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

@@ -20,7 +20,7 @@ import {
   shouldAckReaction as shouldAckReactionGate,
 } from "../../channels/ack-reactions.js";
 import { logTypingFailure, logAckFailure } from "../../channels/logging.js";
-import { createReplyPrefixContext } from "../../channels/reply-prefix.js";
+import { createReplyPrefixOptions } from "../../channels/reply-prefix.js";
 import { recordInboundSession } from "../../channels/session.js";
 import { createTypingCallbacks } from "../../channels/typing.js";
 import { resolveMarkdownTableMode } from "../../config/markdown-tables.js";
@@ -334,7 +334,12 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
     ? deliverTarget.slice("channel:".length)
     : message.channelId;
 
-  const prefixContext = createReplyPrefixContext({ cfg, agentId: route.agentId });
+  const { onModelSelected, ...prefixOptions } = createReplyPrefixOptions({
+    cfg,
+    agentId: route.agentId,
+    channel: "discord",
+    accountId: route.accountId,
+  });
   const tableMode = resolveMarkdownTableMode({
     cfg,
     channel: "discord",
@@ -342,8 +347,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
   });
 
   const { dispatcher, replyOptions, markDispatchIdle } = createReplyDispatcherWithTyping({
-    responsePrefix: prefixContext.responsePrefix,
-    responsePrefixContextProvider: prefixContext.responsePrefixContextProvider,
+    ...prefixOptions,
     humanDelay: resolveHumanDelayConfig(cfg, route.agentId),
     deliver: async (payload: ReplyPayload) => {
       const replyToId = replyReference.use();
@@ -389,9 +393,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
         typeof discordConfig?.blockStreaming === "boolean"
           ? !discordConfig.blockStreaming
           : undefined,
-      onModelSelected: (ctx) => {
-        prefixContext.onModelSelected(ctx);
-      },
+      onModelSelected,
     },
   });
   markDispatchIdle();