diff --git a/CHANGELOG.md b/CHANGELOG.md
index 602c43f..2b7e86a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 ## Unreleased
 
+- Gateway (#144): sender allowlists and the gateway toolset are one
+  `GatewayPolicy`, built from config at startup (`src/gateway/access.ts`).
+  Platform adapters declare `capabilities` (`{ kind: "text", max_reply_chars }`);
+  the runner logs them. **Breaking for custom adapters:** `PlatformAdapter`
+  requires `capabilities`, and `create_idle_adapter` takes it as a third
+  argument.
 - Gateway (#144): conversations queue on the shared `SessionManager` instead of
   their own promise chains. Beyond `max_conversations`, the least recently used
   conversation is evicted (it was the oldest inserted). Only Telegram's `/start`
diff --git a/docs/architecture/extending.md b/docs/architecture/extending.md
index eb82bf6..0b07753 100644
--- a/docs/architecture/extending.md
+++ b/docs/architecture/extending.md
@@ -156,16 +156,23 @@ A platform adapter is an implementation of the `PlatformAdapter` contract
 ```ts
 export interface PlatformAdapter {
   readonly name: string;
+  readonly capabilities: AdapterCapabilities; // { kind: "text", max_reply_chars?: number }
   start(): Promise<void>;
   stop(): Promise<void>;
 }
 ```
 
+`capabilities` declares what the adapter can deliver. Every platform today is
+`kind: "text"` (one plain reply per message); set `max_reply_chars` to the
+platform's message cap and split replies to it. The runner logs it at start.
+
 Inbound flow: the adapter normalizes a platform event into
 `(platform, chat_id, user_id, text)` and calls `run_inbound_message` with the
-shared `InboundHandler`; the handler is the bus's `handle`, which resolves to
-the reply text; the adapter then sends the reply through the platform's send
-API. The bus owns history, serialization, and error sanitization - adapters
+shared `InboundHandler`; the handler is the bus's `reply`, and
+`run_inbound_message` reduces its result to the reply text; the adapter then sends the reply through the platform's send
+API. The bus owns history, serialization, and error sanitization, and checks
+each sender against the `GatewayPolicy` built from config at startup
+(`src/gateway/access.ts`: allowlists plus the gateway toolset) - adapters
 stay thin.
 
 Recipe (mirroring [`telegram.ts`](../../src/gateway/telegram.ts), the
@@ -189,7 +196,7 @@ await send_reply(reply);
 
 3. **Handle missing credentials with the idle-adapter pattern.** When the
    platform's token env var is absent, return
-   `create_idle_adapter("platform", "ENV_VAR not set")` instead of throwing.
+   `create_idle_adapter("platform", "ENV_VAR not set", CAPABILITIES)` instead of throwing.
    The adapter logs once why it is idle and no-ops on start/stop, so the
    gateway keeps serving the platforms that *do* have credentials -
    `run_gateway` only needs one valid platform.
@@ -198,7 +205,7 @@ await send_reply(reply);
    structural `RawSocket` type works on both Bun and Node runtimes),
    `sanitize_agent_error` for reply strings on failure, and the whitespace
    splitter `split_text` from `src/gateway/format.ts` for size-capped
-   transports (telegram caps at 4096, discord at 2000, twitch at 512).
+   transports (telegram caps at 4096, discord at 2000, twitch at 450 to stay under its 500-char limit).
 
 **Testing.** `test/gateway.test.ts` covers the webhook adapter over a real
 `node:http` server (a `on_listening` test hook reports the bound port), the
diff --git a/src/gateway/access.ts b/src/gateway/access.ts
index 3533ccd..b852c3f 100644
--- a/src/gateway/access.ts
+++ b/src/gateway/access.ts
@@ -1,5 +1,7 @@
 /**
- * Gateway access: public-platform allowlists and the safe default toolset.
+ * Gateway access: public-platform allowlists and the safe default toolset,
+ * gathered into one GatewayPolicy built at startup (decision 0001: Profiles
+ * and Policy evolve from this file).
  */
 import type { AgentConfig } from "../agent/config.js";
 import { logger } from "../util/log.js";
@@ -42,6 +44,21 @@ export function is_gateway_sender_allowed(
   return user_ok && chat_ok;
 }
 
