perf(mysql): avoid full parse for ordinary completion scripts

[openai0229]

Related issue

N/A - no issue number was provided.

Summary

Avoids parsing the entire MySQL editor script with the ANTLR root parser when lexer boundaries prove that the input is a balanced ordinary SQL script. Complex routines, DELIMITER scripts, malformed input, and ambiguous no-semicolon statements keep the existing parser/probe path. Adds boundary coverage and a large-SQL performance test for 200-line scripts and 166/500/1000-value IN lists.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • mvn -B -f chat2db-community-server/pom.xml -pl :chat2db-community-mysql -am -Dmaven.test.skip=false -DskipTests=false -Dtest='MysqlSqlCompletionProviderTest,MysqlSqlCompletionScenarioCoverageTest,MysqlSqlCompletionStatementProgressionTest,MysqlSqlCompletionDdlScenarioCoverageTest,MysqlSqlCompletionRuleRangeTest,MysqlSqlCompletionStatementLocatorTest,MysqlSqlCompletionPerformanceTest' -Dsurefire.failIfNoSpecifiedTests=false -Dmaven.test.failure.ignore=false test - 521 tests passed, 0 failures, 0 errors.
  • git diff --check - passed.
• Manual verification: N/A; this is a backend parser/completion change covered by focused tests.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: N/A; no public request or persistence contract changed.
• Database or driver compatibility: MySQL completion only. Stored procedures, triggers, functions, DELIMITER input, malformed input, and ambiguous statements retain the existing parser path.
• Network, privacy, or security: N/A; no SQL text is logged or sent to a new endpoint.
• Community / Local / Pro boundary: Community MySQL plugin only; no Studio or Enterprise code is changed.
• Backward compatibility: Existing completion scenarios remain covered; all 521 focused tests pass.

Reviewer map

• Start here: chat2db-community-server/chat2db-community-plugins/chat2db-community-mysql/src/main/java/ai/chat2db/plugin/mysql/completion/locate/MysqlSqlCompletionStatementLocator.java
• Failure condition: canUseTokenWindow requires balanced parentheses, no CREATE/DELIMITER tokens, no unsafe lexer errors, and a proven separator or single top-level statement; otherwise the existing parser/probe path runs.
• Rollback or disable path: Revert this PR; no runtime flag or migration is required.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: Substantial AI assistance was used for code navigation, implementation, test design, performance measurement, and verification.