Reflow terminal on layout-driven container resizes

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;

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}