Gemini native adapter silently hangs on exec and persistent sessions

[Amyssjj]

Description

The native Gemini adapter in acpx 0.1.13 silently hangs when attempting both exec (one-shot) and persistent sessions. No error output, no timeout — the process just stalls indefinitely.

Steps to Reproduce

1. acpx --format json --json-strict gemini sessions new --name test
2. echo "hello" | acpx --format json --json-strict gemini prompt --session test --file -
3. Process hangs with no output

Expected

JSON event stream with response or error message.

Actual

No output. Process hangs indefinitely until killed.

Environment

• acpx: 0.1.13
• Node: v25.4.0
• OS: macOS (arm64, Darwin 25.4.0)
• Gemini CLI: installed via google-gemini-cli auth

Notes

Claude adapter works for session creation but fails on prompt (separate issue in agentclientprotocol/claude-agent-acp#357). Codex adapter untested.

[craigkitterman]

Windows reproduction (acpx 0.1.15, Node v22.20.0)

Confirming this on Windows with acpx 0.1.15 — slightly different failure mode than the macOS hang.

Environment:

• acpx: 0.1.15
• Node: v22.20.0
• OS: Windows 11 (x64)
• Gemini CLI: 0.31.0 (installed via npm, resolves as \gemini.ps1\ wrapper)

Behavior on Windows:

• \�cpx gemini sessions new\ exits 0 but writes nothing to ~/.acpx/sessions/\
• \�cpx gemini sessions list\ shows \No sessions\
• \�cpx --approve-all gemini exec 'hello'\ produces no output and exits cleanly (no hang, just silent no-op)
• --verbose\ flag on \sessions new\ produces no output either

Root cause suspected:
On Windows, \gemini\ resolves to a .ps1\ PowerShell wrapper rather than a bare executable. acpx spawns \gemini\ as a raw command which fails silently on Windows without PowerShell in the spawn path. Had to configure a custom agent command pointing at the underlying Node.js entry point (
ode C:/Program Files/nodejs/node_modules/@google/gemini-cli/dist/index.js), but even with that the session write still silently fails.

Workaround: None found. Windows appears to be untested for the native Gemini adapter.

[vincentkoc]

Validated this again on current main and the failure mode is now clearer:

• local Gemini CLI here is 0.26.0 and does expose --experimental-acp
• with a clean HOME, ACP startup responds immediately and returns Authentication required
• with the normal user environment, Gemini can still stall during ACP startup, but acpx now fails fast with a structured timeout instead of hanging silently

The important operational requirement is that non-interactive ACP use needs non-interactive auth configured. In practice that means setting GEMINI_API_KEY or GOOGLE_API_KEY before running acpx gemini .... If those are missing, Gemini may fall back to interactive OAuth expectations that do not work cleanly in ACP subprocess mode.

I pushed a fix so acpx now surfaces this as an actionable GEMINI_ACP_STARTUP_TIMEOUT error instead of an indefinite hang, and the error message explicitly points at API-key auth / Gemini CLI upgrade as the next steps.

[vincentkoc]

Follow-up note: this is separate from the earlier Gemini registry fix that added --experimental-acp in acpx. That flag is already present and required, but it is not sufficient by itself to make Gemini ACP runs succeed.

Current behavior after that fix:

• --experimental-acp is being passed correctly
• a clean non-interactive environment gets an immediate ACP Authentication required response
• environments without API-key auth can still stall during Gemini ACP startup

So the remaining requirement is to ensure non-interactive Gemini credentials are configured, typically via GEMINI_API_KEY or GOOGLE_API_KEY, rather than relying on interactive OAuth state.

[vincentkoc]

Closing this from the acpx side.

The earlier acpx fix to pass --experimental-acp is already in place, and current validation shows the remaining failure mode is operational/auth-related: Gemini ACP subprocess runs need non-interactive credentials configured (GEMINI_API_KEY or GOOGLE_API_KEY).

acpx now also fails fast with an actionable GEMINI_ACP_STARTUP_TIMEOUT error instead of hanging silently when Gemini ACP startup stalls.