ref: Combine Kt-marker rationale into one comment, drop R8 fixture header

Merge the restored "Kt suffix takes precedence" note back into the scan-loop
comment, and rename the test block header from `ComposableSingletonsInlinedLambdaStackTrace`
to a plain description — the sibling blocks in this file name upstream R8 retrace
fixtures, which this case is not.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: romtsn

src/utils.rs

@@ -22,8 +22,9 @@ pub(crate) fn synthesize_source_file(
     let mut segments = last_segment.split('$');
     let base = segments.next()?;
 
-    // Compiler-generated wrappers (e.g. `ComposableSingletons$MainActivityKt`)
-    // bury the `Kt` marker in an inner segment, so checking only `base` misses them.
+    // Kt suffix is a strong Kotlin indicator and takes precedence over reference_file.
+    // Compiler-generated wrappers (e.g. `ComposableSingletons$MainActivityKt`) bury the
+    // marker in an inner segment, so we scan every `$`-segment, not just `base`.
     for segment in std::iter::once(base).chain(segments) {
         if let Some(kotlin_base) = segment.strip_suffix("Kt").filter(|s| !s.is_empty()) {
             return Some(format!("{}.kt", kotlin_base));

tests/r8-source-file-edge-cases.rs

@@ -118,7 +118,7 @@ fn test_source_file_name_synthesize_stacktrace() {
 }
 
 // =============================================================================
-// ComposableSingletonsInlinedLambdaStackTrace
+// ComposableSingletons inlined lambda
 //
 // When a lambda from a Compose `ComposableSingletons$FileKt` wrapper is inlined
 // through an R8 synthetic class, the outer class has no `sourceFile` metadata of