From 0dba13a354877c0703bd8aa6b0c2d67dc98a567f Mon Sep 17 00:00:00 2001
From: Fusion <noreply@runfusion.ai>
Date: Sun, 24 May 2026 15:57:29 +0200
Subject: [PATCH] fix: send SIGWINCH to docker exec after PTY resize

When resizing the PTY, docker exec needs to be notified so it can
re-read the terminal size and propagate it to the container's PTY.
Without this, the container shell stays at 80x24 regardless of what
the frontend sends.
---
 apps/api/src/api/terminal.py              |  8 ++++----
 apps/api/src/services/terminal_session.py | 24 ++++++++++++++++++++---
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/apps/api/src/api/terminal.py b/apps/api/src/api/terminal.py
index 26d05f1..c43ed91 100644
--- a/apps/api/src/api/terminal.py
+++ b/apps/api/src/api/terminal.py
@@ -148,10 +148,10 @@ async def _write_loop(session, websocket) -> None:
                             msg_type = ctrl.get("type")
                             
                             if msg_type == "resize":
-                                await session.resize(
-                                    ctrl.get("cols", 80),
-                                    ctrl.get("rows", 24),
-                                )
+                                cols = ctrl.get("cols", 80)
+                                rows = ctrl.get("rows", 24)
+                                logger.info(f"Received resize message for instance {instance_id}: {cols}x{rows}")
+                                await session.resize(cols, rows)
                             elif msg_type == "reset":
                                 # Reset terminal session
                                 logger.info("Resetting terminal session for instance %s", session.instance_id)
diff --git a/apps/api/src/services/terminal_session.py b/apps/api/src/services/terminal_session.py
index 0f6e7d0..76ec714 100644
--- a/apps/api/src/services/terminal_session.py
+++ b/apps/api/src/services/terminal_session.py
@@ -1,9 +1,11 @@
 """Terminal session management for tool instances."""
 
 import asyncio
+import logging
 import os
 import pty
 import select
+import signal
 import struct
 import fcntl
 import time
@@ -11,6 +13,8 @@ import uuid
 from collections import deque
 from typing import Any
 
+logger = logging.getLogger(__name__)
+
 
 class TerminalSession:
     """Manages a single terminal session connected to a docker container.
@@ -55,6 +59,7 @@ class TerminalSession:
         
         # Set the terminal size initially
         self._set_terminal_size(self._cols, self._rows)
+        logger.info(f"Starting terminal session {self.session_id} for container {self.container_id} with initial size {self._cols}x{self._rows}")
         
         # Start docker exec with the slave fd as stdin/stdout/stderr
         # Using -it because the slave fd IS a TTY
@@ -79,16 +84,27 @@ class TerminalSession:
         self.last_activity = time.time()
 
     def _set_terminal_size(self, cols: int, rows: int) -> None:
-        """Set the terminal size using TIOCSWINSZ."""
+        """Set the terminal size using TIOCSWINSZ and signal docker exec."""
         if self._master_fd is None:
+            logger.warning("Cannot resize: master_fd is None (session not started)")
             return
         # TIOCSWINSZ = 0x5414 on Linux
         TIOCSWINSZ = 0x5414
         size = struct.pack('HHHH', rows, cols, 0, 0)
         try:
             fcntl.ioctl(self._master_fd, TIOCSWINSZ, size)
-        except (OSError, IOError):
-            pass
+            logger.info(f"Resized PTY to {cols}x{rows} (fd={self._master_fd})")
+            
+            # Send SIGWINCH to docker exec process so it re-reads terminal
+            # size and propagates it to the container's PTY
+            if self.process and self.process.pid:
+                try:
+                    os.kill(self.process.pid, signal.SIGWINCH)
+                    logger.info(f"Sent SIGWINCH to docker exec pid={self.process.pid}")
+                except (OSError, ProcessLookupError) as e:
+                    logger.warning(f"Failed to send SIGWINCH: {e}")
+        except (OSError, IOError) as e:
+            logger.error(f"Failed to resize PTY: {e}")
 
     async def read_output(self) -> bytes:
         """Read output from the PTY master and store in buffer."""
@@ -134,9 +150,11 @@ class TerminalSession:
     async def resize(self, cols: int, rows: int) -> None:
         """Resize the terminal."""
         if self._closed:
+            logger.warning("Cannot resize: session is closed")
             return
         self._cols = cols
         self._rows = rows
+        logger.info(f"resize() called for session {self.session_id}: {cols}x{rows}")
         self._set_terminal_size(cols, rows)
 
     async def reset(self) -> None: