FOR JSON AUTO not recognized when using dialect tsql with SQL Server 2019

[ronaldmeran]

When defining a model with dialect tsql, SQLMesh fails to parse valid SQL Server syntax that uses FOR JSON AUTO (or FOR JSON PATH).
This syntax is supported in SQL Server since 2016, but SQLMesh throws a parsing error instead of accepting the query.

config.yaml:

gateways:
  local:
    connection:
      type: mssql
      host: <localhost>
      database: <DB>
      driver: pymssql
      user: <user>
      password: <password>
      port: 1433
      trust_server_certificate: True

default_gateway: local

# --- Model Defaults ---
# https://sqlmesh.readthedocs.io/en/stable/reference/model_configuration/#model-defaults
model_defaults:
  dialect: tsql

sample model:

MODEL (
    name silver.policy,
    kind FULL,
    cron '@daily',
    dialect tsql
);

SELECT 
	pol.policy_id,
	pol.product_id
FROM silver.policy pol
FOR JSON AUTO

Error:

Error: Failed to load model from file '/analytics/warehouse/models/policy/silver/policy.sql': Invalid expression / Unexpected token. Line 15, Col: 3. ...(omitted)... <> '' �[4mFOR�[0m JSON PATH

Expected Behavior:

• SQLMesh should allow T-SQL specific syntax (FOR JSON AUTO, FOR JSON PATH, etc.) when dialect tsql is set.
• Query should be passed through to SQL Server instead of being rejected by the parser.

Environment:

• SQLMesh version: 0.202.1
• Database: SQL Server 2019
• Dialect: tsql
• OS: wsl (Ubuntu)

Additional Context:

• Verified that config.yaml points to mssql and default dialect is tsql.
• Removing FOR JSON AUTO makes the query parse successfully.
• JSON_ARRAYAGG is not an option because it requires SQL Server 2022, so SQL Server 2019 users rely on FOR JSON syntax.