[Anrahya]

Closes #112. Part of the 2026-10-02 pivot: Discord stays a thin chat surface, minimal but solid for day-to-day use.

What changes

• The operator's message that is exactly /new (ignoring case and the bot mention; in a DM, a bound channel, an active thread, or with a mention) starts a new conversation. In one store transaction it records the message, makes a new task on the channel's agent current, and queues the reply "Started a new conversation." No turn runs and nothing reaches the node.
• The earlier task is kept, and turns already queued or submitted on it still run and reply.
• A current task that nothing has used yet is reused, so repeated /new adds no empty rows.
• The new task is opened immediately, so an unbound thread keeps answering without a mention.
• A redelivered /new (same message id) changes nothing. A guest's /new, or /new with more text, is an ordinary message.
• The gateway now wakes reply delivery as well as the RCP link (Wake { turns, replies }). The channel lookup runs before /new, so an unseen thread's /new uses its parent channel's agent.
• No schema change and no wire change.

Not in this PR

/cancel, /compact, /model, /reasoning and /status each need an RCP operation first, so the Android app gets them too.

Verification

• scripts/check-module-size.sh, cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace: pass.
• New tests:
  • routing: a new task on the same agent, a thread that still answers, a redelivery answered once, a guest's /new as a message;
  • queued work on the old task kept, /NEW with padding matched, /new please as a turn, a DM /new, reply delivery woken;
  • store: repeated /new keeps one unused task on the channel's agent;
  • live: the fake gateway delivers /new twice, one answer is posted and no command runs.
• Mutation runs: 6 of 6 caught.
  • reply wake removed;
  • operator check removed;
  • no new task;
  • redelivery not ignored;
  • unused task not reused;
  • wrong agent.
• Independent Sonnet review of the store change: no blockers or majors. I applied its minor findings:
  • the lookup now runs before /new;
  • an unused task is reused;
  • tests added for matching, DMs, queued work and the reply wake;
  • the matching rule is now documented.