feat(deno): migrate mvt/ Bun → Deno (Class A, standards#253 longtail) (#53)

## Summary

Class A — pure-Deno port. The only Bun-specific code was
`mvt/src/server.js` (35 lines, `Bun.serve` + `Bun.file` + `Bun.env`)
plus the `mvt/package.json` Bun-runner scripts.

## Changes

1. **`mvt/deno.json`** (new) — Deno-native tasks for
`test`/`test:watch`/`serve`/`dev` + fmt/lint config.
2. **`mvt/src/server.js`** — Bun → Deno API port:
   - `Bun.env.PORT` → `Deno.env.get("PORT")`
   - `Bun.serve({port, fetch})` → `Deno.serve({port}, fetch)`
- `Bun.file(url).exists() + new Response(file)` → `await
Deno.readFile(url)` with `Deno.errors.NotFound` catch (idiomatic Deno
file-serve)
3. **`mvt/package.json`** (deleted) — was Bun-only, no deps; just `bun
test` + `bun src/server.js` scripts.

Tests use `node:test` + `node:assert/strict`, both supported by Deno
natively without flags — no test-file changes needed.

The path-traversal guard (`fileUrl.pathname.startsWith(root.pathname)`)
is preserved unchanged.

## Test plan

- [ ] `deno task test` runs the public-goods kernel test suite (uses
`node:test` which Deno supports natively)
- [ ] `deno task serve` starts the static server on port 5173 (default)
or `$PORT`
- [ ] `curl http://localhost:5173/` returns the UI index.html
- [ ] `curl http://localhost:5173/../etc/passwd` returns 403
(path-traversal guard intact)

Per per-repo follow-up tracker for standards#253 (campaign closed
2026-05-31, longtail tracked in
`project_estate_npm_to_deno_2026_05_28.md`).

Refs hyperpolymath/standards#253.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

mvt/deno.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://deno.land/x/deno/cli/schemas/config-file.v1.json",
+  "name": "@hyperpolymath/econosphere-mvt",
+  "version": "0.1.0",
+  "license": "MPL-2.0",
+  "tasks": {
+    "test": "deno test --allow-read tests/kernel/",
+    "test:watch": "deno test --watch --allow-read tests/kernel/",
+    "serve": "deno run --allow-net --allow-read --allow-env src/server.js",
+    "dev": "deno run --watch --allow-net --allow-read --allow-env src/server.js"
+  },
+  "fmt": {
+    "useTabs": false,
+    "lineWidth": 100,
+    "indentWidth": 2,
+    "singleQuote": false
+  },
+  "lint": {
+    "rules": {
+      "tags": ["recommended"]
+    }
+  }
+}

mvt/package.json

@@ -1,4 +1,4 @@
-const port = Number(Bun.env.PORT ?? 5173);
+const port = Number(Deno.env.get("PORT") ?? 5173);
 const root = new URL("../", import.meta.url);
 
 const contentTypes = {
@@ -9,26 +9,26 @@ const contentTypes = {
   ".md": "text/markdown; charset=utf-8"
 };
 
-Bun.serve({
-  port,
-  async fetch(request) {
-    const url = new URL(request.url);
-    const pathname = url.pathname === "/" ? "/src/ui/index.html" : url.pathname;
-    const fileUrl = new URL(`.${pathname}`, root);
+Deno.serve({ port }, async (request) => {
+  const url = new URL(request.url);
+  const pathname = url.pathname === "/" ? "/src/ui/index.html" : url.pathname;
+  const fileUrl = new URL(`.${pathname}`, root);
 
-    if (!fileUrl.pathname.startsWith(root.pathname)) {
-      return new Response("Forbidden", { status: 403 });
-    }
-
-    const file = Bun.file(fileUrl);
-    if (!(await file.exists())) {
-      return new Response("Not found", { status: 404 });
-    }
+  if (!fileUrl.pathname.startsWith(root.pathname)) {
+    return new Response("Forbidden", { status: 403 });
+  }
 
+  try {
+    const file = await Deno.readFile(fileUrl);
     const extension = fileUrl.pathname.slice(fileUrl.pathname.lastIndexOf("."));
     return new Response(file, {
       headers: { "content-type": contentTypes[extension] ?? "application/octet-stream" }
     });
+  } catch (err) {
+    if (err instanceof Deno.errors.NotFound) {
+      return new Response("Not found", { status: 404 });
+    }
+    throw err;
   }
 });