fix(routes): /api/graph/edges must not write the canonical snapshot

This route called engram_save() over ~/.neuron/engram/snapshot.json — the
engram server's CANONICAL store — then fs_read it back, to answer a READ
query. A read route overwriting the persistence owner's file.

This defect was fixed once before (export redirected to a scratch path). It
came back tonight in the @route dispatch conversion: the hand-written dispatch
block held the FIXED version, the @route-decorated copy held the unfixed one,
and the merge kept the decorated copy. Calling the endpoint afterward
overwrote the canonical snapshot and immediately preceded an engram crash.

Now calls engram_edges_json(limit, offset) — the builtin the route's own TODO
asked for — which reads g->edges directly. No file is written or read.
Bounded: limit defaults to 1000, offset supported, so the whole-graph read
that fell over is not reachable by default.

Verified: same request that previously rewrote snapshot.json now leaves it
byte-identical (sha256 unchanged before/after), and returns real edge records
with every persisted field.

routes.el

@@ -420,14 +420,23 @@ fn r_api_graph_nodes(method: String, path: String, body: String) -> String {
 
 @route("/api/graph/edges", "GET", "exact") @manager
 fn r_api_graph_edges(method: String, path: String, body: String) -> String {
-    // TODO(reliability #8): engram_save races with awareness loop mem_save().
-    // Both now use atomic write-to-temp+rename (el_runtime.c). Serialised
-    // by engram_global_mu. Future: add engram_edges_json() builtin.
-    let snap_path: String = env("HOME") + "/.neuron/engram/snapshot.json"
-    engram_save(snap_path)
-    let snap: String = fs_read(snap_path)
-    let edges_raw: String = json_get_raw(snap, "edges")
-    return if str_eq(edges_raw, "") { "[]" } else { edges_raw }
+    // Reads edges straight from the store. No file is written or read.
+    //
+    // This route used to engram_save() the ENTIRE graph over
+    // ~/.neuron/engram/snapshot.json — the engram server's CANONICAL store —
+    // and then fs_read it back, just to answer a read query. Two defects in
+    // one line: a READ route clobbering the persistence owner's canonical
+    // file (the defect fixed once already, then reintroduced when the
+    // hand-written dispatch block was replaced by @route dispatch and the
+    // unfixed copy is the one that survived), and a 128 MB serialize +
+    // reread + parse per request. Calling it on 2026-08-15 overwrote the
+    // canonical snapshot and preceded an engram crash loop.
+    //
+    // engram_edges_json is the builtin the old TODO here asked for. Bounded
+    // by default (1000) — the unbounded whole-graph read is what fell over.
+    let lim: Int = api_query_int(path, "limit", 1000)
+    let off: Int = api_query_int(path, "offset", 0)
+    return engram_edges_json(lim, off)
 }
 
 // ── GET /api/chat — legacy probe interface; body may be empty ───────────────