fix(csharp): Interface registration + polymorphic BFS bridging + this.Property WRITES

Three C# code intelligence fixes:

1. Register Interface nodes in the symbol registry.
   The registry filter only accepted Function/Method/Class labels. Interface
   nodes were never registered, so resolve_as_class('IExamService') always
   returned NULL. INHERITS edges from C# classes to their interfaces were
   never created (0 → Interface out of 1588 total INHERITS in the largest
   C# repo).

   Fix: add 'Interface' to the registration filter in both pass_definitions.c
   (sequential path) and pass_parallel.c (parallel path, cbm_build_registry_from_cache).

   Additionally, in pass_semantic.c, when the resolved base type is a Class
   but the name follows C# interface convention (I + uppercase), search for
   an Interface node with the same name and prefer it. This handles cross-
   language name collisions (e.g. C++ ILogger class vs C# ILogger interface).

   Result: CometExamService → IExamService INHERITS edge now created.

2. BFS interface method bridging in trace_call_path and get_impact.
   When tracing callers of a concrete method (e.g. PerformSessionAction),
   BFS now also checks if the method's enclosing class INHERITS from an
   Interface. If so, it finds the interface's method with the same name
   and runs additional BFS from that node. This surfaces callers that use
   the interface type (ISimCoordinator.PerformSessionAction) which
   previously showed 0 callers.

   Applied to both handle_trace_call_path (incoming.calls section) and
   handle_get_impact (multi-method BFS merge).

3. Expand WRITES detection for this.Property = value.
   handle_readwrites() only accepted bare identifiers as assignment LHS.
   C#/Java/TypeScript this.PropertyName = value has LHS as
   member_access_expression, which was skipped.

   Fix: add branch for member_access_expression / member_expression LHS.
   When the receiver is this/base/self, extract the property name and push
   as a write. Handles C# this_expression, Java this, TypeScript this,
   Python self.

   Expected: hundreds of additional WRITES edges from method bodies to
   class properties in C# repos.

Requires full reindex of C# repos to rebuild INHERITS edges and WRITES.

Author: Your Name

internal/cbm/extract_semantic.c

@@ -275,6 +275,38 @@ void handle_readwrites(CBMExtractCtx *ctx, TSNode node, const CBMLangSpec *spec,
                     cbm_rw_push(&ctx->result->rw, ctx->arena, rw);
                 }
             }
+            /* member_access_expression: handle this.Property = value
+             * for C#, Java, TypeScript, JavaScript.
+             * Extracts the property name when the receiver is "this" or "base". */
+            else if (strcmp(lk, "member_access_expression") == 0 ||
+                     strcmp(lk, "member_expression") == 0) {
+                TSNode expr = ts_node_child_by_field_name(left, "expression", 10);
+                TSNode name_node = ts_node_child_by_field_name(left, "name", 4);
+                /* member_expression (JS/TS) uses "object" + "property" field names */
+                if (ts_node_is_null(name_node)) {
+                    name_node = ts_node_child_by_field_name(left, "property", 8);
+                }
+                if (ts_node_is_null(expr)) {
+                    expr = ts_node_child_by_field_name(left, "object", 6);
+                }
+                if (!ts_node_is_null(name_node) && !ts_node_is_null(expr)) {
+                    const char *ek = ts_node_type(expr);
+                    /* Accept: this.X, base.X, self.X (Python) */
+                    if (strcmp(ek, "this_expression") == 0 ||
+                        strcmp(ek, "this") == 0 ||
+                        strcmp(ek, "base_expression") == 0 ||
+                        strcmp(ek, "self") == 0) {
+                        char *name = cbm_node_text(ctx->arena, name_node, ctx->source);
+                        if (name && name[0] && !cbm_is_keyword(name, ctx->language)) {
+                            CBMReadWrite rw;
+                            rw.var_name = name;
+                            rw.is_write = true;
+                            rw.enclosing_func_qn = state->enclosing_func_qn;
+                            cbm_rw_push(&ctx->result->rw, ctx->arena, rw);
+                        }
+                    }
+                }
+            }
         }
     }
 }

src/mcp/mcp.c

@@ -1604,6 +1604,57 @@ static char *handle_get_impact(cbm_mcp_server_t *srv, const char *args) {
         free(subs);
     }
 
