diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b947077
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+node_modules/
+dist/
diff --git a/openclaw.plugin.json b/openclaw.plugin.json
new file mode 100644
index 0000000..0fd8a2b
--- /dev/null
+++ b/openclaw.plugin.json
@@ -0,0 +1,20 @@
+{
+  "id": "prism-facet",
+  "name": "PrismFacet",
+  "version": "0.1.0",
+  "description": "Dynamic system prompt injection via routers and rules",
+  "main": "dist/index.js",
+  "configSchema": {
+    "type": "object",
+    "properties": {
+      "routersDir": {
+        "type": "string",
+        "description": "Directory containing router .ts/.js files (default: {pluginDir}/routers)"
+      },
+      "rulesFile": {
+        "type": "string",
+        "description": "Path to rules.json (default: {pluginDir}/rules.json)"
+      }
+    }
+  }
+}
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..bfdc61b
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,47 @@
+{
+  "name": "prism-facet",
+  "version": "0.1.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "prism-facet",
+      "version": "0.1.0",
+      "devDependencies": {
+        "@types/node": "^25.6.0",
+        "typescript": "^5.5.0"
+      }
+    },
+    "node_modules/@types/node": {
+      "version": "25.6.0",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-25.6.0.tgz",
+      "integrity": "sha512-+qIYRKdNYJwY3vRCZMdJbPLJAtGjQBudzZzdzwQYkEPQd+PJGixUL5QfvCLDaULoLv+RhT3LDkwEfKaAkgSmNQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "undici-types": "~7.19.0"
+      }
+    },
+    "node_modules/typescript": {
+      "version": "5.9.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
+      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    },
+    "node_modules/undici-types": {
+      "version": "7.19.2",
+      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-7.19.2.tgz",
+      "integrity": "sha512-qYVnV5OEm2AW8cJMCpdV20CDyaN3g0AjDlOGf1OW4iaDEx8MwdtChUp4zu4H0VP3nDRF/8RKWH+IPp9uW0YGZg==",
+      "dev": true,
+      "license": "MIT"
+    }
+  }
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..b7e9960
--- /dev/null
+++ b/package.json
@@ -0,0 +1,14 @@
+{
+  "name": "prism-facet",
+  "version": "0.1.0",
+  "type": "module",
+  "main": "dist/index.js",
+  "scripts": {
+    "build": "tsc",
+    "watch": "tsc --watch"
+  },
+  "devDependencies": {
+    "@types/node": "^25.6.0",
+    "typescript": "^5.5.0"
+  }
+}
diff --git a/routers/agent-id.js b/routers/agent-id.js
new file mode 100644
index 0000000..5576d47
--- /dev/null
+++ b/routers/agent-id.js
@@ -0,0 +1,4 @@
+// Zero-dependency router: returns agentId directly
+export function resolve(ctx) {
+  return ctx.agentId || "";
+}
diff --git a/routers/position.js b/routers/position.js
new file mode 100644
index 0000000..732671c
--- /dev/null
+++ b/routers/position.js
@@ -0,0 +1,14 @@
+// Reads agent position from ego.json (optional dependency on PaddedCell/ego-mgr)
+import { readFileSync } from "node:fs";
+import { homedir } from "node:os";
+
+const EGO_PATH = `${homedir()}/.openclaw/ego.json`;
+
+export function resolve(ctx) {
+  try {
+    const ego = JSON.parse(readFileSync(EGO_PATH, "utf8"));
+    return ego["agent-scope"]?.[ctx.agentId]?.position || "";
+  } catch {
+    return "";
+  }
+}
diff --git a/routers/role.js b/routers/role.js
new file mode 100644
index 0000000..e6f79d1
--- /dev/null
+++ b/routers/role.js
@@ -0,0 +1,14 @@
+// Reads agent role from ego.json (optional dependency on PaddedCell/ego-mgr)
+import { readFileSync } from "node:fs";
+import { homedir } from "node:os";
+
+const EGO_PATH = `${homedir()}/.openclaw/ego.json`;
+
+export function resolve(ctx) {
+  try {
+    const ego = JSON.parse(readFileSync(EGO_PATH, "utf8"));
+    return ego["agent-scope"]?.[ctx.agentId]?.role || "";
+  } catch {
+    return "";
+  }
+}
diff --git a/rules.json b/rules.json
new file mode 100644
