Fix ANR, false tack detections, and empty-state flash on track load

ANR: getSavedTracks() had no IO dispatcher — TackDetector ran on main
thread at O(n²) cost (~77M ops for a 2.5h track). Added withContext(IO).

TackDetector: replaced O(n) list.filter with O(log n) binary-search
subList for before/after windows; O(n²) → O(n log n). Raised MIN_DELTA
60°→75° to stop detecting ordinary course corrections as maneuvers.
Removed MAX_DELTA cap entirely — 180° crash-tacks are valid; the
circularMAD stability windows are the real quality gate.

TrackDetailSheet: dropped the arbitrary abs(delta)>70 Tack/Jibe
heuristic. Now uses true wind angle when available for classification;
falls back to "Maneuver" when TWD is absent.

SavedTracksFragment: added isLoadingTracks StateFlow (MainViewModel);
combine() suppresses the empty-state layout while the initial IO load
runs so it no longer flashes "No saved tracks yet" before data arrives.

16/16 TackDetector tests pass.

https://claude.ai/code/session_01KXYBuAHZkvv63DeUG6XaZD

1 files changed, 4 insertions, 4 deletions

diff --git a/test-runner/src/test/kotlin/org/terst/nav/track/TackDetectorTest.kt b/test-runner/src/test/kotlin/org/terst/nav/track/TackDetectorTest.kt
index 6d946a0..265ba76 100644
--- a/test-runner/src/test/kotlin/org/terst/nav/track/TackDetectorTest.kt
+++ b/test-runner/src/test/kotlin/org/terst/nav/track/TackDetectorTest.kt
@@ -49,13 +49,13 @@ class TackDetectorTest {
     }
 
     @Test fun `heading change below MIN_DELTA is ignored`() {
-        // 45° delta — below MIN_DELTA=60°
+        // 45° delta — below MIN_DELTA=75°
         assertTrue(TackDetector.detectTacks(tackTrack(90.0, 135.0)).isEmpty())
     }
 
-    @Test fun `heading change above MAX_DELTA is ignored`() {
-        // 170° delta — above MAX_DELTA=160° (U-turn, not a tack)
-        assertTrue(TackDetector.detectTacks(tackTrack(90.0, 260.0)).isEmpty())
+    @Test fun `heading change of 170 degrees is detected`() {
+        // 170° delta — valid crash-tack; no upper cap
+        assertEquals(1, TackDetector.detectTacks(tackTrack(90.0, 260.0)).size)
     }
 
     @Test fun `detects two tacks in sequence with sufficient gap`() {