fix(index): prevent INDEX ON from corrupting source table indexes

[Admnwk]

Summary

• Bug: INDEX ON (SELECT ...) rewrites source table's .cdx files destructively
• Root cause: AdsOpenTable() opens source file instead of using materialized cursor (M10.31 optimization)
• Fix: Validate table name is simple identifier/filename; reject SELECT results with clear error

How it works

When INDEX ON receives a table name that appears to be a SELECT result or parenthesized expression, it rejects with error message directing users to materialize the SELECT first (ORDER BY/DISTINCT/LIMIT).

Test plan

✅ Reproducer: repro_index_on_select.prg (Harbour+SQL)
✅ CI will verify no regressions across all test suites

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request enhances security and stability by validating aggregate fields and table names across SQLite, PostgreSQL, and remote wire sessions. It ensures that aggregate fields are resolved to schema-validated column names to prevent SQL injection, and restricts 'INDEX ON' from running on 'SELECT' results to avoid index corruption. The review feedback highlights a potential bypass in the 'SELECT' query detection due to case sensitivity and leading whitespace, suggesting a more robust validation function.

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[gemini-code-assist]

The check for SELECT is case-sensitive and does not account for leading whitespace before a parenthesis. In SQL, keywords like SELECT can be written in lowercase or mixed-case (e.g., select, Select). If a user executes INDEX ON (select ...), the check will be bypassed, potentially leading to the index corruption bug. Additionally, leading whitespace before the parenthesis (e.g., (SELECT ...) would bypass the tname[0] == '(' check.

We should perform a case-insensitive check and trim/ignore leading whitespace when checking for a parenthesis.

        const auto& tname = ci.value().table;
        auto is_select_query = [](const std::string& str) {
            if (str.empty()) return true;
            std::size_t first = str.find_first_not_of(" \t\r\n");
            if (first != std::string::npos && str[first] == '(') {
                return true;
            }
            std::string upper;
            upper.reserve(str.size());
            for (char c : str) {
                upper.push_back(static_cast<char>(std::toupper(static_cast<unsigned char>(c))));
            }
            return upper.find("SELECT") != std::string::npos;
        };
        if (is_select_query(tname)) {
            return fail(openads::AE_SYNTAX_ERROR,
                "INDEX ON requires a table name, not a SELECT result; "
                "use SELECT ... ORDER BY/DISTINCT/LIMIT to materialize first");
        }