index 0000000..9e26dfe
--- /dev/null
+++ b/rules.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 0000000..57b5a57
--- /dev/null
+++ b/src/index.ts
@@ -0,0 +1,38 @@
+import path from "node:path";
+import { loadRouters } from "./router-loader.js";
+import { initRuleStore } from "./rule-store.js";
+import { resolveInjection } from "./prompt-injector.js";
+import { registerTools } from "./tools.js";
+import type { PluginApi, PluginConfig } from "./types.js";
+
+export function register(api: PluginApi, config?: PluginConfig) {
+  const pluginDir = path.dirname(new URL(import.meta.url).pathname);
+  const routersDir = config?.routersDir || path.resolve(pluginDir, "..", "routers");
+  const rulesFile = config?.rulesFile || path.resolve(pluginDir, "..", "rules.json");
+
+  api.logger.info(`[prism-facet] initializing (routers: ${routersDir}, rules: ${rulesFile})`);
+
+  // Initialize rule store
+  initRuleStore(rulesFile);
+
+  // Load routers
+  loadRouters(routersDir, api.logger).catch((err) => {
+    api.logger.error(`[prism-facet] failed to load routers: ${String(err)}`);
+  });
+
+  // Register before_prompt_build hook
+  api.on("before_prompt_build", async (_event: unknown, ctx: { agentId?: string }) => {
+    const agentId = ctx.agentId || "";
+    if (!agentId) return;
+
+    const result = await resolveInjection({ agentId }, api.logger);
+    if (result.appendSystemContext) {
+      return { appendSystemContext: result.appendSystemContext };
+    }
+  });
+
+  // Register MCP tools
+  registerTools(api, routersDir);
+
+  api.logger.info("[prism-facet] plugin registered");
+}
diff --git a/src/prompt-injector.ts b/src/prompt-injector.ts
new file mode 100644
index 0000000..f92ab68
--- /dev/null
+++ b/src/prompt-injector.ts
@@ -0,0 +1,44 @@
+import { readFileSync } from "node:fs";
+import { getRouters } from "./router-loader.js";
+import { getRulesForRouter } from "./rule-store.js";
+import type { RouterContext } from "./types.js";
+
+export interface InjectionResult {
+  appendSystemContext?: string;
+}
+
+export async function resolveInjection(
+  ctx: RouterContext,
+  logger: { info: (msg: string) => void; warn: (msg: string) => void }
+): Promise<InjectionResult> {
+  const routers = getRouters();
+  const segments: string[] = [];
+
+  for (const router of routers) {
+    try {
+      const key = await router.module.resolve(ctx);
+      if (!key) continue;
+
+      const promptFile = getRulesForRouter(router.name, key);
+      if (!promptFile) continue;
+
+      try {
+        const content = readFileSync(promptFile, "utf8").trim();
+        if (content) {
+          segments.push(content);
+          logger.info(`injecting ${router.name}:${key} → ${promptFile}`);
+        }
+      } catch (err) {
+        logger.warn(`failed to read prompt file ${promptFile}: ${String(err)}`);
+      }
+    } catch (err) {
+      logger.warn(`router ${router.name} failed: ${String(err)}`);
+    }
+  }
+
+  if (segments.length === 0) return {};
+
+  return {
+    appendSystemContext: segments.join("\n\n---\n\n"),
+  };
+}
diff --git a/src/router-loader.ts b/src/router-loader.ts
new file mode 100644
index 0000000..2d3dc73
--- /dev/null
+++ b/src/router-loader.ts
@@ -0,0 +1,53 @@
+import { readdirSync } from "node:fs";
+import path from "node:path";
+import type { LoadedRouter, RouterModule } from "./types.js";
+
+const loadedRouters: Map<string, LoadedRouter> = new Map();
+let loadCounter = 0;
+
+function routerNameFromFile(filename: string): string {
+  return filename.replace(/\.(ts|js|mjs)$/, "");
+}
+
+export async function loadRouters(
+  routersDir: string,
+  logger: { info: (msg: string) => void; warn: (msg: string) => void }
+): Promise<void> {
+  loadedRouters.clear();
+  loadCounter++;
+
+  let files: string[];
+  try {
+    files = readdirSync(routersDir).filter((f) =>
+      /\.(ts|js|mjs)$/.test(f) && !f.startsWith(".")
