The v3 Settings "Save" button posts dlc_dir together with demucs_server_url,
default_arrangement and av_offset_ms in one request. POST /api/settings
validated dlc_dir first and early-returned "DLC directory not found" before it
ever processed demucs_server_url, so on a machine whose DLC path doesn't resolve
(fresh install, unplugged/network drive, a path carried over from another
machine) setting the Demucs server address silently failed — reported in
got-feedBack/feedBack-demucs-server#3 (macOS 07-05 nightly).
- server: a non-resolving dlc_dir is now recorded as a warning and skipped
rather than aborting the whole POST, so the co-submitted keys still persist.
The bad path is surfaced via a new additive `warnings` field and folded into
`message` so the settings status line still shows it.
- client (v3): the Demucs input now autosaves on blur/enter via a single-key
persistSetting POST, like every other v3 setting, so it never depends on the
coupled Save button.
- tests: cover the decoupling and the unchanged happy path.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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