diff --git a/ingestion/internal/mcp/tools_notes.go b/ingestion/internal/mcp/tools_notes.go
index 617d596..0f9ba0c 100644
--- a/ingestion/internal/mcp/tools_notes.go
+++ b/ingestion/internal/mcp/tools_notes.go
@@ -268,6 +268,27 @@ func touchesFrontmatter(oldStr, newStr string) bool {
 // those cases at write time regardless of what this function decides, so
 // the only thing riding on this preview's accuracy is the envelope check
 // itself, not write safety.
+// checkClaimEnvelope previews what old_str->new_str would produce and
+// validates the resulting claim envelope before the real edit runs
+// (hyperguild#123). Seven review rounds closed every plausible bypass in the
+// fence-detection family (field-name substring, block-containment,
+// fence-stripping, CRLF, UTF-8 BOM) and the first instance of a
+// value-extraction gap (a folded YAML block scalar hiding a value behind an
+// empty inline colon).
+//
+// Known, accepted v1 gap: frontmatterScalars's block-scalar fold is a
+// best-effort approximation, not a YAML parser — a blank line interrupting a
+// folded continuation, or other contrived multi-line YAML shapes not yet
+// probed (block-scalar indicators `|`/`>`, inline comments on a key line,
+// quoted multi-line values), can still hide an invalid value from
+// ValidateEnvelope. Accepted deliberately rather than chased indefinitely:
+// every bypass found so far requires the caller to already hold brain_edit
+// write access and to deliberately construct a specific malformed-YAML shape
+// with knowledge of this exact gap — a narrow, low-likelihood threat next to
+// the diminishing returns of another incremental patch round. The real fix
+// (a shared, tested, encoding-normalized frontmatter parser used by all
+// three independent implementations in this codebase) is tracked separately
+// as hyperguild#138, not bolted on here piece by piece.
 func checkClaimEnvelope(brainDir, path, oldStr, newStr string) error {
 	if oldStr == "" {
 		// hyperguild#115: strings.Replace treats "" as matching position 0,