docs: add SVD label unification design spec

docs/superpowers/specs/2026-04-02-svd-label-unification-design.md

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+# SVD Label Unification Design
+
+## Goal
+
+Unify SVD component labels into a single source of truth (`SVD_THEMES`) and automatically compute axis flip directions so right-wing parties consistently appear on the right side of all SVD component axes.
+
+## Background
+
+Currently there are two separate label systems:
+1. `SVD_THEMES` in `explorer.py` - defines labels for all 10 SVD components with detailed explanations
+2. `_LABELS` in `axis_classifier.py` - defines short labels for the classifier (lr, eu, pi, co, pc)
+
+This causes duplication and potential inconsistency. Additionally, flip values are hardcoded in `SVD_THEMES` rather than computed from actual party positions.
+
+## Design
+
+### Single Source of Truth
+
+`SVD_THEMES` in `explorer.py` remains the canonical definition for all SVD component labels. A new shared module `analysis/svd_labels.py` will:
+
+1. Import `SVD_THEMES` from explorer.py (at runtime to avoid circular imports)
+2. Provide helper functions to derive labels for any component
+3. Compute flip direction automatically based on party centroids
+
+### New Module: `analysis/svd_labels.py`
+
+```python
+"""Unified SVD component labels and automatic flip direction computation."""
+
+# Canonical party sets for orientation
+RIGHT_PARTIES = {
+    "PVV", "VVD", "FVD", "BBB", "JA21", 
+    "Nieuw Sociaal Contract", "SGP", "CDA", "ChristenUnie"
+}
+LEFT_PARTIES = {
+    "SP", "PvdA", "GL", "GroenLinks", "GroenLinks-PvdA", 
+    "DENK", "PvdD", "Volt"
+}
+
+def get_svd_label(component: int) -> str:
+    """Get short label for SVD component (e.g., 'EU-integratie–Nationalisme')."""
+    
+def get_svd_theme(component: int) -> dict:
+    """Get full theme dict for SVD component."""
+    
+def compute_flip_direction(component: int, party_scores: dict) -> bool:
+    """
+    Compute flip so right parties appear on the right side.
+    
+    Args:
+        component: SVD component number (1-indexed)
+        party_scores: {party_name: [score_comp1, score_comp2, ...]}
+    
+    Returns:
+        True if axis should be flipped so right parties are on right.
+    """
+    # Get scores for this component (0-indexed internally)
+    idx = component - 1
+    right_scores = [scores[idx] for party, scores in party_scores.items() 
+                    if party in RIGHT_PARTIES and len(scores) > idx]
+    left_scores = [scores[idx] for party, scores in party_scores.items() 
+                   if party in LEFT_PARTIES and len(scores) > idx]
+    
+    if not right_scores or not left_scores:
+        return False  # Default: no flip if insufficient data
+    
+    right_mean = sum(right_scores) / len(right_scores)
+    left_mean = sum(left_scores) / len(left_scores)
+    
+    # Flip if right parties have lower mean (they're on the left)
+    return right_mean < left_mean
+
+def get_fallback_labels() -> tuple[str, str]:
+    """Get fallback labels for x and y axes (components 1 and 2)."""
+    return (get_svd_label(1), get_svd_label(2))
+```
+
+### Changes to `analysis/axis_classifier.py`
+
+1. Remove hardcoded `_LABELS` dict
+2. Import from `svd_labels.py` at runtime (to avoid circular imports)
+3. Update `display_label_for_modal` to derive from SVD_THEMES
+
+```python
+# Remove:
+_LABELS = {
+    "lr": "Verzorgingsstaat–Marktwerking",
+    "eu": "EU-integratie–Nationalisme",
+    ...
+}
+
+# Add:
+def _get_svd_labels():
+    """Lazy import to avoid circular dependency."""
+    from analysis.svd_labels import get_svd_label, get_fallback_labels
+    return get_fallback_labels()
+
+def display_label_for_modal(modal_label: Optional[str], axis: str) -> str:
+    """Return a user-facing axis label for a modal/internal label."""
+    from analysis.svd_labels import get_svd_label
+    
+    if modal_label is None:
+        # Fallback to component 1 (x) or 2 (y)
+        comp = 1 if axis == "x" else 2
+        return get_svd_label(comp)
+    
+    # Map "As 1" / "As 2" to semantic labels
+    if axis == "x" and modal_label in ("As 1", "Stempatroon As 1"):
+        return get_svd_label(1)
+    if axis == "y" and modal_label in ("As 2", "Stempatroon As 2"):
+        return get_svd_label(2)
+    
+    return modal_label
+```
+
+### Changes to `explorer.py`
+
+1. Keep `SVD_THEMES` as canonical source
+2. Remove hardcoded fallback labels in `_build_political_compass_figure`
+3. Use `svd_labels.py` for all label lookups
+4. Add party position charts for components 3-10 in SVD Components tab
+
+#### Party Position Charts for All Components
+
+Currently, `_render_party_axis_chart` only works for components 1 and 2 (which have 2D coords). For components 3-10, we need to show 1D party positions:
+
+```python
+def _render_party_axis_chart_1d(party_coords: dict, component: int, theme: dict, bootstrap_data: dict = None):
+    """Render a 1D party position chart for a single SVD component."""
+    # Extract scores for this component
+    # Show parties on a horizontal axis
+    # Use theme['label'] for axis title
+    # Use theme['positive_pole'] and theme['negative_pole'] for annotations
+```
+
+### Auto-compute Flip Values
+
+On app startup or when loading SVD data:
+1. Load party scores for all components
+2. Compute flip direction for each component using `compute_flip_direction`
+3. Update `SVD_THEMES[component]["flip"]` dynamically OR store precomputed values
+
+### Files Modified
+
+| File | Changes |
+|------|---------|
+| `analysis/svd_labels.py` | **NEW** - Unified label system with auto-flip |
+| `analysis/axis_classifier.py` | Remove `_LABELS`, import from svd_labels |
+| `explorer.py` | Remove fallback labels, add 1D charts for components 3-10 |
+| `tests/test_axis_label_fallback.py` | Update to use new label system |
+| `tests/test_political_compass.py` | Update assertions for new labels |
+
+### Test Plan
+
+1. **Unit tests for `svd_labels.py`**:
+   - `get_svd_label(component)` returns correct label
+   - `compute_flip_direction` returns correct flip based on party scores
+   - `get_fallback_labels()` returns tuple of component 1 and 2 labels
+
+2. **Integration tests**:
+   - Compass plot uses correct labels from SVD_THEMES
+   - Trajectory plot uses correct labels from SVD_THEMES
+   - SVD Components tab shows party positions for all components
+   - Right parties appear on right side of all axes
+
+3. **Regression tests**:
+   - Existing tests pass with new label system
+   - No circular import errors
+
+## Implementation Order
+
+1. Create `analysis/svd_labels.py` with helper functions
+2. Update `axis_classifier.py` to use svd_labels
+3. Update `explorer.py` to use svd_labels for fallback labels
+4. Add 1D party position charts for components 3-10
+5. Update tests
+6. Verify flip directions are correct for all components