Discord: implement stream preview mode (#22111)

* Discord: implement stream preview mode

* Changelog: note Discord stream preview mode

* Tests: type discord draft stream mocks

* Docs: document Discord stream preview

src/discord/draft-chunking.ts

@@ -0,0 +1,41 @@
+import { resolveTextChunkLimit } from "../auto-reply/chunk.js";
+import { getChannelDock } from "../channels/dock.js";
+import type { OpenClawConfig } from "../config/config.js";
+import { normalizeAccountId } from "../routing/session-key.js";
+
+const DEFAULT_DISCORD_DRAFT_STREAM_MIN = 200;
+const DEFAULT_DISCORD_DRAFT_STREAM_MAX = 800;
+
+export function resolveDiscordDraftStreamingChunking(
+  cfg: OpenClawConfig | undefined,
+  accountId?: string | null,
+): {
+  minChars: number;
+  maxChars: number;
+  breakPreference: "paragraph" | "newline" | "sentence";
+} {
+  const providerChunkLimit = getChannelDock("discord")?.outbound?.textChunkLimit;
+  const textLimit = resolveTextChunkLimit(cfg, "discord", accountId, {
+    fallbackLimit: providerChunkLimit,
+  });
+  const normalizedAccountId = normalizeAccountId(accountId);
+  const draftCfg =
+    cfg?.channels?.discord?.accounts?.[normalizedAccountId]?.draftChunk ??
+    cfg?.channels?.discord?.draftChunk;
+
+  const maxRequested = Math.max(
+    1,
+    Math.floor(draftCfg?.maxChars ?? DEFAULT_DISCORD_DRAFT_STREAM_MAX),
+  );
+  const maxChars = Math.max(1, Math.min(maxRequested, textLimit));
+  const minRequested = Math.max(
+    1,
+    Math.floor(draftCfg?.minChars ?? DEFAULT_DISCORD_DRAFT_STREAM_MIN),
+  );
+  const minChars = Math.min(minRequested, maxChars);
+  const breakPreference =
+    draftCfg?.breakPreference === "newline" || draftCfg?.breakPreference === "sentence"
+      ? draftCfg.breakPreference
+      : "paragraph";
+  return { minChars, maxChars, breakPreference };
+}