feat(FN-5544): emit runtime-resolved audit event across engine lanes

Adds a "session runtime resolved" audit event that flows through the engine's main execution lanes — triage, executor, reviewer, merger, heartbeat, step-session-executor, and mission-execution-loop — with runtime mutation support and test coverage, plus a compile-fix for the merger auditor wiring.

Fusion-Task-Id: FN-5544

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>
Fusion-Task-Id: FN-5544

packages/engine/src/step-session-executor.ts

@@ -36,6 +36,7 @@ import { StuckTaskDetector } from "./stuck-task-detector.js";
 import { AgentLogger } from "./agent-logger.js";
 import { createLogger } from "./logger.js";
 import { createFallbackModelObserver } from "./fallback-model-observer.js";
+import { createRunAuditor, generateSyntheticRunId } from "./run-audit.js";
 import { isContextLimitError } from "./context-limit-detector.js";
 import { checkSessionError } from "./usage-limit-detector.js";
 import {
@@ -1015,6 +1016,15 @@ Follow instructions precisely and avoid unrelated changes.`,
             fallbackProvider: settings.fallbackProvider,
             fallbackModelId: settings.fallbackModelId,
             defaultThinkingLevel: taskDetail.thinkingLevel ?? settings.defaultThinkingLevel,
+            runAuditor: createRunAuditor(this.store, {
+              runId: generateSyntheticRunId("workflow-step", taskDetail.id),
+              agentId: taskDetail.assignedAgentId ?? "executor",
+              taskId: taskDetail.id,
+              taskLineageId: taskDetail.lineageId,
+              phase: "execute",
+              source: "step-session-executor",
+            }),
+            settings,
             customTools: [
               ...pluginTools,
               ...documentTools,