fix(cache): prevent over-invalidation of similarly named prompt prefixes in PromptCache

langfuse/_utils/prompt_cache.py

@@ -178,9 +178,17 @@ def delete(self, key: str) -> None:
 
     def invalidate(self, prompt_name: str) -> None:
         """Invalidate all cached prompts with the given prompt name."""
+        if not prompt_name:
+            return
+        version_prefix = f"{prompt_name}-version:"
+        label_prefix = f"{prompt_name}-label:"
         with self._lock:
             for key in list(self._cache):
-                if key.startswith(prompt_name):
+                if (
+                    key == prompt_name
+                    or key.startswith(version_prefix)
+                    or key.startswith(label_prefix)
+                ):
                     del self._cache[key]
 
     def add_refresh_prompt_task(self, key: str, fetch_func: Callable[[], None]) -> None:

tests/unit/test_prompt.py

@@ -748,3 +748,41 @@ def test_get_fresh_prompt_when_version_changes(langfuse: Langfuse):
     result_call_2 = langfuse.get_prompt(prompt_name, version=2)
     assert mock_server_call.call_count == 2
     assert result_call_2 == version_changed_prompt_client
+
+
+def test_prompt_cache_invalidate_exact_prefix_match(langfuse: Langfuse):
+    cache = PromptCache()
+    prompt1 = Prompt_Text(
+        name="summary",
+        version=1,
+        prompt="Summarize this",
+        labels=[],
+        type="text",
+        config={},
+        tags=[],
+    )
+    prompt2 = Prompt_Text(
+        name="summary-detailed",
+        version=1,
+        prompt="Summarize in detail",
+        labels=[],
+        type="text",
+        config={},
+        tags=[],
+    )
+
+    key1 = PromptCache.generate_cache_key("summary", version=1, label=None)
+    key2 = PromptCache.generate_cache_key("summary-detailed", version=1, label=None)
+
+    cache.set(key1, TextPromptClient(prompt1), ttl_seconds=60)
+    cache.set(key2, TextPromptClient(prompt2), ttl_seconds=60)
+
+    assert cache.get(key1) is not None
+    assert cache.get(key2) is not None
+
+    cache.invalidate("summary")
+
+    # summary should be invalidated, but summary-detailed must be preserved
+    assert cache.get(key1) is None
+    assert cache.get(key2) is not None
+