diff --git a/crates/epiphany-testkit/src/migration.rs b/crates/epiphany-testkit/src/migration.rs
index 97d8078..36b2ed2 100644
--- a/crates/epiphany-testkit/src/migration.rs
+++ b/crates/epiphany-testkit/src/migration.rs
@@ -77,11 +77,18 @@ pub fn run_migration_equivalence(n_ops: usize, seed: u64) {
         "v0->v1 migration changed the canonical reduction state (seed {seed})"
     );
 
-    // The migration faithfully inverts the projection on the representative
-    // payloads (a stronger property than reduction-equivalence alone).
+    // Round-trip self-consistency over *this* corpus: because the corpus is
+    // built from the same `valuegen` helpers the migration reconstructs values
+    // with, `migrate(project(env)) == env` holds exactly here. This is a sharper
+    // check than reduction-equivalence for the corpus, but it is NOT a universal
+    // inverse: the v0 projection drops fields the migration cannot recover (e.g.
+    // a `ReplaceWithRest` rest's own voice — recovered from the deleted event's
+    // placement at reduction, not from the value). The spec-level property is the
+    // reduction-equivalence asserted above; widening `operation_envelopes` to emit
+    // such a payload would surface here and is M2's cue to revisit faithfulness.
     assert_eq!(
         v1, migrated,
-        "migration is not the inverse of projection (seed {seed})"
+        "migration round-trip diverged from the original on this corpus (seed {seed})"
     );
 
     // Deterministic: migrating the same projection against the same context
diff --git a/spec/operation_catalog.pdf b/spec/operation_catalog.pdf
index 60e2006..e5734dd 100644
Binary files a/spec/operation_catalog.pdf and b/spec/operation_catalog.pdf differ
diff --git a/spec/operation_catalog.tex b/spec/operation_catalog.tex
index ca20b5a..a873ae5 100644
--- a/spec/operation_catalog.tex
+++ b/spec/operation_catalog.tex
@@ -500,6 +500,15 @@ policy.
 \textbf{Re-anchoring.} The structure participates in the re-anchoring rule table
 when one of its endpoints is later tombstoned (see DeleteEvent).
 
+\textbf{Migration coverage.} The v0$\rightarrow$v1 migration
+(Chapter~\ref{ch:migration}) reconstructs the event-anchored \texttt{Tie},
+\texttt{Slur}, and \texttt{Beam} from the v0 reference (id plus event endpoints).
+A \texttt{Spanner} is anchored by \texttt{TimeAnchor}s rather than a fixed pair
+of event endpoints, so its full value is not reconstructable from the v0
+event-reference projection; a \texttt{Spanner}-create is therefore reported
+unmigratable (read-only) under M1, alongside the respell case of P12-K1. A
+faithful spanner migration joins when the projection carries the anchors --- M2.
+
 \section{ChangeRegionTimeModel}
 \label{sec:k0:change-region-time-model}