+    );
+  } catch {
+    logger.warn(`routers directory not found: ${routersDir}`);
+    return;
+  }
+
+  for (const file of files) {
+    const name = routerNameFromFile(file);
+    const filePath = path.resolve(routersDir, file);
+    try {
+      // Cache-bust: append query param so Node re-imports the module
+      const mod = (await import(`${filePath}?v=${loadCounter}`)) as RouterModule;
+      if (typeof mod.resolve !== "function") {
+        logger.warn(`router ${name}: no resolve() export, skipping`);
+        continue;
+      }
+      loadedRouters.set(name, { name, filePath, module: mod });
+      logger.info(`router loaded: ${name}`);
+    } catch (err) {
+      logger.warn(`router ${name}: failed to load — ${String(err)}`);
+    }
+  }
+}
+
+export function getRouters(): LoadedRouter[] {
+  return Array.from(loadedRouters.values());
+}
+
+export function getRouterNames(): string[] {
+  return Array.from(loadedRouters.keys());
+}
diff --git a/src/rule-store.ts b/src/rule-store.ts
new file mode 100644
index 0000000..3c277fd
--- /dev/null
+++ b/src/rule-store.ts
@@ -0,0 +1,45 @@
+import { readFileSync, writeFileSync } from "node:fs";
+import type { RuleStore } from "./types.js";
+
+let rules: RuleStore = {};
+let rulesFilePath = "";
+
+export function initRuleStore(filePath: string): void {
+  rulesFilePath = filePath;
+  try {
+    const raw = readFileSync(filePath, "utf8");
+    rules = JSON.parse(raw) as RuleStore;
+  } catch {
+    rules = {};
+  }
+}
+
+function save(): void {
+  if (!rulesFilePath) return;
+  writeFileSync(rulesFilePath, JSON.stringify(rules, null, 2) + "\n", "utf8");
+}
+
+export function addRule(router: string, key: string, promptFile: string): void {
+  rules[`${router}:${key}`] = promptFile;
+  save();
+}
+
+export function removeRule(router: string, key: string): boolean {
+  const ruleKey = `${router}:${key}`;
+  if (!(ruleKey in rules)) return false;
+  delete rules[ruleKey];
+  save();
+  return true;
+}
+
+export function getRule(router: string, key: string): string | undefined {
+  return rules[`${router}:${key}`];
+}
+
+export function listRules(): Record<string, string> {
+  return { ...rules };
+}
+
+export function getRulesForRouter(router: string, key: string): string | undefined {
+  return rules[`${router}:${key}`];
+}
diff --git a/src/tools.ts b/src/tools.ts
new file mode 100644
index 0000000..22274b8
--- /dev/null
+++ b/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}`;
+      }
+    },
+  });
+}
diff --git a/src/types.ts b/src/types.ts
new file mode 100644
index 0000000..e92398a
--- /dev/null
+++ b/src/types.ts
@@ -0,0 +1,32 @@
+export interface RouterContext {
+  agentId: string;
+}
+
+export interface RouterModule {
+  resolve(ctx: RouterContext): string | Promise<string>;
+}
+
+export interface LoadedRouter {
+  name: string;
+  filePath: string;
+  module: RouterModule;
+}
+
+export interface RuleStore {
+  [ruleKey: string]: string; // "router:key" → prompt file path
+}
+
+export interface PluginApi {
+  logger: {
+    info(msg: string): void;
+    warn(msg: string): void;
+    error(msg: string): void;
+  };
+  on(hook: string, handler: (...args: any[]) => any): void;
+  registerTool(def: any): void;
+}
+
+export interface PluginConfig {
+  routersDir?: string;
+  rulesFile?: string;
+}
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..16ca579
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "outDir": "dist",
+    "rootDir": "src",
+    "declaration": true,
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true
+  },
+  "include": ["src/**/*"]
+}