omp-antigravity-acp-provider

Google Antigravity's official ACP server, adapted for Oh My Pi (OMP).

An OMP-focused derivative fork of zacbemis/pi-antigravity-acp-provider. Original project by zacbemis and contributors, licensed under MIT.

This is an independent adaptation, NOT an official Google or OMP integration. It uses ACP over stdio. The local HTTP MCP bridge carries tool calls; it is not a model API reverse proxy.

Features

• All server-advertised models, including Claude, GPT-OSS and future IDs when the ACP endpoint advertises them.
• CLI-first selection. When a usable agy CLI is on PATH, the adapter launches it through a generated AGY_ACP_BIN wrapper. The managed runtime is the fallback. An explicit AGY_ACP_BIN always wins.
• Per-model thinking levels, exposed only when the server confirms them.
• OMP tools through an authenticated loopback MCP bridge.
• Optional disabled native-tool mode for strict OMP-only sessions.
• Lazy ACP startup and warm session reuse.
• /login plus /antigravity-acp account, usage and cleanup commands.
• API-equivalent cost estimates from a model-ID rate table, not subscription billing. ACP model records do not include price fields.
• Long-running OMP tools survive the MCP request window through a relay. The model resumes the same result with pi_omp_await_result; the control tool is a separate MCP server and never appears in OMP's tool list.
• Permission requests are tied to the originating session, turn and tool call. Forged, conflicting or previous-turn identities fail closed, while normal requests still use OMP's human review.
• The MCP tools/list reflects the current OMP tool set. The offline wire test covers add, remove and restore on one warm ACP session.
• Tool-argument hardening on the MCP bridge. Habitual alias mistakes such as path for file_path are corrected only when the tool schema makes the mapping unambiguous, and rejected calls return the missing required keys plus the tool's expected signature instead of a bare schema failure.
• Loopback traffic always bypasses proxied environments. When HTTP(S)_PROXY or ALL_PROXY is set for the ACP child process, the adapter appends localhost, 127.0.0.1 and ::1 to NO_PROXY/no_proxy so the loopback MCP bridge is never routed through an external proxy.
• OAuth material is redacted from failure text. Authorization URLs, sensitive query values, Bearer tokens and OAuth pairs such as code_challenge or access_token are masked before messages reach OMP, while ordinary diagnostics like exit code=1 stay intact.

Install: for human

Follow these steps in order. The whole flow takes a few minutes, plus Google's sign-in. A runtime download is only needed when no usable agy CLI is installed.

1. Check prerequisites

• OMP is installed and omp --version works.
• Node.js 22.19 or newer (node --version) and npm are on PATH; the marketplace launcher uses them on first load.
• A supported platform: macOS, Linux or Windows. Live testing has been on macOS.
• Internet access when no usable agy CLI is installed. The managed fallback downloads separately (about 383 MiB on macOS) into ~/.local/opt/agy-acp/.

2. Install exactly one adapter

Use the marketplace (this repository is also the sencha-plugins marketplace):

omp plugin marketplace add SenCha930511/omp-antigravity-acp-provider
omp plugin install omp-antigravity-acp-provider@sencha-plugins

Or install the published npm package directly:

omp plugin install npm:omp-antigravity-acp-provider

Do not install both. Remove or disable any older Antigravity ACP adapter first.

3. Restart OMP

The provider registers at startup. Restart every running OMP process so they agree on session ownership.

4. Sign in

Run /login, choose Google Antigravity (ACP), and complete Google's consent in the browser. On a headless machine the provider relays the callback URL.

5. Load models and pick one

/antigravity-acp refresh
/model

refresh asks the ACP server which models the account can use; /model lists them. Set an effort with OMP's thinking control when the model advertises levels. If OMP's enabledModels whitelist is configured, add antigravity-acp/* to it.

6. Verify

/antigravity-acp status

This shows the runtime, native-tool mode and usage state. Send a short prompt to confirm inference.

Troubleshooting

Install: for agents

The installation runbook is in AGENT_INSTALL.md. Hand that file to an agent with terminal access; it installs and verifies the adapter without starting an interactive login. For example: Read AGENT_INSTALL.md and follow it.

ACP server channels and selection

Google ships the same ACP server through two channels. The adapter chooses one at every OMP startup.

• agy CLI. Preferred whenever agy or agy.exe is on PATH and agy acp --version returns a semantic version. The adapter writes agy-acp-cli.sh or agy-acp-cli.cmd and points AGY_ACP_BIN at that wrapper.
• Managed runtime. The registry-signed release in ~/.local/opt/agy-acp/. It is the fallback when the CLI is missing or unusable.

