Zed nightly: agent: Use receipts and reported state for native turns (#65420)

Activate native acceptance and reported state atomically with its
completion consumers.

• Return acceptance with the retained message ID. Session-owned drivers
  report running/requires-action/idle independently of receipt and
  completion observers.
• Keep completion observers native-only for subagents and eval. Native
  no longer implements the legacy completion-based prompt path; external
  v1 behavior and SDK/wire rollout pins remain unchanged.
• Preserve checkpoints, rewind, command expansion order, retained source
  fields, usage and provider-shaped persistence. Compact markers retain
  identity without user bubbles.
• Use NativeRetryAction for retained command intent. Failed
  preparation retries the resolved action; prepared history resumes
  without duplicate expansion.

Prerequisites #65502 and #65504 are merged. This PR targets main;
conflicts are resolved and only the six-file native slice remains.

Validation on the merged base: 1,815 tests passed, 11 ignored;
100-seed native/subagent/E2E-helper/skill-body checks; eight-crate
Clippy; test-target and E2E-feature compilation; both Zed binary checks;
formatting and diff checks. Scoped conflict-resolution review passed.
Credentialed live E2E/provider, live SIGTERM and non-macOS workflows
remain unrun.

Review thread:
https://delta.dev/trunk/join/thread_01m4e0prq2aaq6k0avcqe3688r#s=Deoszm1s

Release Notes:

• N/A