Fix browser eval CLI output

CLI/cmux.swift

@@ -2007,6 +2007,27 @@ struct CMUXCLI {
             }
         }
 
+        func displayBrowserValue(_ value: Any) -> String {
+            if value is NSNull {
+                return "null"
+            }
+            if let string = value as? String {
+                return string
+            }
+            if let bool = value as? Bool {
+                return bool ? "true" : "false"
+            }
+            if let number = value as? NSNumber {
+                return number.stringValue
+            }
+            if JSONSerialization.isValidJSONObject(value),
+               let data = try? JSONSerialization.data(withJSONObject: value, options: [.prettyPrinted]),
+               let text = String(data: data, encoding: .utf8) {
+                return text
+            }
+            return String(describing: value)
+        }
+
         func nonFlagArgs(_ values: [String]) -> [String] {
             values.filter { !$0.hasPrefix("-") }
         }
@@ -2174,7 +2195,13 @@ struct CMUXCLI {
                 throw CLIError(message: "browser eval requires a script")
             }
             let payload = try client.sendV2(method: "browser.eval", params: ["surface_id": sid, "script": trimmed])
-            output(payload, fallback: "OK")
+            let fallback: String
+            if let value = payload["value"] {
+                fallback = displayBrowserValue(value)
+            } else {
+                fallback = "OK"
+            }
+            output(payload, fallback: fallback)
             return
         }
 

tests/test_browser_eval_cli_output_regression.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+"""Static regression guard for browser eval CLI output formatting.
+
+Ensures `cmux browser <surface> eval <script>` prints the evaluated value
+instead of always printing `OK`.
+"""
+
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+
+
+def repo_root() -> Path:
+    result = subprocess.run(
+        ["git", "rev-parse", "--show-toplevel"],
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode == 0:
+        return Path(result.stdout.strip())
+    return Path(__file__).resolve().parents[1]
+
+
+def extract_block(source: str, signature: str) -> str:
+    start = source.find(signature)
+    if start < 0:
+        raise ValueError(f"Missing signature: {signature}")
+    brace_start = source.find("{", start)
+    if brace_start < 0:
+        raise ValueError(f"Missing opening brace for: {signature}")
+    depth = 0
+    for idx in range(brace_start, len(source)):
+        char = source[idx]
+        if char == "{":
+            depth += 1
+        elif char == "}":
+            depth -= 1
+            if depth == 0:
+                return source[brace_start : idx + 1]
+    raise ValueError(f"Unbalanced braces for: {signature}")
+
+
+def main() -> int:
+    root = repo_root()
+    failures: list[str] = []
+
+    cli_path = root / "CLI" / "cmux.swift"
+    cli_source = cli_path.read_text(encoding="utf-8")
+    browser_block = extract_block(cli_source, "private func runBrowserCommand(")
+
+    if "func displayBrowserValue(_ value: Any) -> String" not in browser_block:
+        failures.append("runBrowserCommand() is missing displayBrowserValue() helper")
+    else:
+        value_block = extract_block(browser_block, "func displayBrowserValue(_ value: Any) -> String")
+        required_guards = [
+            "if value is NSNull",
+            "if let string = value as? String",
+            "if let bool = value as? Bool",
+            "if let number = value as? NSNumber",
+        ]
+        for guard in required_guards:
+            if guard not in value_block:
+                failures.append(f"displayBrowserValue() no longer handles: {guard}")
+
+    eval_block = extract_block(browser_block, 'if subcommand == "eval"')
+    if 'let payload = try client.sendV2(method: "browser.eval"' not in eval_block:
+        failures.append("browser eval path no longer calls browser.eval v2 method")
+    if 'if let value = payload["value"]' not in eval_block:
+        failures.append("browser eval path no longer reads payload value")
+    if "fallback = displayBrowserValue(value)" not in eval_block:
+        failures.append("browser eval path no longer formats payload value for CLI output")
+    if 'output(payload, fallback: "OK")' in eval_block:
+        failures.append("browser eval path regressed to unconditional OK output")
+
+    if failures:
+        print("FAIL: browser eval CLI output regression guard failed")
+        for item in failures:
+            print(f" - {item}")
+        return 1
+
+    print("PASS: browser eval CLI output regression guard is in place")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())