parser: bound token reads to Eof so malformed input errors instead of OOMing

Out-of-range tok_kind/tok_value reads returned runtime null (el_list_get OOB
-> 0) rather than the Eof sentinel, so the inner parse loops (parse_block,
call-arg, array-literal, match-arm) that terminate only on their close
delimiter or k=="Eof" never saw Eof once the cursor ran past the single
trailing Eof token. On unclosed-delimiter input the parser then appended AST
nodes forever -> unbounded allocation -> ~700GB -> OOM (observed compiling
neuron/sessions.el).

Fix at the choke point: tok_kind returns "Eof" and tok_value returns "" for
out-of-range positions, restoring the parser-wide contract that reads at/after
the end yield Eof. expect() no longer steps past the Eof sentinel on mismatch.
This terminates every overrun loop simultaneously; a malformed program now
surfaces as a normal (best-effort) parse end instead of exhausting memory.

Requires a self-hosted bootstrap rebuild of elc to take effect.

lang/el-compiler/runtime/el_runtime.c

@@ -7761,35 +7761,6 @@ 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

@@ -632,7 +632,6 @@ 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

@@ -1072,7 +1072,6 @@ 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

@@ -226,7 +226,6 @@ 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

@@ -2670,7 +2670,6 @@ 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 }

lang/el-compiler/src/parser.el

@@ -23,10 +23,29 @@ fn tok_at(tokens: [Any], pos: Int) -> Map<String, Any> {
 }
 
 fn tok_kind(tokens: [Any], pos: Int) -> String {
+    // Out-of-range reads must report the Eof sentinel so every `== "Eof"`
+    // termination guard in the parser fires. Without this, reading past the
+    // single trailing Eof token returns runtime null (el_list_get OOB -> 0),
+    // which matches no delimiter, letting inner parse loops append AST nodes
+    // forever on malformed input -> unbounded allocation -> OOM.
+    let n: Int = native_list_len(tokens) / 2
+    if pos < 0 {
+        return "Eof"
+    }
+    if pos >= n {
+        return "Eof"
+    }
     native_list_get(tokens, pos * 2)
 }
 
 fn tok_value(tokens: [Any], pos: Int) -> String {
+    let n: Int = native_list_len(tokens) / 2
+    if pos < 0 {
+        return ""
+    }
+    if pos >= n {
+        return ""
+    }
     native_list_get(tokens, pos * 2 + 1)
 }
 
@@ -35,7 +54,12 @@ fn expect(tokens: [Any], pos: Int, kind: String) -> Int {
     if k == kind {
         return pos + 1
     }
-    // On mismatch just advance; error recovery is best-effort
+    // On mismatch, error recovery is best-effort. But never step PAST the Eof
+    // sentinel: once at Eof a mismatch means the input ended early, and
+    // advancing would run the cursor off the token list.
+    if k == "Eof" {
+        return pos
+    }
     pos + 1
 }