Explain the lifecycle of a hook during a single Burr action execution?

Hooks attach at specific points around an action’s run, and Burr calls the matching methods on every registered hook at each point:

sequenceDiagram
    participant App as Application
    participant Hook as Registered Hook(s)
    participant Act as Action

    App->>Hook: pre_run_step(state, action)
    Hook-->>App: (side effect, e.g. log/trace)
    App->>Act: run(state) / update(result, state)
    Act-->>App: result, new_state
    App->>Hook: post_run_step(state, action, result, sequence_id, exception)
    Hook-->>App: (side effect, e.g. log/trace)
    App->>App: merge new_state into application state

class PrintLnHook(PostRunStepHook, PreRunStepHook):
    def pre_run_step(self, *, state, action, **kw):
        print(f"Starting action: {action.node.name}")

    def post_run_step(self, *, state, action, result, sequence_id, exception, **kw):
        print(f"Finishing action: {action.node.name}")

A single hook class can subclass several of these lifecycle interfaces (as long as it doesn’t mix a sync and async version of the same hook). Whether a given hook fires depends on which run method you used: synchronous hooks fire under every method (step, astep, iterate, aiterate, run, arun), while asynchronous-only hooks fire solely under the async methods. The exact ordering across multiple hooks is currently undefined by the framework, though today they run in declaration order.