fix: add explicit record casting to all graph functions for SurrealDB 2.x

Critical fix for SurrealDB 2.x compatibility: Since SurrealDB 2.0, strings
are no longer automatically converted to record types. All graph functions
were broken because they accepted string parameters but used them in FROM
clauses which require record types.

Fixed functions:
1. fn::node_reference() - Added type::thing() conversion before calling fn::node_info()
2. fn::get_transitive_dependencies() - Added $record conversion for FROM ONLY clause
3. fn::trace_call_chain() - Added $record conversion for FROM ONLY clause
4. fn::calculate_coupling_metrics() - Added $record for FROM ONLY and fn::node_info() call
5. fn::get_reverse_dependencies() - Added $record conversion for FROM ONLY clause

Pattern used:
  LET $record = type::thing('nodes', $node_id);
  FROM ONLY $record  // or fn::node_info($record)

This ensures all string node IDs are properly cast to record<nodes> type
before use in graph traversal or function calls.

Ref: https://surrealdb.com/docs/surrealql/datamodel/casting

Author: jruokola

schema/codegraph.surql

@@ -344,7 +344,8 @@ DEFINE FUNCTION fn::node_info($node_id: record) {
 -- FUNCTION: node_reference (UNCHANGED)
 -- -----------------------------------------------------------------------------
 DEFINE FUNCTION fn::node_reference($node_id: string) {
-    LET $info = fn::node_info($node_id);
+    LET $record = type::thing('nodes', $node_id);
+    LET $info = fn::node_info($record);
     IF $info = NONE {
         RETURN NONE;
     };
@@ -369,10 +370,11 @@ DEFINE FUNCTION fn::edge_types() {
 DEFINE FUNCTION fn::get_transitive_dependencies($node_id: string, $edge_type: string, $depth: int) {
     LET $safe_depth = IF $depth > 0 AND $depth <= 10 THEN $depth ELSE 3 END;
     LET $edge_name  = $edge_type ?? 'Calls';
+    LET $record = type::thing('nodes', $node_id);
 
     LET $lvl1 = IF $safe_depth >= 1 THEN
         SELECT VALUE id
-        FROM ONLY $node_id
+        FROM ONLY $record
             ->edges[WHERE edge_type = $edge_name]
             ->to
     ELSE [] END;
@@ -499,6 +501,7 @@ DEFINE FUNCTION fn::detect_circular_dependencies($edge_type: string) {
 -- -----------------------------------------------------------------------------
 DEFINE FUNCTION fn::trace_call_chain($from_node: string, $max_depth: int) {
     LET $safe_depth = IF $max_depth > 0 AND $max_depth <= 10 THEN $max_depth ELSE 5 END;
+    LET $record = type::thing('nodes', $from_node);
 
     LET $raw = (
         SELECT
@@ -510,7 +513,7 @@ DEFINE FUNCTION fn::trace_call_chain($from_node: string, $max_depth: int) {
             ).caller) AS called_by
         FROM (
             SELECT ->edges[WHERE edge_type = 'Calls']
-            FROM ONLY $from_node
+            FROM ONLY $record
         )->to
     );
 
@@ -534,17 +537,18 @@ DEFINE FUNCTION fn::trace_call_chain($from_node: string, $max_depth: int) {
 -- -----------------------------------------------------------------------------
 DEFINE FUNCTION fn::calculate_coupling_metrics($node_id: string) {
     LET $edge_list = fn::edge_types();
+    LET $record = type::thing('nodes', $node_id);
 
     LET $dependents = array::distinct(
         SELECT VALUE id
-        FROM ONLY $node_id
+        FROM ONLY $record
             <-edges[WHERE edge_type INSIDE $edge_list]
             <-from
     );
 
     LET $dependencies = array::distinct(
         SELECT VALUE id
-        FROM ONLY $node_id
+        FROM ONLY $record
             ->edges[WHERE edge_type INSIDE $edge_list]
             ->to
     );
@@ -567,7 +571,7 @@ DEFINE FUNCTION fn::calculate_coupling_metrics($node_id: string) {
     LET $instability = IF $total > 0 THEN math::round($efferent / $total, 6) ELSE 0 END;
 
     RETURN {
-        node: fn::node_info($node_id),
+        node: fn::node_info($record),
         metrics: {
             afferent_coupling: $afferent,
             efferent_coupling: $efferent,
@@ -678,10 +682,11 @@ DEFINE FUNCTION fn::get_hub_nodes($min_degree: int) {
 DEFINE FUNCTION fn::get_reverse_dependencies($node_id: string, $edge_type: string, $depth: int) {
     LET $safe_depth = IF $depth > 0 AND $depth <= 10 THEN $depth ELSE 3 END;
     LET $edge_name  = $edge_type ?? 'Calls';
+    LET $record = type::thing('nodes', $node_id);
 
     LET $lvl1 = IF $safe_depth >= 1 THEN
         SELECT VALUE id
-        FROM ONLY $node_id
+        FROM ONLY $record
             <-edges[WHERE edge_type = $edge_name]
             <-from
     ELSE [] END;