fix: address review feedback from #85512

- /model switch now refreshes agent._custom_providers from the config
  loaded during the switch before re-evaluating cache policy — a
  prompt_caching flag added to config.yaml after session start was
  invisible to a mid-session switch (policy read the stale init-time
  snapshot while context_length resolution used the live list).
- Production-path test: real config.yaml in the modern providers: dict
  shape through the real loader chain, exercising the init-order fallback
  (no _custom_providers attr) for both the fable opt-in and the opus
  explicit opt-out.
- Pin operator kill-switch precedence: _cache_disabled (prompt_caching.
  cache_ttl falsy) beats an explicit per-model prompt_caching: true.

agent/agent_runtime_helpers.py

@@ -2756,6 +2756,13 @@ def switch_model(agent, new_model, new_provider, api_key='', base_url='', api_mo
     )
 
     # ── Re-evaluate prompt caching ──
+    # Refresh the custom-provider snapshot from the config just loaded above
+    # so the per-model ``prompt_caching`` capability lookup sees the same
+    # live list the context-length resolution used — without this, a flag
+    # added to config.yaml after session start is invisible to a /model
+    # switch (the policy would read the stale init-time snapshot).
+    if _sm_custom_providers is not None:
+        agent._custom_providers = _sm_custom_providers
     agent._use_prompt_caching, agent._use_native_cache_layout = (
         agent._anthropic_prompt_cache_policy(
             provider=new_provider,

tests/run_agent/test_anthropic_prompt_cache_policy.py

@@ -231,6 +231,68 @@ class TestThirdPartyAnthropicGateway:
 
         assert agent._anthropic_prompt_cache_policy() == (False, False)
 
+    def test_operator_cache_disable_beats_explicit_capability_true(self):
+        """prompt_caching.cache_ttl disable (agent._cache_disabled) is a
+        global operator kill-switch — it must win over a per-model
+        prompt_caching: true declaration (#33555 semantics)."""
+        agent = _make_agent(
+            provider="custom:anthropic-proxy",
+            base_url="https://gateway.example.com/anthropic",
+            api_mode="anthropic_messages",
+            model="fable",
+        )
+        agent._custom_providers = [
+            {
+                "name": "anthropic-proxy",
+                "base_url": "https://gateway.example.com/anthropic",
+                "models": {"fable": {"prompt_caching": True}},
+            }
+        ]
+        agent._cache_disabled = True
+
+        assert agent._anthropic_prompt_cache_policy() == (False, False)
+
+    def test_modern_providers_yaml_through_real_loader(self, tmp_path, monkeypatch):
+        """Production path: a real config.yaml in the modern ``providers:``
+        dict shape, loaded through the real normalizer chain — including the
+        init-order fallback where ``_custom_providers`` is NOT yet set on the
+        agent and the policy loads config itself."""
+        import textwrap
+
+        hermes_home = tmp_path / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / "config.yaml").write_text(
+            textwrap.dedent(
+                """
+                providers:
+                  anthropic-proxy:
+                    api: https://gateway.example.com/anthropic
+                    transport: anthropic_messages
+                    models:
+                      fable:
+                        context_length: 1000000
+                        prompt_caching: true
+                      opus:
+                        prompt_caching: false
+                """
+            )
+        )
+        monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+        # load_config's cache is keyed by resolved config path, so pointing
+        # HERMES_HOME at a fresh tempdir needs no cache invalidation.
+        agent = _make_agent(
+            provider="custom:anthropic-proxy",
+            base_url="https://gateway.example.com/anthropic",
+            api_mode="anthropic_messages",
+            model="fable",
+        )
+        # No agent._custom_providers — exercises the config fallback the
+        # init-time call (agent_init before the snapshot assignment) hits.
+        assert agent._anthropic_prompt_cache_policy() == (True, True)
+
+        agent.model = "opus"
+        assert agent._anthropic_prompt_cache_policy() == (False, False)
+
 
 class TestMiniMaxAnthropicWire:
     """MiniMax's own model family on its Anthropic-compatible endpoint.