fix: mem0 API v2 compat, prefetch context fencing, secret redaction (#5423)

Consolidated salvage from PRs #5301 (qaqcvc), #5339 (lance0),
#5058 and #5098 (maymuneth).

Mem0 API v2 compatibility (#5301):
- All reads use filters={user_id: ...} instead of bare user_id= kwarg
- All writes use filters with user_id + agent_id for attribution
- Response unwrapping for v2 dict format {results: [...]}
- Split _read_filters() vs _write_filters() — reads are user-scoped
  only for cross-session recall, writes include agent_id
- Preserved 'hermes-user' default (no breaking change for existing users)
- Omitted run_id scoping from #5301 — cross-session memory is Mem0's
  core value, session-scoping reads would defeat that purpose

Memory prefetch context fencing (#5339):
- Wraps prefetched memory in <memory-context> fenced blocks with system
  note marking content as recalled context, NOT user input
- Sanitizes provider output to strip fence-escape sequences, preventing
  injection where memory content breaks out of the fence
- API-call-time only — never persisted to session history

Secret redaction (#5058, #5098):
- Added prefix patterns for Groq (gsk_), Matrix (syt_), RetainDB
  (retaindb_), Hindsight (hsk-), Mem0 (mem0_), ByteRover (brv_)

run_agent.py

@@ -76,6 +76,7 @@ from tools.browser_tool import cleanup_browser
 from hermes_constants import OPENROUTER_BASE_URL
 
 # Agent internals extracted to agent/ package for modularity
+from agent.memory_manager import build_memory_context_block
 from agent.prompt_builder import (
     DEFAULT_AGENT_IDENTITY, PLATFORM_HINTS,
     MEMORY_GUIDANCE, SESSION_SEARCH_GUIDANCE, SKILLS_GUIDANCE,
@@ -7150,7 +7151,9 @@ class AIAgent:
                 if idx == current_turn_user_idx and msg.get("role") == "user":
                     _injections = []
                     if _ext_prefetch_cache:
-                        _injections.append(_ext_prefetch_cache)
+                        _fenced = build_memory_context_block(_ext_prefetch_cache)
+                        if _fenced:
+                            _injections.append(_fenced)
                     if _plugin_user_context:
                         _injections.append(_plugin_user_context)
                     if _injections: