feat: update docs

Author: nadeem4

README.md

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+# Building Adapters
+
+The **Adapter SDK** (`nl2sql-adapter-sdk`) allows you to extend the platform to support new databases or APIs.
+
+## Implementing an Adapter
+
+You must implement the `DatasourceAdapter` interface.
+
+### Mandatory Properties
+
+* `datasource_id`: Unique identifier (e.g. "postgres_prod").
+* `row_limit`: **Safety Breaker**. Must return `1000` (or config value) to prevent massive result sets.
+* `max_bytes`: **Safety Breaker**. limit result size at the network/driver level if possible.
+
+### Mandatory Methods
+
+* `fetch_schema()`: Must return `SchemaMetadata` with `tables`, `columns`, `pks`, `fks`. *Crucially, it should also populate `col.statistics` (samples, min/max) for Indexing.*
+* `execute(sql)`: Returns `QueryResult`.
+* `dry_run(sql)`: Returns validity checks.
+
+### Optional Optimization
+
+* `explain(sql)`: Returns query plan.
+* `cost_estimate(sql)`: Returns estimated rows/time. used by PhysicalValidator.
+
+::: nl2sql_adapter_sdk.interfaces.DatasourceAdapter
+
+## Compliance Testing
+
+The SDK provides a compliance test suite. **All Adapters MUST pass this suite.**
+
+It verifies:
+
+* Schema Introspection (PKs/FKs detected?)
+* Type Mapping (Date -> Python Date, Numeric -> Python Float)
+* Error Handling (Bad SQL -> AdapterError)
+
+```python
+# tests/test_my_adapter.py
+from nl2sql_adapter_sdk.testing import BaseAdapterTest
+from my_adapter import MyAdapter
+
+class TestMyAdapter(BaseAdapterTest):
+    @pytest.fixture
+    def adapter(self):
+        return MyAdapter(...)
+```
+
+## Choosing a Base Class
+
+The platform provides two ways to build adapters. Choose the one that fits your target datasource.
+
+| Feature | `DatasourceAdapter` (Base Interface) | `BaseSQLAlchemyAdapter` (Helper Class) |
+| :--- | :--- | :--- |
+| **Package** | `nl2sql-adapter-sdk` | `nl2sql-adapter-sqlalchemy` |
+| **Best For** | REST APIs, NoSQL, GraphQL, Manual SQL Drivers. | SQL Databases with SQLAlchemy dialects (Postgres, Oracle, Snowflake). |
+| **Schema Fetching** | **Manual Implementation Required**. You must map metadata to `SchemaMetadata`. | **Automatic**. Uses `sqlalchemy.inspect` to reflect tables/FKs. |
+| **Execution** | **Manual Implementation Required**. You handle connections, cursors, and types. | **Automatic**. Handles pooling, transactions, and result formatting. |
+| **Stats Gathering** | **Manual**. You write queries to fetch min/max/nulls. | **Automatic**. Runs optimized generic queries for stats. |
+| **Dry Run** | **Manual**. | **Automatic**. Uses transaction rollback pattern. |
+
+### When to use `DatasourceAdapter`?
+
+Use the raw interface when:
+
+1. You are connecting to a non-SQL source (e.g., Elasticsearch, HubSpot API).
+2. You are using a customized internal SQL driver that is not compatible with SQLAlchemy.
+3. You need complete control over the execution lifecycle (e.g. async-only drivers).
+
+### When to use `BaseSQLAlchemyAdapter`?
+
+Use this helper class when:
+
+1. There is an existing SQLAlchemy dialect for your database (this covers 95% of SQL databases).
+2. You want to save time on boilerplate (connection pooling, schema reflection).
+3. You want consistent behavior with the core supported adapters.
+
+## Building SQL Adapters (The Fast Way)
+
+For SQL databases supported by SQLAlchemy, you should use the `nl2sql-adapter-sqlalchemy` package as described in the comparison above.
+
+### `BaseSQLAlchemyAdapter` Features
+
+This base class implements ~90% of the required functionality for you:
+
+* **Automatic Schema Fetching**: Uses `sqlalchemy.inspect` to get tables, columns, PKs.
+* **Automatic Statistics**: Runs optimized queries to fetch `min/max`, `null_percentage`, `distinct_count`, and `sample_values` for text columns.
+* **Generic Execution**: Handles connection pooling and result formatting.
+* **Safety**: Built-in generic `dry_run` using transaction rollbacks.
+
+### Example Implementation
+
+See `packages/adapters/postgres` for a reference implementation.
+
+```python
+from nl2sql_sqlalchemy_adapter import BaseSQLAlchemyAdapter
+
+class PostgresAdapter(BaseSQLAlchemyAdapter):
+    def construct_uri(self, args: Dict[str, Any]) -> str:
+        return f"postgresql://{args.get('user')}:{args.get('password')}@{args.get('host')}/{args.get('database')}"
+    
+    # Optional: Override dry_run for better performance using EXPLAIN
+    def dry_run(self, sql: str):
+        self.execute(f"EXPLAIN {sql}")
+        return DryRunResult(is_valid=True)
+```
+
+## Reference Adapters
+
+For detailed usage configurations of our supported adapters, please see the **[Supported Adapters](index.md)** section.
+
+Explore the `packages/adapters/` directory for examples:
+
+* `postgres`: Standard implementation using `sqlalchemy`.
+* `sqlite`: Simple, file-based.
+* `mssql` / `mysql`: Standard enterprise drivers.
+
+## Next Steps
+
+Check out the [Postgres Adapter Source Code](https://github.com/nadeem4/nl2sql/tree/main/packages/adapters/postgres) for a complete, production-grade example.

