feat: add OSC 52 clipboard support for container-to-host copy

Programs inside the container (e.g. Claude Code's "hit c to copy") can
now write to the host system clipboard. A shell script shim installed as
xclip/xsel/pbcopy emits OSC 52 escape sequences, which the xterm.js
frontend intercepts and forwards to navigator.clipboard.writeText().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/src/components/terminal/TerminalView.tsx

@@ -82,6 +82,25 @@ export default function TerminalView({ sessionId, active }: Props) {
     // Send initial size
     resize(sessionId, term.cols, term.rows);
 
+    // Handle OSC 52 clipboard write sequences from programs inside the container.
+    // When a program (e.g. Claude Code) copies text via xclip/xsel/pbcopy, the
+    // container's shim emits an OSC 52 escape sequence which xterm.js routes here.
+    const osc52Disposable = term.parser.registerOscHandler(52, (data) => {
+      const idx = data.indexOf(";");
+      if (idx === -1) return false;
+      const payload = data.substring(idx + 1);
+      if (payload === "?") return false; // clipboard read request, not supported
+      try {
+        const decoded = atob(payload);
+        navigator.clipboard.writeText(decoded).catch((e) =>
+          console.error("OSC 52 clipboard write failed:", e),
+        );
+      } catch (e) {
+        console.error("OSC 52 decode failed:", e);
+      }
+      return true;
+    });
+
     // Handle user input -> backend
     const inputDisposable = term.onData((data) => {
       sendInput(sessionId, data);
@@ -170,6 +189,7 @@ export default function TerminalView({ sessionId, active }: Props) {
       aborted = true;
       detector.dispose();
       detectorRef.current = null;
+      osc52Disposable.dispose();
       inputDisposable.dispose();
       scrollDisposable.dispose();
       containerRef.current?.removeEventListener("paste", handlePaste, { capture: true });

app/src/components/terminal/osc52.test.ts

@@ -0,0 +1,59 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+/**
+ * Tests the OSC 52 clipboard parsing logic used in TerminalView.
+ * Extracted here to validate the decode/write path independently.
+ */
+
+// Mirrors the handler registered in TerminalView.tsx
+function handleOsc52(data: string): string | null {
+  const idx = data.indexOf(";");
+  if (idx === -1) return null;
+  const payload = data.substring(idx + 1);
+  if (payload === "?") return null;
+  try {
+    return atob(payload);
+  } catch {
+    return null;
+  }
+}
+
+describe("OSC 52 clipboard handler", () => {
+  it("decodes a valid clipboard write sequence", () => {
+    // "c;BASE64" where BASE64 encodes "https://example.com"
+    const encoded = btoa("https://example.com");
+    const result = handleOsc52(`c;${encoded}`);
+    expect(result).toBe("https://example.com");
+  });
+
+  it("decodes multi-line content", () => {
+    const text = "line1\nline2\nline3";
+    const encoded = btoa(text);
+    const result = handleOsc52(`c;${encoded}`);
+    expect(result).toBe(text);
+  });
+
+  it("handles primary selection target (p)", () => {
+    const encoded = btoa("selected text");
+    const result = handleOsc52(`p;${encoded}`);
+    expect(result).toBe("selected text");
+  });
+
+  it("returns null for clipboard read request (?)", () => {
+    expect(handleOsc52("c;?")).toBe(null);
+  });
+
+  it("returns null for missing semicolon", () => {
+    expect(handleOsc52("invalid")).toBe(null);
+  });
+
+  it("returns null for invalid base64", () => {
+    expect(handleOsc52("c;!!!not-base64!!!")).toBe(null);
+  });
+
+  it("handles empty payload after selection target", () => {
+    // btoa("") = ""
+    const result = handleOsc52("c;");
+    expect(result).toBe("");
+  });
+});