common : add gemma 4 specialized parser (#21418)

* common : add gemma4 dedicated parser

* cont : add '<|tool_response>' as eog

* cont : emit JSON from Gemma4 tool call AST

* cont : more fixes

* cont : refactor convert function

* cont : refine rules and mapping

* cont : add more tests

* cont : clean up

* cont : remove autoparser gemma4 implementation

* cont : more cleanup

* cont : rename gemma4.jinja to match the others

* cont : add custom template to support interleaved thinking

* cont : preserve reasoning in model turns

* cont : fix initializer error

* cont : fix unused vars

* cont : fix accidental static

* cont : fix specialized_template signature

* fix extra semicolon

* remove debug line and extra space [no ci]

common/peg-parser.cpp

@@ -256,6 +256,38 @@ static std::pair<std::vector<common_peg_chars_parser::char_range>, bool> parse_c
     return {ranges, negated};
 }
 
+common_peg_ast_id common_peg_ast_arena::find_by_tag(const common_peg_ast_node & parent, const std::string & tag, int max_depth) const {
+    for (auto child_id : parent.children) {
+        const auto & child = get(child_id);
+        if (child.tag == tag) {
+            return child_id;
+        }
+        if (max_depth > 1) {
+            auto result = find_by_tag(child, tag, max_depth - 1);
+            if (result != COMMON_PEG_INVALID_AST_ID) {
+                return result;
+            }
+        }
+    }
+    return COMMON_PEG_INVALID_AST_ID;
+}
+
+common_peg_ast_id common_peg_ast_arena::find_by_rule(const common_peg_ast_node & parent, const std::string & rule, int max_depth) const {
+    for (auto child_id : parent.children) {
+        const auto & child = get(child_id);
+        if (child.rule == rule) {
+            return child_id;
+        }
+        if (max_depth > 1) {
+            auto result = find_by_rule(child, rule, max_depth - 1);
+            if (result != COMMON_PEG_INVALID_AST_ID) {
+                return result;
+            }
+        }
+    }
+    return COMMON_PEG_INVALID_AST_ID;
+}
+
 void common_peg_ast_arena::visit(common_peg_ast_id id, const common_peg_ast_visitor & visitor) const {
     if (id == COMMON_PEG_INVALID_AST_ID) {
         return;