[arc53-machine]

Adds the second crate, docsgpt-bot: the platform-neutral half of the Telegram bot, generalized so the Slack v2 bot can use it. The answer loop itself (a Surface trait plus run_turn) comes in the next PR.

What's in it

• config: AgentConfig, [storage] and [server] tables for each bot to embed in its own deny_unknown_fields config, ${VAR} / ${VAR:-default} expansion (reports every missing variable at once), load_toml, find_config, and agents_from_env for the single-bot API_KEY / API_KEY_<NAME> layout both existing bots use.
• Agents: validation (lowercase unique names, non-empty keys, at most one default) and routing. A #name prefix wins, then the chat's active agent, then the default. An unknown #tag is an error only when the bot has several agents, so hashtags still work on single-agent bots.
• storage:
  • Scope { bot, space, thread, namespace } uses strings, so Slack's channel and thread_ts and Telegram's numeric ids both fit. The key format matches Telegram v2's.
  • Conversations carry a turn counter. record_turn returns the answer's position, which is feedback's question_index; we chose to count turns in the bots rather than change DocsGPT, and Add the docsgpt crate: Rust client for the DocsGPT API #1 confirmed against a live server that positions are 0-based in ask order.
  • Also: chat state with an extra map, JSON records for platform-only state, and message refs, so a 👍 on an old message maps back to its conversation and position.
  • SQLite and memory backends run one shared contract suite. The SQLite backend opens Telegram v2 files and adds the turns column, so the Telegram bot can move over in place.
• runtime:
  • ScopeLocks: one turn at a time per chat.
  • CancelRegistry: its guards unregister on drop, and re-registering a key is safe.
  • Shutdown: SIGINT/SIGTERM, then drains turns in progress within a grace period. The Telegram bot drops them.
• markdown:
  • Fence-aware markdown_blocks / split_markdown / clamp_markdown. The Telegram bot's clamp_rich could cut inside a code block; that case has a regression test.
  • Also: strip_images, close_open_fence, render_table_monospace, clean_title.

MongoDB is not supported, as agreed for the Slack rewrite.

Verification

• cargo test --workspace --all-features: 25 new tests (contract suite on both backends, SQLite reopen, Telegram v2 file upgrade, routing, config, locks, cancel guards, shutdown drain, Markdown splitting), plus Add the docsgpt crate: Rust client for the DocsGPT API #1's.
• cargo clippy -D warnings, cargo doc -D warnings, the MSRV 1.88 check and cargo publish --workspace --dry-run all pass.