+    /* Interface method bridging: if any start_id method implements an interface
+     * method, also BFS from the interface version to find polymorphic callers. */
+    {
+        struct sqlite3 *sdb = cbm_store_get_db(store);
+        for (int s = 0; s < start_id_count; s++) {
+            sqlite3_stmt *iface_stmt = NULL;
+            sqlite3_prepare_v2(sdb,
+                "SELECT im.id FROM edges e_dm "
+                "JOIN edges e_inh ON e_dm.source_id = e_inh.source_id AND e_inh.type = 'INHERITS' "
+                "JOIN nodes iface ON iface.id = e_inh.target_id AND iface.label = 'Interface' "
+                "JOIN edges e_im ON e_im.source_id = iface.id AND e_im.type = 'DEFINES_METHOD' "
+                "JOIN nodes im ON im.id = e_im.target_id "
+                "JOIN nodes m ON m.id = ?1 "
+                "WHERE e_dm.target_id = ?1 AND e_dm.type = 'DEFINES_METHOD' "
+                "AND im.name = m.name",
+                -1, &iface_stmt, NULL);
+            if (iface_stmt) {
+                sqlite3_bind_int64(iface_stmt, 1, start_ids[s]);
+                while (sqlite3_step(iface_stmt) == SQLITE_ROW) {
+                    int64_t iface_method_id = sqlite3_column_int64(iface_stmt, 0);
+                    cbm_traverse_result_t itr = {0};
+                    cbm_store_bfs(store, iface_method_id, bfs_dir, call_types, 4,
+                                  max_depth, 50, &itr);
+                    /* Merge interface callers into tr */
+                    if (itr.visited_count > 0) {
+                        int new_cap = tr.visited_count + itr.visited_count;
+                        cbm_node_hop_t *new_v = realloc(tr.visited,
+                            (size_t)new_cap * sizeof(cbm_node_hop_t));
+                        if (new_v) {
+                            tr.visited = new_v;
+                            for (int iv = 0; iv < itr.visited_count; iv++) {
+                                /* Dedup by node id */
+                                bool dup = false;
+                                for (int j = 0; j < tr.visited_count; j++) {
+                                    if (tr.visited[j].node.id == itr.visited[iv].node.id) {
+                                        dup = true; break;
+                                    }
+                                }
+                                if (!dup) {
+                                    tr.visited[tr.visited_count++] = itr.visited[iv];
+                                }
+                            }
+                        }
+                    }
+                    free(itr.edges);
+                }
+                sqlite3_finalize(iface_stmt);
+            }
+        }
+    }
+
     /* Group by depth */
     yyjson_mut_val *d1_arr = yyjson_mut_arr(doc);
     yyjson_mut_val *d2_arr = yyjson_mut_arr(doc);
@@ -2420,6 +2471,37 @@ static char *handle_trace_call_path(cbm_mcp_server_t *srv, const char *args) {
                     tr_count++;
                 }
             }
+
+            /* Interface method bridging: if the target method implements an interface
+             * method, also find callers of the interface version. This handles C#/Java
+             * polymorphism where callers use `IFoo.method()` not `Foo.method()`. */
+            {
+                struct sqlite3 *sdb = cbm_store_get_db(store);
+                for (int s = 0; s < start_id_count && tr_count < MAX_TR; s++) {
+                    /* Find: start_id's class → INHERITS → Interface → DEFINES_METHOD → same name */
+                    sqlite3_stmt *iface_stmt = NULL;
+                    sqlite3_prepare_v2(sdb,
+                        "SELECT im.id FROM edges e_dm "
+                        "JOIN edges e_inh ON e_dm.source_id = e_inh.source_id AND e_inh.type = 'INHERITS' "
+                        "JOIN nodes iface ON iface.id = e_inh.target_id AND iface.label = 'Interface' "
+                        "JOIN edges e_im ON e_im.source_id = iface.id AND e_im.type = 'DEFINES_METHOD' "
+                        "JOIN nodes im ON im.id = e_im.target_id "
+                        "JOIN nodes m ON m.id = ?1 "
+                        "WHERE e_dm.target_id = ?1 AND e_dm.type = 'DEFINES_METHOD' "
+                        "AND im.name = m.name",
+                        -1, &iface_stmt, NULL);
+                    if (iface_stmt) {
+                        sqlite3_bind_int64(iface_stmt, 1, start_ids[s]);
+                        while (sqlite3_step(iface_stmt) == SQLITE_ROW && tr_count < MAX_TR) {
+                            int64_t iface_method_id = sqlite3_column_int64(iface_stmt, 0);
+                            cbm_store_bfs(store, iface_method_id, "inbound", call_types, 5, 1,
+                                          EDGE_QUERY_MAX, &all_tr[tr_count]);
+                            if (all_tr[tr_count].visited_count > 0) tr_count++;
+                        }
+                        sqlite3_finalize(iface_stmt);
+                    }
+                }
+            }
         }
         /* Build calls array from all BFS results */
         yyjson_mut_val *calls_arr = yyjson_mut_arr(doc);

