orchestration: FileSubagentPersistence, shared InFlight, result policy helpers, awaiting-user contract #472

Move these generic pieces out of OpenHuman agent/subagent_host/ (see openhuman#7929):

• FileSubagentPersistence. About 580 lines of file-locked persistence: fs2 locks, sha256 key components, a per-task index, atomic replace, terminal records that read both current and legacy formats, and checkpoint-dir canonicalisation. From lifecycle.rs and lifecycle_checkpoint.rs. Upstream currently has only the trait and an in-memory store.
• Shared singleflight. OpenHuman HostInFlight copies the driver's InFlight. Expose one process-shared in-flight dedupe on SubagentDriver, built on harness cache/singleflight.rs.
• SubagentOutcome gaps, so hosts can drop their parallel SubagentRunStatus/request taxonomy (subagent_host/types.rs): worker_thread_id, tier, model_override, usage/cost fields.
• result_policy additions:
  • a UTF-8-safe result cap (ops/runner_result_cap.rs) and is_safe_task_id (ops/pause_checkpoint.rs);
  • outcome framing and detection of unexecuted tool-call stubs (orchestration/tools/dispatch_outcomes.rs);
  • the artifact-offload contract and caps that ops/runner.rs reimplements.
• The [SUBAGENT_AWAITING_USER] pause/resume envelope as a harness contract (orchestration/tools/awaiting_user.rs).
• subagent_framing gaps: result-contract headings and spec dedup on ToolSnapshot (ops/prompt.rs). restrict_tools gaps: ToolScope plus skill_filter narrowing (tool_prep.rs).
• Iteration-cap checkpoint summary with a deterministic fallback (ops/checkpoint.rs, plus build_cap_digest from ops/graph/dispatch.rs), placed in harness summarization.

Done when: merged upstream with tests in sibling *_tests.rs, released or tagged, and the OpenHuman follow-up can delete the host copy after a gitlink bump on vendor/tinyagents.

Parent: tinyhumansai/openhuman#7929, which has the full file-by-file verdict tables.