+/** What the gateway lets in and what its agent may use; built once from config. */
+export interface GatewayPolicy {
+  /** Tools the shared gateway agent registers. */
+  readonly tools_enabled: "all" | readonly string[];
+  /** True when the sender may talk to the agent; logs a denial. */
+  allows(platform: string, chat_id: string, user_id: string): boolean;
+}
+
+export function create_gateway_policy(config: AgentConfig): GatewayPolicy {
+  return {
+    tools_enabled: gateway_tools_enabled(config),
+    allows: (platform, chat_id, user_id) => check_gateway_sender(config, platform, chat_id, user_id),
+  };
+}
+
 /** Logs and returns false when the sender is not on the allowlist. */
 export function check_gateway_sender(
   config: AgentConfig,
diff --git a/src/gateway/bus.ts b/src/gateway/bus.ts
index 61e6573..9447650 100644
--- a/src/gateway/bus.ts
+++ b/src/gateway/bus.ts
@@ -12,7 +12,7 @@ import { history_after_run_error } from "../agent/loop.js";
 import type { Message } from "../providers/types.js";
 import { create_session_manager, type SessionManager } from "../session/manager.js";
 import { logger } from "../util/log.js";
-import { check_gateway_sender } from "./access.js";
+import { create_gateway_policy, type GatewayPolicy } from "./access.js";
 import { sanitize_agent_error, type GatewayReply } from "./types.js";
 
 export interface GatewayBusOptions {
@@ -22,6 +22,8 @@ export interface GatewayBusOptions {
 
 export interface BusParams {
   config: AgentConfig;
+  /** Who may talk to the agent; defaults to `create_gateway_policy(config)`. */
+  policy?: GatewayPolicy;
   agent_factory: () => Agent;
   /** Subscribe to agent tool events for debug logging (creates the agent). */
   wire_tool_logging?: boolean;
@@ -31,7 +33,7 @@ const DEFAULT_HISTORY_CAP = 40;
 const DEFAULT_MAX_CONVERSATIONS = 200;
 
 export class GatewayBus {
-  private readonly config: AgentConfig;
+  private readonly policy: GatewayPolicy;
   private readonly agent_factory: () => Agent;
   private agent: Agent | undefined;
   private readonly histories: Map<string, Message[]> = new Map();
@@ -41,7 +43,7 @@ export class GatewayBus {
   private stop_logging: (() => void) | undefined;
 
   constructor(params: BusParams, options?: GatewayBusOptions) {
-    this.config = params.config;
+    this.policy = params.policy ?? create_gateway_policy(params.config);
     this.agent_factory = params.agent_factory;
     this.history_cap = options?.history_cap ?? DEFAULT_HISTORY_CAP;
     this.max_conversations = options?.max_conversations ?? DEFAULT_MAX_CONVERSATIONS;
@@ -58,7 +60,7 @@ export class GatewayBus {
 
   /** Like `handle`, with the run's usage and whether it failed; undefined when the sender is denied. */
   async reply(platform: string, chat_id: string, user_id: string, text: string): Promise<GatewayReply | undefined> {
-    if (check_gateway_sender(this.config, platform, chat_id, user_id) === false) {
+    if (this.policy.allows(platform, chat_id, user_id) === false) {
       return undefined;
     }
     const key = conversation_key(platform, chat_id);
diff --git a/src/gateway/discord.ts b/src/gateway/discord.ts
index 2e84949..d0dcb92 100644
--- a/src/gateway/discord.ts
+++ b/src/gateway/discord.ts
@@ -7,13 +7,15 @@ import { logger } from "../util/log.js";
 import { sleep } from "../util/sleep.js";
 import { platform_token_env, read_platform_token } from "./token_env.js";
 import type { AdapterParams, PlatformAdapter, RawSocket } from "./types.js";
-import { create_idle_adapter, open_socket, run_inbound_message } from "./types.js";
+import { create_idle_adapter, open_socket, run_inbound_message, type AdapterCapabilities } from "./types.js";
 