src/pipeline/pass_definitions.c

@@ -253,10 +253,12 @@ int cbm_pipeline_pass_definitions(cbm_pipeline_ctx_t *ctx, const cbm_file_info_t
                                      def->qualified_name, def->file_path ? def->file_path : rel,
                                      (int)def->start_line, (int)def->end_line, props);
 
-            /* Register callable symbols in the registry */
+            /* Register callable symbols in the registry.
+             * Interface is included so that C#/Java INHERITS edges can resolve
+             * base type names like "IExamService" to Interface nodes. */
             if (node_id > 0 && def->label &&
                 (strcmp(def->label, "Function") == 0 || strcmp(def->label, "Method") == 0 ||
-                 strcmp(def->label, "Class") == 0)) {
+                 strcmp(def->label, "Class") == 0 || strcmp(def->label, "Interface") == 0)) {
                 cbm_registry_add(ctx->registry, def->name, def->qualified_name, def->label);
             }
 

src/pipeline/pass_parallel.c

@@ -612,7 +612,7 @@ int cbm_build_registry_from_cache(cbm_pipeline_ctx_t *ctx, const cbm_file_info_t
             }
 
             if (strcmp(def->label, "Function") == 0 || strcmp(def->label, "Method") == 0 ||
-                strcmp(def->label, "Class") == 0) {
+                strcmp(def->label, "Class") == 0 || strcmp(def->label, "Interface") == 0) {
                 cbm_registry_add(ctx->registry, def->name, def->qualified_name, def->label);
                 reg_entries++;
             }

src/pipeline/pass_semantic.c

@@ -374,8 +374,9 @@ int cbm_pipeline_pass_semantic(cbm_pipeline_ctx_t *ctx, const cbm_file_info_t *f
             /* INHERITS: base_classes */
             if (def->base_classes) {
                 for (int b = 0; def->base_classes[b]; b++) {
+                    const char *base_name = def->base_classes[b];
                     const char *base_qn =
-                        resolve_as_class(ctx->registry, def->base_classes[b], module_qn, imp_keys,
+                        resolve_as_class(ctx->registry, base_name, module_qn, imp_keys,
                                          imp_vals, imp_count);
                     if (!base_qn) {
                         continue;
@@ -386,6 +387,29 @@ int cbm_pipeline_pass_semantic(cbm_pipeline_ctx_t *ctx, const cbm_file_info_t *f
                         continue;
                     }
 
+                    /* C# interface preference: if the resolved node is a Class but the
+                     * base type name follows C# interface convention (I + uppercase),
+                     * search for an Interface node with the same name and prefer it.
+                     * This handles cross-language name collisions (e.g. C++ ILogger class
+                     * vs C# ILogger interface) that cause INHERITS to miss interfaces. */
+                    if (base_node->label && strcmp(base_node->label, "Class") == 0 &&
+                        base_name[0] == 'I' && base_name[1] >= 'A' && base_name[1] <= 'Z') {
+                        const char **candidates = NULL;
+                        int cand_count = 0;
+                        cbm_registry_find_by_name(ctx->registry, base_name, &candidates, &cand_count);
+                        for (int ci = 0; ci < cand_count; ci++) {
+                            const char *cl = cbm_registry_label_of(ctx->registry, candidates[ci]);
+                            if (cl && strcmp(cl, "Interface") == 0) {
+                                const cbm_gbuf_node_t *iface_node =
+                                    cbm_gbuf_find_by_qn(ctx->gbuf, candidates[ci]);
+                                if (iface_node && iface_node->id != node->id) {
+                                    base_node = iface_node;
+                                    break;
+                                }
+                            }
+                        }
+                    }
+
                     cbm_gbuf_insert_edge(ctx->gbuf, node->id, base_node->id, "INHERITS", "{}");
                     inherits_count++;
                 }