fix: repair streaming output broken by markdown rendering changes

Two bugs were introduced when sendTextMessage was changed to auto-detect
message format (text/post/interactive):

1. Message type mismatch: sendTextMessage could create a text or post
   message, but patchTextMessage only works on interactive cards.
   Fix: add sendInteractiveCardMessage for streaming create (always
   interactive, always patchable).

2. flushTextToSink state corruption: the text management after flush
   had a flawed appendedDuringFlush heuristic that could lose text or
   duplicate it. Fix: properly track sent vs unsent text by removing
   the sent prefix length, keeping only the last chunk for future patches.

Also fix finish() to flush pending text regardless of currentMessageId.

hub/src/feishu/textStream.ts

@@ -144,10 +144,12 @@ export class PatchableTextStream {
 
   async finish(fallbackText: string): Promise<void> {
     await this.flushChain;
-    if (this.currentMessageId !== null && this.text.length > 0) {
+    // If there's pending text to flush, do it now.
+    if (this.text.length > 0) {
       await this.flushTextToSink();
       return;
     }
+    // No pending text. If we never sent anything, send the fallback.
     if (this.currentMessageId === null && fallbackText.length > 0) {
       this.text = fallbackText;
       await this.flushTextToSink();
@@ -184,16 +186,25 @@ export class PatchableTextStream {
     if (firstChunk === undefined) return;
 
     if (this.currentMessageId === null) {
-      for (const chunk of chunks) {
+      // First message: create it with the first chunk, then send overflow
+      // chunks as new messages.
+      this.currentMessageId = await this.sink.create(firstChunk);
+      for (const chunk of chunks.slice(1)) {
         this.currentMessageId = await this.sink.create(chunk);
       }
+      // Keep only the last chunk for future patches; remove already-sent prefix.
+      const sentLength = chunks.slice(0, -1).reduce((sum, c) => sum + c.length, 0);
+      this.text = this.text.slice(sentLength);
     } else {
+      // Patch the current message with the first chunk, then create new
+      // messages for overflow chunks.
       await this.sink.patch(this.currentMessageId, firstChunk);
       for (const chunk of chunks.slice(1)) {
         this.currentMessageId = await this.sink.create(chunk);
       }
+      // Keep only the last chunk for future patches; remove already-sent prefix.
+      const sentLength = chunks.slice(0, -1).reduce((sum, c) => sum + c.length, 0);
+      this.text = this.text.slice(sentLength);
     }
-    const appendedDuringFlush = this.text.startsWith(textToFlush) ? this.text.slice(textToFlush.length) : "";
-    this.text = `${chunks.at(-1) ?? ""}${appendedDuringFlush}`;
   }
 }