Closes #47489

The search worker pool was sized as num_cpus - 1, which spawned zero workers when a devcontainer exposed only 1 CPU. All search channels closed immediately and the search yielded zero results, while file finder and LSP symbols worked fine.

The fix ensures at least 1 worker is always spawned: (num_cpus - 1).max(1). A num_cpus override on TestDispatcher and a new test reproduce the bug with server_cx.executor().set_num_cpus(1).

Manual testing

Add a .devcontainer/ directory to a new project with these files:

// docker-compose.yml
services:
  dev:
    image: debian:bookworm-slim
    cpuset: "0"
    volumes:
      - ..:/workspace:cached
    command: sleep infinity

// devcontainer.json
{
  "name": "zed-sandbox (1 CPU)",
  "dockerComposeFile": "docker-compose.yml",
  "service": "dev",
  "workspaceFolder": "/workspace"
}

Build zed and point it at the new project:

cargo run -p zed -- ~/Repos/zed-sandbox-project

Open the built-in terminal, confirm nproc prints 1.

Finally, run a project search (Cmd+Shift+F) and search for contents that exist in it.

Results should appear 🎉

Release Notes:

• Fixed project search returning no results in devcontainers with a single visible CPU.