fix(caching): use canonical Kimi-family matcher in cache policy

Review finding: the substring check ('kimi' or 'moonshot' in model)
under-matches bare release slugs like k2-thinking that the repo's
canonical _model_name_is_kimi_family matcher (anthropic_adapter.py)
already covers. Reuse it instead of a second ad-hoc matcher; add a
regression test for the bare-slug case.

agent/agent_runtime_helpers.py

@@ -1569,8 +1569,12 @@ def anthropic_prompt_cache_policy(
     # moonshotai/kimi-k2.6 falls through to (False, False), serving ~1%
     # cache hits on 64K-token prompts and re-billing the full prompt on
     # every turn.  Observed within-turn progression with cache enabled:
-    # 1% → 67% → 84% → 97% (#25970).
-    is_kimi = "kimi" in model_lower or "moonshot" in model_lower
+    # 1% → 67% → 84% → 97% (#25970).  Reuses the canonical family matcher
+    # (covers bare k1./k2./k25 release slugs the substring check missed).
+    from agent.anthropic_adapter import _model_name_is_kimi_family
+    is_kimi = (
+        _model_name_is_kimi_family(eff_model) or "moonshot" in model_lower
+    )
     is_openrouter = base_url_host_matches(eff_base_url, "openrouter.ai")
     # Nous Portal proxies to OpenRouter behind the scenes — identical
     # OpenAI-wire envelope cache_control semantics. Treat it as an

tests/run_agent/test_anthropic_prompt_cache_policy.py

@@ -105,6 +105,17 @@ class TestKimiMoonshotOnOpenRouter:
         )
         assert agent._anthropic_prompt_cache_policy() == (True, False)
 
+    def test_kimi_bare_release_slug_on_openrouter_caches(self):
+        """Bare release slugs (k2-thinking) lack the 'kimi'/'moonshot' substring;
+        the canonical family matcher must still catch them."""
+        agent = _make_agent(
+            provider="openrouter",
+            base_url="https://openrouter.ai/api/v1",
+            api_mode="chat_completions",
+            model="k2-thinking",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (True, False)
+
     def test_kimi_on_non_openrouter_host_does_not_cache(self):
         agent = _make_agent(
             provider="custom",