feat(discord): add channel-level model overrides

- Add `model?: string` field to DiscordGuildChannelConfig and DiscordGuildEntry
- Add corresponding Zod schema validation for the new fields
- Update allow-list resolved types to include model field
- Pass channelModelOverride through the reply dispatch chain
- Apply channel model override in model selection (falls back when no session override)
- Add /model-channel command to set/clear channel model via Discord

Priority chain: channel config → guild config → agent default

Closes #3742

src/auto-reply/commands-registry.data.ts

@@ -511,6 +511,20 @@ function buildChatCommands(): ChatCommandDefinition[] {
         },
       ],
     }),
+    defineChatCommand({
+      key: "model_channel",
+      nativeName: "model_channel",
+      description: "Set or clear the default model for this channel.",
+      textAlias: "/model-channel",
+      category: "options",
+      args: [
+        {
+          name: "model",
+          description: "Model id (provider/model or id), or 'clear' to remove override",
+          type: "string",
+        },
+      ],
+    }),
     defineChatCommand({
       key: "models",
       nativeName: "models",

src/auto-reply/reply/commands-core.ts

@@ -16,7 +16,7 @@ import {
 import { handleAllowlistCommand } from "./commands-allowlist.js";
 import { handleApproveCommand } from "./commands-approve.js";
 import { handleSubagentsCommand } from "./commands-subagents.js";
-import { handleModelsCommand } from "./commands-models.js";
+import { handleModelsCommand, handleModelChannelCommand } from "./commands-models.js";
 import { handleTtsCommands } from "./commands-tts.js";
 import {
   handleAbortTrigger,
@@ -53,6 +53,7 @@ const HANDLERS: CommandHandler[] = [
   handleConfigCommand,
   handleDebugCommand,
   handleModelsCommand,
+  handleModelChannelCommand,
   handleStopCommand,
   handleCompactCommand,
   handleAbortTrigger,

src/auto-reply/reply/commands-model-channel.ts

@@ -0,0 +1,149 @@
+import { loadConfig, writeConfigFile } from "../../config/config.js";
+import { resolveChannelConfigWrites } from "../../channels/plugins/config-writes.js";
+import { resolveModelRefFromString, buildModelAliasIndex } from "../../agents/model-selection.js";
+import { DEFAULT_MODEL, DEFAULT_PROVIDER } from "../../agents/defaults.js";
+import type { MoltbotConfig } from "../../config/config.js";
+import type { ReplyPayload } from "../types.js";
+import type { CommandHandler } from "./commands-types.js";
+
+export type ModelChannelCommandContext = {
+  cfg: MoltbotConfig;
+  commandBodyNormalized: string;
+  provider?: string;
+  surface?: string;
+  accountId?: string;
+  groupSpace?: string;
+  groupChannel?: string;
+  channelId?: string;
+  commandAuthorized?: boolean;
+};
+
+function extractChannelId(ctx: ModelChannelCommandContext): string | null {
+  // Try to extract channel ID from groupChannel (e.g., "#channel-name" -> id not available)
+  // or from channelId if passed directly
+  if (ctx.channelId) return ctx.channelId;
+
+  // For Discord, the channel ID is typically in the "To" field as "channel:<id>"
+  return null;
+}
+
+export async function resolveModelChannelCommandReply(
+  ctx: ModelChannelCommandContext,
+): Promise<ReplyPayload | null> {
+  const body = ctx.commandBodyNormalized.trim();
+  if (!body.startsWith("/model-channel") && !body.startsWith("/model_channel")) return null;
+
+  const surface = ctx.surface?.toLowerCase() ?? ctx.provider?.toLowerCase();
+
+  // Only supported for Discord guild channels
+  if (surface !== "discord") {
+    return {
+      text: "The /model-channel command is only available in Discord servers.",
+    };
+  }
+
+  if (!ctx.groupSpace) {
+    return {
+      text: "The /model-channel command can only be used in server channels, not DMs.",
+    };
+  }
+
+  // Check if config writes are enabled
+  if (
+    !resolveChannelConfigWrites({ cfg: ctx.cfg, channelId: "discord", accountId: ctx.accountId })
+  ) {
+    return {
+      text: "Config writes are disabled for this account. Enable `configWrites` in your Discord config to use this command.",
+    };
+  }
+
+  // Check authorization
+  if (ctx.commandAuthorized === false) {
+    return {
+      text: "You are not authorized to use this command.",
+    };
+  }
+
+  const argText = body.replace(/^\/model[-_]channel\b/i, "").trim();
+  const channelId = ctx.channelId;
+  const guildId = ctx.groupSpace;
+
+  if (!channelId) {
+    return {
+      text: "Could not determine the current channel. Please try again or specify the channel in your config directly.",
+    };
+  }
+
+  // Handle clear/reset
+  if (!argText || argText.toLowerCase() === "clear" || argText.toLowerCase() === "reset") {
+    const currentConfig = loadConfig();
+    const guildEntry = currentConfig.channels?.discord?.guilds?.[guildId];
+    const channelEntry = guildEntry?.channels?.[channelId];
+
+    if (!channelEntry?.model) {
+      return {
+        text: `No model override is set for this channel.`,
+      };
+    }
+
+    // Remove the model override
+    delete channelEntry.model;
+
+    // Clean up empty objects
+    if (Object.keys(channelEntry).length === 0 && guildEntry?.channels) {
+      delete guildEntry.channels[channelId];
+    }
+
+    await writeConfigFile(currentConfig);
+    return {
+      text: `Cleared model override for this channel. Messages will now use the guild or agent default model.`,
+    };
+  }
+
+  // Resolve the model reference
+  const aliasIndex = buildModelAliasIndex({
+    cfg: ctx.cfg,
+    defaultProvider: DEFAULT_PROVIDER,
+  });
+
+  const resolved = resolveModelRefFromString({
+    raw: argText,
+    defaultProvider: DEFAULT_PROVIDER,
+    aliasIndex,
+  });
+
+  if (!resolved) {
+    return {
+      text: `Unknown model "${argText}". Use /models to see available models.`,
+    };
+  }
+
+  const modelId = `${resolved.ref.provider}/${resolved.ref.model}`;
+
+  // Update the config
+  const currentConfig = loadConfig();
+
+  // Ensure the path exists
+  if (!currentConfig.channels) currentConfig.channels = {};
+  if (!currentConfig.channels.discord) currentConfig.channels.discord = {};
+  if (!currentConfig.channels.discord.guilds) currentConfig.channels.discord.guilds = {};
+  if (!currentConfig.channels.discord.guilds[guildId]) {
+    currentConfig.channels.discord.guilds[guildId] = {};
+  }
+  if (!currentConfig.channels.discord.guilds[guildId].channels) {
+    currentConfig.channels.discord.guilds[guildId].channels = {};
+  }
+  if (!currentConfig.channels.discord.guilds[guildId].channels[channelId]) {
+    currentConfig.channels.discord.guilds[guildId].channels[channelId] = {};
+  }
+
+  // Set the model
+  currentConfig.channels.discord.guilds[guildId].channels[channelId].model = modelId;
+
+  await writeConfigFile(currentConfig);
+
+  const displayModel = resolved.alias ? `${resolved.alias} (${modelId})` : modelId;
+  return {
+    text: `Set default model for this channel to **${displayModel}**. Use \`/model-channel clear\` to remove this override.`,
+  };
+}

