diff --git a/codex-cli/src/utils/get-diff.ts b/codex-cli/src/utils/get-diff.ts
index 348ee42c..9ac7844d 100644
--- a/codex-cli/src/utils/get-diff.ts
+++ b/codex-cli/src/utils/get-diff.ts
@@ -1,5 +1,26 @@
 import { execSync } from "node:child_process";
 
+// The objects thrown by `child_process.execSync()` are `Error` instances that
+// include additional, undocumented properties such as `status` (exit code) and
+// `stdout` (captured standard output). Declare a minimal interface that captures
+// just the fields we need so that we can avoid the use of `any` while keeping
+// the checks type-safe.
+interface ExecSyncError extends Error {
+  // Exit status code. When a diff is produced, git exits with code 1 which we
+  // treat as a non-error signal.
+  status?: number;
+  // Captured stdout. We rely on this to obtain the diff output when git exits
+  // with status 1.
+  stdout?: string;
+}
+
+// Type-guard that narrows an unknown value to `ExecSyncError`.
+function isExecSyncError(err: unknown): err is ExecSyncError {
+  return (
+    typeof err === "object" && err != null && "status" in err && "stdout" in err
+  );
+}
+
 /**
  * Returns the current Git diff for the working directory. If the current
  * working directory is not inside a Git repository, `isGitRepo` will be
@@ -15,13 +36,86 @@ export function getGitDiff(): {
     execSync("git rev-parse --is-inside-work-tree", { stdio: "ignore" });
 
     // If the above call didn’t throw, we are inside a git repo. Retrieve the
-    // diff including color codes so that the overlay can render them.
-    const output = execSync("git diff --color", {
-      encoding: "utf8",
-      maxBuffer: 10 * 1024 * 1024, // 10 MB ought to be enough for now
-    });
+    // diff for tracked files **and** include any untracked files so that the
+    // `/diff` overlay shows a complete picture of the working tree state.
 
-    return { isGitRepo: true, diff: output };
+    // 1. Diff for tracked files (unchanged behaviour)
+    let trackedDiff = "";
+    try {
+      trackedDiff = execSync("git diff --color", {
+        encoding: "utf8",
+        maxBuffer: 10 * 1024 * 1024, // 10 MB ought to be enough for now
+      });
+    } catch (err) {
+      // Exit status 1 simply means that differences were found. Capture the
+      // diff from stdout in that case. Re-throw for any other status codes.
+      if (
+        isExecSyncError(err) &&
+        err.status === 1 &&
+        typeof err.stdout === "string"
+      ) {
+        trackedDiff = err.stdout;
+      } else {
+        throw err;
+      }
+    }
+
+    // 2. Determine untracked files.
+    //    We use `git ls-files --others --exclude-standard` which outputs paths
+    //    relative to the repository root, one per line. These are files that
+    //    are not tracked *and* are not ignored by .gitignore.
+    const untrackedOutput = execSync(
+      "git ls-files --others --exclude-standard",
+      {
+        encoding: "utf8",
+        maxBuffer: 10 * 1024 * 1024,
+      },
+    );
+
+    const untrackedFiles = untrackedOutput
+      .split("\n")
+      .map((p) => p.trim())
+      .filter(Boolean);
+
+    let untrackedDiff = "";
+
+    const nullDevice = process.platform === "win32" ? "NUL" : "/dev/null";
+
+    for (const file of untrackedFiles) {
+      try {
+        // `git diff --no-index` produces a diff even outside the index by
+        // comparing two paths. We compare the file against /dev/null so that
+        // the file is treated as "new".
+        //
+        // `git diff --color --no-index /dev/null <file>` exits with status 1
+        // when differences are found, so we capture stdout from the thrown
+        // error object instead of letting it propagate.
+        execSync(`git diff --color --no-index -- "${nullDevice}" "${file}"`, {
+          encoding: "utf8",
+          stdio: ["ignore", "pipe", "ignore"],
+          maxBuffer: 10 * 1024 * 1024,
+        });
+      } catch (err) {
+        if (
+          isExecSyncError(err) &&
+          // Exit status 1 simply means that the two inputs differ, which is
+          // exactly what we expect here. Any other status code indicates a
+          // real error (e.g. the file disappeared between the ls-files and
+          // diff calls), so re-throw those.
+          err.status === 1 &&
+          typeof err.stdout === "string"
+        ) {
+          untrackedDiff += err.stdout;
+        } else {
+          throw err;
+        }
+      }
+    }
+
+    // Concatenate tracked and untracked diffs.
+    const combinedDiff = `${trackedDiff}${untrackedDiff}`;
+
+    return { isGitRepo: true, diff: combinedDiff };
   } catch {
     // Either git is not installed or we’re not inside a repository.
     return { isGitRepo: false, diff: "" };