feat: per-channel responsePrefix override (#9001)

* feat: per-channel responsePrefix override

Add responsePrefix field to all channel config types and Zod schemas,
enabling per-channel and per-account outbound response prefix overrides.

Resolution cascade (most specific wins):
  L1: channels.<ch>.accounts.<id>.responsePrefix
  L2: channels.<ch>.responsePrefix
  L3: (reserved for channels.defaults)
  L4: messages.responsePrefix (existing global)

Semantics:
  - undefined -> inherit from parent level
  - empty string -> explicitly no prefix (stops cascade)
  - "auto" -> derive [identity.name] from routed agent

Changes:
  - Core logic: resolveResponsePrefix() in identity.ts accepts
    optional channel/accountId and walks the cascade
  - resolveEffectiveMessagesConfig() passes channel context through
  - Types: responsePrefix added to WhatsApp, Telegram, Discord, Slack,
    Signal, iMessage, Google Chat, MS Teams, Feishu, BlueBubbles configs
  - Zod schemas: responsePrefix added for config validation
  - All channel handlers wired: telegram, discord, slack, signal,
    imessage, line, heartbeat runner, route-reply, native commands
  - 23 new tests covering backward compat, channel/account levels,
    full cascade, auto keyword, empty string stops, unknown fallthrough

Fully backward compatible - no existing config is affected.
Fixes #8857

* fix: address CI lint + review feedback

- Replace Record<string, any> with proper typed helpers (no-explicit-any)
- Add curly braces to single-line if returns (eslint curly)
- Fix JSDoc: 'Per-channel' → 'channel/account' on shared config types
- Extract getChannelConfig() helper for type-safe dynamic key access

* fix: finish responsePrefix overrides (#9001) (thanks @mudrii)

* fix: normalize prefix wiring and types (#9001) (thanks @mudrii)

---------

Co-authored-by: Gustavo Madeira Santana <gumadeiras@gmail.com>

src/gateway/server-methods/chat.ts

@@ -5,15 +5,11 @@ import path from "node:path";
 import type { MsgContext } from "../../auto-reply/templating.js";
 import type { GatewayRequestContext, GatewayRequestHandlers } from "./types.js";
 import { resolveSessionAgentId } from "../../agents/agent-scope.js";
-import { resolveEffectiveMessagesConfig, resolveIdentityName } from "../../agents/identity.js";
 import { resolveThinkingDefault } from "../../agents/model-selection.js";
 import { resolveAgentTimeoutMs } from "../../agents/timeout.js";
 import { dispatchInboundMessage } from "../../auto-reply/dispatch.js";
 import { createReplyDispatcher } from "../../auto-reply/reply/reply-dispatcher.js";
-import {
-  extractShortModelName,
-  type ResponsePrefixContext,
-} from "../../auto-reply/reply/response-prefix-template.js";
+import { createReplyPrefixOptions } from "../../channels/reply-prefix.js";
 import { resolveSendPolicy } from "../../sessions/send-policy.js";
 import { INTERNAL_MESSAGE_CHANNEL } from "../../utils/message-channel.js";
 import {
@@ -477,13 +473,14 @@ export const chatHandlers: GatewayRequestHandlers = {
         sessionKey: p.sessionKey,
         config: cfg,
       });
-      let prefixContext: ResponsePrefixContext = {
-        identityName: resolveIdentityName(cfg, agentId),
-      };
+      const { onModelSelected, ...prefixOptions } = createReplyPrefixOptions({
+        cfg,
+        agentId,
+        channel: INTERNAL_MESSAGE_CHANNEL,
+      });
       const finalReplyParts: string[] = [];
       const dispatcher = createReplyDispatcher({
-        responsePrefix: resolveEffectiveMessagesConfig(cfg, agentId).responsePrefix,
-        responsePrefixContextProvider: () => prefixContext,
+        ...prefixOptions,
         onError: (err) => {
           context.logGateway.warn(`webchat dispatch failed: ${formatForLog(err)}`);
         },
@@ -512,12 +509,7 @@ export const chatHandlers: GatewayRequestHandlers = {
           onAgentRunStart: () => {
             agentRunStarted = true;
           },
-          onModelSelected: (ctx) => {
-            prefixContext.provider = ctx.provider;
-            prefixContext.model = extractShortModelName(ctx.model);
-            prefixContext.modelFull = `${ctx.provider}/${ctx.model}`;
-            prefixContext.thinkingLevel = ctx.thinkLevel ?? "off";
-          },
+          onModelSelected,
         },
       })
         .then(() => {