fix(InlineModelResolver): do not deduplicate distinctly-named component schemas (#24177)

modules/openapi-generator/src/main/java/org/openapitools/codegen/InlineModelResolver.java

@@ -1223,7 +1223,15 @@ private void deduplicateComponents() {
                 String sigKey = schema.getTitle() + "||" + structural;
                 String canonical = canonicalBySig.get(sigKey);
                 if (canonical != null) {
-                    duplicateToCanonical.put(name, canonical);
+                    // Only collapse numbered duplicates (e.g. FlowSegment_1) — those are artifacts
+                    // the Swagger Parser / inline resolver produced when it failed to reuse an
+                    // existing component. A schema the user authored with its own distinct,
+                    // non-numbered name is part of the spec's source of truth and must be kept even
+                    // when it is structurally identical to another named schema (see #24177: two
+                    // schemas 'upper1'/'upper2' with the same title, intentionally distinct).
+                    if (name.matches(".*_\\d+$")) {
+                        duplicateToCanonical.put(name, canonical);
+                    }
                 } else {
                     canonicalBySig.put(sigKey, name);
                 }

modules/openapi-generator/src/test/java/org/openapitools/codegen/InlineModelResolverTest.java

@@ -1487,4 +1487,34 @@ public void deduplicateComponentsRemovesNumberedDuplicateOfTitledSchemaAndRewrit
         assertEquals("$ref must be rewritten from Widget_1 to Widget",
                 "#/components/schemas/Widget", responseSchema.get$ref());
     }
+
+    @Test
+    public void deduplicateComponentsKeepsDistinctlyNamedUserSchemas() {
+        // Regression test for #24177: two component schemas the user authored with distinct,
+        // non-numbered names (upper1 / upper2) that happen to be structurally identical AND share
+        // the same title must NOT be merged. deduplicateComponents() only collapses numbered
+        // duplicates generated by the parser/inline resolver (Foo_1 alongside Foo); user-authored
+        // named types are the source of truth and must both survive.
+        OpenAPI openapi = new OpenAPI();
+        openapi.setComponents(new Components());
+
+        Schema upper1 = new ObjectSchema()
+                .title("foo title identical by purpose")
+                .description("foo")
+                .addProperty("foo", new StringSchema());
+        Schema upper2 = new ObjectSchema()
+                .title("foo title identical by purpose")
+                .description("foo")
+                .addProperty("foo", new StringSchema());
+
+        openapi.getComponents().addSchemas("upper1", upper1);
+        openapi.getComponents().addSchemas("upper2", upper2);
+
+        new InlineModelResolver().flatten(openapi);
+
+        Map<String, Schema> schemas = openapi.getComponents().getSchemas();
+        assertNotNull("upper1 must survive", schemas.get("upper1"));
+        assertNotNull("upper2 must survive — distinctly-named user schemas must not be deduplicated",
+                schemas.get("upper2"));
+    }
 }