feat: auto-load recent sessions after restart (#218)

[succ985]

Summary

After restart, automatically inject recent session context into the first user message so the agent doesn't lose conversational memory. Fixes #218.

Changes

• frontends/startup_recall.py (new, ~150 lines): Scans model_responses/ for recent sessions, extracts real user-agent conversations, formats recall context.
• agentmain.py (+10 lines): Centralized hook in GenericAgent.run() — triggers once per restart on first user message only.

Design Decisions

Decision	Reason
Hook in agentmain.run() not per-frontend	One code path covers all frontends (wechat/tg/feishu/discord/qq)
source == 'user' filter	No injection for reflect/scheduler/internal tasks
History stays clean	Recall injected into raw_query after history.append(), so session history isn't polluted
Env vars only, no mykey.py	Simpler config: GA_STARTUP_RECALL_SESSIONS=5, GA_STARTUP_RECALL_LINES=8 (set SESSIONS=0 to disable)
Regex exact-match for trivial messages	`^(hi

Config

Env Var	Default	Description
GA_STARTUP_RECALL_SESSIONS	5	Recent sessions to scan. 0 disables feature
GA_STARTUP_RECALL_LINES	8	Conversation turns per session to extract

Testing

• ✅ Syntax check: all files pass py_compile
• ✅ Unit tests: trivial message detection, disable via SESSIONS=0, recall extraction
• ✅ End-to-end: restarted wechatapp.py 4 times, verified recall injection on first message each time
• ✅ History integrity: self.history does not contain recall content

PR Checklist

• Issue feat: auto-load recent sessions after restart to avoid cold-start memory loss #218 linked
• Self-documenting code, minimal comments
• Change radius: 2 files only (1 new, 1 modified)
• No new dependencies
• Net lines: +222 (new module + hook)