feat: add openclaw-plugin-dev skill

Plugin development reference and workflows based on real development
experience (Dirigent, ContractorAgent, PrismFacet).

Docs: structure, entry-point, hooks, tools, state, config, debugging
Workflows: create-plugin, add-hook

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

openclaw-plugin-dev/docs/state.md

@@ -0,0 +1,48 @@
+# State Management
+
+## Where to Store What
+
+| Data Type | Location | Reason |
+|-----------|----------|--------|
+| Business state (maps, sets, caches) | `globalThis` | Module vars reset on hot reload |
+| Event dedup (WeakSet/Set) | `globalThis` | Same |
+| Gateway lifecycle flags | `globalThis` | Prevent double init |
+| Connection flags (WebSocket/TCP) | `globalThis` | Prevent duplicate connections |
+| Runtime references | `globalThis` | Closures need living instance |
+| Cross-plugin API objects (`__pluginId`) | `globalThis` | Other plugins access via globalThis |
+| Pure utility functions | Module-level | No state needed |
+| Persistent data | File + memory cache | Survives gateway restart |
+
+## Cross-Plugin API Pattern
+
+### Provider side
+
+```typescript
+const _G = globalThis as Record<string, unknown>;
+
+// Init shared objects once
+if (!(_G["_myRegistry"] instanceof MyRegistry)) {
+  _G["_myRegistry"] = new MyRegistry();
+}
+
+// Overwrite public API every register() (updates closures)
+_G["__myPlugin"] = {
+  registry: _G["_myRegistry"],
+  send: (msg) => (_G["_myRuntime"] as Runtime)?.send(msg) ?? false,
+};
+```
+
+### Consumer side
+
+```typescript
+const provider = (globalThis as any)["__myPlugin"];
+if (!provider) {
+  console.error("[consumer] __myPlugin not found");
+  return;
+}
+provider.registry.register("my_rule", handler);
+```
+
+### Load Order
+
+Provider must be listed before consumer in `plugins.allow`. Consumer must defend against provider not being loaded.