Spreading activation rebuilt the entire per-node adjacency index
(engram_adj_rebuild, O(E)) lazily before every BFS whenever any edge/node
was added — so a curiosity-loop query that touched a small frontier still
paid to rebuild the whole edge set. This makes the index incrementally
maintained behind ENGRAM_STORE: single node/edge creates APPEND to the live
adjacency in amortized O(1) instead of marking it dirty, so a query only
pays for the frontier it touches (one initial O(E) build, then O(1)/edge).
Approach (b), not (a): the store's from/to adjacency B-tree was rejected
because with the store on the whole graph is already resident and activation
reads in-RAM edges, whose hebb/weight only sync to the store at checkpoint
cadence — reading StoreEdge copies would use stale weights and break
byte-identical parity. The incremental in-RAM index reads the exact same
g->edges[ei] the scan path does, so activation is identical by construction.
Correctness: edges are only ever appended, so incremental append reproduces
the rebuild's ascending-edge-index ordering exactly (same skip rule for null
endpoints). Any index-invalidating mutation (forget/prune/clear) still frees
the index + sets adj_dirty=1, falling back to a full rebuild. Flag-off is
untouched: the mutation hooks just set adj_dirty=1 as before — proven
byte-identical.
engram_store.c is NOT modified (avoids the M5 compaction collision).
Tests (plain gcc, ASan/UBSan clean): engram/test/{test_m7_traversal.c,
run_m7_traversal.sh}. Parity gate proves flag-on incremental == flag-on
forced-full-rebuild == flag-off scan, byte-identical on a mutating query
sequence (activated set, weights, ordering, hops, WM promotion). Perf on a
13k-node / 43k-edge graph over 120 (add-edge + activate) iterations:
adjacency edge-touches 5,167,260 -> 43,001 (120x fewer), full rebuilds
120 -> 1, adjacency-maintenance wall-time 0.74s -> 0.006s (~121x). Prior
gates green: M1 store (33), M2 (36), M3 parity, M3.5, M4 bufpool (37).
will.anderson
eb13ce7910