engram_load_merge was added to el-compiler/runtime in 35c1897 but never
ported to the released runtime used by Engram and the soul daemon.
awareness.el calls engram_load_merge in its sync refresh cycle; without
this function in lang/releases/v1.0.0-20260501/el_runtime.c the soul
daemon fails to compile.
Also adds header declarations for engram_wm_count, engram_wm_avg_weight,
engram_wm_top_json, and engram_load_merge — all four were added as
implementations (da116b2 / 35c1897) but their prototypes were missing from
el_runtime.h, causing implicit-function-declaration warnings and potential
ABI breakage on stricter compilers.
Identified during self-review 2026-06-30.