refactor(subagent): unify async readiness and cancellation

packages/subagent/subagent-fork/src/index.ts

@@ -72,11 +72,11 @@ class ForkProvider implements SubagentProvider {
   // Context contract: a forked child IS seeded with the parent's completed-turn prefix.
   readonly inheritsParentContext = true
 
-  constructor(readonly name: string, private readonly ctx: Context) {}
+  constructor(readonly name: string) {}
 
   start(request: SubagentStartRequest) {
     const seed = completedTurnPrefix(request.parent)
-    return startInProcessRun(this.ctx, request, {
+    return startInProcessRun(request, {
       // Only pass a seed when there's a completed turn to inherit; an empty seed
       // is equivalent to a fresh child, so omit it to keep the session unseeded.
       ...seed.length > 0 ? { seed } : {},
@@ -85,5 +85,5 @@ class ForkProvider implements SubagentProvider {
 }
 
 export function apply(ctx: Context, config: Config): void {
-  ctx.subagents.registerProvider(new ForkProvider(config.providerName, ctx))
+  ctx.subagents.registerProvider(new ForkProvider(config.providerName))
 }