refac: introduce consistent convention for linopy operations with subsets and supersets

CLAUDE.md

@@ -110,27 +110,6 @@ When modifying the codebase, maintain consistency with these patterns and ensure
 * Always create a feature branch for new features or bug fixes.
 * Use the github cli (gh) to interact with the Github repository.
 
-### GitHub Claude Code Integration
-
-This repository includes Claude Code GitHub Actions for automated assistance:
-
-1. **Automated PR Reviews** (`claude-code-review.yml`):
-   - Automatically reviews PRs only when first created (opened)
-   - Subsequent reviews require manual `@claude` mention
-   - Focuses on Python best practices, xarray patterns, and optimization correctness
-   - Can run tests and linting as part of the review
-   - **Skip initial review by**: Adding `[skip-review]` or `[WIP]` to PR title, or using draft PRs
-
-2. **Manual Claude Assistance** (`claude.yml`):
-   - Trigger by mentioning `@claude` in any:
-     - Issue comments
-     - Pull request comments
-     - Pull request reviews
-     - New issue body or title
-   - Claude can help with bug fixes, feature implementation, code explanations, etc.
-
-**Note**: Both workflows require the `ANTHROPIC_API_KEY` secret to be configured in the repository settings.
-
 
 ## Development Guidelines
 
@@ -140,3 +119,4 @@ This repository includes Claude Code GitHub Actions for automated assistance:
 4. Use type hints and mypy for type checking.
 5. Always write tests into the `test` directory, following the naming convention `test_*.py`.
 6. Always write temporary and non git-tracked code in the `dev-scripts` directory.
+7. In test scripts use linopy assertions from the testing.py module where useful (assert_linequal, assert_varequal, etc.)

doc/index.rst

@@ -111,6 +111,7 @@ This package is published under MIT license.
    creating-variables
    creating-expressions
    creating-constraints
+   coordinate-alignment
    sos-constraints
    piecewise-linear-constraints
    piecewise-linear-constraints-tutorial

doc/release_notes.rst

@@ -4,6 +4,12 @@ Release Notes
 Upcoming Version
 ----------------
 
+* Harmonize coordinate alignment for operations with subset/superset objects:
+  - Multiplication and division fill missing coords with 0 (variable doesn't participate)
+  - Addition and subtraction of constants fill missing coords with 0 (identity element) and pin result to LHS coords
+  - Comparison operators (``==``, ``<=``, ``>=``) fill missing RHS coords with NaN (no constraint created)
+  - Fixes crash on ``subset + var`` / ``subset + expr`` reverse addition
+  - Fixes superset DataArrays expanding result coords beyond the variable's coordinate space
 * Add ``add_piecewise_constraints()`` for piecewise linear constraints with SOS2 and incremental (pure LP) formulations.
 * Add ``add_disjunctive_piecewise_constraints()`` for disconnected piecewise linear segments (e.g. forbidden operating zones).
 * Add ``linopy.breakpoints()`` factory for convenient breakpoint construction from lists, dicts, or keyword arguments. Includes ``breakpoints.segments()`` for disjunctive formulations.