src/auto-reply/reply/commands-models.ts

@@ -241,3 +241,35 @@ export const handleModelsCommand: CommandHandler = async (params, allowTextComma
   if (!reply) return null;
   return { reply, shouldContinue: false };
 };
+
+export const handleModelChannelCommand: CommandHandler = async (params, allowTextCommands) => {
+  if (!allowTextCommands) return null;
+
+  const { resolveModelChannelCommandReply } = await import("./commands-model-channel.js");
+  const reply = await resolveModelChannelCommandReply({
+    cfg: params.cfg,
+    commandBodyNormalized: params.command.commandBodyNormalized,
+    provider: params.ctx.Provider,
+    surface: params.ctx.Surface,
+    accountId: params.ctx.AccountId,
+    groupSpace: params.ctx.GroupSpace,
+    groupChannel: params.ctx.GroupChannel,
+    channelId: extractChannelIdFromTo(params.ctx.To),
+    commandAuthorized: params.command.isAuthorizedSender,
+  });
+  if (!reply) return null;
+  return { reply, shouldContinue: false };
+};
+
+function extractChannelIdFromTo(to?: string): string | undefined {
+  if (!to) return undefined;
+  // Handle "channel:<id>" format
+  if (to.startsWith("channel:")) {
+    return to.slice("channel:".length);
+  }
+  // Handle "discord:channel:<id>" format
+  if (to.startsWith("discord:channel:")) {
+    return to.slice("discord:channel:".length);
+  }
+  return undefined;
+}

src/auto-reply/reply/get-reply-directives.ts

@@ -106,6 +106,8 @@ export async function resolveReplyDirectives(params: {
   typing: TypingController;
   opts?: GetReplyOptions;
   skillFilter?: string[];
+  /** Channel-level model override (fallback when no session override). */
+  channelModelOverride?: string;
 }): Promise<ReplyDirectiveResult> {
   const {
     ctx,
@@ -386,6 +388,7 @@ export async function resolveReplyDirectives(params: {
     provider,
     model,
     hasModelDirective: directives.hasModelDirective,
+    channelModelOverride: params.channelModelOverride ?? opts?.channelModelOverride,
   });
   provider = modelState.provider;
   model = modelState.model;

src/auto-reply/reply/get-reply.ts

@@ -166,6 +166,7 @@ export async function getReplyFromConfig(
     typing,
     opts,
     skillFilter: opts?.skillFilter,
+    channelModelOverride: opts?.channelModelOverride,
   });
   if (directiveResult.kind === "reply") {
     return directiveResult.reply;