Selection order:

1. An explicit non-wrapper AGY_ACP_BIN wins. The adapter's generated wrapper is not a user override.
2. If runtimeSource is cli or managed, the adapter uses that source exclusively. A missing pinned source fails the first ACP use and is not downloaded.
3. If runtimeSource is auto, a usable CLI wins, even when its version is older than the managed runtime.
4. In auto, if the CLI is missing or unusable, the adapter uses the managed runtime. If the managed runtime is missing, it downloads it from Google's registry.
5. In auto, if writing the CLI wrapper or runtime record fails, the adapter falls back to the managed runtime.

The adapter never installs the agy CLI. It downloads the managed runtime only in auto when no usable CLI is selected. Inference and quota use the same selection.

On the first session start after OMP launches, the adapter attempts one background model refresh. A successful refresh re-registers the provider so newly advertised models and their API-equivalent rates become available. If login or ACP startup fails, the cached catalog remains usable and /antigravity-acp refresh still forces a refresh.

Create or edit ~/.omp/agent/antigravity-acp-provider/config.json:

{
  "permissions": "yolo",
  "runtimeSource": "auto",
  "nativeTools": "prefer",
  "debugToolUpdates": false,
  "usageMode": "off",
  "diagnostics": false
}

permissions accepts default, auto_edit, or yolo. runtimeSource accepts auto, cli, or managed. nativeTools accepts prefer or disabled. usageMode accepts auto or off. debugToolUpdates and diagnostics are booleans. Missing fields use these defaults: permissions: "yolo", runtimeSource: "auto", nativeTools: "prefer", debugToolUpdates: false, usageMode: "off", and diagnostics: false. Slash commands write the command-backed fields and keep the legacy setting files in sync. Context budgets remain in context.json; cleanup policy remains in cleanup.json.

• auto uses the CLI first and falls back to the managed runtime. If no usable CLI exists, it downloads the managed runtime.
• cli requires a usable agy CLI. If the CLI is missing or unusable, the first ACP use fails and nothing is downloaded.
• managed requires the managed runtime. If it is missing, the first ACP use fails and nothing is downloaded.

A pinned source never falls back to the other channel and never downloads it. An explicit non-wrapper AGY_ACP_BIN still wins over this setting. If PI_CODING_AGENT_DIR is set, use its actual path for config.json. Other runtimeSource values fail provider startup.

Session storage follows the server's own --app_data_dir. The generated wrapper pins antigravity-acp — the managed runtime's own default — so CLI-launched ACP sessions land in ~/.gemini/antigravity-acp/, where /antigravity-acp cleanup and session ownership tracking operate. Personal agy CLI chats stay in ~/.gemini/antigravity-cli/ and are never read or deleted by the adapter. GEMINI_HOME relocates the managed runtime's tree (upstream behavior); the agy CLI stores under ~/.gemini regardless.

The active channel and its versions are recorded in ~/.omp/agent/antigravity-acp-provider/acp-runtime-source.json whenever the CLI is chosen.

Permission IDs differ between the channels. Managed ACP 1.4.5 supports default, auto_edit, and yolo directly. CLI ACP 1.5.3 advertises default, accept-edits, and plan instead. The adapter maps auto-edit to accept-edits. For yolo, it selects wire mode default and passes the CLI's official --dangerously-skip-permissions flag. This preserves auto-approval instead of substituting accept-edits. Changing permission modes recreates the ACP runtime so a process with auto-approval cannot serve a later default or auto-edit request. An explicit AGY_ACP_BIN is left unchanged.

CLI ACP 1.5.3 omits mcpCapabilities from its initialization response, but it still discovers HTTP MCP servers and calls tools/list. The adapter normalizes this capability for that server identity so OMP tools remain available. CLI 1.5.3 reports no audio input, while the adapter's model catalog already limits input to text and images.

Context occupancy and compaction

ACP may report live occupancy with usage_update. When it does, the adapter forwards that server value. When a runtime (for example CLI ACP 1.5.4) reports only cumulative billable usage, the adapter estimates the full OMP context from the system prompt, retained messages and tool schemas with estimateTransferTokens, then sets usage.contextTokens and marks contextTokensSource: "estimate". The billable input, cacheRead and output counters are left untouched.

The estimate is a heuristic, not a server measurement. To use managed ACP when exact occupancy matters, set AGY_ACP_BIN to the managed binary. CLI-first selection does not switch automatically. In this source checkout, scripts/with-managed-context.sh starts OMP with the installed managed binary while preserving an explicit AGY_ACP_BIN. Run /antigravity-acp refresh afterward to inspect the models that runtime actually advertises.

Keep compaction.autoContinue enabled for normal long-running work. The false context rollover was fixed at the occupancy signal, not by disabling automatic continuation.

Commands

Use the /antigravity-acp prefix once, followed by a row below. For example, status means /antigravity-acp status.

