fix(gateway): init memory store for flush agent

[r266-tech]

Summary

Fixes #6157 — the gateway pre-reset memory flush created a temporary AIAgent with skip_memory=True, which prevented _memory_store from being initialised. Since the memory tool was still in enabled_toolsets, the model could call it but every call returned "Memory is not available." — making the flush path completely non-functional for all messaging platform sessions (Telegram, Discord, Matrix, etc.).

Changes

• gateway/run.py: skip_memory=True → skip_memory=False (1 line)
• tests/gateway/test_flush_memory_store.py: AST-based regression test that verifies skip_memory=False in the flush agent constructor

Root cause

tmp_agent = AIAgent(
    ...
    skip_memory=True,   # ← prevents _memory_store initialization
    enabled_toolsets=["memory", "skills"],  # ← memory tool IS available
)

When skip_memory=True, run_agent.py:977-992 skips MemoryStore(...) creation, leaving _memory_store = None. The memory tool at memory_tool.py:452 then returns an error on every call.

Test plan

• Regression test passes (pytest tests/gateway/test_flush_memory_store.py)
• Manual: trigger a session reset on a messaging platform, verify memory flush produces writes

[teknium1]

Thanks for the careful investigation and fix, @r266-tech! The root cause you identified was real at the time.

This is an automated hermes-sweeper review.

Unfortunately this PR is now obsolete:

• Commit ea01bdceb (merged Apr 25 2026, refactor(memory): remove flush_memories entirely #15696) removed the entire flush_memories subsystem from main — GatewayRunner._flush_memories_for_session, _async_flush_memories, AIAgent.flush_memories(), and all call sites in gateway/run.py, run_agent.py, and cli.py were deleted.
• The bug this PR fixes (skip_memory=True on the flush agent) can no longer occur because the flush code path no longer exists.
• grep -rn '_flush_memories\|flush_memories' gateway/ returns no results on current main.
• The test file this PR adds (tests/gateway/test_flush_memory_store.py) does not exist on main and would be testing a removed feature.

The underlying concern (memory extraction on session reset) is now handled by the background memory review loop, which runs every 10 turns on both CLI and gateway without the blocking/cache-invalidating flush approach. Closing as superseded.