docs: add AGENTS.md and agent guidance docs

.github/copilot-instructions.md

@@ -0,0 +1 @@
+See [AGENTS.md](../AGENTS.md) for project overview, architecture, commands, conventions, and agent guardrails.

AGENTS.md

@@ -0,0 +1,93 @@
+# AGENTS.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**GemsPy** is a Python interpreter for the GEMS (Generic Energy Modeling System) framework — a high-level modeling language for simulating energy systems under uncertainty. It allows users to define energy system models via YAML without writing solver code directly.
+
+## Commands
+
+**Install:**
+```bash
+pip install -r requirements.txt -r requirements-dev.txt
+```
+
+**Test:**
+```bash
+pytest                                          # run all tests
+pytest tests/path/to/test_file.py::test_name   # run a single test
+pytest --cov gems --cov-report xml         # with coverage
+```
+
+**Lint & Format:**
+```bash
+black --config pyproject.toml src/ tests/
+isort --profile black --filter-files src/ tests/
+mypy
+```
+
+**Running:**
+```bash
+# CLI entry point
+gemspy \
+  --model-libs  path/to/lib1.yml path/to/lib2.yml \
+  --components   path/to/components.yml \
+  --timeseries   path/to/timeseries/ \
+  --duration     8760 \
+  --scenarios    1
+
+# Python API (minimal example)
+from gems.main.main import build_problem
+```
+
+## Architecture
+
+The pipeline flows: **YAML input → parsing → model resolution → network building → optimization problem → OR-Tools solver → results**
+
+### Core Modules (`src/gems/`)
+
+**`model/`** — Immutable model templates.
+- `Model`: defines component behavior (parameters, variables, constraints, ports)
+- `Library`: a collection of models, loaded from YAML
+- Models are never instantiated directly — they are referenced by components
+
+**`expression/`** — Mathematical expression language and AST.
+- `ExpressionNode`: base frozen dataclass for all expression tree nodes
+- Node types cover: arithmetic (`+`, `-`, `*`, `/`), comparisons (`<=`, `>=`, `==`), time/scenario operators (`time_sum()`), and functions (`max()`, `min()`, `ceil()`, `floor()`)
+- Grammar is defined in `/grammar/` and parsed via ANTLR4 (generated files live in `expression/parsing/antlr/`)
+- `ExpressionVisitor` is the dominant pattern for traversing and transforming expression trees (evaluation, linearization, printing, degree analysis)
+- Expressions support operator overloading: `var('x') + 5 * param('p')`
+
+**`study/`** — Study definition and network instantiation.
+- `System`: top-level structure parsed from YAML (before instantiation)
+- `Network`: instantiated graph of `Node`s, `Component`s, and connections
+- `Component`: an instance of a `Model` with concrete parameter values
+- `DataBase`: manages time series and scenario data
+
+**`simulation/`** — Optimization problem construction and solving.
+- `OptimizationProblem`: main interface; translates network + database into OR-Tools constraints
+- `LinearExpression`: the linearized form of model constraints used by the solver
+- `BendersDecomposedProblem`: temporal decomposition strategy for large problems
+- `TimeBlock`: structure for defining temporal decomposition
+- `OutputValues`: result extraction and formatting
+
+### Key Design Patterns
+
+- **Frozen dataclasses** throughout for immutability (models, expressions, constraints)
+- **Visitor pattern** for all expression tree operations (`ExpressionVisitor` subclasses)
+- **Indexing dimensions**: parameters and variables carry time and scenario indices explicitly; expressions track these automatically
+- **`ValueType`** enum (`INTEGER`, `CONTINUOUS`, `BOOLEAN`) for variable typing
+
+### Type Checking
+
+Strict mypy is enforced (`disallow_untyped_defs`, `disallow_untyped_calls`). All new code must be fully typed. Configuration is in `mypy.ini`.
+
+## Further Reading
+
+- [Python Convention](docs/agents/python-convention.md) — Code style, conventions, and agent guardrails
+- [Testing](docs/agents/testing.md) — Testing strategy and layer overview
+- [docs/getting-started.md](docs/getting-started.md) — Installation and first study walkthrough
+- [docs/user-guide.md](docs/user-guide.md) — Full user documentation
+- [docs/developer-guide.md](docs/developer-guide.md) — Contributor guide
+- [grammar/](grammar/) — ANTLR4 grammar source (`Expr.g4`)

docs/agents/python-convention.md

@@ -0,0 +1,37 @@
+# Python conventions
+
+## Code Style & Conventions
+
+- **Formatter**: Black, line-length 88. Never adjust line breaks manually—let Black decide.
+- **Import order**: isort with `profile = "black"`. One `import` block, no manual blank lines between
+  groups.
+- **Type annotations**: All functions and methods **must** have full type annotations. mypy is run in
+  strict mode (`disallow_untyped_defs`, `disallow_untyped_calls`).
+- **Dataclasses**: Prefer `@dataclass(frozen=True)` for value objects (expression nodes, model
+  definitions). Mutability must be justified explicitly.
+- **Pydantic**: Use `ConfigDict(alias_generator=to_camel)` or kebab-case alias generation for YAML
+  round-tripping; use Pydantic v2 APIs only.
+- **Naming**:
+  - Classes: `PascalCase`
+  - Functions / variables: `snake_case`
+  - Constants / type-level aliases: `UPPER_SNAKE_CASE`
+  - YAML keys: `kebab-case`
+- **Commit messages**: Follow Conventional Commits — `<type>(<scope>): <summary>`, e.g.
+  `feat(expression): add floor operator`. Types used in this repo: `feat`, `fix`, `docs`, `refactor`,
+  `test`, `chore`, `release`.
+
+---
+
+## Agent Guardrails
+
+Rules for automated agents (CI bots, AI coding assistants, Dependabot, etc.):
+
+1. **Never auto-merge** to `main`; all changes require at least one human review.
+2. **Do not edit generated files** under `src/gems/expression/parsing/antlr/`; regenerate them
+   from `grammar/Expr.g4` instead.
+3. **Do not modify `pyproject.toml` version** manually; version bumps are handled via the
+   `feat(release):` commit workflow.
+4. **Keep pre-commit hooks passing**: any commit that breaks `black`, `isort`, or `mypy` must not
+   be auto-pushed.
+5. **Test coverage must not decrease** on `main`; PRs that drop coverage without justification
+   should be flagged.

docs/agents/testing.md

@@ -0,0 +1,15 @@
+# Testing Strategy
+
+## Philosophy
+
+Tests live alongside the module they exercise. Fixtures (YAML snippets, small networks) are kept
+in `tests/` sub-directories. No mocking of the solver—tests use real OR-Tools calls.
+
+## Layers
+
+| Layer | Location | Description |
+|---|---|---|
+| Unit | `tests/unittests/` | One file per module area; covers AST visitors, parsing, model loading, linearisation |
+| Integration | `tests/unittests/simulation/` | Full problem build + solve on tiny networks |
+| End-to-end | `tests/e2e/` | CLI-level tests reading real YAML fixtures |
+| Converter | `tests/input_converter/`, `tests/pypsa_converter/`, `tests/antares_historic/` | Format-specific conversion tests |