fix(terminal): contain IME composition layout

src/renderer/src/TerminalPanel.test.tsx

@@ -221,6 +221,18 @@ describe('TerminalPanel', () => {
     )
   })
 
+  it('contains IME composition layout inside the terminal', () => {
+    expect(terminalStylesheet).toMatch(
+      /\.terminal-panel__emulator\s*\{[^}]*contain:\s*size layout paint;[^}]*overflow-anchor:\s*none;/u
+    )
+    expect(terminalStylesheet).toMatch(
+      /\.terminal-panel__emulator \.xterm\s*\{[^}]*width:\s*100%;[^}]*max-width:\s*100%;[^}]*overflow:\s*hidden;/u
+    )
+    expect(terminalStylesheet).toMatch(
+      /\.terminal-panel__emulator \.xterm-helpers\s*\{[^}]*max-width:\s*0;[^}]*overflow:\s*visible;/u
+    )
+  })
+
   it('creates only after the first valid fitted size and forwards input', async () => {
     const backend = adapterHarness()
     const emulator = emulatorHarness()

src/renderer/src/terminal-panel.css

@@ -116,11 +116,24 @@
   flex: 1;
   padding: 0;
   overflow: hidden;
+  contain: size layout paint;
+  overflow-anchor: none;
   background: var(--surface-canvas);
 }
 
 .terminal-panel__emulator .xterm {
+  position: relative;
+  width: 100%;
+  min-width: 0;
+  max-width: 100%;
   height: 100%;
+  overflow: hidden;
+}
+
+/* IME composition must stay inside the terminal's own scroll boundary. */
+.terminal-panel__emulator .xterm-helpers {
+  max-width: 0;
+  overflow: visible;
 }
 
 .terminal-panel__status {