feat(plugins): add /planwith command for inline plan mode prompts

[danjin250]

Problem

Currently, /plan only toggles plan mode on/off—it doesn't accept inline arguments. Users who want to plan a specific task must:

1. Type /plan to enable plan mode
2. Wait for plan mode to activate
3. Type their planning prompt separately

This two-step workflow adds friction, especially for power users who already know what they want to plan.

Solution

Since /plan is a built-in CLI command that can't be modified directly, this PR adds a /planwith plugin command that demonstrates the desired functionality. The command combines both steps into one:

Workflow	Before	After
Enable plan mode + start planning	/plan → wait → type prompt	/planwith <prompt>
Just enable plan mode	/plan	/plan (unchanged)

Example:

/planwith implement user authentication with OAuth 2.0

This immediately enters plan mode and begins planning the task.

Implementation

The command uses allowed-tools: EnterPlanMode in its frontmatter to call the EnterPlanMode tool, which activates real plan mode—identical to /plan.

Files Added

• plugins/planwith/.claude-plugin/plugin.json - Plugin metadata
• plugins/planwith/commands/planwith.md - Command definition
• plugins/planwith/README.md - Documentation
• Updated plugins/README.md - Added planwith to plugin table

Testing

Tested locally:

> /planwith Verify that we've entered plan mode, with this prompt.

Entered plan mode
Claude is now exploring and designing an implementation approach.

We have successfully entered plan mode. The verification is confirmed:

  1. EnterPlanMode tool was called - The tool returned "Entered plan mode"
  2. System reminder confirms plan mode is active
  3. A plan file path was assigned
  4. Read-only restrictions are now in effect

The /planwith command worked as expected - it entered plan mode with your
inline prompt. Since your request was simply to verify we entered plan mode,
and that's now confirmed, I'll exit plan mode.

Exited plan mode

Done. The /planwith command successfully:
  1. Entered plan mode
  2. Processed the inline prompt
  3. Confirmed plan mode was active
  4. Exited plan mode

The feature is working correctly.