Expose identity-bound awaited host admission for native Remote input

## Feature request

Please expose and document a supported host admission contract for native Remote-origin input that combines runtime-attested input identity with an awaited allow/deny/hold decision before the relevant history persistence, model dispatch and effects.

This is a public API-contract request, **not a newly reproduced runtime failure or a claim that current hooks provide this guarantee**. It is also separate from owner-connection/RPC transport failures.

## Public versions and evidence

- Released SDK: [v1.0.13](https://github.com/github/copilot-sdk/releases/tag/v1.0.13), commit `f13e4a2cc7e4e220974d2333142234e162a3252e`.
- Public main examined: `f45c46fd1812f8bed5b4cbc250f47177c83068f0`; [comparison from the release](https://github.com/github/copilot-sdk/compare/f13e4a2cc7e4e220974d2333142234e162a3252e...f45c46fd1812f8bed5b4cbc250f47177c83068f0).
- [Submitted-hook documentation at that revision](https://github.com/github/copilot-sdk/blob/f45c46fd1812f8bed5b4cbc250f47177c83068f0/docs/hooks/user-prompt-submitted.md) does not provide the required explicit rejection contract.
- [Experimental authorization events](https://github.com/github/copilot-sdk/blob/f45c46fd1812f8bed5b4cbc250f47177c83068f0/nodejs/src/generated/session-events.ts#L9485-L9689) describe message/effect authority and replay after a turn is read. They are not a documented identity-bound pre-input barrier.

Caller-supplied `MessageOptions.source`, turn indexes, timestamps, text-derived IDs, mutation-only hooks and unawaited event observers do not establish the requested combination. Throwing from a callback is not a substitute for documented fail-closed semantics.

## Minimal contract demonstration

Using the published hook types, dispatch semantics and submitted-hook documentation above, a host cannot express a supported identity-bound rejection that is guaranteed to run before both history/model admission and effects for a native Remote-origin message. Later authorization records necessarily reference an already-read message. No live accounts, private prompts or runtime traces are needed to demonstrate this interface gap.

If a supported API already provides this, please identify its exact version, schema, ordering guarantees and Remote-origin example.

## Requested acceptance criteria

1. Runtime-attested principal/origin, source session and generation, plus stable original root message/event and causal identities that remain consistent across reconnect. Caller-provided provenance labels must not be treated as authentication.
2. An explicitly awaited host decision before the documented persistence/model/effect boundaries, including auxiliary model activity. Please identify whether the guarantee covers remote/cloud persistence, local persistence, or only source-side dispatch. A source callback must not imply that GitHub has not already received the input.
3. Explicit denial, malformed responses, timeout, exception, missing owner and disconnect produce typed non-success and prevent the covered downstream actions. No swallowed-exception or unawaited-observer success path.
4. Real native Remote positive and negative/spoofed/replayed cases use the same admission path. Reconnect preserves decisions and identities without duplicate model/tool/history effects; distinct equal-text turns remain distinct.
5. Publish supported CLI/SDK version pins, ordering tests and an example retaining ordinary allowed custom-tool/permission handling after admission.

## Important separation

Awaited custom-tool and permission handlers are useful for controlling effects after input. This request is for the earlier admission boundary; it does not propose weakening existing permission checks. Likewise, fixing a transport problem, selecting a different model or enabling BYOK is not by itself evidence about cloud intake, account visibility or data retention.

Start by comparing the released and public-main revisions, then read docs/hooks/user-prompt-submitted.md and nodejs/src/generated/session-events.ts around the cited sections. Trace the documented hook and authorization entry points before proposing changes. Done means the supported contract, ordering, failure behavior, identity continuity, version pins, and native Remote tests are documented and verified.

索引モデルが issue の本文から書いたものです。