Add .github/copilot-instructions.md (#38)

* Initial plan

* Add .github/copilot-instructions.md with project-specific Copilot guidance

Co-authored-by: nank1ro <60045235+nank1ro@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: nank1ro <60045235+nank1ro@users.noreply.github.com>

Author: Copilot

.github/copilot-instructions.md

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+# Copilot Instructions
+
+## Project Overview
+
+**Disco** is a Flutter library providing scoped dependency injection that is independent of any specific state management solution. It is organized as a Dart workspace (monorepo).
+
+Key packages:
+- `packages/disco` — the main library published to pub.dev.
+- `packages/disco_lint` — a custom lint plugin for Disco-specific lint rules.
+- `examples/` — runnable Flutter example apps.
+
+## Repository Structure
+
+```
+disco/
+├── packages/
+│   ├── disco/          # Main library (lib/, test/, benchmark/, example/)
+│   └── disco_lint/     # Custom lint plugin (lib/, example/)
+├── examples/           # Example Flutter apps
+├── pubspec.yaml        # Workspace root — links all packages together
+└── analysis_options.yaml
+```
+
+## Build & Dependency Installation
+
+Install dependencies from the workspace root:
+
+```bash
+flutter pub get
+```
+
+## Testing
+
+Run the test suite for the main library:
+
+```bash
+cd packages/disco
+flutter test
+```
+
+Run with coverage:
+
+```bash
+cd packages/disco
+flutter test --coverage
+```
+
+## Linting & Static Analysis
+
+Run Dart static analysis from the workspace root:
+
+```bash
+dart analyze
+```
+
+The project uses [`very_good_analysis`](https://pub.dev/packages/very_good_analysis) (strict lint rules). All lint warnings must be resolved before merging.
+
+## Code Style
+
+- Follow the [Dart style guide](https://dart.dev/effective-dart/style).
+- Comply with `very_good_analysis` rules — treat all lint warnings as errors.
+- **Do NOT use `const` constructors on `Provider` subclasses.** Providers are used as identity keys; `const` would cause providers with the same signature to share the same hash code, making them indistinguishable. The `prefer_const_constructors_in_immutables` lint rule is intentionally disabled.
+- Keep the public API minimal and well-documented with DartDoc comments.
+- New features or breaking changes require a motivation/discussion before implementation.
+
+## Adding / Changing Dependencies
+
+- Add dependencies only to the relevant `pubspec.yaml` (e.g. `packages/disco/pubspec.yaml`), not the workspace root.
+- Prefer Flutter/Dart SDK packages and packages already in use before introducing new ones.
+- Run `flutter pub get` after any `pubspec.yaml` change.
+
+## Pull Request Guidelines
+
+- Include tests for any new behaviour in `packages/disco/test/`.
+- Update `CHANGELOG.md` in `packages/disco/` for user-facing changes.
+- Documentation lives at <https://disco.mariuti.com>; update the `docs/` folder if the public API changes.
+- PRs that only touch `**.md` files skip CI automatically (see `flutter-test.yaml`).