diff --git a/core/dr-pipeline/src/sidecar.rs b/core/dr-pipeline/src/sidecar.rs
index f70d91c..6f83616 100644
--- a/core/dr-pipeline/src/sidecar.rs
+++ b/core/dr-pipeline/src/sidecar.rs
@@ -1727,6 +1727,24 @@ mod tests {
         assert!(!restored.is_neutral());
     }
 
+    /// TRACES: FR-PLG-8
+    /// FR-PLG-8's preservation clause, and only that clause.
+    ///
+    /// The requirement opens by saying the sidecar "already preserves lines it
+    /// does not understand verbatim and writes them back untouched", and that
+    /// the property "is now load-bearing and shall be treated as such". This is
+    /// the test that makes it load-bearing rather than incidental.
+    ///
+    /// **It is weaker than the requirement's stated acceptance criterion**,
+    /// which is that the re-saved file be *byte-identical* to the original.
+    /// This asserts `contains`. The two halves of that criterion exist
+    /// separately — `writing_the_same_state_twice_is_byte_identical` proves
+    /// byte identity for content this build understands, and this proves
+    /// survival for content it does not — and nothing yet joins them into the
+    /// one claim FR-PLG-8 makes. Everything else the requirement asks for
+    /// (aggregated alerts, the export gate, rendering without rather than
+    /// guessing) is unbuilt, which is why the tag is on these two tests and
+    /// not on the module.
     #[test]
     fn an_unknown_operation_survives_a_round_trip() {
         // The data-loss case that matters: a device running an older build
@@ -1742,6 +1760,13 @@ mod tests {
         );
     }
 
+    /// TRACES: FR-PLG-8
+    /// The other half of preservation: kept in the file, kept out of the edit.
+    ///
+    /// "Render without, never render a guess" is a separate clause, and this is
+    /// not it — that one is about a *recognised* operation whose plugin is
+    /// missing. This is the narrower claim that an unparsed line cannot reach
+    /// the graph by accident, which is what makes preserving it safe.
     #[test]
     fn an_unknown_operation_does_not_reach_the_graph() {
         let text = "drsc 1\n\n[version u1]\nname = Default\nrevision = 1\nmodified = 0\n\