capture: refuse the multi-track ranged item render, silence the track's children and receives for it, and gate every exact-bounds capture on its frame count

tests/test_render_settings.cpp

@@ -216,11 +216,12 @@ static void testScopeSourceModes() {
 }
 
 static void testRangedItemScopeRendersTimeBounded() {
-    // The Ψ.7 defect pinned at the bit level. A window the item extent does NOT
-    // print must never reach the &32 selected-items source: that source takes its
-    // bounds from the item extents, so RENDER_STARTPOS/ENDPOS cannot narrow it and
-    // the capture widens to the whole item. The ranged item capture renders through
-    // the selected-tracks source instead, which IS time-bounded.
+    // The widening defect pinned at the bit level. A window the item extent does NOT
+    // print must never reach the &32 selected-items source: that source is INFERRED
+    // (unverified — src/core/capture/CLAUDE.md §Gotchas) to take its bounds from the
+    // item extents, so RENDER_STARTPOS/ENDPOS cannot narrow it and the capture widens
+    // to the whole item. The ranged item capture renders through the selected-tracks
+    // source instead, which IS time-bounded.
     const SourceMode ranged = sourceModeForScope(CaptureScope::Item, false);
     CHECK(ranged == SourceMode::SelectedTracks);
 
@@ -242,6 +243,41 @@ static void testRangedItemScopeRendersTimeBounded() {
     CHECK(fxBypassPlanFor(CaptureScope::Item).bypassSelfFx);
 }
 
+static void testMultiTrackRangedItemRenderIsNamedForRefusal() {
+    // The one shape that cannot land: a ranged item capture (item scope re-sourced to
+    // the selected-tracks render) whose items span more than one track. That source
+    // renders one file per track with no single-file bit available, so N stems would
+    // collapse onto one render pattern and one track's audio would land as a
+    // successful capture.
+    CHECK(isMultiTrackRangedItemRender(CaptureScope::Item,
+                                       SourceMode::SelectedTracks, 2));
+    CHECK(isMultiTrackRangedItemRender(CaptureScope::Item,
+                                       SourceMode::SelectedTracks, 7));
+
+    // One track is the whole point of the re-source — it must still render.
+    CHECK(!isMultiTrackRangedItemRender(CaptureScope::Item,
+                                        SourceMode::SelectedTracks, 1));
+    CHECK(!isMultiTrackRangedItemRender(CaptureScope::Item,
+                                        SourceMode::SelectedTracks, 0));
+
+    // A full-extent item capture keeps the selected-items source, whose single-file
+    // bit already sums a multi-track item selection into one file.
+    CHECK(!isMultiTrackRangedItemRender(CaptureScope::Item,
+                                        SourceMode::SelectedItems, 3));
+
+    // Track scope renders through the same source and is deliberately untouched here
+    // — that per-track output predates the item re-source and is filed in docs/TODO.md.
+    CHECK(!isMultiTrackRangedItemRender(CaptureScope::Track,
+                                        SourceMode::SelectedTracks, 3));
+
+    // The predicate is reachable from the mapping it guards: the ranged item capture's
+    // own source mode is the one it names.
+    CHECK(isMultiTrackRangedItemRender(CaptureScope::Item,
+                                       sourceModeForScope(CaptureScope::Item, false), 2));
+    CHECK(!isMultiTrackRangedItemRender(CaptureScope::Item,
+                                        sourceModeForScope(CaptureScope::Item, true), 2));
+}
+
 // --- inferRangeSource: razor-else-time (orthogonal to scope) -----------------
 
 static void testRangeInference() {
@@ -339,6 +375,7 @@ int main() {
     testRazorUnionBounds();
     testScopeSourceModes();
     testRangedItemScopeRendersTimeBounded();
+    testMultiTrackRangedItemRenderIsNamedForRefusal();
     testRangeInference();
     testItemScopeBypassesEverythingButTake();
     testTrackScopeKeepsSelfBypassesAncestorsAndMaster();