fix(mcp): emit newline-delimited JSON responses over stdio

CHANGELOG.md

@@ -7,6 +7,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [1.6.2] - 2026-06-23
+
+### Fixed
+- MCP stdio responses are now emitted as newline-delimited JSON-RPC instead of
+  `Content-Length` framed (LSP-style) messages. The previous output framing was
+  not understood by MCP stdio clients and caused connection/initialization to
+  hang. Input still accepts both framings for compatibility.
+- Added a `write_message` test asserting newline-delimited output without
+  `Content-Length` headers.
+
 ## [1.6.1] - 2026-06-23
 
 ### Fixed

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mem-cli"
-version = "1.6.1"
+version = "1.6.2"
 edition = "2024"
 
 [dependencies]

src/mcp.rs

@@ -110,11 +110,12 @@ fn read_message<R: BufRead>(reader: &mut R) -> Result<Option<Value>> {
 
 fn write_message<W: Write>(writer: &mut W, message: &Value) -> Result<()> {
     let body = serde_json::to_vec(message).context("failed to serialize MCP response")?;
-    write!(writer, "Content-Length: {}\r\n\r\n", body.len())
-        .context("failed to write MCP response header")?;
     writer
         .write_all(&body)
         .context("failed to write MCP response body")?;
+    writer
+        .write_all(b"\n")
+        .context("failed to write MCP response newline")?;
     Ok(())
 }
 
@@ -783,4 +784,20 @@ mod tests {
             .expect("message");
         assert_eq!(parsed, request);
     }
+
+    #[test]
+    fn write_message_emits_newline_delimited_json() {
+        let message = json!({"jsonrpc":"2.0","id":1,"result":{}});
+        let mut buffer = Vec::new();
+        write_message(&mut buffer, &message).expect("write message");
+
+        let output = String::from_utf8(buffer).expect("utf8 output");
+        assert!(
+            !output.contains("Content-Length"),
+            "output must not use LSP framing"
+        );
+        assert!(output.ends_with('\n'), "message must be newline-delimited");
+        let parsed: Value = serde_json::from_str(output.trim_end()).expect("parse written message");
+        assert_eq!(parsed, message);
+    }
 }