[M4n5ter]

Summary

CI still asserted the cleanup propagation policy from before #6527: a failed child retired its caller or made the caller's scope fail. Align those regression tests with invocation isolation. The original wrapper must remain usable, the actual failed child must retain its payload and capacity, and original receipts and shutdown failures remain observable. Remove the obsolete native-caller failure polling and redundant internal call/phase assertions.

The crash-recovery test from #6519 could reconnect while SIGKILL was still taking effect. Own the first real Host process and await its SIGKILL exit before recovery through connect_root. Keep the changed incarnation, ended original turn, preserved history and successful new-message checks. All five modified files are tests.

Verification

• All 63 existing Host JS and transport integration tests pass with compiler warnings denied.
• The focused caller-isolation behavior test passes after the final assertion cleanup.
• Real Host SIGKILL/restart integration passes (19.19s).
• Clippy with warnings denied passes for Host JS, transport and CLI, including all targets.
• Rust formatting and diff whitespace checks pass.
• Read-only advisor review found no blockers in either the custody checks or process ownership.
• Full CI will verify the merged revision and native archive replay.

AI use

• Generative tooling made a substantive contribution

Tool(s) and scope: OpenAI Codex diagnosed the CI failures, updated the existing tests, and validated and reviewed the changes.

Checklist

• Existing behavioral tests protect caller availability, retained failed ownership and crash recovery.
• Relevant local integration and lint checks pass as listed above.

Does this PR entail a change in behavior?

• No