Function execute_from_step

crates/buzz-workflow/src/executor.rs:1029–1086

Resume execution from a specific step index (used for approval resume). Acquires a concurrency permit from `engine.run_semaphore` before executing — returns [`WorkflowError::CapacityExceeded`] immediately if all permits are taken. Transitions the run to `Running` after acquiring a permit, so that approval-resumed runs correctly reflect their active state. `initial_outputs` should be reconstruct

(
    engine: &WorkflowEngine,
    community_id: CommunityId,
    run_id: Uuid,
    def: &WorkflowDef,
    trigger_ctx: &TriggerContext,
    start_index: usize,
    initial_outputs: Option<HashMap<Str

/// calling this function on resume, so that steps after the resume point can
/// reference `{{steps.PREV_STEP.output.X}}` correctly.
pub async fn execute_from_step(
    engine: &WorkflowEngine,
    community_id: CommunityId,
    run_id: Uuid,
    def: &WorkflowDef,
    trigger_ctx: &TriggerContext,
    start_index: usize,
    initial_outputs: Option<HashMap<String, JsonValue>>,
) -> Result<ExecutionResult, (WorkflowError, crate::error::PartialProgress)> {
    // Fail fast if all concurrency permits are in use — no queuing.
    let _permit = engine.run_semaphore.try_acquire().map_err(|_| {
        (
            WorkflowError::CapacityExceeded,
            crate::error::PartialProgress::default(),
        )
    })?;

    // Mark run as Running now that we have a permit (resume from approval).
    // Preserve the existing execution trace from pre-approval steps.
    let existing_trace = match engine.db.get_workflow_run(community_id, run_id).await {
        Ok(r) => r.execution_trace,
        Err(e) => {
            warn!(
                run_id = %run_id,
                "Failed to read existing trace for resume — pre-approval trace will be lost: {e}"
            );
            serde_json::json!([])
        }
    };
    engine
        .db
        .update_workflow_run(
            community_id,
            run_id,
            buzz_db::workflow::RunStatus::Running,
            start_index as i32,
            &existing_trace,
            None,
        )
        .await
        .map_err(|e| {
            (
                WorkflowError::from(e),
                crate::error::PartialProgress::default(),
            )
        })?;

    execute_steps(
        engine,
        community_id,
        run_id,
        def,
        trigger_ctx,
        start_index,
        initial_outputs,
    )
    .await
}