feat: PrismFacet core implementation

- Plugin scaffold: manifest, tsconfig, package.json
- Router loader with dynamic import + cache busting for hot reload
- Rule store: CRUD on rules.json
- Prompt injector: resolve routers → match rules → read files → inject
- MCP tool: prompt_rules (add/remove/list/test/reload-routers/list-routers)
- Built-in routers: agent-id (zero-dep), role, position (ego.json)
- before_prompt_build hook for system prompt injection

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

src/tools.ts

@@ -0,0 +1,118 @@
+import { addRule, removeRule, listRules } from "./rule-store.js";
+import { loadRouters, getRouterNames } from "./router-loader.js";
+import { resolveInjection } from "./prompt-injector.js";
+import type { PluginApi } from "./types.js";
+
+export function registerTools(
+  api: PluginApi,
+  routersDir: string
+): void {
+  api.registerTool({
+    name: "prompt_rules",
+    description:
+      "Manage PrismFacet prompt injection rules. " +
+      "Actions: add (register a rule), remove (delete a rule), list (show all rules), " +
+      "test (preview which prompts would be injected for an agent), " +
+      "reload-routers (hot-reload all router functions), list-routers (show loaded routers).",
+    parameters: {
+      type: "object",
+      properties: {
+        action: {
+          type: "string",
+          enum: [
+            "add",
+            "remove",
+            "list",
+            "test",
+            "reload-routers",
+            "list-routers",
+          ],
+          description: "The action to perform",
+        },
+        router: {
+          type: "string",
+          description: "Router name (for add/remove)",
+        },
+        key: {
+          type: "string",
+          description: "Rule key (for add/remove)",
+        },
+        file: {
+          type: "string",
+          description: "Prompt file path (for add)",
+        },
+        agent: {
+          type: "string",
+          description: "Agent ID (for test)",
+        },
+      },
+      required: ["action"],
+    },
+    handler: async (params: {
+      action: string;
+      router?: string;
+      key?: string;
+      file?: string;
+      agent?: string;
+    }) => {
+      switch (params.action) {
+        case "add": {
+          if (!params.router || !params.key || !params.file) {
+            return "Error: add requires --router, --key, and --file";
+          }
+          addRule(params.router, params.key, params.file);
+          return `Rule added: ${params.router}:${params.key} → ${params.file}`;
+        }
+
+        case "remove": {
+          if (!params.router || !params.key) {
+            return "Error: remove requires --router and --key";
+          }
+          const removed = removeRule(params.router, params.key);
+          return removed
+            ? `Rule removed: ${params.router}:${params.key}`
+            : `Rule not found: ${params.router}:${params.key}`;
+        }
+
+        case "list": {
+          const rules = listRules();
+          const entries = Object.entries(rules);
+          if (entries.length === 0) return "No rules registered.";
+          return entries
+            .map(([k, v]) => `${k} → ${v}`)
+            .join("\n");
+        }
+
+        case "test": {
+          if (!params.agent) {
+            return "Error: test requires --agent";
+          }
+          const result = await resolveInjection(
+            { agentId: params.agent },
+            api.logger
+          );
+          if (!result.appendSystemContext) {
+            return `No prompts matched for agent: ${params.agent}`;
+          }
+          return `Matched prompts for ${params.agent}:\n\n${result.appendSystemContext}`;
+        }
+
+        case "reload-routers": {
+          await loadRouters(routersDir, api.logger);
+          const names = getRouterNames();
+          return `Routers reloaded: ${names.join(", ") || "(none)"}`;
+        }
+
+        case "list-routers": {
+          const names = getRouterNames();
+          return names.length > 0
+            ? `Loaded routers: ${names.join(", ")}`
+            : "No routers loaded.";
+        }
+
+        default:
+          return `Unknown action: ${params.action}`;
+      }
+    },
+  });
+}