refactor(FN-2161): standardize on createFnAgent naming

- Rename engine export and call sites to use createFnAgent consistently across runtime flows
- Update core lazy engine loader and dashboard agent-generation/planning/chat paths to reference createFnAgent
- Refresh affected unit and integration tests, including renaming pi-create-kb-agent.test.ts to pi-create-fn-agent.test.ts
- Update AGENTS.md documentation references to match the new createFnAgent name

packages/engine/src/mission-execution-loop.ts

@@ -19,7 +19,7 @@ import type {
   MissionFeature,
   MissionValidatorRun,
 } from "@fusion/core";
-import { createKbAgent, promptWithFallback, type AgentResult } from "./pi.js";
+import { createFnAgent, promptWithFallback, type AgentResult } from "./pi.js";
 import { createLogger } from "./logger.js";
 
 /** Logger for the mission execution loop subsystem. */
@@ -325,7 +325,7 @@ export class MissionExecutionLoop extends EventEmitter {
 
     try {
       // Create validation agent session
-      session = await createKbAgent({
+      session = await createFnAgent({
         cwd: this.rootDir,
         systemPrompt: this.buildValidationSystemPrompt(feature, assertions, taskContext),
         tools: "readonly",
@@ -383,7 +383,7 @@ export class MissionExecutionLoop extends EventEmitter {
    * Run the actual validation session with the AI agent.
    */
   private async runValidationSession(
-    agentSession: Awaited<ReturnType<typeof createKbAgent>>["session"],
+    agentSession: Awaited<ReturnType<typeof createFnAgent>>["session"],
     prompt: string,
   ): Promise<void> {
     // Use promptWithFallback for resilience - if the primary model fails,
@@ -401,7 +401,7 @@ export class MissionExecutionLoop extends EventEmitter {
    * We extract the text from the AI's messages and parse the JSON response.
    */
   private async parseValidationResult(
-    agentSession: Awaited<ReturnType<typeof createKbAgent>>["session"],
+    agentSession: Awaited<ReturnType<typeof createFnAgent>>["session"],
     assertions: MissionContractAssertion[],
   ): Promise<ValidationResult> {
     try {
@@ -467,7 +467,7 @@ export class MissionExecutionLoop extends EventEmitter {
    * Looks for the last assistant message with text content.
    */
   private extractResponseTextFromSession(
-    agentSession: Awaited<ReturnType<typeof createKbAgent>>["session"],
+    agentSession: Awaited<ReturnType<typeof createFnAgent>>["session"],
   ): string | undefined {
     try {
       // Access the session state to get messages