chore: apply linting fixes and expand ruff coverage to test suite

src/pygui/backend/visualization/wafer_map_item.py

@@ -290,6 +290,12 @@ class WaferMapItem(QQuickPaintedItem):
                 return idx
         return -1
 
+    # TODO P6.1: build batch export on top of this single-frame export
+    #   THINKING: export_image() already does the hard part (grabToImage → PNG);
+    #   batch export is just a loop over file_browser.files that loads each CSV
+    #   through the existing wafer-map pipeline and calls this per file into a
+    #   chosen output dir, plus an optional summary CSV of (file, min/max/mean).
+    #   No new rendering code needed — see docs/pending/alpha-release-polish-plan.md §6.1.
     @Slot(str, result=bool)
     def export_image(self, file_path: str) -> bool:
         """Export the current wafer map rendering to a PNG file
@@ -377,6 +383,13 @@ class WaferMapItem(QQuickPaintedItem):
         r = max(math.hypot(s.x, s.y) for s in self._sensors)
         return r * 1.05
 
+    # TODO P6.2: reuse this for the edge-to-center delta metric
+    #   THINKING: radial_metrics.py (new) needs the same "which sensors are near
+    #   the edge vs. near the center" bucketing this function already computes
+    #   for ring-line drawing — do NOT re-derive ring boundaries separately, this
+    #   already handles round vs. square wafer shapes correctly (see family_spec.py
+    #   square-wafer work). Outermost group ≈ edge sensors, innermost ≈ center.
+    #   See docs/pending/alpha-release-polish-plan.md §6.2.
     def _sensor_ring_radii_mm(self) -> list[float]:
         """Distinct radial distances of sensor groups, sorted ascending, plus the outer boundary."""
         if not self._sensors:
@@ -413,6 +426,15 @@ class WaferMapItem(QQuickPaintedItem):
         self._markers = {i: self._to_px(s.x, s.y, cx, cy, sc)
                          for i, s in enumerate(self._sensors)}
 
+    # TODO P2.2 + P2.3: fixed-resolution RBF grid, then offload to QThreadPool
+    #   THINKING: width=height=ds couples RBF cost to widget pixel size — a 600px
+    #   viewport solves a 360k-point system per frame where a fixed 100×100 grid
+    #   (10k points, GPU bilinear-scales the QImage up) is visually identical
+    #   through the 0.4-opacity blend. Do P2.2 first: it may make P2.3 (QRunnable
+    #   worker emitting heatmapReady(QImage), guarding against stale results when
+    #   sensors change mid-flight) unnecessary for alpha. Grid width param lands
+    #   in interpolate_field (see matching TODO in rbf_heatmap.py).
+    #   See docs/pending/alpha-release-polish-plan.md §2.2/§2.3.
     def _rebuild_heatmap(self) -> None:
         if not self._sensors or not self._values or self._blend == 0.0:
             self._heatmap = None
@@ -612,6 +634,13 @@ class WaferMapItem(QQuickPaintedItem):
                 ox = getattr(s, "offset_x", 0.0) * r
                 oy = getattr(s, "offset_y", 0.0) * r
 
+                # TODO P2.1: hoist fontMetrics() out of the sensor loop
+                #   THINKING: id_font/temp_font are fixed for the whole paint pass,
+                #   but fontMetrics() is re-queried per sensor — 65+ OS font-engine
+                #   round-trips per frame on a dense wafer, ~30/s in Live mode.
+                #   Compute id_fm/temp_fm once before `for i, s in ...` (they only
+                #   change when r/font_scale change). Verified by P4.3 benchmark.
+                #   See docs/pending/alpha-release-polish-plan.md §2.1.
                 painter.setFont(id_font)
                 id_fm = painter.fontMetrics()
                 id_line_h = id_fm.height()