refactor: dedupe preview streaming helpers

src/plugin-sdk/channel-streaming.ts

@@ -21,6 +21,7 @@ export type {
 
 type StreamingCompatEntry = {
   streaming?: unknown;
+  streamMode?: unknown;
   chunkMode?: unknown;
   blockStreaming?: unknown;
   draftChunk?: unknown;
@@ -42,6 +43,27 @@ function asBoolean(value: unknown): boolean | undefined {
   return typeof value === "boolean" ? value : undefined;
 }
 
+function normalizeStreamingMode(value: unknown): string | null {
+  if (typeof value !== "string") {
+    return null;
+  }
+  const normalized = value.trim().toLowerCase();
+  return normalized || null;
+}
+
+function parsePreviewStreamingMode(value: unknown): "off" | "partial" | "block" | null {
+  const normalized = normalizeStreamingMode(value);
+  if (
+    normalized === "off" ||
+    normalized === "partial" ||
+    normalized === "block" ||
+    normalized === "progress"
+  ) {
+    return normalized === "progress" ? "partial" : normalized;
+  }
+  return null;
+}
+
 function asBlockStreamingCoalesceConfig(value: unknown): BlockStreamingCoalesceConfig | undefined {
   return asObjectRecord(value) as BlockStreamingCoalesceConfig | undefined;
 }
@@ -99,3 +121,24 @@ export function resolveChannelStreamingNativeTransport(
   const config = getChannelStreamingConfigObject(entry);
   return asBoolean(config?.nativeTransport) ?? asBoolean(entry?.nativeStreaming);
 }
+
+export function resolveChannelPreviewStreamMode(
+  entry: StreamingCompatEntry | null | undefined,
+  defaultMode: "off" | "partial",
+): "off" | "partial" | "block" {
+  const parsedStreaming = parsePreviewStreamingMode(
+    getChannelStreamingConfigObject(entry)?.mode ?? entry?.streaming,
+  );
+  if (parsedStreaming) {
+    return parsedStreaming;
+  }
+
+  const legacy = parsePreviewStreamingMode(entry?.streamMode);
+  if (legacy) {
+    return legacy;
+  }
+  if (typeof entry?.streaming === "boolean") {
+    return entry.streaming ? "partial" : "off";
+  }
+  return defaultMode;
+}