Common operations

Quota results use a 60-second cache. When the adapter selects the CLI, the quota command runs the CLI's print-mode /usage command with the same --app_data_dir as the CLI ACP wrapper. When it selects managed ACP, the quota command uses a short-lived ACP session. An explicit AGY_ACP_BIN remains authoritative. If an ACP runtime does not advertise usage, the adapter reports the limitation without sending a model prompt. The quota display excludes usage counters for temporary ACP sessions.

OMP's built-in omp usage, interactive /usage, and the statusline usage segment read the same quota through the provider's registered usage source. The adapter uses the CLI /usage command first and queries an installed managed runtime only when the user is signed in. A usage probe never downloads a runtime. Statusline selects the active model's limit group when that group maps to one model. Multi-model groups remain visible in /usage. The custom /antigravity-acp quota command remains the detailed text view.

Advanced maintenance

Context KEY is one of contextWindow, maxTokens, inputTokenBudget, reserveTokens, maxTransferBytes or maxImageBytes.

The OMP input autocompletes this command. Type /antigravity-acp to list the subcommands, and keep typing to filter them. Fixed values such as permissions modes and context set targets (default plus the cached model IDs) complete the same way.

Steering and queued messages

By default a new user message waits for the active ACP turn to finish (OMP_ACP_STEER_MODE=queue) and then continues on the warm session, avoiding a full replay and OMP auto-compaction. Set OMP_ACP_STEER_MODE=steer to restore immediate interruption. At tool/permission boundaries the adapter falls back to steer and waits for the ACP terminal response; OMP_ACP_STEER_GRACE_MS (default 60000) and OMP_ACP_STEER_GRACE_MAX_MS (default 300000) bound that wait. Explicit user cancellation is never held: the adapter aborts the upstream prompt immediately, so the ACP server receives session/cancel at once. Queue steering still holds the active turn, and the graceful drain and checkpoint reuse semantics are unchanged.

ACP runtimes stay warm for 15 minutes by default. Set OMP_ACP_IDLE_TIMEOUT_MS=0 to keep them until OMP exits, or lower the value to reclaim memory sooner.

An ACP turn that ends at the model's output limit is continued on the same session up to three times. OMP_ACP_MAX_CONTINUATIONS=0 disables the loop; if agy already reported its own output-cap continuation, the adapter does not add another.

Inference and /antigravity-acp refresh refuse to start ACP when no local Google login is available; run /login (or /antigravity-acp login) first instead of waiting for an interactive consent flow inside session/new.

Long tools and relay

A tool call that outlives OMP_ACP_TOOL_RELAY_MS (default 85000, 0 disables, otherwise 5000 through 165000) returns a relay notice instead of holding the MCP request open. The model calls pi_omp_await_result with the notice's call_id; the adapter returns the same original result, not a second execution. The control tool is a separate MCP server and is not added to OMP's tool list. If the ACP turn ends before the result arrives, the adapter retries the same result in a fresh ACP turn; it never delivers a stale result to a new writer.

Permission requests are correlated by session, turn and toolCallId with structured mcpServerName/mcpToolName metadata. A conflicting update, a previous-turn id, or a permission-before-update that claims MCP identity is rejected with reject_once when available, otherwise cancelled. Normal requests still go through OMP's human review.

The bridge's MCP tools/list always reflects the current OMP tool set. The offline wire test covers add, remove and restore on one warm ACP session. A live agent re-list has not been verified against the official agy runtime, so the adapter does not claim that the agent will always see a changed list.

A refusal stop reason is reported as an explicit provider refusal. An empty end_turn remains tolerated to preserve OMP's warm /retry path.

Limitations vs direct OAuth

• No direct model API endpoint or reverse-proxy mode.
• No API-key, service-account, or raw OAuth-token authentication; Google browser consent is required.
• Only models advertised by the ACP server are available.
• Only thinking levels confirmed by the ACP server are selectable.
• No arbitrary generation controls: temperature, top_p, seed, stop sequences, tool_choice, response format, or output-token limit.
• No exact API billing or complete subagent usage; cost and quota figures are estimates.
• No guaranteed prompt-cache hits, cache discounts, or identical tokenization.
• No full native history or hidden reasoning across a cold rebuild; server-side compaction is outside adapter control.
• No per-tool native allowlist; native-tools supports only prefer and disabled, and global MCP servers remain.
• No standalone client; a usable ACP server, either the agy CLI or the managed runtime, is required.

Detailed behavior, advanced settings and limitations: docs/ and CHANGELOG.md.

License

MIT. See LICENSE and THIRD_PARTY_NOTICES.md. Upstream source is vendored under extension/vendor/pi-antigravity-acp-provider (MIT) and kept with attribution. Official Google executables and their licenses are separate.