fix(heartbeat): honor heartbeat.model config for heartbeat turns (#14103)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: f46080b0adb882c4d18af7ac0e80055505ff640c
Co-authored-by: shtse8 <8020099+shtse8@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

src/auto-reply/reply/get-reply.ts

@@ -80,7 +80,10 @@ export async function getReplyFromConfig(
   let model = defaultModel;
   let hasResolvedHeartbeatModelOverride = false;
   if (opts?.isHeartbeat) {
-    const heartbeatRaw = agentCfg?.heartbeat?.model?.trim() ?? "";
+    // Prefer the resolved per-agent heartbeat model passed from the heartbeat runner,
+    // fall back to the global defaults heartbeat model for backward compatibility.
+    const heartbeatRaw =
+      opts.heartbeatModelOverride?.trim() ?? agentCfg?.heartbeat?.model?.trim() ?? "";
     const heartbeatRef = heartbeatRaw
       ? resolveModelRefFromString({
           raw: heartbeatRaw,

src/auto-reply/types.ts

@@ -27,6 +27,8 @@ export type GetReplyOptions = {
   onTypingCleanup?: () => void;
   onTypingController?: (typing: TypingController) => void;
   isHeartbeat?: boolean;
+  /** Resolved heartbeat model override (provider/model string from merged per-agent config). */
+  heartbeatModelOverride?: string;
   onPartialReply?: (payload: ReplyPayload) => Promise<void> | void;
   onReasoningStream?: (payload: ReplyPayload) => Promise<void> | void;
   onBlockReply?: (payload: ReplyPayload, context?: BlockReplyContext) => Promise<void> | void;