fix(files): keep file extensions on extensionless downloads

[waleedlatif1]

Summary

• Files whose stored name has no extension (a file renamed to <name> in the Files UI, or a URL fetch whose path ends in a bare download segment) downloaded with no extension, so the saved image could not be opened until one was added by hand
• Add ensureFileNameExtension and apply it to zip entry paths (internal + v2 bulk download, Chat compress), to createFileResponse for single-file downloads (generalizes the existing Sim-page .html re-append), and to the URL-fetch save path so new files are stored with an extension
• getExtensionFromMimeType now ignores content-type parameters such as ; charset=utf-8

Follow-ups, out of scope here: the markdown export's embedded-asset zip and the v1/v2 single-file routes build their own Content-Disposition and still emit the extensionless name; the Chat agent's private ensureFileExtension can be consolidated onto the shared helper.

Type of Change

• Bug fix

Testing

• Unit tests added for the helper, zip entry paths, createFileResponse, and the URL-fetch naming; affected suites pass
• bun run lint, bun run check:audits (45 audits), docs-manifest:check, and type-check pass

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Sep 7, 2026 11:29pm UTC

[greptile-apps]

Greptile Summary

This PR preserves MIME-derived extensions when extensionless files are fetched, served individually, or placed into ZIP archives.

• Adds a shared ensureFileNameExtension helper and parameter-tolerant MIME lookup.
• Applies the helper across single-file responses, external URL imports, and bulk/archive paths.
• Adds focused coverage for MIME parameters, duplicate ZIP names, longer extensions, and page names containing punctuation.
• The previously reported extension-length issue is fixed, and its thread was resolved.

Confidence Score: 5/5

The PR appears safe to merge with no outstanding correctness, security, or repository-rule issues.

The follow-up replaces the capped extension regex with the repository’s existing alphanumeric-extension predicate, preserving long extensions while retaining the intended behavior for punctuation-bearing page names. The previous finding was fully addressed and its thread was resolved.

Important Files Changed

Filename	Overview
apps/sim/lib/uploads/utils/file-utils.ts	Adds shared MIME-derived extension handling and fixes extension detection without imposing a length cap.
apps/sim/app/api/files/utils.ts	Uses the shared helper when deriving single-file response names before secure disposition selection.
apps/sim/lib/uploads/contexts/workspace/fetch-external-url.ts	Adds a MIME-derived extension to extensionless URL path names before workspace upload.
apps/sim/lib/uploads/zip-entry-path.ts	Adds missing MIME-derived extensions before ZIP-path sanitization and collision handling.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Stored or fetched filename] --> B{Alphanumeric extension exists?}
  B -- Yes --> C[Preserve filename]
  B -- No --> D[Map content type to extension]
  D --> E[Append mapped extension]
  C --> F[Single-file response or ZIP entry]
  E --> F

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[waleedlatif1]

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[waleedlatif1]

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