feat(agent): tell cloud agents to upload deliverables as artifacts

[puemos]

Problem

Cloud agents can create downloadable files but leave them only in the workspace, making those deliverables inaccessible to users. Even after uploading a file, an agent may reference its local path instead of the working download URL.

Changes

• Tell cloud agents to upload non-code file deliverables before their final response.
• Require the final response to link the download URL returned by upload_artifact, never the local workspace path.
• Keep source code and repository changes in commits and pull requests.

Why: Users should receive a working download link whenever an agent produces a file, without needing to remind the agent how to deliver it.

How did you test this?

• git diff --check
• Biome and the agent typecheck could not run in this fresh clone because dependencies are not installed.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[posthog]

Done. Opened #3944 (draft) in posthog/code.

What the tool is: upload_artifact (mcp__posthog-code-tools__upload_artifact) is a cloud-only local tool that uploads a file from the session workspace to PostHog storage so it shows up in the user's artifact panel as a download. It's already gated to cloud sessions with a live task run, and its own description says to call it for non-code deliverables — but nothing in the system prompt reinforced that, so the agent only did it when told.

The change: added a "Delivering non-code files (artifacts)" section to the cloud task system prompt (agent-server.ts) telling the agent to call upload_artifact for reports, images, rendered canvases, data files, etc. before its final reply — and not for source/repo changes. It's skipped for Slack-origin sessions, since those get a runtime "no artifact delivery" constraint instead (this very session is one). Also exported UPLOAD_ARTIFACT_QUALIFIED_TOOL_NAME so the prompt references the tool id from one source, matching the signed-commit pattern.

I put it in the cloud prompt rather than the base desktop instructions on purpose — the tool doesn't exist in local desktop sessions, so a global instruction would reference a missing tool.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit ecc0aba.}

[posthog]

✅ Visual changes approved by @puemos — baseline updated in f8ef7a6.

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