feat(cloud): add native steering to agent adapters

[tatoalo]

Problem

Active Codex and Claude cloud turns cannot accept native steering safely.

Changes

Adds adapter-level steer support with explicit acceptance and turn-boundary handling.

[trunk-io]

Merging to main in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here

[tatoalo]

• feat(cloud): expose steering controls for cloud sessions #3541
• fix(cloud): hydrate resumed transcripts atomically #3540
• fix(cloud): reconcile resumed events by leaf identity #3539
• feat(cloud): negotiate idempotent steer delivery #3538
• feat(cloud): add native steering to agent adapters #3537 👈 (View in Graphite)
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit eba3248.}

[greptile-apps]

This review was skipped because it would exceed your organization's monthly flex usage limit. Raise the limit in billing settings or wait until the next billing period resets limits.

[posthog]

👋 Visual changes detected for this PR.

Review and approve in PostHog Visual Review

If these changes are unexpected, they may be caused by a flaky test or a broken snapshot on master. Don't approve — rerun the job or wait for a fix.

[stamphog]

Complex behavioral change to agent steering across both Claude and Codex adapters — the Codex path now returns immediately on steer instead of awaiting turn completion, and the Claude path introduces deferred turn completion keyed on a UUID set that must be cleared by an incoming echo. No human has reviewed this. Request a team review before merging.