fusion/docs/grok-cli-contract.md

Grok CLI Contract (FN-7790 / FN-7796, updated for ACP transport)

Date: 2026-07-11

Ground truth

Fusion shells out to an operator-installed grok binary. The binary is not downloaded or bundled by Fusion, so the authoritative contract is the installed xAI CLI's own help/version output plus live execution on an authenticated machine.

External integration evidence:

• Canonical upstream: xAI official Grok CLI / Grok Build TUI, surfaced by the installed binary as grok 0.2.93 (f00f96316d4b).
• Docs/homepage: https://grok.com/, https://docs.x.ai/, https://docs.x.ai/build/overview, and grok --help / grok agent --help / grok agent stdio --help for exact flags.
• ACP protocol: https://agentclientprotocol.com
• Release/download: operator-installed; Fusion resolves grok from PATH or grokCliBinaryPath and does not bundle a release artifact.
• Binary name: grok.
• Checksum: upstream-pending-verification because Fusion does not pin or download the operator's binary.

The previously documented https://github.com/superagent-ai/grok-cli contract is a different product that happens to use the same binary name. Its grok --prompt <text> --format json invocation is not accepted by xAI's CLI.

Agent session transport — ACP (grok agent stdio)

Fusion's GrokRuntimeAdapter drives Grok as an ACP (Agent Client Protocol) agent over JSON-RPC/stdio, following xAI Headless & Scripting:

# Official automation shape (docs.x.ai): suppress update checks in CI/scripts
grok --no-auto-update agent stdio
# with optional model + session skills plugin:
grok --no-auto-update agent --plugin-dir <session-plugin> -m grok-4.5 stdio

ACP session lifecycle (official contract):

1. initialize (protocolVersion 1)
2. authenticate — prefer xai.api_key when XAI_API_KEY is set and advertised, else cached_token, with _meta: { headless: true }
3. session/new (cwd, mcpServers, optional _meta.pluginDirs / rules)
4. session/prompt — completion metadata on the response; assistant text arrives as session/update agent_message_chunks

Auth: local grok login (cached token in ~/.grok/auth.json) or XAI_API_KEY. Fusion forwards XAI_API_KEY on the spawn allow-list.

Implementation uses a vendored ACP client under plugins/fusion-plugin-grok-runtime/src/acp/ (copied from the ACP runtime plugin; not a package import) with Grok-specific settings:

Setting	Grok value
Binary	grok (or configured path)
Args	["agent", "--plugin-dir", "<session-plugin>", …, "stdio"] (optional -m <id>)
Env	Allow-list including HOME/PATH/USER/XDG + optional XAI_API_KEY/GROK_API_KEY (never full process.env)
acpFsRead / acpFsWrite	false (Grok has native tools; client-side fs stays off)
acpAllowUnrestricted	true (operator-selected first-party CLI; non-allow policy categories still gated)
session/new.mcpServers	Operator MCP servers (stdio/http/sse) + Fusion fusion-custom-tools bridge for fn_*
Skills	Session-scoped Grok plugin (--plugin-dir + _meta.pluginDirs) with bundled Fusion skill + additionalSkillPaths

Fusion tools and skills

1. Operator MCP — options.mcpServers is reshaped to ACP wire format and forwarded on session/new.
2. Fusion custom tools (fn_*) — engine customTools are hosted by a loopback HTTP bridge + stdio MCP server (mcp-schema-server.cjs) named fusion-custom-tools. Grok invokes tools via real MCP tools/call; the bridge runs ToolDefinition.execute in-process.
3. Skills — the bundled Fusion skill (packages/cli/skill/fusion) plus any additionalSkillPaths skill roots are staged into a temp plugin directory and loaded via grok agent --plugin-dir and _meta.pluginDirs. Requested skill names and tool counts are also written into _meta.rules / system prompt context.

Session lifecycle

1. createSession — spawn grok agent stdio, ACP initialize, session/new over the task cwd.
2. promptWithFallback — ACP session/prompt with text + optional chat image ContentBlocks from prompt options; stream session/update notifications until terminal stopReason.
3. dispose — best-effort session/cancel + process-registry SIGKILL (authoritative no-orphan guarantee).

Streamed update mapping

ACP sessionUpdate	Fusion callback
agent_message_chunk	onText
agent_thought_chunk	onThinking
tool_call	onToolStart
tool_call_update (terminal)	onToolEnd

Multi-turn conversations reuse the same ACP session/connection (no cold spawn per prompt).

Auth

Grok owns authentication. Preferred path is a cached session in ~/.grok/auth.json (requires HOME in the allow-list). Optional key-based auth uses XAI_API_KEY or GROK_API_KEY when no cached token is present. The readiness probe (grok --version) proves only binary presence, not authenticated ACP readiness.

Permissions

Tool calls from the Grok agent surface as ACP session/request_permission and route through Fusion's per-category action gate (same floor as the generic ACP runtime). Unrestricted policy + acpAllowUnrestricted auto-allows sensitive categories for autonomous executor turns; require-approval / block still apply when configured.

Failures that shaped the prior headless contract (historical)

Wrong-product flags (FN-7790)

The old adapter invocation fails against the real xAI binary:

grok --prompt "say hello" --format json

Streaming JSON cancellation with zero text (FN-7796)

--output-format streaming-json intermittently ended stopReason:"Cancelled" with zero text events. That motivated the temporary switch to single-object --output-format json. ACP replaces both headless modes for agent sessions because it streams reliably over JSON-RPC and carries tool/permission structure.

Probe and model discovery (unchanged)

Version probe

grok --version

Model discovery

grok models is plain text, not JSON. Observed shape:

You are logged in with grok.com.

Default model: grok-4.5

Available models:
  * grok-4.5 (default)
  - grok-composer-2.5-fast

Fusion parses the bullet list conservatively and exposes ids under provider grok-cli when the useGrokCli toggle is enabled.

Runtime routing

The Grok runtime adapter is reached when:

1. an agent explicitly sets runtimeConfig.runtimeHint === "grok"; or
2. the FN-7753/FN-7758 no-visible-key fallback derives the same runtime hint for a grok-cli/* default/fallback provider selection and the bundled Grok Runtime plugin is registered.

The selected grok-cli/<id> or grok/<id> model is normalized to <id> and passed as grok agent -m <id> stdio. The explicit no-model Runtime-mode path keeps grok/default and omits -m.

Diagnostics and empty-output invariant

The adapter preserves the resolve-never-reject runtime contract while surfacing concrete diagnostics:

• ACP create/handshake failure → dead session + diagnostic onText (create does not throw to the engine).
• ACP prompt failure → diagnostic onText when no assistant text streamed; never reject.
• Abnormal stopReason (not end_turn) with zero text → stop-reason diagnostic.
• Clean end_turn with no assistant text → legitimate silent response, not a diagnostic.
• Partial text before a failed close → keep the assistant text; do not replace it with an error.

This invariant prevents blank/no-message assistant bubbles while still allowing genuinely empty model turns.