Add relay-up plugin: Session Relay — cross-session task & chat relay

[Great-us]

What user problem does this solve?

Coordinating multiple ZCode windows (e.g. an expensive model as leader + cheap models as workers) currently means copy-pasting between windows by hand. relay-up turns dispatch → execute → report → review → dispatch into a fully automated loop. All transport is plain file I/O — the relay itself never calls any model API, and workers always remain visible native windows (a deliberate principle).

What's included

• /relay-up skill — scaffolds the mailbox (relay-task v1.1 card lane + directed chat lane), the relay-next worker skill, runtime skeletons, and two small tools into any project. Idempotent: existing files are never overwritten (restore semantics). /relay-up down backs everything out to a timestamped folder.
• Hooks (SessionStart / UserPromptSubmit / Stop) — session registration for model accounting, pending-chat delivery as context, and atomic claim of the next card + chat with continuation injection. Activated only in projects containing the relay/relay.enabled marker that /relay-up writes; entirely fail-open (any exception exits silently with exit 0).
• Worker flow — drain-mode execution (all pending cards in one turn), optional per-window 5-minute watcher cron installed from the included bootstrap card template, 9-field report contract.
• Leader flow — tools/verify_report.py: 7-check acceptance (field presence, dual SHA-256, task-id match, status enum, artifacts existence), plus idle governance (sustained idleness stands workers down and throttles the leader; one sentence revives everything).

Reference implementation and full docs: https://github.com/Great-us/relay-up

How it was tested

• 25 stdlib-only tests in plugins/relay-up/tests/ — python tests/test_relay_hook_chat.py → 20 OK; python tests/test_chat_send.py → 5 OK (claim/inject/merge/dedupe/quarantine/gating/fail-open/multi-project marker routing; chat_send CLI).
• Platform behaviors verified against live ZCode sessions (2026-09): Stop continuation injection via {"decision":"block"}, UserPromptSubmit additionalContext delivery, the 3-continuations-per-turn cap, cron self-wake, and one full end-to-end loop (bootstrap → dispatch → execution → report → acceptance → review chat).

Version and marketplace registration

relay-up v0.1.0, category developer-tools, registered in the root marketplace.json with name/version/description identical to the manifest.

Dependencies, network, permissions, and side effects

• Requires python (3.8+, stdlib only) on PATH.
• No network access. No model/API dependencies beyond the user's own sessions. No credentials are read.
• File writes: only inside the target project's relay/ tree, .zcode/skills/relay-next/, and two tool files (tools/chat_send.py, tools/verify_report.py) — all created by /relay-up and declared in the plugin README.
• Hooks read session metadata from stdin and write only under the marked project's relay/runtime/ (session registry, chain log, chain state).
• Optional automations: the bootstrap card creates a per-window watcher cron via the platform scheduler; /relay-up down and shutdown cards remove them.
• Third-party code/assets: none. All original code, MIT licensed.

Checklist

• plugin name is unique and kebab-case
• .zcode-plugin/plugin.json present; name/version/description match the root marketplace.json
• bilingual README.md / README_CN.md with side effects documented
• python scripts/validate.py → OK: 27 plugin(s) validated
• python scripts/build_dist.py → exit 0 (relay-up 0.1.0 zip, 34,740 bytes)
• git diff --check clean