Add support for mid-stream exception detection via X-ClickHouse-Exception-Tag header

[alex-clickhouse]

See ClickHouse/ClickHouse#88818 for the changes in core.

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Note

Introduces mid-stream exception detection when the server sets X-ClickHouse-Exception-Tag (25.11+), converting truncated reads into meaningful ClickHouseServerException with parsed error codes/messages.

• Adds ExceptionTagAwareStream that buffers recent bytes and extracts __exception__<token> markers to build ClickHouseServerException
• Updates ClickHouseDataReader to read the X-ClickHouse-Exception-Tag header, wrap the response stream, and on EndOfStreamException try TryExtractMidStreamException()
• Extends ClickHouseServerException with FromMidStreamException and code parsing; adds Feature.ExceptionTag
• Adds unit/integration tests for detection behavior and parsing: MidStreamExceptionTests, ExceptionTagAwareStreamTests
• Updates RELEASENOTES.md documenting the new behavior

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[codecov]

Codecov Report

❌ Patch coverage is 91.45299% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ickHouse.Driver/Formats/ExceptionTagAwareStream.cs	89.13%	8 Missing and 2 partials ⚠️

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[Copilot]

Pull request overview

This PR introduces support for detecting mid-stream exceptions in ClickHouse queries when the server is configured with http_write_exception_in_output_format (ClickHouse 25.11+). Previously, exceptions occurring during result streaming would surface as generic EndOfStreamExceptions. Now, when the server includes an X-ClickHouse-Exception-Tag header, the client wraps the response stream with ExceptionTagAwareStream to buffer recent bytes and detect exception markers (format: __exception__<token>\n<message>\n<size> <token>__exception__). When an EndOfStreamException occurs, the system extracts and throws a proper ClickHouseServerException with the server's error message and code.

Changes:

• Adds ExceptionTagAwareStream with a 4KB ring buffer to track recent bytes and parse exception markers
• Updates ClickHouseDataReader to conditionally wrap HTTP streams and convert mid-stream failures to ClickHouseServerException
• Extends ClickHouseServerException.FromMidStreamException to handle parsed error messages
• Introduces Feature.ExceptionTag enum value for version detection (25.11+)
• Comprehensive test coverage for stream parsing logic and ADO integration

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
RELEASENOTES.md	Documents the new mid-stream exception detection feature for ClickHouse 25.11+
ClickHouse.Driver/Formats/ExceptionTagAwareStream.cs	Implements ring buffer stream wrapper with marker detection and exception parsing
ClickHouse.Driver/ClickHouseServerException.cs	Adds factory method for creating exceptions from mid-stream error messages
ClickHouse.Driver/ADO/Readers/ClickHouseDataReader.cs	Integrates exception-aware stream wrapping and converts EndOfStreamException to ClickHouseServerException
ClickHouse.Driver/ADO/Feature.cs	Adds ExceptionTag feature flag for ClickHouse 25.11+
ClickHouse.Driver.Tests/Formats/ExceptionTagAwareStreamTests.cs	Unit tests for stream buffering, marker detection, and exception parsing
ClickHouse.Driver.Tests/ADO/MidStreamExceptionTests.cs	Integration test verifying end-to-end exception detection with ClickHouse server