docs/#000018 §9.2: mark resolved — φ_PRG = HMAC-SHA-512 (#000035 closed)

#000035 closed 2026-05-11 (commit 4b85eb1: v7 substrate spec into the
repo at docs/_source/merkle-agi-dag-v7.rst, § 9.10 folded in). Update
soft-hash-channel-analysis.md §9 open-question 2 from "Phase 2 lands
when v7 gains a deployment target" to resolved: φ_PRG = HMAC-SHA-512
with a 32-byte committed seed, little-endian.

docs/soft-hash-channel-analysis.md

@@ -451,9 +451,14 @@ The reduction in §4 leaves three loose threads:
    rule documented in §9.10.1); plus a `dim_h ≤ 16·2^32` exhaustion
    guard and a seed-independence / single-purpose-seed requirement.
    The reference implementation + 31 tests + 10 KAT vectors are
-   pinned to these choices. Phase 2 lands the §9.10 text into the
-   v7 plastic-training spec when one gains an active deployment
-   target.
+   pinned to these choices. **Phase 2 landed 2026-05-11** (`4b85eb1`):
+   the v7 substrate spec was brought into the repo as
+   ``docs/_source/merkle-agi-dag-v7.rst`` and § 9.10 + § 9.10.1 were
+   folded in after § 9.9. **This open question is resolved — φ_PRG =
+   HMAC-SHA-512(seed, C(M) ‖ counter_le32), 32-byte committed seed,
+   little-endian.** #000035 → closed. (A full upstream v7 spec
+   revision remains exogenous; the amendment now lives version-
+   controlled in the in-repo copy where future amendments land.)
 
 3. **T3 per-window budget formal bound.** ~~§6 lists "bounded by
    per-window budget" without giving the bound.~~ **Closed