feat: update terminal theme without remounting the xterm instance

packages/app/src/terminal/runtime/terminal-emulator-runtime.test.ts

@@ -6,6 +6,9 @@ type StubTerminal = {
   write: (text: string, callback?: () => void) => void;
   reset: () => void;
   focus: () => void;
+  refresh?: (start: number, end: number) => void;
+  options?: { theme?: unknown };
+  rows?: number;
 };
 
 function createRuntimeWithTerminal(): {
@@ -33,6 +36,9 @@ function createRuntimeWithTerminal(): {
       terminal.resetCalls = resetCalls;
     },
     focus: () => {},
+    refresh: () => {},
+    options: { theme: undefined },
+    rows: 0,
     resetCalls,
   };
 
@@ -171,4 +177,23 @@ describe("terminal-emulator-runtime", () => {
     expect(fitAndEmitResize).toHaveBeenNthCalledWith(1, false);
     expect(fitAndEmitResize).toHaveBeenNthCalledWith(2, true);
   });
+
+  it("updates terminal theme without remounting", () => {
+    const runtime = new TerminalEmulatorRuntime();
+    const refresh = vi.fn();
+    const terminal: StubTerminal = {
+      write: () => {},
+      reset: () => {},
+      focus: () => {},
+      refresh,
+      options: { theme: { background: "before" } },
+      rows: 12,
+    };
+    (runtime as unknown as { terminal: StubTerminal }).terminal = terminal;
+
+    runtime.setTheme({ theme: { background: "after" } as never });
+
+    expect(terminal.options?.theme).toEqual({ background: "after" });
+    expect(refresh).toHaveBeenCalledWith(0, 11);
+  });
 });

packages/app/src/terminal/runtime/terminal-emulator-runtime.ts

@@ -464,6 +464,30 @@ export class TerminalEmulatorRuntime {
     this.fitAndEmitResize?.(input?.force ?? false);
   }
 
+  setTheme(input: { theme: ITheme }): void {
+    const terminal = this.terminal;
+    if (!terminal) {
+      return;
+    }
+
+    try {
+      terminal.options.theme = input.theme;
+      terminalDebugLog({
+        scope: "emulator-runtime",
+        event: "theme:update",
+      });
+    } catch {
+      // ignore
+      return;
+    }
+
+    try {
+      terminal.refresh(0, Math.max(0, terminal.rows - 1));
+    } catch {
+      // ignore
+    }
+  }
+
   focus(): void {
     this.terminal?.focus();
   }