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/agents/pi-embedded-runner/run/attempt.ts

@@ -390,7 +390,7 @@ export async function runEmbeddedAttempt(
       tools,
     });
     const systemPromptOverride = createSystemPromptOverride(appendPrompt);
-    const systemPromptText = systemPromptOverride();
+    const systemPromptText = systemPromptOverride;
 
     const sessionLock = await acquireSessionWriteLock({
       sessionFile: params.sessionFile,

src/agents/pi-embedded-runner/system-prompt.ts

@@ -78,11 +78,8 @@ export function createSystemPromptOverride(systemPrompt: string): string {
   return systemPrompt.trim();
 }
 
-export function applySystemPromptOverrideToSession(
-  session: AgentSession,
-  override: (defaultPrompt?: string) => string,
-) {
-  const prompt = override().trim();
+export function applySystemPromptOverrideToSession(session: AgentSession, override: string) {
+  const prompt = override.trim();
   session.agent.setSystemPrompt(prompt);
   const mutableSession = session as unknown as {
     _baseSystemPrompt?: string;