { 0 };

The pipe_mode guard is essential: in console-sharing (ConPTY) mode the child
inherits the parent's live console for interactive I/O, where CREATE_NO_WINDOW
must not be set (it would detach the child and break the interactive shell). The
mxc-sdk streaming dispatch always spawns with StdioMode::Pipes, so pipe_mode
is always true for SDK callers.

🔗 References

n/a

🔍 Validation

• cargo fmt --all -- --check, cargo clippy -p wxc_common -p mxc-sdk --all-targets -- -D warnings, and cargo test -p wxc_common -p mxc-sdk pass on the pinned 1.93 toolchain.
• The two runner files are cfg(windows)-gated and can't be compiled on macOS; the change only conditionally OR-s CREATE_NO_WINDOW into the existing creation flags and was matched against rustfmt output. Windows build/test coverage comes from CI.

✅ Checklist

• Signed the Contributor License Agreement
• Linked to an issue
• Updated documentation (if applicable)
• Updated Copilot instructions (if build, architecture, or conventions changed)

📋 Issue Type

• Bug fix
• Feature
• Task

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR prevents brief “empty console window” flashes when the Windows ProcessContainer backends (BaseContainer + AppContainer) spawn console-subsystem children with piped stdio (the mxc-sdk streaming path). It does so by conditionally adding CREATE_NO_WINDOW to the process creation flags only when pipe_mode is active, preserving ConPTY/console-sharing behavior for interactive runs.

Changes:

• Add CREATE_NO_WINDOW to BaseContainer child creation flags when pipe_mode is true (including the env-not-supported retry path).
• Add CREATE_NO_WINDOW to AppContainer CreateProcessW flags when pipe_mode is true.

Show a summary per file

File	Description
src/backends/appcontainer/common/src/base_container_runner.rs	ORs CREATE_NO_WINDOW into BaseContainer process creation flags when pipe_mode is enabled, including retry without env block.
src/backends/appcontainer/common/src/appcontainer_runner.rs	ORs CREATE_NO_WINDOW into AppContainer CreateProcessW flags when pipe_mode is enabled.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0