Add AGENTS.md with session instructions for OpenCode

AGENTS.md

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+# AGENTS.md — instructions for OpenCode sessions on the Lumen repo
+
+## Language and user context
+- The user does not write code (the bot was built with Claude's help). Explain in Russian, in detail: what was done, why, and the result in plain terms.
+
+## Agreement with the owner
+- Small fixes and requested changes: do them right away. Large changes (new dependencies, behavior changes, restructuring, touching streaming or security layers): present a short plan first and get the owner's approval.
+- Publishing (git commit/push, deploy to the HF Space, contacting the live bot): propose it, wait for explicit confirmation, never do it unprompted.
+
+## What this repo is
+- Lumen: a Telegram bot (persona styled after Claude) running as a single FastAPI + aiogram webhook service on a Hugging Face Space (Docker). LLM backbone: Google Gemini + free OpenRouter models with per-message routing.
+- Entry point is bot.py (orchestrator, ~5000 lines). Focused modules sit next to it: lumen_router_config.py (model routing), lumen_formatting.py (markdown to Telegram HTML), lumen_security.py (injection/leak defenses), lumen_images.py, lumen_tts.py, lumen_tiktok.py, lumen_telegram_transport.py, lumen_state_storage.py, lumen_typing_pace.py, plus system_prompt.py.
+
+## Commands (verified against CI, .github/workflows/ci.yml)
+- Full gate: pip install -r requirements.txt -r requirements-dev.txt; pyflakes bot.py lumen_*.py system_prompt.py conftest.py test_*.py; pytest -q; pip-audit -r requirements.txt
+- Single test file: pytest test_bot.py -v; single test: pytest test_bot.py::test_classify_model_error_rate_limit_by_status -v
+- Proxy (Deno): deno test proxy_test.ts (no external imports, works offline; see proxy_test.ts header)
+
+## Gotchas
+- Every push to main that passes CI auto-deploys to the live HF Space (.github/workflows/sync-to-hf.yml waits for the CI workflow, then force-pushes the checked commit). A green CI run is a deploy.
+- Versions in requirements.txt are pinned with == (HF rebuilds the image from scratch on every deploy; see the file header comment). Bumping a version is a deliberate decision followed by a manual smoke test (/diag + main commands), not a side effect.