sky tab: decouple table rebuilds from sky updates, update cells in-place

- Sky widget always gets the latest data immediately (off-thread render)
- Table rebuilds throttled to ~2 Hz via single-shot QTimer
- Cell values updated in-place when satellite set is unchanged, preserving
  scroll position; full rebuild only when satellites appear/disappear

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui/sky_tab.py

@@ -11,7 +11,7 @@ from PyQt5.QtWidgets import (
     QListWidgetItem, QTableWidget, QTableWidgetItem, QHeaderView,
     QSplitter, QGroupBox,
 )
-from PyQt5.QtCore import Qt
+from PyQt5.QtCore import Qt, QTimer
 from PyQt5.QtGui  import QColor, QBrush
 
 from data_model import ReceiverManager, GNSS_NAMES, GNSS_COLORS
@@ -24,7 +24,8 @@ class SkyTab(QWidget):
     def __init__(self, model: ReceiverManager):
         super().__init__()
         self._model = model
-        self._store: dict = {}   # (rid, gnss_id, sv_id) -> SatelliteData
+        self._store:      dict = {}   # (rid, gnss_id, sv_id) -> SatelliteData
+        self._table_keys: list = []   # current row order as (rid, gnss_id, sv_id)
 
         outer = QVBoxLayout(self)
         outer.setContentsMargins(4, 4, 4, 4)
@@ -39,7 +40,7 @@ class SkyTab(QWidget):
         self._src_list.setFlow(QListWidget.LeftToRight)
         self._src_list.setWrapping(True)
         self._src_list.setResizeMode(QListWidget.Adjust)
-        self._src_list.itemChanged.connect(self._refresh)
+        self._src_list.itemChanged.connect(self._refresh_immediate)
         src_bl.addWidget(self._src_list)
         outer.addWidget(src_box)
 
@@ -63,6 +64,12 @@ class SkyTab(QWidget):
         splitter.setStretchFactor(1, 1)
         outer.addWidget(splitter)
 
+        # ── Table throttle timer (max ~2 Hz rebuilds) ─────────────────────────
+        self._table_timer = QTimer(self)
+        self._table_timer.setSingleShot(True)
+        self._table_timer.setInterval(500)
+        self._table_timer.timeout.connect(self._rebuild_table_from_store)
+
         # ── Model signals ─────────────────────────────────────────────────────
         model.receiver_added.connect(self._on_receiver_added)
         model.receiver_removed.connect(self._on_receiver_removed)
@@ -85,7 +92,7 @@ class SkyTab(QWidget):
         keys = [k for k in self._store if k[0] == rid]
         for k in keys:
             del self._store[k]
-        self._refresh()
+        self._refresh_immediate()
 
     def _selected_rids(self) -> set:
         result = set()
@@ -95,27 +102,51 @@ class SkyTab(QWidget):
                 result.add(item.data(Qt.UserRole))
         return result
 
+    def _visible_sats(self) -> list:
+        selected = self._selected_rids()
+        return [(k[0], self._store[k])
+                for k in self._store if k[0] in selected]
+
     # ── Data update ───────────────────────────────────────────────────────────
 
     def _on_sat_update(self, rid: str, sats: list):
         for sat in sats:
             self._store[(rid, sat.gnss_id, sat.sv_id)] = sat
-        self._refresh()
-
-    def _refresh(self):
-        selected = self._selected_rids()
-        visible  = [(rid, self._store[k])
-                    for k in self._store
-                    if (rid := k[0]) in selected]
+        # Sky widget: always submit latest (render is off-thread, trivially cheap)
+        self._sky.update_data(self._visible_sats())
+        # Table: schedule a rebuild if one isn't already pending
+        if not self._table_timer.isActive():
+            self._table_timer.start()
 
+    def _refresh_immediate(self):
+        """Called on source-checkbox toggle or receiver removal — rebuild now."""
+        self._table_timer.stop()
+        visible = self._visible_sats()
         self._sky.update_data(visible)
         self._rebuild_table(visible)
 
+    def _rebuild_table_from_store(self):
+        self._rebuild_table(self._visible_sats())
+
     # ── Table ─────────────────────────────────────────────────────────────────
 
     def _rebuild_table(self, sats: list):
         sorted_sats = sorted(sats, key=lambda x: (x[1].gnss_id, x[1].sv_id))
+        new_keys = [(rid, sat.gnss_id, sat.sv_id) for rid, sat in sorted_sats]
 
+        if new_keys == self._table_keys:
+            # Only values changed — update in place, scroll position untouched
+            for row, (_, sat) in enumerate(sorted_sats):
+                self._table.item(row, 2).setText(f"{sat.elevation:.0f}")
+                self._table.item(row, 3).setText(f"{sat.azimuth:.0f}")
+                self._table.item(row, 4).setText(f"{sat.cno:.1f}")
+                self._table.item(row, 5).setText("✓" if sat.used_in_fix else "")
+            return
+
+        # Satellite set changed — full rebuild
+        self._table_keys = new_keys
+        vp = self._table.viewport()
+        vp.setUpdatesEnabled(False)
         self._table.setSortingEnabled(False)
         self._table.setRowCount(len(sorted_sats))
 
@@ -140,3 +171,4 @@ class SkyTab(QWidget):
             self._table.setItem(row, 6, cell(rid))
 
         self._table.setSortingEnabled(True)
+        vp.setUpdatesEnabled(True)