refactor(agent-loop): inline the turn error shaping

packages/core/agent-loop/src/agent.ts

@@ -60,20 +60,6 @@ function requestProposal(header: EpochHeader): LlmCallConfig {
 }
 
 /** Drives one session through turn and step boundaries. */
-/**
- * Shape a caught turn error into its durable reason: every failure is a
- * structured LlmFailure — an `LlmError` keeps its facts, anything else
- * flattens to `errorChain` text under the `UNKNOWN` code.
- */
-function turnErrorReason(error: unknown): Extract<TurnEndReason, { kind: 'error' }> {
-  return {
-    kind: 'error',
-    error: error instanceof LlmError
-      ? error.failure
-      : { message: errorChain(error), code: 'UNKNOWN' },
-  }
-}
-
 export class ReactLoopAgent implements Agent {
   readonly inbox: Inbox
   private phase: Phase
@@ -293,7 +279,14 @@ export class ReactLoopAgent implements Agent {
         turnEnds = { kind: 'aborted', reason: signal.reason as AgentCancelCause }
         throw error
       }
-      turnEnds = turnErrorReason(error)
+      // Every failure is structured: an `LlmError` keeps its facts, anything
+      // else flattens to `errorChain` text under the `UNKNOWN` code.
+      turnEnds = {
+        kind: 'error',
+        error: error instanceof LlmError
+          ? error.failure
+          : { message: errorChain(error), code: 'UNKNOWN' },
+      }
       this.throwError(error)
     } finally {
       try {