Ψ-W1-T1 second-round remediation: ±1-frame bounds tolerance, self-cleanup a refused render, hedge two unverified render-source inferences

Loosens the exact-bounds gate against REAPER's edge rounding; deletes the bytes a BoundsMismatch refusal writes, per prune_fs's self-cleanup carve-out.

tests/test_render_settings.cpp

@@ -246,9 +246,10 @@ static void testRangedItemScopeRendersTimeBounded() {
 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.
+    // is INFERRED to render one file per track with no single-file bit available
+    // (unverified; see src/shell/capture/CLAUDE.md §Gotchas for what that inference
+    // rests on), 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,