[FEATURE] Skill flag that force allows executing during plan mode

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Plan mode blocks all Bash tool usage, including skills that only perform read-only side effects like opening files in an editor. For example, skills like these just launch an application and don't modify the codebase at all:

---
name: open-configs
description: Opens the Configs folder in VS Code
disable-model-invocation: true
allowed-tools: Bash(*)
---

When a user invokes one of these during plan mode, it's blocked because Bash is classified as a non-readonly tool. The user must either exit plan mode, run the skill, and re-enter plan mode — or manually copy-paste the command into a terminal.

Proposed Solution

Add optional skill frontmatter (e.g., readonly: true or plan-mode: allow) that signals to Claude Code that the skill is safe to execute during plan mode:

---
name: open-game-configs
description: Opens the GameConfigs folder in VS Code
disable-model-invocation: true
allowed-tools: Bash(*)
readonly: true # <-- allows execution during plan mode
---

When plan mode encounters a skill invocation with this flag, it would permit the Bash calls within that skill rather than blocking them.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Project has several /open-* skills that launch Visual Studio, VS Code, or other editors to view files. These are inherently read-only from the codebase's perspective and safe to run at any time, including during planning.

Additional Context

_No response_