 const DISCORD_API = "https://discord.com/api/v10";
 const GATEWAY_URL = "wss://gateway.discord.gg/?v=10&encoding=json";
 /** Guild messages + message content + direct messages. */
 const INTENTS = 512 | 32768 | 4096;
 export const DISCORD_BACKOFF_MS = [5000, 10000, 20000, 30000] as const;
+export const DISCORD_MAX_MESSAGE_CHARS = 2000;
+export const DISCORD_CAPABILITIES: AdapterCapabilities = { kind: "text", max_reply_chars: DISCORD_MAX_MESSAGE_CHARS };
 /** Auth / sharding / API-version failures — reconnecting cannot recover. */
 const DISCORD_FATAL_CLOSE = new Set([4004, 4010, 4011, 4012, 4013, 4014]);
 /** Live heartbeat timers keyed by socket, cleared when the session ends. */
@@ -41,13 +43,14 @@ interface DiscordSessionState {
 export function create_discord_adapter(params: AdapterParams): PlatformAdapter {
   const token = read_platform_token(params.config, "discord");
   if (token === undefined) {
-    return create_idle_adapter("discord", `${platform_token_env(params.config, "discord")} not set`);
+    return create_idle_adapter("discord", `${platform_token_env(params.config, "discord")} not set`, DISCORD_CAPABILITIES);
   }
   let running = false;
   let socket: RawSocket | undefined;
   let stop_controller = new AbortController();
   return {
     name: "discord",
+    capabilities: DISCORD_CAPABILITIES,
     start: async () => {
       running = true;
       stop_controller = new AbortController();
@@ -226,7 +229,7 @@ async function rest_send_message(params: AdapterParams, channel_id: string, text
   if (token === undefined || channel_id === "") {
     return;
   }
-  for (const chunk of split_chunks(text, 2000)) {
+  for (const chunk of split_chunks(text, DISCORD_MAX_MESSAGE_CHARS)) {
     const response = await fetch(`${DISCORD_API}/channels/${channel_id}/messages`, {
       method: "POST",
       headers: { authorization: `Bot ${token}`, "content-type": "application/json" },
diff --git a/src/gateway/runner.ts b/src/gateway/runner.ts
index 298abe5..8cb3653 100644
--- a/src/gateway/runner.ts
+++ b/src/gateway/runner.ts
@@ -5,7 +5,7 @@
 import { create_agent_with_plugins, type Agent } from "../agent/agent.js";
 import type { AgentConfig } from "../agent/config.js";
 import { logger } from "../util/log.js";
-import { gateway_tools_enabled } from "./access.js";
+import { create_gateway_policy } from "./access.js";
 import { GatewayBus } from "./bus.js";
 import { create_discord_adapter } from "./discord.js";
 import { create_telegram_adapter } from "./telegram.js";
@@ -15,9 +15,10 @@ import { create_webhook_adapter } from "./webhook.js";
 
 /** Preload plugins, then hand that same agent to the bus factory. */
 export async function create_gateway_bus(config: AgentConfig): Promise<{ agent: Agent; bus: GatewayBus }> {
-  const agent_config = { ...config, tools_enabled: gateway_tools_enabled(config) };
+  const policy = create_gateway_policy(config);
+  const agent_config = { ...config, tools_enabled: policy.tools_enabled };
   const agent = await create_agent_with_plugins(agent_config);
-  const bus = new GatewayBus({ config, agent_factory: () => agent, wire_tool_logging: true });
+  const bus = new GatewayBus({ config, policy, agent_factory: () => agent, wire_tool_logging: true });
   return { agent, bus };
 }
 
