fix: resolve undefined $agent_id and $job_snapshot in AIStep::executeStep() (#826)

Both variables were defined in validateStepConfiguration() but used in
executeStep() without being re-defined. PHP treated them as null, which
silently broke per-agent tool policies (ToolPolicyResolver skipped
agent filtering) and per-agent model overrides (global defaults used
instead).

Adds the two missing lines at the top of executeStep() to read from
the engine snapshot, matching the pattern already used in
validateStepConfiguration().

Author: chubes4

inc/Core/Steps/AI/AIStep.php

@@ -179,7 +179,9 @@ protected function executeStep(): array {
 		$max_turns = PluginSettings::get( 'max_turns', PluginSettings::DEFAULT_MAX_TURNS );
 
 		// Resolve user_id and agent_id from engine snapshot (set by RunFlowAbility).
-		$user_id = (int) ( $job_snapshot['user_id'] ?? 0 );
+		$job_snapshot = $this->engine->get( 'job' );
+		$agent_id     = (int) ( $job_snapshot['agent_id'] ?? 0 );
+		$user_id      = (int) ( $job_snapshot['user_id'] ?? 0 );
 
 		$payload = array(
 			'job_id'       => $this->job_id,