Auto-acquire the built-in ACP agents, and let users turn them off

[Ukaykhingmarma28]

Fixes #160.

Cursor, OpenCode and Kilo were shown as "Built-in" while Atlas bundled nothing and offered no way to install them. Their specs shell out to bare CLIs (cursor-agent acp, opencode acp, kilo acp); on a machine without those, the spawn failed, the error was swallowed, and the only visible symptom was a chat with no model picker. Claude and Codex were fine because npx -y self-installs their adapter.

This makes Atlas do for those three what npx already does for the other two — then lets you turn them off if you don't want them.

Acquisition — cache-first, the model Zed uses

RegistryStore::ensure_builtin downloads the official per-platform binary from the ACP registry manifest on first use and caches it, reusing the existing versioned-cache / sha256 / prune machinery rather than adding a parallel one. It hangs off the pre-flight agents_spawn already ran for registry externals.

Never fatal. No manifest yet, unsupported platform, offline, bad checksum — every failure falls back to the bare PATH command, which is exactly today's behaviour. sha256 is verified where the manifest publishes one (kilo, opencode); Cursor ships none upstream, so it installs unverified, as it does in Zed.

AUTO_MANAGED_BUILTIN_IDS marks the three, and known_specs lets an acquired binary replace the bare command in place — same id, same slot, same display name — so the plugin catalogue never sees two entries for one agent. Built-in specs are emitted after installed ones, so a manifest-current binary outranks a frozen install record; a machine that installed OpenCode from the marketplace before it shipped built-in has both, and that case has a test.

First-use progress

The composer's boot pill reads "Setting up Cursor… 42%" instead of stalling silently through a 77 MB download.

Progress is throttled to whole-percent changes. The registry's callback fires once per HTTP chunk — ~56k times for Cursor's archive — and one IPC event each would flood the bridge and jank the UI. acquire_pct_to_emit collapses that to 101 events, pinned by a test that replays the real byte/chunk counts.

These get their own atlas:agent-acquire:* events rather than reusing the marketplace's install events: only the install flow clears that progress map, so feeding it from here would leak entries, and the built-in cards short-circuit to the "Built-in" badge before the progress branch anyway.

Sign-in

These adapters advertise an auth method but ship no _meta.terminal-auth, so Atlas's existing terminal-auth runner had nothing to execute — and since the CLI now lives in Atlas's app-data dir rather than on PATH, "run cursor-agent login" was advice a user could not follow. enrich_auth_methods synthesises the missing spec from the managed binary for both the list and run commands, so what the UI offers is exactly what executes. An adapter-supplied spec always wins.

Worth knowing for future work: Cursor rejects session/new, not the prompt. An unauthenticated agent therefore dies at bind time and never reaches the turn-failure route that raises atlas:auth-required. Both paths now offer the same one-click "Sign in", and the bind path retries itself once credentials land. Bind failures were previously a bare console.warn, so they are now actually reported.

Turning them off

AppSettings::disabled_builtin_agents, with a switch on the three built-in marketplace cards. Off means hidden from the picker and never spawned — including both background pre-warms and a resume of an older session recorded against that agent.

The Rust guard is the authority and hard-filters against AUTO_MANAGED_BUILTIN_IDS, so a hand-edited state.json cannot switch off Claude, Codex or Cersei. Chat history is never hidden.

Verification

Verified against the real binaries, not just mocks:

• Cursor cold-downloaded (77 MB, ~19 s), extracted, and answered an ACP initialize with protocol v1 and the cursor_login auth method — i.e. it now spawns on a machine with no Cursor CLI.
• Each agent's login argv was read off its own --help (cursor login; opencode/kilo auth login), not assumed.
• The -32000 Authentication required response was reproduced against the CLI and is pinned verbatim in a regression test.

Automated: 512 frontend tests, 230 Rust app tests, 14 atlas-acp, 12 atlas-registry; typecheck and lint clean.

Not covered

• The full sign-in loop is unverified end to end — browser → authenticate() → rebind needs a real account.
• OpenCode and Kilo will hang on the "Sign in" button. Their auth login is an interactive TUI (provider picker, then an API-key prompt) and the auth runner spawns with stdin closed. Cursor is unaffected (browser OAuth). Setting a key works today via the CLI in a terminal, or via the provider env vars the binary reads (ANTHROPIC_API_KEY, OPENAI_API_KEY, OPENROUTER_API_KEY, GEMINI_API_KEY, GOOGLE_GENERATIVE_AI_API_KEY). The clean follow-up is to inject Atlas's existing BYOK keys into those agents' env at spawn.
• Separately noticed and left alone: adaptiveSuggestions exists in the frontend AppSettings but has no field in the Rust struct, so serde drops it on every save and it does not survive a restart.

🤖 Generated with Claude Code