Add grounded edge-propagation spec (task #50): core algorithm, proof harness, gated integration patches

LTP/LTD-style belief grounding propagated along graph edges, with
union-find independence-guarded corroboration. Package: core C algorithm
(gep_core.h), a self-contained deterministic proof harness with recorded
output, staged runtime integration, and gated .el patches for the beat
hook and HTTP route.

Per the author's own LEDGER.md: built + proven on a clone, GATED pending
the engine/HNSW cutover — not wired into the live beat or routes.
Preserved here as a spec/reference artifact, not a request to merge into
the live path.

engram/spec/grounded-edge-propagation/server.route.patch.el

@@ -0,0 +1,29 @@
+// ─────────────────────────────────────────────────────────────────────────
+// server.route.patch.el — GATED route for task #50, for engram/src/server.el.
+// NOT APPLIED. Exposes the engram_ground_propagate native over HTTP so the
+// soul's consolidation beat can fire one grounded edge-propagation pass.
+// ─────────────────────────────────────────────────────────────────────────
+
+// [1] New handler — add beside route_strengthen (server.el ~line 194).
+//     Mutation (appends grounding events, updates confidence), so it is gated
+//     on _auth via check_auth_ok, exactly like /api/edges. Persists once after
+//     the beat — the whole point of running propagation as one batched beat
+//     rather than per-node is to pay the snapshot cost a single time.
+fn route_ground_propagate(method: String, path: String, body: String) -> String {
+    if !check_auth_ok(method, body) { return err_json("unauthorized") }
+    let tel: String = engram_ground_propagate()   // native — one beat over the store
+    let saved: Int = persist_canonical()
+    return tel                                     // gep_* telemetry JSON straight through
+}
+
+// [2] Dispatch — register in handle_request (server.el ~line 461, next to the
+//     /api/strengthen arm):
+//
+//     if str_eq(method, "POST") && (str_eq(clean, "/api/ground/propagate")) {
+//         return route_ground_propagate(method, clean, body)
+//     }
+//
+// [3] Native declaration — engram_ground_propagate must be declared as an
+//     extern runtime builtin (el_runtime.h) and seed-wrapped (el_seed.c /
+//     el_seed.h __engram_ground_propagate) so the EL side can call it, same as
+//     engram_strengthen / engram_hebb_drain_json.