fix(dashboard,core,engine): statically import @fusion/engine to fix createFnAgent undefined in published CLI

The dashboard modules used a variable-specifier dynamic import
(`const m = "@fusion/engine"; await import(m)`) to defeat bundler static
analysis. tsup honored that and left the dynamic import in dist/bin.js,
so the published `@runfusion/fusion` package failed at runtime with
"createFnAgent2 is not a function" — `@fusion/engine` isn't on npm and
the silent catch set the binding to undefined. Replaces the trick with
static imports across planning, chat, subtask-breakdown, mission-interview,
agent-generation, ai-refine, roadmap-suggestions, milestone-slice-interview,
and routes. Core can't statically import engine (cycle), so it now exposes
setCreateFnAgent and engine wires itself in at module load. Documents the
pattern in AGENTS.md.

Fixes Runfusion/Fusion#9.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/ai-engine-loader.ts

@@ -1,45 +1,40 @@
 /**
- * Shared lazy loader for `@fusion/engine`'s `createFnAgent`.
+ * Shared lazy accessor for `@fusion/engine`'s `createFnAgent`.
  *
- * @fusion/engine must be imported dynamically (not statically) so that:
- *   - core can be consumed in test environments where engine isn't resolvable
- *   - a missing engine package fails soft instead of breaking module load
+ * Core can't import engine statically (engine depends on core, so a static
+ * import would create a cycle). Instead, engine wires its `createFnAgent` in
+ * via `setCreateFnAgent` when its module loads, and consumers in core read it
+ * back through `getFnAgent`.
  *
- * Using a variable module specifier also prevents bundlers (Vite) from
- * statically analysing and trying to resolve the import at build time.
+ * If engine never loads (e.g. tests that only import core), `getFnAgent`
+ * returns `undefined` and callers degrade gracefully.
  */
 
 // Engine exports a function type we intentionally don't pull in here — importing
-// the type would reintroduce the static resolution this module is designed to avoid.
+// the type would reintroduce the cycle this module is designed to avoid.
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 type CreateFnAgent = any;
 
 let createFnAgent: CreateFnAgent | undefined;
 
-async function initEngine(): Promise<void> {
-  try {
-    const engineModule = "@fusion/engine";
-    const engine = await import(/* @vite-ignore */ engineModule);
-    createFnAgent = engine.createFnAgent;
-  } catch {
-    createFnAgent = undefined;
-  }
-}
-
 /** Shape of a message in an agent session's state. */
 export interface AgentMessage {
   role: string;
   content?: string | Array<{ type: string; text: string }>;
 }
 
-/** Promise that resolves once the initial load attempt has completed. */
-const engineReady: Promise<void> = initEngine();
+/**
+ * Wire engine's `createFnAgent` into core. Called by `@fusion/engine` at module
+ * load. Tests can also call this with a stub.
+ */
+export function setCreateFnAgent(fn: CreateFnAgent | undefined): void {
+  createFnAgent = fn;
+}
 
 /**
- * Returns `createFnAgent` from `@fusion/engine`, or `undefined` if the engine
- * could not be loaded (typical in tests or when engine isn't installed).
+ * Returns `createFnAgent` from `@fusion/engine`, or `undefined` if engine has
+ * not registered itself yet (typical in tests).
  */
 export async function getFnAgent(): Promise<CreateFnAgent> {
-  await engineReady;
   return createFnAgent;
 }

packages/core/src/index.ts

@@ -8,6 +8,9 @@ export {
   getTemplatesForRole,
 } from "./agent-prompts.js";
 
+// ── Engine wiring (set by @fusion/engine at module load) ────────────
+export { setCreateFnAgent, getFnAgent, type AgentMessage } from "./ai-engine-loader.js";
+
 // ── Prompt Overrides ─────────────────────────────────────────────────
 export {
   PROMPT_KEY_CATALOG,