fix: set inline disposition for renderable blob elements

[axelray-dev]

Fixes #2946

Summary

SQLAlchemyDataLayer.create_element never passed content_disposition to storage_provider.upload_file. Azure Blob Storage defaults to Content-Disposition: attachment in this case, which causes browser-renderable elements (PDF, images, audio, video) to render blank on chat resume because iframes and media tags refuse to display content served with an attachment disposition.

This fix sets content_disposition='inline' for browser-renderable MIME types while preserving the existing behavior for non-renderable uploads.

Scope

Only browser-renderable MIME types are affected:

• application/pdf
• image/*
• audio/*
• video/*

All other element types (generic files, text/plain, application/octet-stream, etc.) keep content_disposition=None, preserving the existing download behavior.

Changes

• backend/chainlit/data/sql_alchemy.py: determine content_disposition before upload_file call based on element.mime
• backend/tests/data/test_sql_alchemy.py: 3 new tests verifying disposition behavior for PDF, image, and text/plain elements

Testing

Backend tests run locally:

• tests/data/test_sql_alchemy.py: 18/18 passed (including 3 new tests)
• tests/data/: 71/71 passed, 1 pre-existing error (test_get_data_layer fails without built frontend)
• ruff check: all passed
• ruff format --check: all passed
• git diff --check: clean

Note: pre-commit hooks could not run locally (frontend build OOMs on VPS). CI will verify lint and format.

Backward Compatibility

This change is fully backward-compatible per AGENTS.md requirements:

• Non-renderable element types are unaffected
• The content_disposition parameter was already accepted by all storage clients but never used by SQLAlchemyDataLayer
• The fix follows the same pattern used in chainlit_data_layer.py

---

Summary by cubic

Serve browser-renderable blobs with inline Content-Disposition so PDFs, images, audio, and video display in iframes/media on chat resume. The policy is now centralized on Element and applied across data layers; non-renderable files keep download behavior.

• Bug Fixes
  • Centralized disposition in Element.get_content_disposition() and used by SQLAlchemyDataLayer, ChainlitDataLayer, and DynamoDB.
  • Set inline for pdf, image, audio, video; keep default for others. ChainlitDataLayer preserves attachment; filename=... for generic files (non-GCS). Tests added for inline/default cases and Element behavior.

^{Written for commit 3d7346e. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[dokterbob]

@codex review

[dokterbob]

Please see my comment.

[dokterbob]

Is there a more structural/consistent way to define renderable mime types?

I don't think this definition belongs inside a storage engine. I also don't think it should be in a single storage engine (how are others doing it?).

Sanity would dictate that some piece of code somewhere decides whether some attachment is rendered inline. Probably closer to the frontend than the storage backend. If this code already determines it, we should get the info from where it's determined, and there should be a well-defined interface for all data backends to look this up in the same way.

[axelray-dev]

Moved the renderable disposition policy out of SQLAlchemy into Element.get_content_disposition().

It is based on element.type (image/pdf/audio/video), not MIME, because that is what the frontend uses for rendering. Element.display is still only UI placement.

SQLAlchemy, DynamoDB, and ChainlitDataLayer now all use the same helper. ChainlitDataLayer still keeps its previous attachment/GCS fallback for non-renderable files.

Also fixed the backend typecheck issues in the SQLAlchemy tests.