Bug: Connect downloaded and shared model directories to engine search paths #107

Summary

model_downloader.py:211 places ComfyUI models in the shared engine/models tree, but the ComfyUI launch command supplies no corresponding extra-model-path configuration. WebUI download paths use Path.home()/.ai-workflow/engine/webui/models, whereas the managed supervisor supplies directories under its configured engine root. Custom scan roots only index files.

Environment and evidence

• Review finding: F07 (2026-10-05 product/technical review).
• Baseline: Windows, dev at c1c5dbe. The remote dev matched this commit when filing.
• Evidence: Code.
• Priority recommendation: P1 - proposed first-release blocker. This is review triage, not a production-incident severity declaration.
• No real credentials, paid inference, engine installation, or unrelated process termination were used for review probes. Mocked observations establish the stated code behavior, not live-provider/GPU acceptance.

Reproduction or validation

Compare ModelDownloader target paths with the managed supervisors' launch arguments. ComfyUI downloads use engine/models without corresponding extra-model-path configuration. WebUI download paths are rooted under the home-directory engine tree while its supervisor uses the configured engine root. Adding a scan root only indexes files. Real model loading remains an integration test to perform.

User impact

A successful download or model scan does not guarantee that the chosen engine can load the model.

Proposed approach

Centralize path resolution; configure ComfyUI shared paths and WebUI model directories from the same registry; confirm a newly downloaded model appears in engine discovery and completes inference without manual relocation.

Acceptance criteria

• Resolve download, scan, and execution paths through one engine/path registry.
• Configure shared ComfyUI paths and WebUI model directories consistently.
• A newly downloaded compatible model appears in engine discovery and runs without manual relocation.
• Custom roots work by reference where supported and never imply compatibility from location alone.

Verification scope

Real GPU inference, paid-provider compatibility, and a clean-machine packaged desktop journey remain unverified. Any follow-up implementation should target dev under the repository's contribution/branching rules.