fix(cli_mcp_server): handle start launcher prefix in allow-list validation

[david-built-by-dc]

Problem

When an agent issues run_shell(bash_command='start msedge https://...'), the server blocks it with:

WARNING - Blocked CLI command not in allow-list: start
ToolError: Command blocked by security policy. Only allow-listed applications may be launched.

start is a Windows CMD shell built-in used to launch applications. It is not an executable in its own right and therefore cannot appear in ALLOWED_CLI_COMMANDS. However, msedge (and other apps the agent may want to open) is already in the allow-list — the validation just never reaches it because start is parsed as the base command.

A secondary issue: even if start were added to the allow-list, subprocess.Popen(["start", ...], shell=False) would fail because start is not a standalone executable.

Fix

Two new helpers:

• _strip_start_prefix(tokens) — if the token list begins with start/start.exe, removes the launcher, any optional window title, and all /flag arguments, leaving only the real executable and its arguments.
• _resolve_launch_args(command_str) — uses the same stripping logic when building the argument list for subprocess.Popen, so shell=False continues to hold.

_is_cli_command_allowed now normalises through _strip_start_prefix before checking the base command, so start msedge https://... is treated identically to msedge https://... for security purposes. All existing dangerous-pattern checks still run against the full original command string.

Behaviour

Command	Before	After
msedge https://example.com	✅ allowed	✅ allowed
start msedge https://example.com	❌ blocked (start not in list)	✅ allowed
start /d C:\tmp msedge https://example.com	❌ blocked	✅ allowed
start cmd.exe /c whoami	❌ blocked	❌ blocked (dangerous pattern)
notepad	✅ allowed	✅ allowed
start powershell -enc ...	❌ blocked	❌ blocked (dangerous pattern)

Testing

Manually verified with the token-level logic. No existing tests were broken; a targeted unit test can be added to tests/ if the maintainers prefer.

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