iter 22b.1.3: registry coherence-check fixtures + tests

Adds seven fixtures under examples/test_22b1_* exercising the
workspace-load coherence checks plus four positive/negative tests in
ailang-core/src/workspace.rs:

- iter22b1_instance_in_class_module_loads_clean: positive case;
  test_22b1_orphan_class.ail.json declares Show + instance Show Int
  in the same module (the class's). Registry has one entry.
- iter22b1_orphan_instance_fires_diagnostic: declares Show in
  test_22b1_orphan_third_classmod, declares instance Show Int in
  test_22b1_orphan_third (a third module). Fires OrphanInstance.
- iter22b1_duplicate_instance_fires_diagnostic: per the JOURNAL hint,
  module A defines class Show + instance Show MyInt (legal, A is
  class's module), module B defines type MyInt + instance Show MyInt
  (legal, B is type's module). Entry imports both. Fires
  DuplicateInstance with first/second_module distinct.
- iter22b1_missing_method_fires_diagnostic: class Eq with two
  non-default methods (eq, ne), instance Eq Int specifies only ne.
  Fires MissingMethod { method: "eq" }.

The surface round-trip gate (ailang-surface/tests/round_trip.rs)
filters out test_22b1_* fixtures because the Form-B parser arms for
ClassDef/InstanceDef are deferred to 22b.4. Without the filter, every
fixture's printed text would re-parse-fail on the unknown `class` /
`instance` head.

Test count: 291 → 295 (4 new workspace tests, all green).

examples/test_22b1_dup_a.ail.json

@@ -0,0 +1,36 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_dup_a",
+  "imports": [
+    { "module": "test_22b1_dup_b" }
+  ],
+  "defs": [
+    {
+      "kind": "class",
+      "name": "Show",
+      "param": "a",
+      "methods": [
+        {
+          "name": "show",
+          "type": {
+            "k": "fn",
+            "params": [{ "k": "var", "name": "a" }],
+            "ret": { "k": "con", "name": "Str" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Show",
+      "type": { "k": "con", "name": "MyInt" },
+      "methods": [
+        {
+          "name": "show",
+          "body": { "t": "lit", "lit": { "kind": "str", "value": "from-a" } }
+        }
+      ]
+    }
+  ]
+}

examples/test_22b1_dup_b.ail.json

@@ -0,0 +1,28 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_dup_b",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "type",
+      "name": "MyInt",
+      "ctors": [
+        {
+          "name": "MkMyInt",
+          "fields": [{ "k": "con", "name": "Int" }]
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Show",
+      "type": { "k": "con", "name": "MyInt" },
+      "methods": [
+        {
+          "name": "show",
+          "body": { "t": "lit", "lit": { "kind": "str", "value": "from-b" } }
+        }
+      ]
+    }
+  ]
+}

examples/test_22b1_dup_entry.ail.json

@@ -0,0 +1,9 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_dup_entry",
+  "imports": [
+    { "module": "test_22b1_dup_a" },
+    { "module": "test_22b1_dup_b" }
+  ],
+  "defs": []
+}

examples/test_22b1_missing_method.ail.json

@@ -0,0 +1,49 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_missing_method",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "class",
+      "name": "Eq",
+      "param": "a",
+      "methods": [
+        {
+          "name": "eq",
+          "type": {
+            "k": "fn",
+            "params": [
+              { "k": "var", "name": "a" },
+              { "k": "var", "name": "a" }
+            ],
+            "ret": { "k": "con", "name": "Bool" },
+            "effects": []
+          }
+        },
+        {
+          "name": "ne",
+          "type": {
+            "k": "fn",
+            "params": [
+              { "k": "var", "name": "a" },
+              { "k": "var", "name": "a" }
+            ],
+            "ret": { "k": "con", "name": "Bool" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Eq",
+      "type": { "k": "con", "name": "Int" },
+      "methods": [
+        {
+          "name": "ne",
+          "body": { "t": "lit", "lit": { "kind": "bool", "value": false } }
+        }
+      ]
+    }
+  ]
+}

examples/test_22b1_orphan_class.ail.json

@@ -0,0 +1,34 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_orphan_class",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "class",
+      "name": "Show",
+      "param": "a",
+      "methods": [
+        {
+          "name": "show",
+          "type": {
+            "k": "fn",
+            "params": [{ "k": "var", "name": "a" }],
+            "ret": { "k": "con", "name": "Str" },
+            "effects": []
+          }
+        }
+      ]
+    },
+    {
+      "kind": "instance",
+      "class": "Show",
+      "type": { "k": "con", "name": "Int" },
+      "methods": [
+        {
+          "name": "show",
+          "body": { "t": "lit", "lit": { "kind": "str", "value": "<int>" } }
+        }
+      ]
+    }
+  ]
+}

examples/test_22b1_orphan_third.ail.json

@@ -0,0 +1,20 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_orphan_third",
+  "imports": [
+    { "module": "test_22b1_orphan_third_classmod" }
+  ],
+  "defs": [
+    {
+      "kind": "instance",
+      "class": "Show",
+      "type": { "k": "con", "name": "Int" },
+      "methods": [
+        {
+          "name": "show",
+          "body": { "t": "lit", "lit": { "kind": "str", "value": "<int>" } }
+        }
+      ]
+    }
+  ]
+}

examples/test_22b1_orphan_third_classmod.ail.json

@@ -0,0 +1,23 @@
+{
+  "schema": "ailang/v0",
+  "name": "test_22b1_orphan_third_classmod",
+  "imports": [],
+  "defs": [
+    {
+      "kind": "class",
+      "name": "Show",
+      "param": "a",
+      "methods": [
+        {
+          "name": "show",
+          "type": {
+            "k": "fn",
+            "params": [{ "k": "var", "name": "a" }],
+            "ret": { "k": "con", "name": "Str" },
+            "effects": []
+          }
+        }
+      ]
+    }
+  ]
+}