Summary

Fixes the root cause of per-turn agent eviction that causes memory provider bridges to spawn on every message (issue #20939).

Two independent bugs in the gateway agent cache were causing the cached AIAgent (and its MemoryProvider) to be destroyed and recreated on every turn instead of persisting across messages:

1. Model normalization mismatch — _agent.model (normalized by AIAgent.__init__) never matched _cfg_model (raw gateway config with vendor prefix), so the eviction check at ~L13131 fired every turn.
2. Session signature instability — was_auto_reset notice and message_id were feeding into the cache signature hash, causing it to flip between turns.

Root Cause Details

1. Model Normalization Mismatch

gateway/run.py ~L13131 compares the cached agent's model against the gateway config model to decide whether to evict:

• _agent.model = "deepseek-v4-pro" (normalized by AIAgent.__init__ via normalize_model_for_provider)
• _cfg_model = "deepseek/deepseek-v4-pro" (raw gateway config, vendor-prefixed)

"deepseek-v4-pro" != "deepseek/deepseek-v4-pro" → _evict_cached_agent() → AIAgent destroyed → MemoryProvider destroyed → next turn creates fresh MemoryProvider → initialize() → new bridge pair. Every. Single. Turn.

Fix: Normalize _cfg_model using the same normalize_model_for_provider() function that AIAgent.__init__ uses, before the equality check.

2. Session Signature Instability

Even after the model fix, the cache signature was flip-flopping (ec05b8ea → 67f721c3 → f3d18768 → 67f721c3). Two unstable inputs were feeding the sig hash:

• was_auto_reset notice was prepended to context_prompt, which feeds into the sig hash. Being a one-turn transient flag, it flipped the sig on the first post-restart turn, then back.
• message_id was in the Discord IDs block in build_session_context_prompt(). Per-message value would change the sig every turn.

Fix: Decouple the reset notice from context_prompt (inject into combined_ephemeral after sig is computed). Remove message_id from the context prompt.

Results (live gateway, ~16 hour burn-in)

# Bridge processes: 8 (4 sessions × 2 processes)
# Before fix: 60-100 bridges/day

# Cache log — 20+ consecutive HITs overnight:
04:56  CACHE HIT (sig=155bc36b)  Sanctuary
05:21  CACHE HIT (sig=155bc36b)
05:42  CACHE HIT (sig=155bc36b)
...
06:33  CACHE HIT (sig=155bc36b)
06:35  CACHE HIT (sig=155bc36b)

# Zero "CACHE MISS: sig changed" lines since the fix.
# Signature stable across all sessions.

Commits

Related

• Closes [Bug]: MemOS memory provider spawns new bridge.cts process on every turn instead of once per session #20939 (MemOS bridge spawns per turn)
• Complementary to PR fix: guard memory provider initialize() against repeated calls (#20939) #20961 — that PR adds an idempotency guard at the MemoryProvider layer (belt); this PR fixes the root cause of unnecessary agent evictions at the gateway layer (suspenders). Both should be applied.