Define portable nonterminal messages and owned asynchronous child lifetimes

[irl-dan]

Use case

While composing an evidence observatory, we want a coordinator to start a detective, receive a declared nonterminal snapshot message, start an independent auditor against that immutable snapshot, and send a follow-up direction to the still-running detective. Auditors produce findings only; a later synthesis contract owns any record changes. The case can remain open throughout.

This is a design-time expressiveness finding, not a report of a failed executable run. We currently use completed, bounded responsibility renders and pinned snapshots as the supported fallback.

Current boundary

At fc2810e:

• ProseScript scope is intra-node; Forme wires maintained responsibilities.
• The ProseScript grammar provides calls and parallel joins, but no first-class live child handle or nonterminal message surface.
• Runtime delegation waits for delegated work before resuming the caller.
• Maintained truth commits after successful completion; an informal progress message must not be mistaken for a maintained-state commit.

Focused request

Define whether author-visible, owned asynchronous child interaction belongs in the portable contract/ProseScript surface. If supported, specify nonterminal message versus terminal return/failure, routing, child lifetime, cancellation, and capability requirements before choosing syntax. If intentionally unsupported, document that boundary and the bounded-render lowering clearly.

This is distinct from #20: adapting an asynchronous host to a blocking call would solve host compatibility while leaving this author-visible interaction unexpressed. It is also distinct from #169, which can teach an existing topology without adding live-frame semantics. No imperative cross-node scheduler is requested here.

Retestable scenario

1. Parent starts detective child D.
2. D emits message M referring to an immutable, explicitly preserved snapshot S1; D remains live.
3. Parent starts auditor A with S1 only.
4. A returns findings F; this has no authority to mutate D or adjudicated claims.
5. Parent sends D a follow-up question derived from F.
6. Parent completes or is cancelled; required children must settle, with no silent orphaning.

Acceptance conditions: each message has an attributable sender/recipient and snapshot identity; messages are nonterminal; a message does not publish maintained truth implicitly; cancelled descendants have defined outcomes; unsupported hosts reject a required capability or use an explicitly permitted fallback; crash/restart behavior distinguishes persisted memory from a resumable live frame.

Alternatives and layer

Completed snapshot renders already allow ongoing case work, independent review, and later synthesis. We will use that model unless live interaction is needed. Adapter-specific background workers are possible but do not establish portable language semantics.

The semantic decision belongs in contract/VM/ProseScript documentation, with a focused conformance scenario. Host transport belongs in adapters. No implementation, hosted scheduling feature, private evidence, or proposed syntax is included in this issue.

[irl-dan]

Follow-up from an actual multi-cycle observatory run: we used host subagents and manually interpreted contracts, not a compiled/mounted OpenProse runtime. The requested live-child semantics therefore remain an unimplemented language-level need; these runs are not evidence of conformance.

The practical pressure was strongest around checkpoint review and follow-up direction. We needed to distinguish preparation while an input was unavailable, readiness of an exact preserved snapshot, final audit completion, and whether a detective could continue. The coordinator managed those states and pinned references manually. An early handoff once failed to state its preparatory boundary; a later supplement did not retroactively fix the original task. We clarified the local contract and observed a subsequent preparation → exact ready-snapshot → completed review sequence.

This strengthens the value of the existing acceptance scenario: a nonterminal message needs an attributable immutable subject and must not implicitly commit maintained truth or grant an auditor mutation authority. For hosts without portable live-frame support, documented completed-snapshot renders remain a sound fallback. Deadline shutdown also needs to settle/checkpoint children without treating an open investigation as exhausted.

No new syntax proposal or demonstrated OpenProse runtime defect is implied. This adds operational context to the existing issue rather than requesting a second async API.