chore(experiments): state the description cap on experiment-create-from-prompt too

The definition JSONs already carried the sentence for this tool; the yaml
source now matches so a regeneration keeps it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: rubychilds

products/experiments/mcp/tools.yaml

@@ -308,7 +308,8 @@ tools:
             experiment-prompt-templates for the allowed template keys. Builds one variant per version, each carrying a
             feature flag payload with the prompt name and version so the SDK can resolve which version to serve, and
             attaches one primary metric per template, scoped to the prompt. The feature flag is auto-created — do not
-            create one separately. Launch the experiment with the launch tool when ready.
+            create one separately. Launch the experiment with the launch tool when ready. The description accepts at
+            most 3,000 characters and longer text is rejected, so keep the hypothesis summary short.
         ui_app: experiment
         response:
             include:

services/mcp/schema/generated-tool-definitions.json

@@ -4430,7 +4430,7 @@
         }
     },
     "experiment-create-from-prompt": {
-        "description": "Create a draft experiment that compares versions of an existing LLM prompt (managed with the llma-prompt tools). Pass the prompt's exact name (call llma-prompt-list to discover names), two or more of its version numbers (the first entry becomes the control variant), and one or more metric templates — call experiment-prompt-templates for the allowed template keys. Builds one variant per version, each carrying a feature flag payload with the prompt name and version so the SDK can resolve which version to serve, and attaches one primary metric per template, scoped to the prompt. The feature flag is auto-created — do not create one separately. Launch the experiment with the launch tool when ready.",
+        "description": "Create a draft experiment that compares versions of an existing LLM prompt (managed with the llma-prompt tools). Pass the prompt's exact name (call llma-prompt-list to discover names), two or more of its version numbers (the first entry becomes the control variant), and one or more metric templates — call experiment-prompt-templates for the allowed template keys. Builds one variant per version, each carrying a feature flag payload with the prompt name and version so the SDK can resolve which version to serve, and attaches one primary metric per template, scoped to the prompt. The feature flag is auto-created — do not create one separately. Launch the experiment with the launch tool when ready. The description accepts at most 3,000 characters and longer text is rejected, so keep the hypothesis summary short.",
         "category": "Experiments",
         "feature": "experiments",
         "summary": "Create experiment from LLM prompt",