Runtime errors in a batch surface as "Expected ColumnMetadata in context" (mssql-tds-preview drain_stream) #37

Found while testing #34.

Problem

When one statement in a batch fails with a runtime error and a later statement in the same batch returns rows, the driver can't parse the rest of the response. The user sees a misleading error instead of the real SQL error:

SQL Server connection failure: IO error: Expected ColumnMetadata in context

This happens at every compatibility level.

Cause

mssql-tds-preview's drain_stream (src/connection/tds_client.rs) reads every token after an ERROR token with ParserContext::None and doesn't handle COLMETADATA. So when a later statement returns a result set, the ROW tokens that follow can't be parsed, because the parser has no column metadata for them.

The latest release (0.1.0-preview.9) has the same drain_stream. We pin =0.1.0-preview.1.

Where it hits the plugin

• update_record / insert_record: the plugin appends SELECT CAST(@@ROWCOUNT AS BIGINT) AS [__tabularis_affected_rows] to the DML (src/driver/helpers.rs). Any runtime error in the DML (arithmetic overflow, constraint violation, etc.) is followed by that SELECT, so it always takes this path and the real error is lost.
• execute_query: SELECT 1/0; SELECT 2 hangs.

Repro

1. Against any SQL Server, run SELECT 1/0; SELECT 2 through execute_query. It hangs instead of returning error 8134.
2. Update a REAL column to a value that overflows (for example 3.4028235e38 at compatibility level below 130, Msg 232). It returns Expected ColumnMetadata in context instead of the overflow error.

Options

1. Upstream fix in mssql-tds-preview (https://github.com/saurabh500/mssql-rs): make drain_stream handle COLMETADATA (or skip result sets correctly) after an error.
2. Plugin-side workaround: avoid batches where a result set can follow a failing statement. For DML, that could mean getting the row count from the DONE token instead of a trailing SELECT @@ROWCOUNT, if the crate exposes it.

Option 1 is the real fix; option 2 would at least surface the right error for update_record / insert_record until upstream ships one.