Files tab: 'Failed to load text content' for markdown files — content-disposition: attachment prevents inline rendering

[vybe]

Summary

The Files tab shows "Failed to load text content" when trying to open any text/markdown file in an agent's workspace. The file is never displayed.

Reproduction

1. Navigate to any agent's Files tab
2. Click to preview a markdown file (e.g. CLAUDE.md, README.md)
3. The preview panel shows: "Failed to load text content"

Root Cause

The /api/agents/{name}/files/preview endpoint returns a Content-Disposition: attachment header:

Content-Type: text/markdown; charset=utf-8
Content-Disposition: attachment; filename="CLAUDE.md"

The attachment disposition instructs the client to treat the response as a file download rather than displayable content. The frontend receives an HTTP 200 with a body, but the disposition causes it to fail to render the content inline — hence "Failed to load text content".

Fix

Change the Content-Disposition header on the file preview endpoint from:

Content-Disposition: attachment; filename="..."

to:

Content-Disposition: inline; filename="..."

This applies to all text-based file types served by the preview endpoint (.md, .txt, .yaml, .py, .ts, etc.).

Observed on

• Instance: eu2 (Trinity v3a3e9a72)
• File types confirmed affected: .md (markdown)
• Likely affects all text file types given the header is set at the endpoint level

Expected Behaviour

Clicking a text file in the Files tab displays its content inline in the preview panel.

[vybe]

/claim

[github-actions]

Claimed by @vybe. Label status-in-progress added.

Next steps:

1. Create branch: feature/784-<short-slug>
2. Implement the feature
3. Open a PR with Fixes #784

[vybe]

Shipped in v0.6.0 (released via #998).