feat: add /api/open-file route to reveal file in OS explorer

Supports Windows (explorer /select), macOS (open -R), and Linux
(xdg-open on parent dir). Modeled on existing /api/open-directory.

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

src/app/api/open-file/route.ts

@@ -0,0 +1,83 @@
+import { NextRequest, NextResponse } from "next/server";
+import { execFile } from "child_process";
+import { promisify } from "util";
+import { stat } from "fs/promises";
+import path from "path";
+import os from "os";
+
+const execFileAsync = promisify(execFile);
+
+export async function POST(req: NextRequest) {
+    try {
+        const body = await req.json();
+        const { filePath: inputPath } = body;
+
+        if (!inputPath || typeof inputPath !== "string") {
+            return NextResponse.json(
+                { success: false, error: "File path is required" },
+                { status: 400 }
+            );
+        }
+
+        // Normalize and resolve the path to prevent traversal attacks
+        const normalizedPath = path.resolve(inputPath);
+
+        // Validate that the path exists and is a file
+        try {
+            const stats = await stat(normalizedPath);
+            if (!stats.isFile()) {
+                return NextResponse.json(
+                    { success: false, error: "Path is not a file" },
+                    { status: 400 }
+                );
+            }
+        } catch {
+            return NextResponse.json(
+                { success: false, error: "File does not exist" },
+                { status: 400 }
+            );
+        }
+
+        const platform = os.platform();
+        let command = "";
+        let args: string[] = [];
+
+        switch (platform) {
+            case "darwin":
+                command = "open";
+                args = ["-R", normalizedPath];
+                break;
+            case "win32":
+                command = "explorer";
+                args = [`/select,${normalizedPath}`];
+                break;
+            case "linux":
+                // Linux has no universal "reveal in folder" — open parent directory
+                command = "xdg-open";
+                args = [path.dirname(normalizedPath)];
+                break;
+            default:
+                command = "xdg-open";
+                args = [path.dirname(normalizedPath)];
+        }
+
+        try {
+            await execFileAsync(command, args);
+        } catch (err: unknown) {
+            // Windows explorer returns non-zero exit code even on success
+            if (platform === "win32" && err && typeof err === "object" && "code" in err) {
+                // Explorer launched successfully despite non-zero exit
+            } else {
+                throw err;
+            }
+        }
+
+        return NextResponse.json({ success: true });
+    } catch (error) {
+        console.error("Failed to reveal file:", error);
+        return NextResponse.json(
+            { success: false, error: "Failed to open file location" },
+            { status: 500 }
+        );
+    }
+}