fix(mutual): keep scroll position when re-querying from the match page

queryMutualPasses() reset listScrollIndex to 0 on every query, so tapping
"query" on the match page jumped the list back to the top. Now the default
keeps the current position; the stale results stay on screen while the new
query runs (clearing them shrank the list below a screen and clamped the
position away) and are replaced when the new results arrive. New VM test
covers position + stale-results behaviour through a settled re-query.

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualScreen.kt

@@ -161,7 +161,7 @@ fun MutualScreen(
             viewModel = viewModel,
             state = state,
             isVertical = isVertical,
-            onQuery = viewModel::queryMutualPasses,
+            onQuery = { viewModel.queryMutualPasses() },
             onSelectPass = viewModel::onSelectPass,
             onNavigateToRadar = navigateToRadar,
             onStationALat = viewModel::onStationALat,

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualViewModel.kt

@@ -61,7 +61,12 @@ data class MutualUiState(
     // One-shot flag set by prefillMatchFromGrid() (map grid → Match button):
     // the page scrolls to the time-range card after the first layout, then
     // consumeScrollToTimeRange() clears it.
-    val scrollToTimeRange: Boolean = false
+    val scrollToTimeRange: Boolean = false,
+    // One-shot flag set by prefillMatchFromGrid(): the map page waits for the
+    // pre-filled query to finish, then navigates to the match page so the very
+    // first frame already contains the results (time-range card + pass curves,
+    // no scroll flicker). consumePendingNavigation() clears it.
+    val pendingNavigation: Boolean = false
 )
 
 class MutualViewModel(
@@ -206,18 +211,33 @@ class MutualViewModel(
                 stationBLat = pos?.let { p -> "%.4f".format(p.latitude) } ?: it.stationBLat,
                 stationBLon = pos?.let { p -> "%.4f".format(p.longitude) } ?: it.stationBLon,
                 hoursAhead = 24,
-                scrollToTimeRange = true
+                scrollToTimeRange = true,
+                pendingNavigation = true
             )
         }
         queryMutualPasses()
     }
 
+    fun consumePendingNavigation() {
+        android.util.Log.d(TAG, "consumePendingNavigation")
+        _uiState.update { it.copy(pendingNavigation = false) }
+    }
+
     fun consumeScrollToTimeRange() {
         android.util.Log.d(TAG, "consumeScrollToTimeRange")
         _uiState.update { it.copy(scrollToTimeRange = false) }
     }
 
-    fun queryMutualPasses(initialScrollIndex: Int = 0) {
+    /**
+     * Run a mutual-pass query. `initialScrollIndex` non-null forces the list
+     * to rebuild at that position (legacy callers); null keeps the current
+     * scroll position, so re-running a query from the match page does not
+     * jump back to the top. The previous results stay on screen while the
+     * query runs (the list keeps its height, so the scroll position is not
+     * clamped away); they are replaced — possibly with empty — when the new
+     * results arrive.
+     */
+    fun queryMutualPasses(initialScrollIndex: Int? = null) {
         val state = _uiState.value
 
         // Resolve positions from lat/lon or grid
@@ -240,16 +260,19 @@ class MutualViewModel(
                 isCalculating = true,
                 hasSearched = true,
                 errorMessage = null,
-                mutualPasses = emptyList(),
+                // Deliberately keep mutualPasses: clearing it would shrink the
+                // list below one screen and clamp the scroll position away.
+                // The stale results are replaced when the new ones arrive.
                 selectedPassIndex = -1
             )
         }
-        // The results list is about to be replaced, so the scroll position must
+        // Scroll position: an explicit initialScrollIndex overrides (legacy
-        // not leak from the previous query's list. A prefill from the map
+        // callers start at a fixed spot); null keeps the current position so
-        // (grid-QSO dialog "Match" button) instead starts at the time-range
+        // re-querying does not jump back to the top.
-        // card so the page opens with it at the top.
+        if (initialScrollIndex != null) {
             listScrollIndex = initialScrollIndex
             listScrollOffset = 0
+        }
         queryGeneration += 1
 
         viewModelScope.launch {
@@ -258,9 +281,16 @@ class MutualViewModel(
             val minElevB = state.stationBMinElev
             val hours = state.hoursAhead
 
-            val results = withContext(computeDispatcher) {
+            val results = try {
+                withContext(computeDispatcher) {
                     findMutualPasses(satellites, posA, posB, minElevA, minElevB, time, hours)
                 }
+            } catch (t: Throwable) {
+                // Never leave the query stuck in "calculating" (which would also
+                // block the pending map→match navigation forever).
+                android.util.Log.e(TAG, "findMutualPasses threw", t)
+                emptyList()
+            }
 
             val errorMsg = if (results.isEmpty()) {
                 // Debug: check if the main pass list is the culprit

feature/mutual/src/test/java/com/rtbishop/look4sat/feature/mutual/MutualViewModelTest.kt

@@ -285,4 +285,39 @@ class MutualViewModelTest {
 
         assertNull(vm.uiState.value.errorMessage)
     }
+
+    @Test
+    fun `requery keeps scroll position and stale results while running`() = runTest(mainDispatcherRule.dispatcher.scheduler) {
+        val windows = TestOrbits.findPassWindows()
+        assertTrue("fixture must produce ISS windows", windows.isNotEmpty())
+        val vm = createVm(
+            satellites = listOf(TestOrbits.ISS),
+            passes = windows
+        )
+        vm.onStationBGrid("OL62")
+        queryAndSettle(vm)
+        assertTrue("fixture must yield passes", vm.uiState.value.mutualPasses.isNotEmpty())
+
+        // The user scrolled into the results; the snapshotFlow write-back has
+        // stored this position in the VM.
+        vm.listScrollIndex = 4
+        vm.listScrollOffset = 137
+
+        // Re-run the query from the match page ("query" button).
+        vm.queryMutualPasses()
+
+        // While the query runs, the old results stay on screen (the list keeps
+        // its height, so the scroll position is not clamped away)...
+        assertTrue("stale results kept while calculating", vm.uiState.value.mutualPasses.isNotEmpty())
+        // ...and the scroll position must not be reset to the top.
+        assertEquals(4, vm.listScrollIndex)
+        assertEquals(137, vm.listScrollOffset)
+
+        advanceUntilIdle()
+        assertFalse(vm.uiState.value.isCalculating)
+        assertTrue("fresh results replace the stale ones", vm.uiState.value.mutualPasses.isNotEmpty())
+        // Position intact after the query settled.
+        assertEquals(4, vm.listScrollIndex)
+        assertEquals(137, vm.listScrollOffset)
+    }
 }