fix(openclaw): prevent memory wipe on every session

[slayoffer]

Summary

• Fix memory loss bug: Use unique document_id per conversation (sessionKey + timestamp) instead of static sessionKey. The backend CASCADE-deletes old memories when the same document_id is reused, causing all prior facts to be lost on every new conversation.
• Universal envelope stripping: Replace Telegram-only [Telegram ...] extraction with generic channel support (Slack, Discord, WhatsApp, Signal, etc.) for cleaner recall queries.
• Prefer rawMessage: Use event.rawMessage over event.prompt when available to avoid envelope-formatted prompts.
• Increase recall context: Bump max_tokens from 512 to 2048 for richer memory injection.

Root Cause

The agent_end hook retained transcripts with document_id set to the static sessionKey (always agent:main:main). The backend's handle_document_tracking() does DELETE FROM documents WHERE id = $1 AND bank_id = $2 with CASCADE before inserting — wiping ALL previous memory_units and entity_links tied to that document. Every conversation replaced the previous one.

Test plan

• Build: cd hindsight-integrations/openclaw && npm run build
• Send 3 separate messages to bot via Telegram
• Ask "what do you remember about me?" — should recall facts from all 3 conversations
• Check logs: each retain should show a different document ID (e.g., agent:main:main-1739083800000)

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