Add engram_get_node_by_label runtime native to unblock soul link

chat.el calls the runtime native engram_get_node_by_label to fetch
well-known nodes (conv:history, session:summary) by stable label rather
than by ID — immune to vector-index drift across restarts. The current
runtime never defined it, so the regenerated dist/soul.c fails to link.

Backport the function verbatim (idiom-adapted to jb_finish) from release
runtime v1.0.0-20260501 and register it as an EL builtin exactly like its
siblings: runtime definition + prototype, __-prefixed seed wrapper +
prototype, and codegen arity entry. No search-site code is touched.

lang/el-compiler/runtime/el_runtime.c

@@ -7761,6 +7761,35 @@ el_val_t engram_get_node_json(el_val_t id) {
     return el_wrap_str(jb_finish(&b));
 }
 
+/* engram_get_node_by_label — find the first node whose label field exactly
+ * matches the given string. Returns the node as a JSON object string, or "{}"
+ * if no match is found.
+ *
+ * Used by chat.el to retrieve well-known nodes (e.g. "conv:history",
+ * "session:summary") by their stable label rather than by ID, which is immune
+ * to vector index drift across restarts.
+ *
+ * Exact match (strcmp, not istr_contains) because labels like "conv:history"
+ * must not collide with nodes whose content happens to contain that substring.
+ *
+ * Backported verbatim (idiom-adapted to jb_finish) from release runtime
+ * v1.0.0-20260501 to unblock the soul regen link: chat.el references this
+ * native but the current runtime lacked its definition. */
+el_val_t engram_get_node_by_label(el_val_t label) {
+    const char* lbl = EL_CSTR(label);
+    if (!lbl || !*lbl) return el_wrap_str(el_strdup("{}"));
+    EngramStore* g = engram_get();
+    for (int64_t i = 0; i < g->node_count; i++) {
+        EngramNode* n = &g->nodes[i];
+        if (n->label && strcmp(n->label, lbl) == 0) {
+            JsonBuf b; jb_init(&b);
+            engram_emit_node_json(&b, n);
+            return el_wrap_str(jb_finish(&b));
+        }
+    }
+    return el_wrap_str(el_strdup("{}"));
+}
+
 el_val_t engram_search_json(el_val_t query, el_val_t limit) {
     EngramStore* g = engram_get();
     const char* q = EL_CSTR(query);

lang/el-compiler/runtime/el_runtime.h

@@ -632,6 +632,7 @@ el_val_t  engram_load(el_val_t path);
  * can pass results straight through without round-tripping ElList/ElMap
  * through json_stringify. */
 el_val_t  engram_get_node_json(el_val_t id);
+el_val_t  engram_get_node_by_label(el_val_t label);
 el_val_t  engram_search_json(el_val_t query, el_val_t limit);
 el_val_t  engram_scan_nodes_json(el_val_t limit, el_val_t offset);
 el_val_t  engram_scan_nodes_by_type_json(el_val_t node_type, el_val_t limit, el_val_t offset);

lang/el-compiler/runtime/el_seed.c

@@ -1072,6 +1072,7 @@ el_val_t __engram_save(el_val_t path)                       { return engram_save
 el_val_t __engram_load(el_val_t path)                       { return engram_load(path); }
 
 el_val_t __engram_get_node_json(el_val_t id)               { return engram_get_node_json(id); }
+el_val_t __engram_get_node_by_label(el_val_t label)        { return engram_get_node_by_label(label); }
 
 el_val_t __engram_search_json(el_val_t query, el_val_t limit) {
     return engram_search_json(query, limit);

lang/el-compiler/runtime/el_seed.h

@@ -226,6 +226,7 @@ el_val_t  __engram_activate(el_val_t query, el_val_t depth);
 el_val_t  __engram_save(el_val_t path);
 el_val_t  __engram_load(el_val_t path);
 el_val_t  __engram_get_node_json(el_val_t id);
+el_val_t  __engram_get_node_by_label(el_val_t label);
 el_val_t  __engram_search_json(el_val_t query, el_val_t limit);
 el_val_t  __engram_scan_nodes_json(el_val_t limit, el_val_t offset);
 el_val_t  __engram_scan_nodes_by_type_json(el_val_t node_type, el_val_t limit, el_val_t offset);

lang/el-compiler/src/codegen.el

@@ -2670,6 +2670,7 @@ fn builtin_arity(name: String) -> Int {
     if str_eq(name, "engram_save") { return 1 }
     if str_eq(name, "engram_load") { return 1 }
     if str_eq(name, "engram_get_node_json") { return 1 }
+    if str_eq(name, "engram_get_node_by_label") { return 1 }
     if str_eq(name, "engram_search_json") { return 2 }
     if str_eq(name, "engram_scan_nodes_json") { return 2 }
     if str_eq(name, "engram_neighbors_json") { return 3 }