fix(memory): degrade gracefully after repeated at-capacity consolidation failures (#42405)

Builds on the zero-match feedback fix (previous commit) to close the silent-hang
symptom: when memory is at capacity, a failed `add`/`replace`/`remove`
consolidation could loop the whole turn to iteration-budget exhaustion and
deliver no user-facing reply.

#41755 turned the at-capacity overflow error into a *commanded* in-turn retry
("...then retry this add — all in this turn"); combined with the fragile
substring-only `replace`/`remove` matching (LLMs can't reliably re-quote a long
entry verbatim), the model loops add↔replace on inexact guesses until the turn
dies. The existing tool_guardrails halt would catch this, but hard_stop_enabled
is opt-in (off by default), so a default install still hangs.

This fixes it at the memory layer without changing global guardrail behavior:
- MemoryStore tracks per-turn consolidation failures; after a cap (3) it drops
  the "retry in this turn" instruction and returns a terminal "leave memory
  unchanged, continue your reply" result, so a failed memory side effect can
  never block the turn's reply.
- The counter resets on any successful write (progress) and at each turn
  boundary (turn_context.reset_consolidation_failures, guarded via getattr so
  plugin memory stores without the method are a no-op).

Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>

agent/turn_context.py

@@ -223,6 +223,9 @@ def build_turn_context(
     agent._unicode_sanitization_passes = 0
     agent._tool_guardrails.reset_for_turn()
     agent._tool_guardrail_halt_decision = None
+    _reset_consol = getattr(agent._memory_store, "reset_consolidation_failures", None)
+    if callable(_reset_consol):
+        _reset_consol()
     agent._vision_supported = True
 
     # Pre-turn connection health check: clean up dead TCP connections.