Host skill catalog rejects "." and "..", and a desktop skill switch variable is added

What

Skills are packaged instructions Claude can load. A host program running Claude Code can limit which skills load through the CLAUDE_CODE_HOST_SKILL_CATALOG environment variable, a named value set outside Claude Code that it reads when it starts. This release changes that and related startup steps.

• CLAUDE_CODE_HOST_SKILL_CATALOG now also refuses the folder names . and ... The warning now reads: Ignoring CLAUDE_CODE_HOST_SKILL_CATALOG: expected {"skills": 1 to 64 folder names of ASCII letters, digits, ".", "_" or "-", other than "." and ".."}. The skill set is now built by a helper instead of directly from the list.
• The condition for using the host skill catalog no longer checks whether this is a child session.
• A new environment variable, CLAUDE_CODE_DESKTOP_SKILL_SWITCHES, is read at startup and passed to setDesktopSkillSwitches.
• The startup step that gathers details about your environment now leaves package managers, runtimes, deployment environment, WSL version, Linux distribution and version control unset under one condition. Before, package managers and runtimes were always looked up.

Why

The folder names . and .. mean the current folder and the folder above it, so refusing them stops a catalog from pointing outside the skills folder. A desktop host can now also pass skill switches, and in some runs less information about your environment is collected at startup.