[Bug]: Windows LM Studio installation remains at 75% and is not detected after successful llmster install

PAIR version or commit

PAIR desktop application 0.91.7

Affected component

Engine or model management

Environment

• OS: Microsoft Windows 11 Pro 10.0.26200, build 26200
• Architecture: x64
• GPU: NVIDIA RTX PRO 6000 Blackwell Workstation Edition
• GPU driver: 32.0.15.8216
• LM Studio CLI: 1.3.3, commit 07b7252
• llmster: 0.0.23-1
• Cluster size: 2

Steps to reproduce

1. Have LM Studio installed on Windows with its server running on port 1234.
2. Install and open PAIR 0.91.7.
3. Select the LM Studio Download/install action.
4. Observe progress reach 75% at the installing stage.
5. Wait approximately 108 seconds.
6. Stop the existing server with lms server stop, then fully stop the daemon with lms daemon down.
7. Run the same official https://lmstudio.ai/install.ps1 script manually.
8. Confirm that it successfully installs llmster 0.0.23-1.
9. Restart PAIR and retry the LM Studio installation.

This was reproduced three times, including after confirming that lms.exe was present on PATH and executable by the same Windows user.

Expected behavior

PAIR should detect or adopt the existing LM Studio installation, configure its managed backend on port 1235, and complete registration. If an existing daemon must be stopped first, PAIR should report that requirement instead of remaining at 75%.

Actual behavior

PAIR reaches 75% and later reports:

engine "lmstudio" was not detected after install

PAIR's proxy takes port 1234 and repeatedly checks its expected backend at 127.0.0.1:1235, but that backend is not registered or kept running. engine-state.json continues to contain only Ollama.

Running the official LM Studio installer manually succeeds:

Install completed at %USERPROFILE%\.cache\lm-studio\llmster\0.0.23-1.
Installation finished successfully! llmster is ready to launch.

Closing PAIR and restoring the original LM Studio service returns port 1234 and the existing models to normal operation.

Sanitized logs

engine:install-progress
engine=lmstudio percent=75 stage=installing

[nvpair-engine-manager] WARN engine error reported
id=engine-manager:install-failed:lmstudio
message="engine \"lmstudio\" was not detected after install"

engine:install-progress
engine=lmstudio
error="engine \"lmstudio\" was not detected after install"
percent=-1
stage=failed

[lmstudio-proxy] INFO local backend updated
engine=lmstudio host=127.0.0.1 port=1235 healthy=false

Confirmations

• I searched existing issues for duplicates.
• This is not a security vulnerability.
• I agree to follow the Code of Conduct.