From e3e879db9248153b932ffe77c570e23559669213 Mon Sep 17 00:00:00 2001
From: Paul van Dyk <paul@vandyk.fr>
Date: Tue, 30 Jun 2026 14:47:56 +0200
Subject: [PATCH] Reflow terminal on layout-driven container resizes

The xterm resize path was gated on window.resize / resizeEpoch, so
container resizes driven by CSS/flex layout (split-pane drag, sidebar
collapse) changed the terminal's DOM size without firing fit() or sending
terminalResize. The pty never resized, so no SIGWINCH reached the child.

Observe the xterm container with a ResizeObserver (rAF-coalesced to one
fit per frame) and refit + send terminalResize directly, instead of
relying on window.resize.

Also surface resize failures: when a process resize throws (e.g. a Bun
build without terminal.resize), the frontend command swallows the error.
Log it once per process via Effect.logWarning at the shared
resizePtyProcess chokepoint so the cause is visible without spamming.
---
 apps/server/src/terminal/Manager.ts           | 20 +++++++++++-
 .../src/components/ThreadTerminalDrawer.tsx   | 31 +++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/apps/server/src/terminal/Manager.ts b/apps/server/src/terminal/Manager.ts
index 6347fdfc64d..9cf2203e641 100644
--- a/apps/server/src/terminal/Manager.ts
+++ b/apps/server/src/terminal/Manager.ts
@@ -200,6 +200,11 @@ interface TerminalSubprocessInspector {
   ): Effect.Effect<TerminalSubprocessInspectResult, TerminalSubprocessCheckError>;
 }
 
+// Resize can fail permanently (e.g. a Bun build without `terminal.resize`). The frontend
+// command swallows the error, so warn once per process to keep the cause visible in logs
+// without spamming on every resize.
+const resizeFailureWarned = new WeakSet<PtyAdapter.PtyProcess>();
+
 const resizePtyProcess = (
   session: TerminalSessionState,
   process: PtyAdapter.PtyProcess,
@@ -217,7 +222,20 @@ const resizePtyProcess = (
         rows,
         cause,
       }),
-  });
+  }).pipe(
+    Effect.tapError((error) =>
+      Effect.gen(function* () {
+        if (resizeFailureWarned.has(process)) return;
+        resizeFailureWarned.add(process);
+        yield* Effect.logWarning("terminal resize failed; size changes will not propagate", {
+          threadId: session.threadId,
+          terminalId: session.terminalId,
+          terminalPid: process.pid,
+          cause: error.cause,
+        });
+      }),
+    ),
+  );
 
 export interface ShellCandidate {
   shell: string;
diff --git a/apps/web/src/components/ThreadTerminalDrawer.tsx b/apps/web/src/components/ThreadTerminalDrawer.tsx
index 1641bb6b109..a73a4041286 100644
--- a/apps/web/src/components/ThreadTerminalDrawer.tsx
+++ b/apps/web/src/components/ThreadTerminalDrawer.tsx
@@ -794,6 +794,37 @@ export function TerminalViewport({
       window.cancelAnimationFrame(frame);
     };
   }, [drawerHeight, environmentId, resizeEpoch, terminalId, threadId]);
+
+  // CSS/flex-driven container resizes (split-pane drag, sidebar collapse) change the xterm
+  // size without firing window.resize, so resizeEpoch never advances. Observe the container
+  // directly and refit. rAF-coalesced to one fit per frame, matching the effect above.
+  useEffect(() => {
+    const container = containerRef.current;
+    if (!container) return;
+    let frame: number | null = null;
+    const observer = new ResizeObserver(() => {
+      if (frame !== null) return;
+      frame = window.requestAnimationFrame(() => {
+        frame = null;
+        const terminal = terminalRef.current;
+        const fitAddon = fitAddonRef.current;
+        if (!terminal || !fitAddon) return;
+        const wasAtBottom = terminal.buffer.active.viewportY >= terminal.buffer.active.baseY;
+        fitTerminalSafely(fitAddon);
+        if (wasAtBottom) {
+          terminal.scrollToBottom();
+        }
+        void resizeTerminal(terminal.cols, terminal.rows);
+      });
+    });
+    observer.observe(container);
+    return () => {
+      if (frame !== null) {
+        window.cancelAnimationFrame(frame);
+      }
+      observer.disconnect();
+    };
+  }, [environmentId, terminalId, threadId]);
   return (
     <div
       ref={containerRef}