fix(task): preserved deferred fallback chains

Install subagent retry fallback chains after deferred model patterns resolve so runtime-only candidates keep their ordered fallbacks.\n\nFixes #4421

packages/coding-agent/src/task/executor.ts

@@ -2164,6 +2164,8 @@ export async function runSubprocess(options: ExecutorOptions): Promise<SingleRes
 				modelPattern: model || modelOverride === undefined ? undefined : modelPatterns,
 				modelPatternAuthFallback:
 					model || modelOverride === undefined ? undefined : options.parentActiveModelPattern,
+				modelPatternFallbackRole:
+					model || modelOverride === undefined ? undefined : `${SUBAGENT_RETRY_FALLBACK_ROLE_PREFIX}${id}`,
 				thinkingLevel: effectiveThinkingLevel,
 				toolNames,
 				outputSchema,