fix: skip unsupported files in a batch instead of rejecting the whole upload

[dai123x]

Summary

Dropping several files at once where one has an unsupported type rejects the entire selection: validateFiles bails out with Unsupported file type: … on the first offender, so a drop of photo.png + notes.txt + setup.exe attaches nothing and the supported files have to be picked again one by one (reported with a recording in #16659). #15358 already made duplicates and oversized files drop out of a selection one by one while the rest uploads; unsupported types were left all-or-nothing. This change moves the per-file MIME check into that same partition step, so the supported files attach and a toast names the skipped ones: "Skipped unsupported file(s): setup.exe".

Fixes #16659

How it works

selection
  partitionUploads          # per-file rules: duplicate → fileSize → type (inference + allowlist)
    survivors → validateFiles       # unchanged; still the safety net plus batch rules
    skipped   → reportSkippedUploads  # per-file skip toasts

partitionUploads now screens each file's type alongside duplicate and size: it infers the MIME type, re-types the file in fileList in place exactly as validateFiles does, and skips files the allowlist rejects with a new unsupported skip reason. The allowlist choice — the endpoint's own list, or the configured text/OCR/STT lists for context tool resources — moved into a shared getMimeTypesToCheck helper so the partition and validation paths cannot drift, and both processFiles partition calls (pre- and post-processing, the latter after HEIC conversion and resize) pass fileConfig and toolResource through. validateFiles keeps its type loop unchanged: when the partition keeps nothing, the untouched selection still goes through the usual all-or-nothing checks and reports the pre-existing "Unsupported file type: …" error, and the loop remains the guard for callers that do not partition.

Type of change

• Bug fix

Testing

Tested environments/configuration:

• OS: Windows 11, Node v24.17; the verification below is the client unit suites (jsdom via jest).

Automated tests:

• Added partition cases in client/src/utils/__tests__/validateFiles.spec.ts: an unsupported file skipped while the files picked alongside it are kept, a fully unsupported selection, inference re-typing, an undeterminable type, and the context tool-resource allowlist.
• Added hook cases in client/src/hooks/Files/__tests__/useFileHandling.test.ts: a batch of photo.png + setup.exe uploads the png and reports com_error_files_skipped_unsupported, while a fully unsupported batch is still rejected in full with the pre-existing error and no skip notice.
• npx jest src/utils/__tests__/validateFiles.spec.ts src/hooks/Files/__tests__/useFileHandling.test.ts — 93 passing (32 + 61); the wider src/hooks/Files + src/utils suites pass except pre-existing locale-dependent formatCost expectations in tokens.spec.ts ($ vs US$, unrelated to this change).

Screenshots / recordings

No screenshot: no visual component changed. The only visible difference is the skip toast, which reuses the same error-toast mechanism as the existing duplicate and size skip notices ("Skipped duplicate file(s): …", "Skipped file(s) over the {{0}} MB size limit: …"), and the suites above assert the new com_error_files_skipped_unsupported key.

Risk / compatibility

Low. The only behavior change is on the upload-selection path (processFiles), and only when a selection contains a file the endpoint cannot accept: previously everything was rejected, now the unsupported file is skipped and the rest uploads. A selection where nothing survives is still rejected in full with the same messages as before. Server-side validation is untouched — the client merely stops sending files the server would have rejected anyway.

Checklist

• I reviewed my own changes
• Relevant tests have been added or updated
• Existing relevant tests pass
• The change does not introduce new warnings or errors
• User-facing or complex behavior is documented where necessary (N/A — no documentation change needed)
• Required dependency changes have been merged/published (N/A)
• Required documentation PR: N/A

[dai123x]

Friendly ping — none of the workflows have run on the current head (0abcac82); all seven are sitting at action_required:

• Static Checks
• Frontend Unit Tests
• Playwright E2E Tests
• Lighthouse CI
• Docker Build Smoke Tests
• Bombadil Property Exploration
• Codegraph Select (observe)

Could a maintainer approve the runs and take a look? The change reuses the existing per-file drop behaviour added in #15358 and only extends it to unsupported MIME types, so dropping photo.png + notes.txt + setup.exe now attaches the two supported files instead of rejecting the whole selection. Closes #16659.

Happy to rework the approach if you would rather handle it differently.