feat: Register "What-if Analysis" community extension

extensions/whatif/README.md

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+# What-if Analysis Extension
+
+Preview the downstream impact of requirement changes before committing to them.
+
+## Overview
+
+The What-if Analysis extension provides a read-only simulation tool for spec-driven development. It allows teams to preview how a proposed change will affect:
+
+- **Complexity**: Heuristic scoring of project difficulty.
+- **Effort**: Estimated person-hours for implementation.
+- **Tasks**: Delta in the task list (added, removed, changed).
+- **Risks**: Potential technical debt, breaking changes, or conflicts.
+
+## Installation
+
+```bash
+specify extension add whatif
+```
+
+Or for development:
+
+```bash
+specify extension add --dev path/to/whatif
+```
+
+## Usage
+
+Invoke the command through your AI assistant:
+
+```bash
+/speckit.whatif.analyze "Change the database from SQLite to PostgreSQL"
+```
+
+The agent will analyze your current artifacts (`spec.md`, `plan.md`, `tasks.md`, `constitution.md`) and generate a detailed impact report without modifying any files.
+
+## Commands
+
+### `speckit.whatif.analyze`
+
+Performs the simulation and generates the report.
+
+**Arguments**: The hypothetical scenario or requirement change to analyze.

extensions/whatif/commands/analyze.md

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+---
+description: Preview the downstream impact (complexity, effort, tasks, risks) of requirement changes before committing to them.
+scripts:
+  sh: ../../scripts/bash/check-prerequisites.sh --json --include-tasks
+  ps: ../../scripts/powershell/check-prerequisites.ps1 -Json -IncludeTasks
+---
+
+# What-if Analysis
+
+Use this command to preview the impact of requirement changes on complexity, effort, and task breakdown without modifying any files.
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+You **MUST** use this input as the "What-if Scenario" to analyze. If empty, prompt the user for a scenario.
+
+## Goal
+
+Provide a detailed, read-only simulation of how the proposed requirement change would impact the project's specification, implementation plan, and task breakdown. Help the team make data-driven decisions about whether to proceed with the change.
+
+## Operating Constraints
+
+**STRICTLY READ-ONLY**: Do **not** modify any files. This is a pure in-memory simulation.
+
+## Execution Steps
+
+### 1. Initialize Simulation Context
+
+Run `{SCRIPT}` once from repo root and parse JSON for FEATURE_DIR and AVAILABLE_DOCS.
+Load core artifacts from FEATURE_DIR:
+- **spec.md**: Current requirements and priorities.
+- **plan.md**: Current architecture and technical choices.
+- **tasks.md**: Current task list and effort markers.
+- **constitution**: Project principles (from `/memory/constitution.md`).
+
+### 2. Formulate Simulated State
+
+In your context, model the project as it would look *after* the proposed change:
+- **Requirements**: Which are added, removed, or modified?
+- **Architecture**: What technical changes are required (new libraries, DB schema changes, API updates)?
+- **Tasks**: What is the delta in the task list?
+
+### 3. Calculate Impact Metrics
+
+Derive the following deltas based on your assessment:
+
+#### A. Complexity Score (1-100)
+- **Current Score**: Based on requirement count, dependency depth, and technical risk.
+- **Simulated Score**: Based on the project state after the change.
+- **Delta**: (Simulated - Current).
+
+#### B. Effort Delta (Hours)
+- Estimate the total person-hours required to implement the change.
+- Breakdown: Research, Development, Testing, Refactoring.
+
+#### C. Task Count Delta
+- Number of tasks to be added, removed, or significantly altered.
+
+### 4. Risk Assessment
+
+Identify potential pitfalls:
+- **Breaking Changes**: Impact on existing APIs or data.
+- **Architecture Drift**: Does the change move the project away from its original goal?
+- **Constitution Conflicts**: Does the change violate any project principles?
+- **Integration Debt**: New dependencies or maintenance overhead.
+
+### 5. Generate Simulation Report
+
+Output a structured Markdown report (no file writes) with the following structure:
+
+# "What-if" Analysis: [Scenario Summary]
+
+## Executive Summary
+
+| Metric | Current | Simulated | Delta |
+|--------|---------|-----------|-------|
+| Complexity Score | [Score] | [Score] | [+/- Delta] |
+| Total Tasks | [Count] | [Count] | [+/- Delta] |
+| Estimated Effort | [Hours] | [Hours] | [+/- Hours] |
+
+**Risk Level**: [LOW | MEDIUM | HIGH | CRITICAL]
+
+---
+
+## 🏗️ Impacted Artifacts
+
+### 📋 Specification (spec.md)
+- **Changes**: [Briefly list requirement alterations]
+- **Impact**: [High-level impact on user value]
+
+### 📐 Implementation Plan (plan.md)
+- **Changes**: [Briefly list architectural updates]
+- **Impact**: [Technological implications]
+
+### ✅ Task Breakdown (tasks.md)
+- **[ADDED]**: [T-NEW-1] Description...
+- **[REMOVED]**: [T-OLD-4] Description...
+- **[CHANGED]**: [T-MOD-12] Description...
+
+---
+
+## 🚦 Risk Assessment
+
+| Potential Risk | Severity | Mitigation Suggestion |
+|----------------|----------|-----------------------|
+| [Risk Title] | [Severity] | [Strategy] |
+
+---
+
+## 📊 Side-by-Side Preview (Simulated)
+
+Show a diff-like preview for the most significant file change (typically spec.md or plan.md).
+
+```markdown
+<<<< CURRENT
+[Original Content Snippet]
+==== SIMULATED
+[New Content Snippet]
+>>>>
+```
+
+## 🏁 Recommendation
+
+Provide a clear "Go / No-Go" recommendation based on the data. Suggest follow-up commands (e.g., "/speckit.specify" to apply these changes) if the user decides to proceed.
+
+## Context
+
+$ARGUMENTS

extensions/whatif/extension.yml

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+schema_version: "1.0"
+
+extension:
+  id: whatif
+  name: "What-if Analysis"
+  version: "1.0.0"
+  description: "Preview the downstream impact (complexity, effort, tasks, risks) of requirement changes before committing to them."
+  author: "DevAbdullah90"
+  repository: "https://github.com/github/spec-kit"
+  license: "MIT"
+
+requires:
+  speckit_version: ">=0.6.0"
+
+provides:
+  commands:
+    - name: speckit.whatif.analyze
+      file: commands/analyze.md
+      description: "Analyze the impact of requirement changes"
+
+tags:
+  - "analysis"
+  - "planning"
+  - "simulation"