diff --git a/crates/omnigraph-compiler/src/lint/codes.rs b/crates/omnigraph-compiler/src/lint/codes.rs
index e53bf31..b719236 100644
--- a/crates/omnigraph-compiler/src/lint/codes.rs
+++ b/crates/omnigraph-compiler/src/lint/codes.rs
@@ -98,9 +98,23 @@ pub const OG_MF_104: DiagnosticCode = DiagnosticCode {
     short: "tighten nullable to non-nullable",
 };
 
+/// Narrow an enum's value-set by removing one or more allowed values
+/// (e.g. `enum(a, b, c)` → `enum(a, b)`). The physical column is
+/// unchanged (enums are stored as `String`), but a pre-existing row may
+/// hold a now-disallowed value. Validated tier: apply scans existing
+/// rows and fails loudly (listing the offending value) rather than
+/// silently dropping data.
+pub const OG_MF_105: DiagnosticCode = DiagnosticCode {
+    code: "OG-MF-105",
+    family: Family::MF,
+    tier: SafetyTier::Validated,
+    default_severity: Severity::Error,
+    short: "narrow enum value set",
+};
+
 /// Narrow a scalar (e.g. I64 → I32, F64 → F32). Lossy cast that may
-/// truncate or overflow. Today emitted on any `prop_type` change since
-/// the v1 planner doesn't yet distinguish widening from narrowing.
+/// truncate or overflow. Emitted for a genuine scalar-type change
+/// (enum value-set changes are handled by OG-MF-105 / OG-MF-107).
 pub const OG_MF_106: DiagnosticCode = DiagnosticCode {
     code: "OG-MF-106",
     family: Family::MF,
@@ -109,14 +123,29 @@ pub const OG_MF_106: DiagnosticCode = DiagnosticCode {
     short: "narrowing scalar type",
 };
 
+/// Constrain a free `String` property to an `enum` (e.g. `status: String`
+/// → `status: enum(open, closed)`). Tightening: existing rows may hold a
+/// value outside the new set. Validated tier: apply scans existing rows
+/// and fails loudly on the first out-of-set value.
+pub const OG_MF_107: DiagnosticCode = DiagnosticCode {
+    code: "OG-MF-107",
+    family: Family::MF,
+    tier: SafetyTier::Validated,
+    default_severity: Severity::Error,
+    short: "constrain String to enum",
+};
+
 /// All v0 catalog entries. Used for chassis-level invariants
 /// (uniqueness, family coverage).
 pub const ALL_CODES: &[DiagnosticCode] = &[
-    OG_DS_101, OG_DS_102, OG_DS_103, OG_DS_104, OG_DS_105, OG_MF_103, OG_MF_104, OG_MF_106,
+    OG_DS_101, OG_DS_102, OG_DS_103, OG_DS_104, OG_DS_105, OG_MF_103, OG_MF_104, OG_MF_105,
+    OG_MF_106, OG_MF_107,
 ];
 
 /// Codes actually emitted by the planner in v0 (i.e. not reserved).
-pub const EMITTED_IN_V0: &[&str] = &["OG-DS-102", "OG-DS-103", "OG-DS-104", "OG-MF-103", "OG-MF-106"];
+pub const EMITTED_IN_V0: &[&str] = &[
+    "OG-DS-102", "OG-DS-103", "OG-DS-104", "OG-MF-103", "OG-MF-105", "OG-MF-106", "OG-MF-107",
+];
 
 /// Look up a code by its string identifier.
 pub fn lookup(code: &str) -> Option<&'static DiagnosticCode> {