fix: exclude quarterly windows from all PCA/SVD computation

- analysis/explorer_data.py: add AND window_id NOT LIKE '%-Q%' to
  _UNIFORM_DIM_SQL so quarterly windows are filtered at the source
- explorer.py: remove stale comment justifying quarterly inclusion;
  remove redundant '-Q' guard in SVD tab trajectory view
- scripts/recompute_svd.py: replace quarter_bounds() with year_bounds()
  that handles annual window IDs like '2024'; filter window list to
  annual-only before recomputing SVD

analysis/explorer_data.py

@@ -64,6 +64,7 @@ _UNIFORM_DIM_SQL = """
     SELECT window_id
     FROM dominant
     WHERE dim >= 25 AND cnt >= 10
+      AND window_id NOT LIKE '%-Q%'
     ORDER BY window_id
 """
 

explorer.py

@@ -481,10 +481,7 @@ def load_positions(
     """
     from analysis.political_axis import compute_2d_axes
 
-    # Always compute PCA on ALL uniform-dim windows (quarterly + annual) so that
-    # the principal components are determined by the full temporal spread of data.
-    # Using only annual windows (11) causes PC1 to capture cross-temporal drift
-    # instead of left-right ideology, resulting in a ~90° rotation.
+    # Use only annual windows (quarterly windows are excluded by get_uniform_dim_windows).
     all_available = get_uniform_dim_windows(db_path)
 
     if not all_available:
@@ -2715,11 +2712,8 @@ def build_svd_components_tab(db_path: str) -> None:
     # Render party axis chart (single window or time trajectory)
     if view_mode == "Tijdtraject" and selected_parties_for_trajectory:
         # Load party scores for all windows and render time trajectory
-        # Filter to annual windows only (exclude quarters)
         available_windows = get_uniform_dim_windows(db_path)
-        year_windows = sorted(
-            w for w in available_windows if w != "current_parliament" and "-Q" not in w
-        )
+        year_windows = sorted(w for w in available_windows if w != "current_parliament")
         has_current = "current_parliament" in available_windows
         all_windows = year_windows + (["current_parliament"] if has_current else [])
 

scripts/recompute_svd.py

@@ -28,17 +28,20 @@ logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(mess
 logger = logging.getLogger("recompute_svd")
 
 
-def quarter_bounds(window_id: str) -> Tuple[str, str]:
-    # window_id like '2026-Q1'
-    year, q = window_id.split("-Q")
-    y = int(year)
-    qn = int(q)
-    starts = {1: (1, 1), 2: (4, 1), 3: (7, 1), 4: (10, 1)}
-    ends = {1: (3, 31), 2: (6, 30), 3: (9, 30), 4: (12, 31)}
-    s_m, s_d = starts[qn]
-    e_m, e_d = ends[qn]
-    start = date(y, s_m, s_d).isoformat()
-    end = date(y, e_m, e_d).isoformat()
+def year_bounds(window_id: str) -> Tuple[str, str]:
+    """Return (start_date, end_date) for an annual window_id like '2024'.
+
+    Quarterly window IDs (containing '-Q') are not supported — this script
+    only processes annual windows.
+    """
+    if "-Q" in window_id:
+        raise ValueError(
+            f"Quarterly window '{window_id}' is not supported. "
+            "Only annual windows should be recomputed."
+        )
+    y = int(window_id)
+    start = date(y, 1, 1).isoformat()
+    end = date(y, 12, 31).isoformat()
     return start, end
 
 
@@ -76,12 +79,14 @@ def main(argv: List[str] | None = None) -> int:
     db = MotionDatabase(dst)
 
     # find windows from original DB via trajectory helper
-    window_ids = traj._load_window_ids(src)
+    all_window_ids = traj._load_window_ids(src)
+    # Only process annual windows — quarterly windows are excluded from all PCA/SVD computation
+    window_ids = [w for w in all_window_ids if "-Q" not in w]
     if not window_ids:
-        logger.error("No windows found in source DB %s", src)
+        logger.error("No annual windows found in source DB %s", src)
         return 3
 
-    logger.info("Will recompute SVD for windows: %s", window_ids)
+    logger.info("Will recompute SVD for annual windows: %s", window_ids)
 
     # clear existing svd_vectors rows for these windows in dst DB
     import duckdb
@@ -100,7 +105,7 @@ def main(argv: List[str] | None = None) -> int:
 
     # Run SVD per window
     for wid in window_ids:
-        start, end = quarter_bounds(wid)
+        start, end = year_bounds(wid)
         logger.info("Running SVD for %s (%s -> %s) k=%d", wid, start, end, args.k)
         res = run_svd_for_window(
             db=db, window_id=wid, start_date=start, end_date=end, k=args.k