Headless CLI: remaining headless CLI capabilities (attachments, per-run model/backend selection, npm publication)

[ewen-poch]

Summary

The first-milestone headless CLI from #276 / #316 is shipped. This issue tracks the capabilities that were intentionally deferred until their runtime contracts can be made stable.

Deferred items

1. File and directory attachments (--attach)

open-science run --project "systematic-review" --attach ./papers --prompt-file task.md --wait

Needs a stable contract for how files/directories are ingested, scoped, and cleaned up by the daemon.

2. Per-run model selection

Allow specifying the model for an individual run without changing global configuration. Requires a stable per-run runtime contract.

3. Per-run agent-backend selection

Allow specifying the agent backend for an individual run. Same stability requirement as above.

4. npm package publication

The @aipoch/open-science package (packages/open-science/package.json) is ready but not yet published to the npm registry. Currently only usable from the installed application or a source checkout.

Non-goals

The Web UI session deep-link and live-sync work is separately scoped in #314 and is not part of this issue.

Context

• Original proposal: Feature request: Add a true headless CLI for running research tasks #276
• Implemented milestone: feat(cli): add headless task SDK and CLI #316