feat(v3): add string diagnostic axis vocabulary

src/v3/compiler/tests/integration/m2_substrate_inhabitance_test.rs

@@ -2549,6 +2549,55 @@ fn special_value_policy_axes_are_closed_sums() {
     );
 }
 
+#[test]
+fn string_diagnostic_ordering_axes_live_in_emit_model_authority() {
+    let dag = v3_compiler::generated_full_bootstrap_dag();
+
+    for name in [
+        "StringOwnershipAxis",
+        "StringLifetimeAxis",
+        "StringGrowabilityAxis",
+        "StringEncodingAxis",
+    ] {
+        let decl = dag
+            .declaration_by_name(name)
+            .unwrap_or_else(|| panic!("`{name}` missing from full bootstrap"));
+        assert_eq!(
+            decl.span.file, "src/v3/std/emit_model.dag",
+            "`{name}` must stay with target emission-model substrate; \
+             per-target diagnostic-ordering rows land in target specs later"
+        );
+    }
+}
+
+#[test]
+fn string_diagnostic_ordering_axes_are_closed_structural_values() {
+    let dag = v3_compiler::generated_full_bootstrap_dag();
+
+    assert_eq!(
+        disj_variant_labels(&dag, "StringOwnershipAxis"),
+        ["Owned", "Borrowed"].map(String::from),
+        "string ownership must be a typed axis, not a boolean or target string"
+    );
+    assert_eq!(
+        disj_variant_labels(&dag, "StringLifetimeAxis"),
+        ["SelfContained", "Caller"].map(String::from),
+        "string lifetime must use canonical substrate names, not Rust enum \
+         escaping or target-local strings"
+    );
+    assert_eq!(
+        disj_variant_labels(&dag, "StringGrowabilityAxis"),
+        ["Growable", "Fixed", "NotApplicable"].map(String::from),
+        "`NotApplicable` must be an explicit growability value, not absence"
+    );
+    assert_eq!(
+        disj_variant_labels(&dag, "StringEncodingAxis"),
+        ["Utf8FreeMonoidChar"].map(String::from),
+        "R2 string encoding vocabulary must name the FreeMonoid<Char> / UTF-8 \
+         row shape structurally"
+    );
+}
+
 #[test]
 fn runtime_value_carrier_matches_pb_runtime_shape_and_marker_boundary() {
     let dag = v3_compiler::generated_full_bootstrap_dag();

src/v3/compiler/tests/integration/parse_corpus_manifest.txt

@@ -36,7 +36,7 @@ src/v3/std/computation_model.dag	14	22953	20e458fe097d175a
 src/v3/std/diagnostics.dag	11	20274	a317777d55e36b19
 src/v3/std/dimensions.dag	21	40239	d595746d2bda22f6
 src/v3/std/effects.dag	53	97984	1acdbeaa68acfd2e
-src/v3/std/emit_model.dag	36	68760	30bb483bab671fa7
+src/v3/std/emit_model.dag	40	73232	109e5f6becc954c6
 src/v3/std/extdeps_bootstrap_fixtures.dag	4	14463	909ca7a1c1705e89
 src/v3/std/go_method_template_contracts.dag	5	110898	7eb5c9f1296f4a45
 src/v3/std/induction.dag	56	88794	546f74c63c189c50

src/v3/std/emit_model.dag

@@ -84,6 +84,39 @@ type ParameterDisposition
   = Borrowed
   | Consumed
 
+// 🟢 TERMINAL at string-family diagnostic-ordering axis scope. Ownership is a
+// target-row property for string-family candidates, distinct from callable
+// `ParameterDisposition`: it classifies the candidate carrier itself, not how a
+// callee receives one argument. Rows land in target specs later; this slice
+// only provides canonical structural values so consumers do not normalize
+// strings locally.
+type StringOwnershipAxis
+  = Owned
+  | Borrowed
+
+// 🟢 TERMINAL at string-family diagnostic-ordering axis scope. These are the R2
+// lifetime roles shared by lifetime analyzer facts and future target rows.
+// `SelfContained` avoids leaking Rust's `Self_` identifier escaping into the
+// substrate vocabulary; `Caller` names the call-frame-bounded role.
+type StringLifetimeAxis
+  = SelfContained
+  | Caller
+
+// 🟢 TERMINAL at string-family diagnostic-ordering axis scope. `NotApplicable`
+// is an explicit value, not absence: borrowed candidates and returns can say
+// the growability axis does not apply without becoming unknown.
+type StringGrowabilityAxis
+  = Growable
+  | Fixed
+  | NotApplicable
+
+// 🟢 TERMINAL at R2 string-family encoding scope. The design-doc correction
+// makes `.dag` `String` the `FreeMonoid<Char>` family; this value names the
+// UTF-8 target-row semantics consumed by the analyzer/fold bridge. Additional
+// byte or target-specific encodings belong in later LanguageSpec rows.
+type StringEncodingAxis
+  = Utf8FreeMonoidChar
+
 type TypeInstantiationRealization {
   language: DeclarationRef
   target: DeclarationRef