docs/adapters/development.md

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+# Supported Adapters
+
+The NL2SQL Platform supports a variety of datasources through specialized adapters. Each adapter is designed to handle the specific idiosyncrasies of its underlying database engine, from connection strings to specialized `EXPLAIN` plans.
+
+## SQL Adapters
+
+We provide first-class support for the following SQL databases via SQLAlchemy.
+
+| Adapter | Description | Status |
+| :--- | :--- | :--- |
+| **[PostgreSQL](postgres.md)** | Full support including `EXPLAIN`, JSONB, and SSL. | 🟢 Stable |
+| **[MySQL](mysql.md)** | Support for 5.7+ and 8.0. Includes `MAX_EXECUTION_TIME` management. | 🟢 Stable |
+| **[Microsoft SQL Server](mssql.md)** | Enterprise support via `pyodbc` and `T-SQL` dialect. | 🟡 Beta |
+| **[SQLite](sqlite.md)** | File-based local development. | 🟢 Stable |
+
+## Missing your database?
+
+Can't find what you need? Check out the **[Building Adapters](development.md)** guide to see how to implement your own.
+
+## Configuration
+
+All adapters are configured in your `configs/datasources.yaml` file.
+
+```yaml
+version: 1
+datasources:
+  - id: "sales_db"
+    connection:
+      type: "postgres"
+      host: "${env:DB_HOST}"
+      port: 5432
+      # ... see specific adapter docs for full reference
+```

docs/adapters/index.md

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+# Microsoft SQL Server (MSSQL) Adapter
+
+Support for SQL Server 2017+ and Azure SQL.
+
+!!! info "Implementation"
+    This adapter extends `BaseSQLAlchemyAdapter` but provides specialized `dry_run` logic using `SET NOEXEC ON` to safely validate T-SQL.
+
+## Configuration
+
+**Type**: `mssql`
+
+```yaml
+
+connection:
+  type: "mssql"
+  host: "localhost"
+  port: 1433
+  user: "sa"
+  password: "${env:DB_PASS}"
+  database: "my_db"
+  driver: "ODBC Driver 17 for SQL Server" # Default
+  trusted_connection: false
+```
+
+### Connection Details
+
+* **Driver**: `pyodbc`. **Requires system ODBC headers installed.**
+* **URI Constructed**: `mssql+pyodbc://{user}:{pass}@{host}:{port}/{db}?driver={driver}`
+
+## Features
+
+| Feature | Implementation | Note |
+| :--- | :--- | :--- |
+| **Timeout** | Not strictly enforced by driver | Rely on global statement timeout. |
+| **Dry Run** | `SET NOEXEC ON` | Validates syntax without execution. |
+| **Costing** | `SET SHOWPLAN_XML ON` | Parses XML for `StatementSubTreeCost`. |
+
+## Requirements
+
+You must have the MS ODBC Driver installed in your Docker image or local environment.
+
+[Download ODBC Driver for SQL Server](https://learn.microsoft.com/en-us/sql/connect/odbc/download-odbc-driver-for-sql-server)
+
+```bash
+# Debian / Ubuntu
+sudo apt-get install unixodbc-dev
+```

docs/adapters/mssql.md

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+# MySQL Adapter
+
+Support for MySQL 5.7+ and 8.0+.
+
+!!! info "Implementation"
+    This adapter extends `BaseSQLAlchemyAdapter`. It overrides `connect()` to handle `MAX_EXECUTION_TIME` session variables.
+
+## Configuration
+
+**Type**: `mysql`
+
+```yaml
+
+connection:
+  type: "mysql"
+  host: "localhost"
+  port: 3306
+  user: "root"
+  password: "${env:DB_PASS}"
+  database: "my_db"
+  options:
+    charset: "utf8mb4"
+```
+
+### Connection Details
+
+* **Driver**: `pymysql` (Pure Python).
+* **URI Constructed**: `mysql+pymysql://{user}:{pass}@{host}:{port}/{db}?{options}`
+
+## Features
+
+| Feature | Implementation | Note |
+| :--- | :--- | :--- |
+| **Timeout** | `SET MAX_EXECUTION_TIME={ms}` | Session-level enforcement. |
+| **Dry Run** | Transaction Rollback | Starts transaction, runs SQL, rolls back. |
+| **Costing** | `EXPLAIN FORMAT=JSON` | Extracts `query_cost`. |
+| **Stats** | `SELECT count(*), min(), max()` | Standard aggregation. |
+
+## Limitations
+
+* **Row Estimation**: MySQL's `EXPLAIN` does not always provide a reliable "Total Rows" estimate for complex joins compared to Postgres.