fix(llm): isolate retry policy histories

examples/headless-agent/retry.cordis.snapshot.yml

@@ -0,0 +1,12 @@
+# Keyless provider-retry composition for the headless stream-json snapshot.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: llm-deepseek
+        name: '@deepseek-ai/dsh-llm-deepseek'
+        disabled: true
+      - insert:
+          - id: retry-snapshot-backend
+            name: './tests/fixtures/retry-snapshot-backend.mjs'