Make session refresh retries idempotent

Preserve the successor session for legitimate refresh retries so transient failures no longer revoke the user's session family.

src/test/kotlin/com/osglab/account/config/DeploymentConsistencyTest.kt

@@ -20,6 +20,24 @@ class DeploymentConsistencyTest : FunSpec({
         documentedPaths shouldBe EXPECTED_PUBLIC_PATHS
     }
 
+    test("session refresh idempotency stays aligned across API, schema, and deployment") {
+        val openApi = root.read("docs/openapi.yaml")
+        val migration = root.read(
+            "src/main/resources/db/migration/V29__idempotent_session_refresh.sql",
+        )
+
+        openApi shouldContain "refreshOperationId"
+        migration shouldContain "encrypted_replacement_refresh_token"
+        migration shouldContain "refresh_replay_until"
+        listOf(
+            root.read("src/main/resources/application.yaml"),
+            root.read(".env.example"),
+            root.read("compose.yaml"),
+        ).forEach { configuration ->
+            configuration shouldContain "LEGACY_REFRESH_REPLAY_SECONDS"
+        }
+    }
+
     test("OpenAPI defines admin pagination and response contracts") {
         val openApi = root.read("docs/openapi.yaml")
         val sessionSchema = openApi