capture: close batch-quarantine silence, 0-byte asymmetry, and round-two doc overclaims

Batch captures now name the retained-render folder once instead of nothing; Auto/Manual tail modes refuse a 0-byte render like None does; VERIFICATION.md steps 1-3 no longer invite a false conclusion; docs/comments no longer overclaim.

src/shell/capture/render_bounds_gate.cpp

@@ -3,6 +3,7 @@
 #include "shell/capture/render_bounds_gate.h"
 
 #include <cmath>
+#include <cstdint>
 #include <filesystem>
 #include <system_error>
 #include <vector>
@@ -46,6 +47,24 @@ std::string retainRefusedRender(const std::string& renderedPath,
 
 }  // namespace
 
+std::string refusedRenderFolder(const std::string& projectDir) {
+    return projectDir + "/" + kRefusedSubfolder;
+}
+
+BoundsVerdict checkRenderedFileNotEmpty(const std::string& renderedPath,
+                                        const std::string& projectDir) {
+    BoundsVerdict v;
+    std::error_code ec;
+    const std::uintmax_t size = std::filesystem::file_size(renderedPath, ec);
+    if (ec || size != 0) return v;  // stat failure isn't this check's job — leave it be
+
+    v.refused = true;
+    v.message = "Render at " + renderedPath + " is 0 bytes -- REAPER produced an empty "
+                "file, so there is nothing to check the requested range against." +
+                retainRefusedRender(renderedPath, projectDir);
+    return v;
+}
+
 BoundsVerdict checkRenderedBounds(const std::string& renderedPath,
                                   const std::string& projectDir,
                                   const CaptureRequest& request) {
@@ -66,10 +85,11 @@ BoundsVerdict checkRenderedBounds(const std::string& renderedPath,
     // a file whose frames were never counted.
     if (!layout.valid || layout.sampleRate == 0) {
         v.refused = true;
-        v.message = "Render at " + renderedPath + " could not be measured -- its WAV "
-                    "header did not parse, or declared no sample rate -- so the frames "
-                    "it holds were never checked against the requested range." + source +
-                    retainRefusedRender(renderedPath, projectDir);
+        v.message = "Render at " + renderedPath + " could not be measured -- it could "
+                    "not be read (locked, missing, or a permissions error), its WAV "
+                    "header did not parse, or it declared no sample rate -- so the "
+                    "frames it holds were never checked against the requested range." +
+                    source + retainRefusedRender(renderedPath, projectDir);
         return v;
     }