Make core orchestration state transitions explicit

[JustYannicc]

The status schemas name run, provider-turn, and runtime-request states, but they do not describe legal transitions. The code also repeats provider-turn terminal checks in several places. That makes each state change harder to review and gives those checks room to drift.

A previous upstream issue (#1882) asked for guards in the older Turn decider and was closed as misfiled. This proposal covers current Orchestration V2 event types and keeps transition decisions in command handlers.

I propose starting with a narrow contract-first slice:

• Define typed transition tables and shared terminal predicates for runs, provider turns, and runtime requests in the shared contracts.
• Reuse the run and provider-turn predicates where the server and adapters make terminal decisions. Command handlers remain authoritative; transition edges act as a test contract.
• Add forbidden-edge tests and one replay test that checks a named approval scenario against the tables through the existing orchestrator replay testkit.

The working branch is proposal/explicit-lifecycle-catalog-20261018 at 4f9cd5ccb15dae75ad64d1261726387f9e36c2d3, based on upstream main at 9c161462c94f7d9d6d9169da5c841457cbadf213. The replay uses a recorded Codex protocol fixture and a temporary workspace. It checks the resulting domain-event history and stored events; it does not seed projections directly. The demo data is a local file operation that requires approval.

This branch covers only run, provider-turn, and runtime-request transitions plus one replay path in a static catalog. It is not a loader that seeds a development environment into arbitrary named states. Provider-session and other lifecycle tables, the UI states that surface them, a scenario CLI or dev menu, an all-state coverage gate, and model-based command-invariant tests remain separate follow-ups. No runtime dependency was added.

Would maintainers approve this first slice? Which additional lifecycles, if any, should be included before a PR?

Verification on the branch:

The focused lifecycle contract and replay tests passed (2 files, 3 tests). Filtered contracts/server typechecks passed with concurrency 2. Targeted lint passed on all changed files; after removing one unused import, lint passed again on the changed execution file.