claude-code - 💡(How to fix) Fix [FEATURE] Allow plan-preview UI for skill-generated plans/specs, not only ExitPlanMode

Preflight Checklist

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

Problem Statement

When Claude Code is in plan mode and the model calls ExitPlanMode, the VSCode extension shows a dedicated preview UI for the plan file with Accept / Reject / Edit buttons. This is a great review experience.

However, the same UI is only available for the built-in plan mode. Skills that generate plans or specifications — including the official superpowers:writing-plans, superpowers:brainstorming, and many community skills — write their output as plain Markdown files and then surface them as text in the chat. There is no way for the user to review them in the same dedicated UI.

In practice, plan/spec content from skills is often more substantial than what ExitPlanMode produces (multi-section documents that are explicitly meant to be reviewed before execution). Yet they get a worse review experience than the simpler built-in plans. The asymmetry is confusing for users and discourages using rich planning skills.

Proposed Solution

Provide a way for skills (or the model when not in plan mode) to render an arbitrary Markdown file in the same plan-preview UI that ExitPlanMode uses. Concretely:

1. Either expose a new tool — for example ShowPlanPreview(path: string) — that any skill or top-level agent can call to display the file in the existing preview UI with Accept / Reject / Edit semantics.
2. Or extend ExitPlanMode (or add a sibling) so it can be called outside plan mode with an explicit path parameter, and the extension renders that file in the preview UI.

Either approach lets superpowers:writing-plans (and similar skills) finish by saying "here's the plan at <path>" and surface it in the dedicated UI for one-click review.

Alternative Solutions

• Manual Cmd+K V (Markdown side preview): Lets the user read the file in a side panel, but provides no Accept / Reject buttons and is read-only.
• AskUserQuestion with preview field: Designed for comparing short snippets across multiple-choice options; not suitable for reviewing a full plan/spec document.
• Linking the file with [plan.md](path) syntax: Opens the Markdown source, not a preview, and still no Accept / Reject affordance.
• Custom VSCode extension via registerCustomEditorProvider + Webview API: Technically possible to build a third-party extension that watches for plan/spec files and opens a custom Webview with Accept / Reject buttons (sample at microsoft/vscode-extension-samples/custom-editor-sample). But it would be unofficial, subject to break on Claude Code updates, and not portable across users.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

(area:skills would also fit, but the dropdown does not have it; the underlying issue is the TUI/UI.)

Use Case Example

Typical planning workflow:

1. I ask Claude Code to plan a multi-step refactor using the superpowers:writing-plans skill (in auto mode, not plan mode).
2. The skill writes a multi-section Markdown plan to a file under docs/.../plan.md (sections: Context / Approach / Tasks / Verification).
3. Today: the skill's output is summarized in chat; to review the actual plan I have to open the Markdown file manually, scroll through it, and reply "approve" / "change X" by hand.
4. With the proposed feature: the skill ends with ShowPlanPreview('<path>') and the dedicated preview UI pops up. I can read the whole plan with proper rendering, and click Accept to proceed (or Reject / Edit) — the same one-keystroke review flow that built-in plan mode already offers.
5. This saves time per planning session and (more importantly) makes me actually read the plan instead of skimming the chat summary.

Additional Context

• Existing related issues that touch overlapping areas (different problem, but same skill-vs-plan-mode tension):
  • #10073: Skill tool blocked in plan mode (closed as not planned)
  • #24072: Plan subagent cannot use Skill tool
  • #9846: AskUserQuestion not callable from skills until plan mode toggled
• VSCode-side technical references:
  • Custom Editor API
  • Webview API
  • microsoft/vscode#298924 (Custom Diff Editors proposed API) — adjacent area, indicates VSCode is moving towards more flexible review UIs
• I'm happy to provide more detail or test a preview build if useful.