Phase 1a scores one (parent, child) fork at a time; Phase 1b is the
consensus paper. Neither persists multiple candidate branches at the
same checkpoint — and #000037 §12 Trigger 1 ("ForkScore regularly
receives ≥4 candidate branches per checkpoint") gates the multi-
branch path of the Prometheus-Σ controller on this data existing.
Phase 1c lands the missing seam.
Schema (arborist/store.py): _migrate_fork_score_branches creates the
sibling table with PK (branch_set_id, branch_id) + indexes on
branch_set_id and parent_root. Sibling — never enters
audit_events.event_hash preimage, so re-scoring or back-filling
cannot break the audit chain.
Helpers (arborist/substrate/fork_score.py): persist_branch_score
upserts one row via ON CONFLICT (branch_set_id, branch_id) DO UPDATE
so re-scoring the same fork under the same checkpoint is a clean
overwrite, not a duplicate. branch_set_density(conn, branch_set_id)
returns the count of distinct branches recorded under a checkpoint
— the function the #000037 §12 Trigger 1 probe reads.
ESTIMATOR_VERSION = "fork-score-v1" pins the producer generation on
every persisted row.
CLI (arborist/cli.py): arborist substrate score gains six new flags
(--branch-set, --branch-id, --parent-root, --child-root,
--persist-shard, --weights-id). Default off — --branch-set absent
preserves Phase 1a pure-function semantics for every existing
caller. When present, requires --parent-root and either --branch-id
or --child-root; missing inputs return exit code 2.
Tests (tests/test_fork_score.py, count 18 → 23): migration creates
the table + both indexes; persist writes one row carrying
parent/child roots + verdict + weights_id + estimator_version;
upsert on the PK refreshes child_root + weights_id + recorded_at
without duplicating; branch_set_density counts per-checkpoint and
ignores cross-set rows; breakdown_blob round-trips as canonical
JSON whose values sum to the persisted score.
Status sync: #000012 §7 Phase 1c flipped from "proposed, not yet
open" to "landed 2026-05-10" with the original proposal preserved
below as design log. TICKETS row 117 mirror-updated. AUTOCOUNT
counters in #000012 + cookbook bumped 18 → 23 plus the cookbook's
fork_score.py LOC row refreshed (298 → 386 module, 403 → 609
tests, density 1.35 → 1.58).
End-to-end smoke verified: arborist substrate score writes a
fork_score_branches row with the expected schema (verdict / weights_id
/ estimator_version) and the row survives a clean SQLite read.
russell@unturf.com
d53115efd7