Feature request: signal deletion / TTL for signals

[tablecik44-ship-it]

Summary

Signals (memory_signal_send / memory_signal_read) have no way to be deleted or expired. Over time, the signal store grows without bound, making it hard to find relevant messages.

Current behavior

• memory_signal_send creates signals
• memory_signal_read reads them (marks as read)
• No memory_signal_delete or TTL mechanism exists
• REST: GET /agentmemory/signals, POST /agentmemory/signals/send — no DELETE

Suggested solution

1. Signal deletion: Add memory_signal_delete(signalId) MCP tool + DELETE /agentmemory/signals/:id REST endpoint
2. TTL support: Add configurable TTL (e.g. AGENTMEMORY_SIGNAL_TTL_DAYS) that auto-expires read/old signals on read or via a cleanup job. Note: mem::signal-cleanup already exists in the engine but has no public endpoint.

Environment

• agentmemory v0.9.29
• iii-engine v0.11.2