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
    manipulating-models
    testing-framework

doc/release_notes.rst

@@ -6,6 +6,12 @@ Upcoming Version
 
 * Fix docs (pick highs solver)
 * Add the `sphinx-copybutton` to the documentation
+* 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 ``auto_mask`` parameter to ``Model`` class that automatically masks variables and constraints where bounds, coefficients, or RHS values contain NaN. This eliminates the need to manually create mask arrays when working with sparse or incomplete data.
 * Speed up LP file writing by 2-2.7x on large models through Polars streaming engine, join-based constraint assembly, and reduced per-constraint overhead
 * Fix multiplication of constant-only ``LinearExpression`` with other expressions