gsd-mvp-phase

<objective> Guide the user through MVP-mode planning for a phase. The command: 1. Prompts for an "As a / I want to / So that" user story (three structured questions) 2. Runs SPIDR splitting check — if the story is too large, walks through Spike/Paths/Interfaces/Data/Rules and offers to split into multiple phases 3. Writes `**Mode:** mvp` and the reformatted `**Goal:**` to the phase's ROADMAP.md section 4. Delegates to `/gsd plan-phase <N>` which auto-detects MVP mode via the roadmap field Phase 1 of the vertical-mvp-slice PRD shipped the planner-side machinery; this command is the user entry point for it. </objective> <execution_context> @~/.claude/gsd-core/workflows/mvp-phase.md @~/.claude/gsd-core/references/spidr-splitting.md @~/.claude/gsd-core/references/user-story-template.md </execution_context> <runtime_note> **Copilot (VS Code):** Use `vscode_askquestions` wherever this workflow calls `AskUserQuestion`. Equivalent API. </runtime_note> <context> Phase number: $ARGUMENTS (required — integer or decimal like `2.1`) The phase must already exist in ROADMAP.md (created via `/gsd new-project`, `/gsd add-phase`, or `/gsd insert-phase`). This command does not create new phases — it converts an existing phase to MVP mode. </context> <process> Execute the mvp-phase workflow from @~/.claude/gsd-core/workflows/mvp-phase.md end-to-end. Preserve all gates: phase existence, status guard (refuse in_progress/completed), user-story format validation, SPIDR splitting check, ROADMA...