@@ -102,7 +103,8 @@ async function start_all_adapters(adapters: readonly PlatformAdapter[]): Promise
   for (const adapter of adapters) {
     try {
       await adapter.start();
-      logger.info(`gateway adapter started: ${adapter.name}`);
+      const cap = adapter.capabilities.max_reply_chars;
+      logger.info(`gateway adapter started: ${adapter.name} (${adapter.capabilities.kind}${cap === undefined ? "" : `, replies split at ${cap} chars`})`);
     } catch (error) {
       logger.error(`gateway adapter failed to start: ${adapter.name}`, error);
     }
diff --git a/src/gateway/telegram.ts b/src/gateway/telegram.ts
index e7ffe9a..28465fc 100644
--- a/src/gateway/telegram.ts
+++ b/src/gateway/telegram.ts
@@ -7,9 +7,10 @@ import { sleep } from "../util/sleep.js";
 import { logger } from "../util/log.js";
 import { platform_token_env, read_platform_token } from "./token_env.js";
 import type { AdapterParams, PlatformAdapter } from "./types.js";
-import { create_idle_adapter, run_inbound_message } from "./types.js";
+import { create_idle_adapter, run_inbound_message, type AdapterCapabilities } from "./types.js";
 
 export const TELEGRAM_MAX_MESSAGE_CHARS = 4096;
+export const TELEGRAM_CAPABILITIES: AdapterCapabilities = { kind: "text", max_reply_chars: TELEGRAM_MAX_MESSAGE_CHARS };
 
 interface TelegramUpdate {
   update_id?: number;
@@ -25,11 +26,12 @@ export const TELEGRAM_BACKOFF_MS = [2000, 4000, 8000, 16000, 30000] as const;
 export function create_telegram_adapter(params: AdapterParams): PlatformAdapter {
   const token = read_platform_token(params.config, "telegram");
   if (token === undefined) {
-    return create_idle_adapter("telegram", `${platform_token_env(params.config, "telegram")} not set`);
+    return create_idle_adapter("telegram", `${platform_token_env(params.config, "telegram")} not set`, TELEGRAM_CAPABILITIES);
   }
   let running = false;
   return {
     name: "telegram",
+    capabilities: TELEGRAM_CAPABILITIES,
     start: async () => {
       running = true;
       void poll_loop(params, token, () => running);
diff --git a/src/gateway/twitch.ts b/src/gateway/twitch.ts
index d4ceb51..38501a9 100644
--- a/src/gateway/twitch.ts
+++ b/src/gateway/twitch.ts
@@ -8,11 +8,12 @@ import { logger } from "../util/log.js";
 import { sleep } from "../util/sleep.js";
 import { platform_token_env, read_platform_token } from "./token_env.js";
 import type { AdapterParams, PlatformAdapter, RawSocket } from "./types.js";
-import { create_idle_adapter, open_socket, run_inbound_message } from "./types.js";
+import { create_idle_adapter, open_socket, run_inbound_message, type AdapterCapabilities } from "./types.js";
 
 export const TWITCH_IRC_URL = "wss://irc-ws.chat.twitch.tv:443";
 /** Content budget under Twitch's 500-char message / 512-byte IRC line caps. */
 export const TWITCH_MESSAGE_CAP = 450;
+export const TWITCH_CAPABILITIES: AdapterCapabilities = { kind: "text", max_reply_chars: TWITCH_MESSAGE_CAP };
 export const TWITCH_BACKOFF_MS = [5000, 10000, 20000, 30000] as const;
 const TWITCH_CHUNK_GAP_MS = 1600;
 
@@ -34,13 +35,14 @@ export function create_twitch_adapter(params: AdapterParams): PlatformAdapter {
   if (twitch === undefined) {
     const token_env = platform_token_env(params.config, "twitch");
     const reason = token_env === "LICH_TWITCH_OAUTH_TOKEN" ? "LICH_TWITCH_OAUTH_TOKEN / NICK not set" : `${token_env} / LICH_TWITCH_NICK not set`;
-    return create_idle_adapter("twitch", reason);
+    return create_idle_adapter("twitch", reason, TWITCH_CAPABILITIES);
   }
   let running = false;
   let socket: RawSocket | undefined;
   let stop_controller = new AbortController();
   return {
     name: "twitch",
+    capabilities: TWITCH_CAPABILITIES,
     start: async () => {
       running = true;
       stop_controller = new AbortController();
diff --git a/src/gateway/types.ts b/src/gateway/types.ts
index f2b20cd..d8bfae2 100644
--- a/src/gateway/types.ts
+++ b/src/gateway/types.ts
@@ -23,9 +23,20 @@ export interface ReplySink {
   send(text: string): Promise<void>;
 }
 
