fix: flush block streaming on paragraph boundaries for chunkMode=newline (#7014)

* feat: Implement paragraph boundary flushing in block streaming

- Added `flushOnParagraph` option to `BlockReplyChunking` for immediate flushing on paragraph breaks.
- Updated `EmbeddedBlockChunker` to handle paragraph boundaries during chunking.
- Enhanced `createBlockReplyCoalescer` to support flushing on enqueue.
- Added tests to verify behavior of flushing with and without `flushOnEnqueue` set.
- Updated relevant types and interfaces to include `flushOnParagraph` and `flushOnEnqueue` options.

* fix: Improve streaming behavior and enhance block chunking logic

- Resolved issue with stuck typing indicator after streamed BlueBubbles replies.
- Refactored `EmbeddedBlockChunker` to streamline fence-split handling and ensure maxChars fallback for newline chunking.
- Added tests to validate new chunking behavior, including handling of paragraph breaks and fence scenarios.
- Updated changelog to reflect these changes.

* test: Add test for clamping long paragraphs in EmbeddedBlockChunker

- Introduced a new test case to verify that long paragraphs are correctly clamped to maxChars when flushOnParagraph is enabled.
- Updated logic in EmbeddedBlockChunker to handle cases where the next paragraph break exceeds maxChars, ensuring proper chunking behavior.

* refactor: streamline logging and improve error handling in message processing

- Removed verbose logging statements from the `processMessage` function to reduce clutter.
- Enhanced error handling by using `runtime.error` for typing restart failures.
- Updated the `applySystemPromptOverrideToSession` function to accept a string directly instead of a function, simplifying the prompt application process.
- Adjusted the `runEmbeddedAttempt` function to directly use the system prompt override without invoking it as a function.

src/auto-reply/reply/block-reply-coalescer.ts

@@ -18,6 +18,7 @@ export function createBlockReplyCoalescer(params: {
   const maxChars = Math.max(minChars, Math.floor(config.maxChars));
   const idleMs = Math.max(0, Math.floor(config.idleMs));
   const joiner = config.joiner ?? "";
+  const flushOnEnqueue = config.flushOnEnqueue === true;
 
   let bufferText = "";
   let bufferReplyToId: ReplyPayload["replyToId"];
@@ -57,7 +58,7 @@ export function createBlockReplyCoalescer(params: {
     if (!bufferText) {
       return;
     }
-    if (!options?.force && bufferText.length < minChars) {
+    if (!options?.force && !flushOnEnqueue && bufferText.length < minChars) {
       scheduleIdleFlush();
       return;
     }
@@ -86,6 +87,19 @@ export function createBlockReplyCoalescer(params: {
       return;
     }
 
+    // When flushOnEnqueue is set (chunkMode="newline"), each enqueued payload is treated
+    // as a separate paragraph and flushed immediately so delivery matches streaming boundaries.
+    if (flushOnEnqueue) {
+      if (bufferText) {
+        void flush({ force: true });
+      }
+      bufferReplyToId = payload.replyToId;
+      bufferAudioAsVoice = payload.audioAsVoice;
+      bufferText = text;
+      void flush({ force: true });
+      return;
+    }
+
     if (
       bufferText &&
       (bufferReplyToId !== payload.replyToId || bufferAudioAsVoice !== payload.audioAsVoice)