toolpath: agent/tool handoff via provenance docs in dispatch

[bdelanghe]

Motivation

prx dispatches independent task sessions (the dispatch door / --remote-serve, ADR-DISPATCH-*). As work moves between sessions — and across heterogeneous agent tooling (Claude / Codex / Gemini / Cursor) — there's no neutral carrier for "here's the work and how it got here." toolpath is exactly that: a vendor-neutral session document that path resume / path export <harness> can project back into any supported agent.

This issue makes a dispatched unit of work carry its toolpath doc, and lets a resume project it into the operator's agent of choice.

Proposed approach

• On dispatch, seed the task session with (or attach) the originating toolpath doc, so the child starts with the provenance context of what preceded it.
• On resume/handoff, path resume <ref> (or path export <harness> --project) projects the doc into a fresh session in Claude/Codex/Gemini/etc.
• Ref transport uses the pathbased broker (claude-box#239) or a local CAS — no token in the box.

Acceptance criteria

• A dispatched task session can be started from a toolpath doc ref and sees the prior provenance.
• A completed session's doc can be resumed into a DIFFERENT harness than it was produced in (e.g. Claude session → path export codex), demonstrating the vendor-neutral handoff.
• The handoff carries no ambient Pathbase/agent credential into the box (broker-mediated).
• Documented as a handoff flow (sibling to HANDOFF.md / the dispatch ADRs).

Refs

Builds on the dispatch door (ADR-DISPATCH-*), claude-box#239 (pathbased share/resume). Value: heterogeneous agent/tool handoff.

🤖 Filed with Claude Code