+/**
+ * What an adapter can deliver (decision 0001: adapters declare capabilities).
+ * Every platform adapter today is "text": a plain reply per message, split
+ * into chunks of at most `max_reply_chars` when the platform caps length.
+ */
+export interface AdapterCapabilities {
+  readonly kind: "text";
+  readonly max_reply_chars?: number;
+}
+
 /** Lifecycle contract implemented by every platform adapter. */
 export interface PlatformAdapter {
   readonly name: string;
+  readonly capabilities: AdapterCapabilities;
   start(): Promise<void>;
   stop(): Promise<void>;
 }
@@ -81,10 +92,11 @@ export function sanitize_agent_error(error: unknown): string {
 }
 
 /** Adapter that logs why it is idle once and otherwise does nothing. */
-export function create_idle_adapter(name: string, reason: string): PlatformAdapter {
+export function create_idle_adapter(name: string, reason: string, capabilities: AdapterCapabilities): PlatformAdapter {
   logger.warn(`gateway ${name} adapter idle: ${reason}`);
   return {
     name,
+    capabilities,
     start: async () => undefined,
     stop: async () => undefined,
   };
diff --git a/src/gateway/webhook.ts b/src/gateway/webhook.ts
index fafb775..b1ba21d 100644
--- a/src/gateway/webhook.ts
+++ b/src/gateway/webhook.ts
@@ -35,6 +35,8 @@ export function create_webhook_adapter(params: WebhookAdapterParams): PlatformAd
 
