[Feature Request] Activity interceptors

[chris-olszewski]

No activity-level inbound/outbound interceptors.

[sachinsharma3191]

Proposed design for activity interceptors (seeking alignment before PR).

Goal

Provide hooks around activity execution that are useful for logging/metrics/tracing and validation:

• before execute (activity type, task token, attempt, workflow metadata)
• after execute (success/failure + duration)

API sketch

Add temporalio_sdk::interceptors::ActivityInterceptor with non-async hooks:

• fn on_activity_start(&self, ctx: &ActivityInterceptorContext)
• fn on_activity_finish(&self, ctx: &ActivityInterceptorContext, result: &Result<(), ActivityError>)

ActivityInterceptorContext includes:

• namespace
• task_queue
• workflow_id/run_id (from activity task)
• activity_id, activity_type
• attempt

Storage

• Add activity_interceptors: Vec<Arc<dyn ActivityInterceptor>> to WorkerOptions.

Minimal first slice PR

• Wire hooks in the activity task handler right before dispatch to user activity fn and right after completion is formed.
• Add a unit test that runs an activity-only worker against a mocked core worker/task stream or the existing test harness, asserting hooks are invoked.

Non-goals

• No mutation of activity input/output in v1 (just observation).
• No async hooks.

If this is aligned, I’ll implement the minimal slice + tests and then extend to cover cancellation/heartbeat events.

[sachinsharma3191]

Follow-up: The design proposal is in the thread above. Implementation will wait for maintainer approval (or requested revisions) before any new PR.

The first PR after approval will include concrete hook wiring and tests per the agreed scope.

Please let us know when the design is good to implement.

[sachinsharma3191]

@chris-olszewski, whenever you have a moment, could you take a look at the design for this? Also, let me know if you’re already tackling this so we don't double up on effort.