fix(coding-agent): use strict JSONL framing fixes #1911

packages/coding-agent/docs/rpc.md

@@ -24,6 +24,17 @@ Common options:
 
 All commands support an optional `id` field for request/response correlation. If provided, the corresponding response will include the same `id`.
 
+### Framing
+
+RPC mode uses strict JSONL semantics with LF (`\n`) as the only record delimiter.
+
+This matters for clients:
+- Split records on `\n` only
+- Accept optional `\r\n` input by stripping a trailing `\r`
+- Do not use generic line readers that treat Unicode separators as newlines
+
+In particular, Node `readline` is not protocol-compliant for RPC mode because it also splits on `U+2028` and `U+2029`, which are valid inside JSON strings.
+
 ## Commands
 
 ### Prompting
@@ -1292,13 +1303,39 @@ For a complete example of handling the extension UI protocol, see [`examples/rpc
 
 ```javascript
 const { spawn } = require("child_process");
-const readline = require("readline");
+const { StringDecoder } = require("string_decoder");
 
 const agent = spawn("pi", ["--mode", "rpc", "--no-session"]);
 
-readline.createInterface({ input: agent.stdout }).on("line", (line) => {
+function attachJsonlReader(stream, onLine) {
+    const decoder = new StringDecoder("utf8");
+    let buffer = "";
+
+    stream.on("data", (chunk) => {
+        buffer += typeof chunk === "string" ? chunk : decoder.write(chunk);
+
+        while (true) {
+            const newlineIndex = buffer.indexOf("\n");
+            if (newlineIndex === -1) break;
+
+            let line = buffer.slice(0, newlineIndex);
+            buffer = buffer.slice(newlineIndex + 1);
+            if (line.endsWith("\r")) line = line.slice(0, -1);
+            onLine(line);
+        }
+    });
+
+    stream.on("end", () => {
+        buffer += decoder.end();
+        if (buffer.length > 0) {
+            onLine(buffer.endsWith("\r") ? buffer.slice(0, -1) : buffer);
+        }
+    });
+}
+
+attachJsonlReader(agent.stdout, (line) => {
     const event = JSON.parse(line);
-    
+
     if (event.type === "message_update") {
         const { assistantMessageEvent } = event;
         if (assistantMessageEvent.type === "text_delta") {