   return {
     name: "webhook",
+    // One JSON reply per request; no length cap.
+    capabilities: { kind: "text" },
     start: async () => {
       assert_bind_allowed(host, token);
       server = createServer((request, response) => {
diff --git a/test/gateway.test.ts b/test/gateway.test.ts
index c56c261..79d3166 100644
--- a/test/gateway.test.ts
+++ b/test/gateway.test.ts
@@ -4,15 +4,20 @@
  * No real network to telegram/discord/twitch — webhook binds an ephemeral
  * port (0) on loopback only.
  */
-import { afterEach, describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { mkdirSync, mkdtempSync, rmSync } from "node:fs";
 import { join } from "node:path";
 import { parse_agent_config } from "../src/agent/config.js";
 import {
+  create_gateway_policy,
   DEFAULT_GATEWAY_TOOLS_ENABLED,
   gateway_tools_enabled,
   is_gateway_sender_allowed,
+  type GatewayPolicy,
 } from "../src/gateway/access.js";
+import { create_discord_adapter } from "../src/gateway/discord.js";
+import { create_twitch_adapter } from "../src/gateway/twitch.js";
+import { logger } from "../src/util/log.js";
 import { assert_bind_allowed, create_webhook_adapter, MAX_WEBHOOK_BODY_BYTES } from "../src/gateway/webhook.js";
 import { format_agent_reply, split_text } from "../src/gateway/format.js";
 import { create_telegram_adapter } from "../src/gateway/telegram.js";
@@ -607,6 +612,60 @@ describe("gateway access", () => {
       rmSync(work_dir, { recursive: true, force: true });
     }
   });
+
+  it("builds one GatewayPolicy from config: toolset plus the sender allowlists", () => {
+    const work_dir = temp_work_dir();
+    try {
+      const policy = create_gateway_policy(config_for(work_dir, { allowed_users: { discord: ["u1"] } }));
+      expect(policy.tools_enabled).toEqual([...DEFAULT_GATEWAY_TOOLS_ENABLED]);
+      expect(policy.allows("webhook", "c", "anyone")).toBe(true);
+      expect(policy.allows("discord", "c", "u1")).toBe(true);
+      expect(policy.allows("discord", "c", "u2")).toBe(false);
+      expect(policy.allows("telegram", "c", "u1")).toBe(false);
+    } finally {
+      rmSync(work_dir, { recursive: true, force: true });
+    }
+  });
+
+  it("lets the bus use an injected policy instead of the config's", async () => {
+    const work_dir = temp_work_dir();
+    try {
+      const records: RunRecord[] = [];
+      const deny_all: GatewayPolicy = { tools_enabled: [], allows: () => false };
+      const bus = new GatewayBus({ config: config_for(work_dir), policy: deny_all, agent_factory: () => recording_agent(records) });
+      expect(await bus.handle("webhook", "c1", "u1", "hello")).toBeUndefined();
+      expect(records).toEqual([]);
+    } finally {
+      rmSync(work_dir, { recursive: true, force: true });
+    }
+  });
+});
+
+describe("adapter capabilities", () => {
+  it("declares each platform's reply cap, also on idle adapters", () => {
+    const saved = { ...process.env };
+    for (const key of ["LICH_TELEGRAM_BOT_TOKEN", "LICH_DISCORD_BOT_TOKEN", "LICH_TWITCH_OAUTH_TOKEN", "LICH_TWITCH_NICK"]) {
+      delete process.env[key];
+    }
+    const params = {
+      config: parse_agent_config({ providers: [{ kind: "openai_compat", name: "m", model: "x" }] }),
+      handle_message: async () => "",
+      get_agent: (): Agent => {
+        throw new Error("not used");
+      },
+      reply_router: () => undefined,
+    };
+    vi.spyOn(logger, "warn").mockImplementation(() => undefined);
+    try {
+      expect(create_telegram_adapter(params).capabilities).toEqual({ kind: "text", max_reply_chars: 4096 });
+      expect(create_discord_adapter(params).capabilities).toEqual({ kind: "text", max_reply_chars: 2000 });
+      expect(create_twitch_adapter(params).capabilities).toEqual({ kind: "text", max_reply_chars: TWITCH_MESSAGE_CAP });
+      expect(create_webhook_adapter({ ...params, port: 0, host: "127.0.0.1" }).capabilities).toEqual({ kind: "text" });
+    } finally {
+      vi.restoreAllMocks();
+      process.env = saved;
+    }
+  });
 });
 
 describe("webhook adapter", () => {
diff --git a/test/gateway_shutdown.test.ts b/test/gateway_shutdown.test.ts
index 2802e43..a6a835f 100644
--- a/test/gateway_shutdown.test.ts
+++ b/test/gateway_shutdown.test.ts
@@ -22,11 +22,13 @@ describe("shutdown_gateway", () => {
     const { agent, bus } = tracked(order);
     const slow: PlatformAdapter = {
       name: "slow",
+      capabilities: { kind: "text" },
       start: async () => undefined,
       stop: () => new Promise((resolve) => setTimeout(() => resolve(order.push("slow.stop") as unknown as void), 20)),
     };
     const broken: PlatformAdapter = {
       name: "broken",
+      capabilities: { kind: "text" },
       start: async () => undefined,
       stop: async () => {
         throw new Error("socket gone");
@@ -41,7 +43,7 @@ describe("shutdown_gateway", () => {
   it("stops waiting after the timeout when an adapter hangs", async () => {
     const order: string[] = [];
     const { agent, bus } = tracked(order);
-    const hung: PlatformAdapter = { name: "hung", start: async () => undefined, stop: () => new Promise(() => undefined) };
+    const hung: PlatformAdapter = { name: "hung", capabilities: { kind: "text" }, start: async () => undefined, stop: () => new Promise(() => undefined) };
     const warn = vi.spyOn(logger, "warn").mockImplementation(() => undefined);
     await shutdown_gateway(agent, bus, [hung], 20);
     expect(order).toEqual(["bus.stop", "agent.close"]);