Ψ-W3 remediation: fix the verify doc's wrong render source, add missing content checks, soften unverified claims

Corrected the Render-dialog source name the refusal's evidence depends on, added a by-ear content check and a file-size channel proxy, and stopped two comments from overclaiming.

src/core/capture/render_settings.cpp

@@ -117,6 +117,11 @@ bool isMultiTrackStemRender(SourceMode mode, int sourceTrackCount) {
 }
 
 std::string multiTrackRefusalMessage(CaptureScope scope) {
+    // Deliberately does not name realtime capture as a way out, though it is the one
+    // action that sums correctly here: realtime is non-deterministic (hardware/performed
+    // FX, no bit-identical-repeats guarantee), so pointing an offline refusal at it would
+    // trade one invariant for another rather than just naming a substitute. A stated
+    // choice, not an oversight.
     switch (scope) {
         case CaptureScope::Item:
             return "This range is narrower than the selected items, so it renders "