src/auto-reply/reply/model-selection.ts

@@ -231,6 +231,8 @@ export async function createModelSelectionState(params: {
   provider: string;
   model: string;
   hasModelDirective: boolean;
+  /** Channel-level model override (used as fallback when no session override). */
+  channelModelOverride?: string;
 }): Promise<ModelSelectionState> {
   const {
     cfg,
@@ -242,6 +244,7 @@ export async function createModelSelectionState(params: {
     storePath,
     defaultProvider,
     defaultModel,
+    channelModelOverride,
   } = params;
 
   let provider = params.provider;
@@ -310,6 +313,20 @@ export async function createModelSelectionState(params: {
       provider = candidateProvider;
       model = storedOverride.model;
     }
+  } else if (channelModelOverride?.trim()) {
+    // Apply channel-level model override as fallback when no session override exists.
+    const channelRef = resolveModelRefFromString({
+      raw: channelModelOverride.trim(),
+      defaultProvider,
+      aliasIndex: { byAlias: new Map(), byKey: new Map() },
+    });
+    if (channelRef) {
+      const key = modelKey(channelRef.ref.provider, channelRef.ref.model);
+      if (allowedModelKeys.size === 0 || allowedModelKeys.has(key)) {
+        provider = channelRef.ref.provider;
+        model = channelRef.ref.model;
+      }
+    }
   }
 
   if (sessionEntry && sessionStore && sessionKey && sessionEntry.authProfileOverride) {

src/auto-reply/types.ts

@@ -39,6 +39,8 @@ export type GetReplyOptions = {
   skillFilter?: string[];
   /** Mutable ref to track if a reply was sent (for Slack "first" threading mode). */
   hasRepliedRef?: { value: boolean };
+  /** Channel-level model override (fallback when no session override). */
+  channelModelOverride?: string;
 };
 
 export type ReplyPayload = {

src/config/types.discord.ts

@@ -37,6 +37,8 @@ export type DiscordGuildChannelConfig = {
   users?: Array<string | number>;
   /** Optional system prompt snippet for this channel. */
   systemPrompt?: string;
+  /** Optional model override for this channel. */
+  model?: string;
 };
 
 export type DiscordReactionNotificationMode = "off" | "own" | "all" | "allowlist";
@@ -51,6 +53,8 @@ export type DiscordGuildEntry = {
   reactionNotifications?: DiscordReactionNotificationMode;
   users?: Array<string | number>;
   channels?: Record<string, DiscordGuildChannelConfig>;
+  /** Optional model override for this guild. */
+  model?: string;
 };
 
 export type DiscordActionConfig = {

src/config/zod-schema.providers-core.ts

@@ -196,6 +196,7 @@ export const DiscordGuildChannelSchema = z
     users: z.array(z.union([z.string(), z.number()])).optional(),
     systemPrompt: z.string().optional(),
     autoThread: z.boolean().optional(),
+    model: z.string().optional(),
   })
   .strict();
 
@@ -208,6 +209,7 @@ export const DiscordGuildSchema = z
     reactionNotifications: z.enum(["off", "own", "all", "allowlist"]).optional(),
     users: z.array(z.union([z.string(), z.number()])).optional(),
     channels: z.record(z.string(), DiscordGuildChannelSchema.optional()).optional(),
+    model: z.string().optional(),
   })
   .strict();
 

src/discord/monitor/allow-list.ts

@@ -33,8 +33,10 @@ export type DiscordGuildEntryResolved = {
       users?: Array<string | number>;
       systemPrompt?: string;
       autoThread?: boolean;
+      model?: string;
     }
   >;
+  model?: string;
 };
 
 export type DiscordChannelConfigResolved = {
@@ -47,6 +49,7 @@ export type DiscordChannelConfigResolved = {
   autoThread?: boolean;
   matchKey?: string;
   matchSource?: ChannelMatchSource;
+  model?: string;
 };
 
 export function normalizeDiscordAllowList(
@@ -215,6 +218,7 @@ function resolveDiscordChannelConfigEntry(
     users: entry.users,
     systemPrompt: entry.systemPrompt,
     autoThread: entry.autoThread,
+    model: entry.model,
   };
   return resolved;
 }

src/discord/monitor/message-handler.process.ts

@@ -368,6 +368,9 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
     }).onReplyStart,
   });
 
+  // Resolve channel-level model override: channel config takes precedence over guild config.
+  const channelModelOverride = channelConfig?.model ?? guildInfo?.model;
+
   const { queuedFinal, counts } = await dispatchInboundMessage({
     ctx: ctxPayload,
     cfg,
@@ -382,6 +385,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
       onModelSelected: (ctx) => {
         prefixContext.onModelSelected(ctx);
       },
+      channelModelOverride,
     },
   });
   markDispatchIdle();