feat(stepfunctions): real activity worker pool

[vieiralucas]

Summary

Replaces the synthetic GetActivityTask shortcut with a real worker pool: a Task state inserts a PENDING token, GetActivityTask long-polls for the oldest pending task, SendTaskSuccess/Failure unblocks the interpreter. Heartbeat + timeout windows enforced. New introspection endpoint lets tests inject pending tasks directly.

• Extends TaskTokenState with input/created_at/last_heartbeat_at/heartbeat_seconds/timeout_seconds
• Interpreter `invoke_activity` polls until the worker resolves the token, with HeartbeatSeconds and TimeoutSeconds enforced
• GetActivityTask returns empty taskToken after FAKECLOUD_SFN_GET_ACTIVITY_TIMEOUT_SECS (default 5s) when no task is queued, matching AWS
• SendTaskHeartbeat now refreshes last_heartbeat_at instead of mutating status
• New POST /_fakecloud/stepfunctions/enqueue-activity-task introspection endpoint
• Conformance test sfn_task_token_round_trip rewired to use the introspection endpoint (old shortcut no longer applies)
• New E2E tests cover round-trip success + worker failure propagation

Test plan

• cargo test -p fakecloud-stepfunctions --lib (137 pass)
• cargo test -p fakecloud-conformance --test stepfunctions sfn_task_token_round_trip
• cargo test -p fakecloud-e2e --test stepfunctions sfn_activity_worker_pool_round_trip + sfn_activity_failure_propagates_to_execution
• cargo clippy --workspace --all-targets -- -D warnings
• CI green
• Cubic clean

---

Summary by cubic

Implements a real Step Functions activity worker pool: Task states enqueue pending work, workers long‑poll GetActivityTask, and executions resolve via SendTaskSuccess/SendTaskFailure with HeartbeatSeconds/TimeoutSeconds enforced. Adds a test-only endpoint to enqueue tasks directly (uses the default account).

• New Features

  • Real worker pool for activities: oldest pending task is dequeued by GetActivityTask (long-polls up to FAKECLOUD_SFN_GET_ACTIVITY_TIMEOUT_SECS, default 5s; returns empty token on timeout).
  • Heartbeat/timeout enforcement in the interpreter; SendTaskHeartbeat now updates last_heartbeat_at only; emits States.HeartbeatTimeout or States.Timeout when windows close.
  • Introspection: POST /_fakecloud/stepfunctions/enqueue-activity-task inserts a pending task for an activity (accepts activityArn, optional input, heartbeatSeconds, timeoutSeconds; returns taskToken). Tasks are enqueued in the default account namespace.
  • TaskTokenState extended with input, created_at, last_heartbeat_at, heartbeat_seconds, timeout_seconds; tokens are cleaned up on completion.

• Migration

  • Code relying on synthetic GetActivityTask tokens must handle empty tokens and poll until a task is available.
  • Tests that exercised SendTask* without a state machine should use /_fakecloud/stepfunctions/enqueue-activity-task or start a real execution; for multi-account setups, switch the default account or create the activity in the default account.
  • When HeartbeatSeconds is set, workers must call SendTaskHeartbeat periodically.
  • Adjust long‑poll window via FAKECLOUD_SFN_GET_ACTIVITY_TIMEOUT_SECS if needed.

^{Written for commit c70cb0b. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 8 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="crates/fakecloud-server/src/main.rs">

<violation number="1" location="crates/fakecloud-server/src/main.rs:3886">
P2: Don’t derive Step Functions account state from the request ARN in this introspection route; use the emulator’s default account state so task injection targets the same account namespace as the rest of Step Functions endpoints.

(Based on your team's feedback about treating FakeCloud as single-account by default and avoiding account derivation from arbitrary ARNs.) [FEEDBACK_USED]</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[codecov]

Codecov Report

❌ Patch coverage is 3.28638% with 206 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/fakecloud-stepfunctions/src/interpreter.rs	6.54%	100 Missing ⚠️
crates/fakecloud-stepfunctions/src/service.rs	0.00%	65 Missing ⚠️
crates/fakecloud-server/src/main.rs	0.00%	39 Missing ⚠️
crates/fakecloud-stepfunctions/src/state.rs	0.00%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!