add retry example (#1179)

Author: zzstoatzz

examples/task_retries.py

@@ -0,0 +1,36 @@
+"""Example showing how to control retries for Tasks with pydantic output."""
+
+from pydantic import BaseModel, Field, field_validator
+
+import marvin
+
+
+class SpecialCode(BaseModel):
+    """A model with a custom validation rule that requires learning from errors."""
+
+    code: str = Field(description="The special code")
+
+    @field_validator("code")
+    def validate_code(cls, v):
+        # This validator has a special requirement: the code must end with "-42X"
+        # The agent won't know this initially and will learn from the error
+        if not v.endswith("-42X"):
+            raise ValueError("Code must end with '-42X' (company policy)")
+        return v
+
+
+# Set custom retry limit (default is 10)
+marvin.settings.agent_retries = 3
+
+# Use a thread to maintain conversation history across retries
+thread = marvin.Thread()
+
+# Create a task that will likely fail on first attempt
+task = marvin.Task[SpecialCode](
+    instructions="Generate a special code for project ALPHA",
+    result_type=SpecialCode,
+)
+
+print(f"Running task with retry limit of {marvin.settings.agent_retries}...")
+result = task.run(thread=thread)
+print(f"Successfully generated: {result}")