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/signal/monitor/event-handler.ts

@@ -19,7 +19,7 @@ import { finalizeInboundContext } from "../../auto-reply/reply/inbound-context.j
 import { createReplyDispatcherWithTyping } from "../../auto-reply/reply/reply-dispatcher.js";
 import { resolveControlCommandGate } from "../../channels/command-gating.js";
 import { logInboundDrop, logTypingFailure } 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 { readSessionUpdatedAt, resolveStorePath } from "../../config/sessions.js";
@@ -171,7 +171,12 @@ export function createSignalEventHandler(deps: SignalEventHandlerDeps) {
       logVerbose(`signal inbound: from=${ctxPayload.From} len=${body.length} preview="${preview}"`);
     }
 
-    const prefixContext = createReplyPrefixContext({ cfg: deps.cfg, agentId: route.agentId });
+    const { onModelSelected, ...prefixOptions } = createReplyPrefixOptions({
+      cfg: deps.cfg,
+      agentId: route.agentId,
+      channel: "signal",
+      accountId: route.accountId,
+    });
 
     const typingCallbacks = createTypingCallbacks({
       start: async () => {
@@ -195,8 +200,7 @@ export function createSignalEventHandler(deps: SignalEventHandlerDeps) {
     });
 
     const { dispatcher, replyOptions, markDispatchIdle } = createReplyDispatcherWithTyping({
-      responsePrefix: prefixContext.responsePrefix,
-      responsePrefixContextProvider: prefixContext.responsePrefixContextProvider,
+      ...prefixOptions,
       humanDelay: resolveHumanDelayConfig(deps.cfg, route.agentId),
       deliver: async (payload) => {
         await deps.deliverReplies({
@@ -224,9 +228,7 @@ export function createSignalEventHandler(deps: SignalEventHandlerDeps) {
         ...replyOptions,
         disableBlockStreaming:
           typeof deps.blockStreaming === "boolean" ? !deps.blockStreaming : undefined,
-        onModelSelected: (ctx) => {
-          prefixContext.onModelSelected(ctx);
-        },
+        onModelSelected,
       },
     });
     markDispatchIdle();