feat: gemini-cli as a codeoid backend over ACP (bundled, Google-subscription auth)

docs/provider-gemini-acp-design.md

@@ -0,0 +1,63 @@
+# Google-subscription backend — gemini-cli over ACP (design)
+
+> Untracked design doc. Spike verified 2026-07-10. Supersedes the earlier
+> "Antigravity SDK" idea — see Findings. Template: pi (#131–135) + codex (#142).
+
+## Findings (verified)
+
+- **There is no official Google "Antigravity SDK"** on npm. The `antigravity-sdk`
+  package (1.7.0) is a *community* kit for building Antigravity IDE
+  *extensions* — wrong direction (extends the IDE, doesn't expose the agent),
+  community-owned (supply-chain risk), no subscription-auth story for us.
+- **`@google/gemini-cli@0.50.0` (official) ships a STABLE `--acp` flag** —
+  "Starts the agent in ACP mode" (`--experimental-acp` now deprecated). This is
+  the Google-subscription harness: gemini-cli's auth is the user's Google
+  account OAuth in `~/.gemini` (free tier / AI Pro / Code Assist), exactly the
+  codex/claude posture — codeoid never touches tokens.
+- **ACP = Agent Client Protocol** (`@zed-industries/agent-client-protocol`,
+  0.4.5) — a STANDARDIZED editor↔agent protocol: JSON-RPC over stdio, same
+  transport shape as codex app-server. Native seams:
+  - `session/new` / `session/load` → backing session
+  - `session/prompt` → turn; `session/update` notifications → text/thought/
+    tool-call streaming; `session/cancel` → interrupt
+  - `session/request_permission` (server→client request) → `canUseTool` —
+    native approvals again, no bridge
+  - `fs/read_text_file` + `fs/write_text_file` (agent asks the CLIENT to do
+    file I/O) — decide policy: implement + gate writes through canUseTool, or
+    decline capability so the agent uses its own tools
+  - gemini-cli `--approval-mode default` prompts for approval — pin it
+    (fail-closed parity with pi/codex).
+
+## Why this beats a bespoke integration
+
+An `AcpProvider` is **agent-agnostic**: gemini-cli first, but any ACP-speaking
+agent (the growing Zed ecosystem) becomes a codeoid backend for free —
+registry entries per agent binary over one protocol client. Strongest possible
+expression of the meta-harness bet.
+
+## Shape (mirror codex/)
+
+`src/daemon/providers/acp/{rpc,translate,resolve,index}.ts`:
+- reuse the newline JSON-RPC client pattern from codex/rpc.ts (consider
+  extracting a shared `jsonrpc-stdio.ts` — codex + acp are near-identical)
+- `GeminiAcpProvider` (or generic `AcpProvider` parameterized by binary +
+  id/displayName) — warm process, `initialize` (ACP version + client caps),
+  `session/new {cwd, mcpServers: []}`, prompt turns, permission requests →
+  canUseTool, `session/update` → ProviderEvent
+- resolution: config `providers.gemini_cli.command` → PATH → bundled
+  `@google/gemini-cli` optionalDependency (pure JS like pi — bundling audit
+  should pass; pin exact)
+- env: `buildGeminiCliEnv` — `GEMINI_`, `GOOGLE_` prefixes + shared basics
+  (`~/.gemini` via HOME)
+- naming: provider id `gemini-cli` (distinct from stateless `gemini`);
+  displayName "Gemini CLI (Google)"
+- fake-acp fixture + C-series tests, per the codex template
+
+## Open questions
+1. ACP schema details: pull `@zed-industries/agent-client-protocol` types
+   (typed, versioned) instead of hand-rolling frames.
+2. fs/* capability: v1 recommendation — advertise `fs: false` so gemini-cli
+   uses its own tools (all gated by approval-mode), revisit later.
+3. Does Antigravity itself ever expose an official agent protocol/SDK? Re-check
+   before GA; if yes, it likely also speaks ACP (it's Zed-adjacent tooling) —
+   the AcpProvider would absorb it.

package.json

@@ -81,6 +81,7 @@
   },
   "license": "MIT",
   "optionalDependencies": {
-    "@earendil-works/pi-coding-agent": "0.80.6"
+    "@earendil-works/pi-coding-agent": "0.80.6",
+    "@google/gemini-cli": "0.50.0"
   }
 }

src/config.ts

@@ -434,10 +434,18 @@ const ProvidersSchema = z
         command: z.string().default("codex"),
       })
       .default({ enabled: true, command: "codex" }),
+    /** Google gemini-cli driven over ACP (`gemini --acp`). */
+    geminiCli: z
+      .object({
+        enabled: z.boolean().default(true),
+        command: z.string().default("gemini"),
+      })
+      .default({ enabled: true, command: "gemini" }),
   })
   .default({
     pi: { enabled: true, command: "pi" },
     codex: { enabled: true, command: "codex" },
+    geminiCli: { enabled: true, command: "gemini" },
   });
 
 const RootSchema = z.object({
@@ -580,6 +588,10 @@ export interface CodeoidConfig {
       enabled: boolean;
       command: string;
     };
+    geminiCli: {
+      enabled: boolean;
+      command: string;
+    };
   };
   /**
    * Daemon-native hooks — dispatched at Session's seams for every backend.