fix: bind M5.2 reviewer digest in tool schema

[veil-chow-fyaic]

Summary

• replace model copying of findingDigest from the read-tool output with a coordinator-bound schema constant
• keep exact reviewer path and counterexample validation against the detached checkout
• retain action/lifecycle/Git/verifier digest bindings and wrong-content negative coverage
• record attempt 13 and its selected-vs-completed diagnosis

Evidence

Attempt 13 emitted 5 selected actions but only 4 completed actions, proving the second reviewer callback was rejected before completion. The read callback completed. This removes the redundant copying obligation without weakening content verification.

Validation

• focused M5.2 suite: 17/17
• real-effects positive and wrong-finding negative both pass
• documentation lint: 114 files, zero issues
• CI runs the full 385-test suite

Advances #91.