fix(lexer): handle special chars in text segments

Modify lexer logic to handle special characters (@, /, $) at the start of text segments by transitioning to appropriate states (AGENT_BLOCK, COMMAND_BLOCK, VARIABLE_BLOCK) and returning corresponding tokens.

Author: phodal

exts/devins-lang/src/grammar/DevInLexer.flex

@@ -109,8 +109,21 @@ SHARP=#
                 return comment();
             }
 
-            yypushback(yylength());
-            yybegin(YYUSED);
+            // get first char, if $, @, /, #, should be a YYUSED
+            char first  = text.charAt(0);
+            if (first == '@') {
+                yypushback(yylength() - 1);
+                yybegin(AGENT_BLOCK);
+                return AGENT_START;
+            } else if (first == '/') {
+                yypushback(yylength() - 1);
+                yybegin(COMMAND_BLOCK);
+                return COMMAND_START;
+            } else if (first == '$') {
+                yypushback(yylength() - 1);
+                yybegin(VARIABLE_BLOCK);
+                return VARIABLE_START;
+            }
 
             return TEXT_SEGMENT;
         }

exts/devins-lang/src/test/testData/parser/BasicTest.txt

@@ -1,9 +1,5 @@
 DevInFile
-  PsiElement(DevInTokenType.TEXT_SEGMENT)('你好 ')
-  DevInUsedImpl(USED)
-    PsiElement(DevInTokenType.AGENT_START)('@')
-    PsiElement(DevInTokenType.AGENT_ID)('hello-world')
-  PsiElement(DevInTokenType.TEXT_SEGMENT)(' sm')
+  PsiElement(DevInTokenType.TEXT_SEGMENT)('你好 @hello-world sm')
   PsiElement(DevInTokenType.NEWLINE)('\n')
   PsiElement(DevInTokenType.TEXT_SEGMENT)('解释一下代码')
   PsiElement(DevInTokenType.NEWLINE)('\n')