feat(agent): preview post-tool convergence before boundaries

[zhengdaqi]

Summary

• add a bounded, domain-neutral PostToolUse convergence preview transported only through internal lifecycle metadata
• defer one required Progress Lease boundary only for confirmed progress, completion, or an in-budget handoff; fail closed before the model when the next PreModelRequest does not confirm it
• adapt Legal Coverage only for durable legal-state writes and state-changing plugin CLI commands, with independent Gateway and O1 decisions

Why

The preserved V24R14 Case 09 trajectory spent an estimated 10-15 minutes on 19 forced full compactions. In the dominant ordering defect, a tool had already written a valid state-bound proposal, but AgentLoop compacted before the next PreModelRequest could expose the new handoff.

Boundaries

• no validator, model, Router, Memory, deadline, corpus, prompt, or Lease threshold change
• no Case 09 text matching
• repair-only, replayed, over-budget, and multi-scope previews cannot defer
• PostToolUse previews are advisory and never persist lease state

Verification

• focused cross-layer gate: 103 passed, 0 failed
• full repository suite: 325 passed, 0 failed
• real local Gateway: two deferred boundaries, zero forced full compactions, complete O1 model/tool/turn pairing, zero recorder drops
• stale-preview counterexample: stopped with boundary_preview_unconfirmed before a third model request
• git diff --check: clean

Evidence: .omo/evidence/20260727-convergence-v24r15-post-tool-preview/QA.md

Product gate

This PR completes only the code gate. Case 09 must run once in a new immutable V24R15 campaign using the unchanged V24R14 runner controls before V25 or the 85-case campaign can proceed.