fix(persona-kit): defer @relayfile/local-mount import to call site (#121)

`@relayfile/local-mount` imports `@parcel/watcher` at module top, which
loads a per-platform native binary at evaluation time (e.g.
`@parcel/watcher-linux-x64-glibc` on Lambda). Eagerly importing it from
`mount.ts` meant every `import('@agentworkforce/persona-kit')` evaluated
the binary load — including server-side validation paths that never call
`applyPersonaMount`.

Concrete blast: cloud's deploy POST does
`await import("@agentworkforce/persona-kit")` to call `parsePersonaSpec`
on the uploaded bundle. The Lambda runtime is linux-x64-glibc, but
OpenNext's tracer doesn't bundle @parcel/watcher's optional native
prebuild, so the import resolution throws:

  "Persona validation is unavailable:
   @agentworkforce/persona-kit could not be loaded
   ... No prebuild or local build of @parcel/watcher found.
   Tried @parcel/watcher-linux-x64-glibc."

Fix: lazy-import `@relayfile/local-mount` inside a small helper that
`applyPersonaMount` awaits at call time. Mount is a CLI/runtime concern,
not a server concern, so deferring is correct semantically and lets the
native binary stay un-loaded on hosts that never apply a mount.

The barrel `index.ts` re-exports stay intact — back-compat for any
direct consumer of `applyPersonaMount`. The change is purely the
import timing inside `mount.ts`.

Verified:
* 170/170 persona-kit tests pass.
* 544 tests across the whole workforce repo pass (`pnpm run test`).
* Probe script: `import('@agentworkforce/persona-kit')` followed by
  `parsePersonaSpec(...)` succeeds with NO `@parcel/watcher` load on
  the call path.

Co-authored-by: Ricky Schema Cascade <ricky@agent-relay.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: 3 people

packages/persona-kit/src/mount.ts

@@ -1,6 +1,23 @@
-import { createMount } from '@relayfile/local-mount';
 import type { ResolvedMountPolicy } from './plan.js';
 
+// `@relayfile/local-mount` pulls in `@parcel/watcher`, which loads a
+// per-platform native binary at module evaluation time
+// (`@parcel/watcher-linux-x64-glibc`, `-darwin-arm64`, …). When
+// persona-kit is loaded server-side just to call `parsePersonaSpec`
+// (e.g. cloud's `import('@agentworkforce/persona-kit')` to validate a
+// deploy bundle), eagerly importing local-mount fails any host that
+// doesn't ship a matching prebuild — most notably AWS Lambda's
+// `@parcel/watcher-linux-x64-glibc`, which OpenNext doesn't bundle.
+//
+// Deferring the local-mount import to `applyPersonaMount`'s call site
+// means the native binary only loads when a mount is actually being
+// applied (which is a CLI/runtime concern, never a server-side
+// validation concern).
+async function loadCreateMount(): Promise<typeof import('@relayfile/local-mount').createMount> {
+  const mod = await import('@relayfile/local-mount');
+  return mod.createMount;
+}
+
 export interface PersonaMountHandle {
   /**
    * Working directory the harness should be spawned in. When the mount is
@@ -68,6 +85,7 @@ export async function applyPersonaMount(
       'applyPersonaMount: options.personaId is required when a mount policy is supplied'
     );
   }
+  const createMount = await loadCreateMount();
   const handle = await createMount(options.cwd, options.mountDir, {
     ignoredPatterns: [...mount.ignoredPatterns],
     readonlyPatterns: [...mount.readonlyPatterns],