brainiac v0.20.45

Changed

• Model work is capped machine-wide, so parallel searches no longer exhaust
  memory. At most two processes load or run a model at once
  ($BRAIN_MODEL_SLOTS, default 2); a queued search waits before its rerank
  budget starts, so it never loses its rerank. Ten brain search processes
  at once had taken a 24 GB Mac to a forced reset; the same replay now peaks
  at 5.7 GB in total. The reranker also scores in batches of 4
  ($BRAIN_RERANK_BATCH), so a long-lived process such as the MCP server
  keeps 4.6 GB after 20 searches instead of 12 GB. Scores are unchanged.
• The embedder and the reranker use 4 threads by default, not every core.
  Measured on a 12-core Mac: the same wall time at about 40% of the CPU.
  $BRAIN_EMBED_THREADS and $BRAIN_RERANK_THREADS still override.

Fixed

• brain update no longer times out on a slow engine install. Every
  install channel (uv, pipx, pip --user, venv wheel, editable) ran under the
  120-second bound meant for claude plugin calls. The 0.20.44 venv install
  took 6m39s, so the update stopped before it re-staged any workspace. The
  install now gets 30 minutes, the same bound as the workspace sync.