From 00a9167223abc576ce95d2b5b56152f91308ff9a Mon Sep 17 00:00:00 2001
From: Wolfgang Schoenberger <221313372+wolfiesch@users.noreply.github.com>
Date: Wed, 22 Jul 2026 19:13:53 -0700
Subject: [PATCH] fix(rpc): accept exact-boundary v2 chunks

---
 .../coding-agent/src/modes/rpc/rpc-frame.ts   |  2 +-
 packages/coding-agent/test/rpc-frame.test.ts  | 21 +++++++++++
 python/omp-rpc/src/omp_rpc/client.py          |  2 +-
 python/omp-rpc/tests/test_client.py           | 35 +++++++++++++++++++
 4 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/packages/coding-agent/src/modes/rpc/rpc-frame.ts b/packages/coding-agent/src/modes/rpc/rpc-frame.ts
index cce90beea..abfb0cf6c 100644
--- a/packages/coding-agent/src/modes/rpc/rpc-frame.ts
+++ b/packages/coding-agent/src/modes/rpc/rpc-frame.ts
@@ -147,7 +147,7 @@ export class RpcFrameDecoder {
 			count < 2 ||
 			count > Math.ceil(MAX_RPC_REASSEMBLED_BYTES / RPC_CHUNK_PAYLOAD_BYTES) ||
 			index >= count ||
-			byteLength <= MAX_RPC_FRAME_BYTES ||
+			byteLength < MAX_RPC_FRAME_BYTES ||
 			byteLength > MAX_RPC_REASSEMBLED_BYTES
 		)
 			throw new Error("invalid rpc chunk metadata");
diff --git a/packages/coding-agent/test/rpc-frame.test.ts b/packages/coding-agent/test/rpc-frame.test.ts
index f558537f0..2117054ba 100644
--- a/packages/coding-agent/test/rpc-frame.test.ts
+++ b/packages/coding-agent/test/rpc-frame.test.ts
@@ -208,6 +208,27 @@ describe("RPC frame encoding", () => {
 		expect(decoded).toEqual(frame);
 	});
 
+	it("accepts a chunked logical frame at the exact physical-frame boundary", () => {
+		const frame = {
+			id: "request-boundary",
+			type: "response",
+			command: "get_state",
+			success: true,
+			data: { payload: "" },
+		};
+		const emptyBytes = Buffer.byteLength(JSON.stringify(frame), "utf8");
+		frame.data.payload = "x".repeat(MAX_RPC_FRAME_BYTES - emptyBytes);
+		expect(Buffer.byteLength(JSON.stringify(frame), "utf8")).toBe(MAX_RPC_FRAME_BYTES);
+
+		const encoder = new RpcFrameEncoder();
+		encoder.setProtocolVersion(2);
+		const decoder = new RpcFrameDecoder();
+		let decoded: object | undefined;
+		for (const line of encoder.encode(frame).trimEnd().split("\n")) decoded = decoder.push(JSON.parse(line));
+
+		expect(decoded).toEqual(frame);
+	});
+
 	it("preserves terminal message counts above the protocol v2 ceiling", () => {
 		const encoder = new RpcFrameEncoder();
 		encoder.setProtocolVersion(2);
diff --git a/python/omp-rpc/src/omp_rpc/client.py b/python/omp-rpc/src/omp_rpc/client.py
index 688d7dea0..b43482f22 100644
--- a/python/omp-rpc/src/omp_rpc/client.py
+++ b/python/omp-rpc/src/omp_rpc/client.py
@@ -164,7 +164,7 @@ class _RpcFrameDecoder:
             or count < 2
             or count > max_chunk_count
             or index >= count
-            or byte_length <= _MAX_RPC_FRAME_BYTES
+            or byte_length < _MAX_RPC_FRAME_BYTES
             or byte_length > _MAX_RPC_REASSEMBLED_BYTES
             or not isinstance(data, str)
             or not data
diff --git a/python/omp-rpc/tests/test_client.py b/python/omp-rpc/tests/test_client.py
index 7d5c2b88b..dda1ebdb3 100644
--- a/python/omp-rpc/tests/test_client.py
+++ b/python/omp-rpc/tests/test_client.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import base64
+import json
 import os
 import shutil
 import signal
@@ -11,6 +13,7 @@ import time
 import unittest
 
 from omp_rpc import RpcClient, RpcCommandError, RpcConcurrencyError, RpcError, host_tool
+from omp_rpc.client import _RpcFrameDecoder
 
 
 FAKE_SERVER = textwrap.dedent(
@@ -735,6 +738,38 @@ class RpcClientTests(unittest.TestCase):
             **kwargs,
         )
 
+    def test_protocol_v2_decoder_accepts_exact_logical_boundary(self) -> None:
+        frame = {
+            "id": "request-boundary",
+            "type": "response",
+            "command": "get_state",
+            "success": True,
+            "data": {"payload": ""},
+        }
+        encoded_empty = json.dumps(frame, separators=(",", ":")).encode("utf-8")
+        frame["data"]["payload"] = "x" * (1024 * 1024 - len(encoded_empty))
+        encoded = json.dumps(frame, separators=(",", ":")).encode("utf-8")
+        self.assertEqual(len(encoded), 1024 * 1024)
+
+        decoder = _RpcFrameDecoder()
+        chunk_size = 256 * 1024
+        count = (len(encoded) + chunk_size - 1) // chunk_size
+        decoded = None
+        for index in range(count):
+            chunk = encoded[index * chunk_size : (index + 1) * chunk_size]
+            decoded = decoder.push(
+                {
+                    "type": "rpc_chunk",
+                    "chunkId": "exact-boundary",
+                    "index": index,
+                    "count": count,
+                    "byteLength": len(encoded),
+                    "data": base64.b64encode(chunk).decode("ascii"),
+                }
+            )
+
+        self.assertEqual(decoded, frame)
+
     def test_command_builder_supports_common_rpc_options(self) -> None:
         client = RpcClient(
             executable="omp",