Bug Description

The resolveTarget() function in extensions/whatsapp/src/channel.ts has multiple code paths where it silently redirects outbound messages to allowList[0] instead of returning an error. This causes messages to be delivered to unintended WhatsApp conversations.

Steps to Reproduce

1. Configure WhatsApp with dmPolicy: "allowlist" and multiple conversations accessible
2. When the agent responds in implicit/heartbeat mode without an explicit target, messages may be delivered to the wrong conversation

Root Cause

There are 3-4 points in resolveTarget() where the function returns { ok: true, to: allowList[0] } as a fallback instead of { ok: false, error: ... }:

1. When the recipient cannot be normalized (implicit/heartbeat mode) — silently redirects to allowList[0]
2. When the normalized recipient is NOT in the allowList (implicit mode) — silently redirects to allowList[0]
3. When no recipient is specified — silently redirects to allowList[0]

Expected Behavior

In all three cases, the function should return { ok: false, error: "..." } instead of silently redirecting to a different recipient.

Affected Channels

The same pattern also exists in:

• extensions/twitch/src/channel.ts
• extensions/googlechat/src/channel.ts

Impact

Messages intended for one conversation are silently delivered to another, which is a privacy/security concern.

Workaround

Manually patching resolveTarget() to return { ok: false } in the fallback paths.