chore: import upstream snapshot with attribution

presets/lean/commands/speckit.constitution.md

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+---
+description: Create or update the project constitution.
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+## Outline
+
+1. Create or update the project constitution and store it in `.specify/memory/constitution.md`.
+   - Project name, guiding principles, non-negotiable rules
+   - Derive from user input and existing repo context (README, docs)

presets/lean/commands/speckit.implement.md

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+---
+description: Execute the implementation plan by processing all tasks in tasks.md.
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+## Outline
+
+1. Read `.specify/feature.json` to get the feature directory path.
+
+2. **Load context**: `.specify/memory/constitution.md` and `<feature_directory>/spec.md` and `<feature_directory>/plan.md` and `<feature_directory>/tasks.md`.
+
+3. **Execute tasks** in order:
+   - Complete each task before moving to the next
+   - Mark completed tasks by changing `- [ ]` to `- [x]` in `<feature_directory>/tasks.md`
+   - Halt on failure and report the issue
+
+4. **Validate**: Verify all tasks are completed and the implementation matches the spec.

presets/lean/commands/speckit.plan.md

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+---
+description: Create a plan and store it in plan.md.
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+## Outline
+
+1. Read `.specify/feature.json` to get the feature directory path.
+
+2. **Load context**: `.specify/memory/constitution.md` and `<feature_directory>/spec.md`.
+
+3. Create an implementation plan and store it in `<feature_directory>/plan.md`.
+   - Technical context: tech stack, dependencies, project structure
+   - Design decisions, architecture, file structure

presets/lean/commands/speckit.specify.md

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+---
+description: Create a specification and store it in spec.md.
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+## Outline
+
+1. **Ask the user** for the feature directory path (e.g., `specs/my-feature`). Do not proceed until provided.
+
+2. Create the directory and write `.specify/feature.json`:
+   ```json
+   { "feature_directory": "<feature_directory>" }
+   ```
+
+3. Create a specification from the user input and store it in `<feature_directory>/spec.md`.
+   - Overview, functional requirements, user scenarios, success criteria
+   - Every requirement must be testable
+   - Make informed defaults for unspecified details

presets/lean/commands/speckit.tasks.md

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+---
+description: Create the tasks needed for implementation and store them in tasks.md.
+---
+
+## User Input
+
+```text
+$ARGUMENTS
+```
+
+## Outline
+
+1. Read `.specify/feature.json` to get the feature directory path.
+
+2. **Load context**: `.specify/memory/constitution.md` and `<feature_directory>/spec.md` and `<feature_directory>/plan.md`.
+
+3. Create dependency-ordered implementation tasks and store them in `<feature_directory>/tasks.md`.
+   - Every task uses checklist format: `- [ ] [TaskID] Description with file path`
+   - Organized by phase: setup, foundational, user stories in priority order, polish