SciMesh/docs/artifact-preview-task.md

Task: safely preview partial CSV artifacts in the UI

Assignment

You are the junior developer implementing one contained UI feature: an authenticated operator can preview a small portion of a CSV artifact belonging to the job they are viewing. This is a diagnostic aid, not a final-results page.

Read first

1. AGENTS.md
2. .agents/coordinator.md
3. docs/web-interface-plan.md
4. docs/api-contract.md
5. coordinator/internal/transport/http/ui.go and its tests

Current baseline

The coordinator serves an authenticated local web UI. Job detail pages already list partial result artifacts and provide job-scoped downloads. The browser has no worker token and must not learn storage paths. A partial shard CSV is never a global or final molecular-search result.

Scope

Add a Preview action next to eligible CSV artifacts on a job detail page.

• Preview only artifacts that belong to the requested job.
• Show at most the first 30 rows and read at most 64 KiB from storage.
• State clearly when content was truncated.
• Preserve the existing download action.
• For a non-CSV artifact, return a friendly, sanitized explanation rather than attempting to render bytes as text.
• Use an existing UI route pattern or add a small UI-authenticated endpoint; keep it separate from worker API routes.

Security rules

• Require UI Basic Auth for every preview request.
• Verify job ownership in the coordinator before opening the artifact; an artifact ID from another job must not be previewable.
• Never expose storage_key, filesystem paths, database errors, bearer tokens, or worker-local information.
• Do not use innerHTML for CSV fields. Use html/template escaping or textContent so strings such as <script>alert(1)</script> are displayed as data, not executed.
• Do not load the complete artifact into memory.

Out of scope

• Charts, molecule imagery, RDKit rendering, client-side CSV libraries, React, and a new frontend service.
• Changing job/task state, retrying tasks, or implementing reducer output.
• Redesigning the broader dashboard or job-creation workflow; that belongs to docs/user-space-task.md.

Suggested implementation shape

Keep UI transport, use case, and storage responsibilities separate. Return a small view model containing artifact metadata, column headers, rows, and a truncated flag. Reuse existing coordinator-owned artifact access rather than reading a path supplied by the browser. Keep the handler streaming/limited.

Acceptance criteria

• A valid partial CSV can be previewed from its own job detail page.
• The result shows no more than 30 data rows and marks 64 KiB/row truncation.
• Empty and malformed CSV content fail safely with a clear message.
• A non-CSV artifact is rejected safely.
• Unauthenticated access is rejected; a cross-job artifact request is not disclosed or served.
• HTML-like values are escaped in the rendered preview.
• Existing artifact downloads still work.
• Add Go tests for all cases above and run go test ./... and go vet ./....

Handoff

Work in one focused branch and one PR. Report files changed, any API impact, test commands/results, and known limitations. Do not commit datasets, generated CSV files, Docker volumes, .venv, or worker-data/.