add(plugin): mcp-server-dev — skills for building MCP servers

Three skills guiding developers through MCP server design:
- build-mcp-server: entry-point decision guide (remote HTTP vs MCPB vs local)
- build-mcp-app: interactive UI widgets rendered in chat
- build-mcpb: bundled local servers with runtime

Includes reference files for scaffolds, tool design, auth (DCR/CIMD),
widget templates, manifest schema, and local security hardening.

plugins/mcp-server-dev/skills/build-mcpb/references/manifest-schema.md

@@ -0,0 +1,132 @@
+# MCPB Manifest Schema
+
+Every `.mcpb` bundle has a `manifest.json` at its root. The host validates it before install.
+
+---
+
+## Top-level fields
+
+| Field | Type | Required | Notes |
+|---|---|---|---|
+| `name` | string | ✅ | Unique identifier. Lowercase, hyphens only. Shown in settings. |
+| `version` | string | ✅ | Semver. Host compares for update prompts. |
+| `description` | string | ✅ | One line. Shown in the install prompt. |
+| `entry` | object | ✅ | How to launch the server — see below. |
+| `permissions` | object | ✅ | What the server needs — see below. |
+| `config` | object | — | User-settable values surfaced in settings UI. |
+| `icon` | string | — | Path to PNG inside the bundle. 256×256 recommended. |
+| `homepage` | string | — | URL shown in settings. |
+| `minHostVersion` | string | — | Refuse install on older hosts. |
+
+---
+
+## `entry`
+
+```json
+{ "type": "node", "main": "server/index.js" }
+```
+
+| `type` | `main` points at | Runtime resolution |
+|---|---|---|
+| `node` | `.js` or `.mjs` file | `runtime/node` if present, else host-bundled Node |
+| `python` | `.py` file | `runtime/python` if present, else host-bundled Python |
+| `binary` | executable | Run directly. Must be built per-platform. |
+
+**`args`** (optional array) — extra argv passed to the entry. Rarely needed.
+
+**`env`** (optional object) — static env vars set at launch. For user-configurable values use `config` instead.
+
+---
+
+## `permissions`
+
+```json
+{
+  "filesystem": { "read": true, "write": false },
+  "network": { "allow": ["localhost:*", "127.0.0.1:*"] },
+  "process": { "spawn": false }
+}
+```
+
+### `filesystem`
+
+| Value | Meaning |
+|---|---|
+| `false` or omitted | No filesystem access beyond the bundle itself |
+| `{ "read": true }` | Read anywhere the OS user can |
+| `{ "read": true, "write": true }` | Read and write |
+
+There's no path scoping at the manifest level — scope in your code. The manifest permission is a coarse consent gate, not a sandbox.
+
+### `network`
+
+| Value | Meaning |
+|---|---|
+| `false` or omitted | No network (most local-first servers) |
+| `{ "allow": ["host:port", ...] }` | Allowlisted destinations. `*` wildcards ports. |
+| `true` | Unrestricted. Heavy scrutiny — explain why in `description`. |
+
+### `process`
+
+| Value | Meaning |
+|---|---|
+| `false` or omitted | Can't spawn child processes |
+| `{ "spawn": true }` | Can spawn. Needed for wrapping CLIs. |
+| `{ "spawn": true, "allow": ["git", "ffmpeg"] }` | Spawn only allowlisted binaries |
+
+---
+
+## `config`
+
+User-editable settings, surfaced in the host UI. Each key becomes an env var: `MCPB_CONFIG_<UPPERCASE_KEY>`.
+
+```json
+{
+  "config": {
+    "rootDir": {
+      "type": "string",
+      "description": "Directory to expose",
+      "default": "~/Documents"
+    },
+    "maxFileSize": {
+      "type": "number",
+      "description": "Skip files larger than this (MB)",
+      "default": 10,
+      "min": 1,
+      "max": 500
+    },
+    "includeHidden": {
+      "type": "boolean",
+      "description": "Include dotfiles in listings",
+      "default": false
+    },
+    "apiKey": {
+      "type": "string",
+      "description": "Optional API key for the sync feature",
+      "secret": true
+    }
+  }
+}
+```
+
+**`type`** — `string`, `number`, `boolean`. Enums: use `string` with `"enum": ["a", "b", "c"]`.
+
+**`secret: true`** — host masks the value in UI and stores it in the OS keychain instead of a plain config file.
+
+**`required: true`** — host blocks server launch until the user sets it. Use sparingly — a server that won't start until configured is a bad first-run experience.
+
+---
+
+## Minimal valid manifest
+
+```json
+{
+  "name": "hello",
+  "version": "0.1.0",
+  "description": "Minimal MCPB server.",
+  "entry": { "type": "node", "main": "server/index.js" },
+  "permissions": {}
+}
+```
+
+Empty `permissions` means no filesystem, no network, no spawn — pure computation only. Valid, if unusual.