Fix invalid DDL for multi-column SummingMergeTree

[alex-clickhouse]

Problem

HasSummingMergeTreeEngine("Clicks", "Impressions") generated invalid DDL:

ENGINE = SummingMergeTree(`Clicks`, `Impressions`)

ClickHouse rejects this at CREATE TABLE time:

Code: 42. DB::Exception: With extended storage definition syntax storage
SummingMergeTree requires 0 to 1 parameters. (NUMBER_OF_ARGUMENTS_DOESNT_MATCH)

SummingMergeTree's single optional parameter is the list of columns to sum, which must be a tuple when there is more than one column — unlike ReplacingMergeTree/VersionedCollapsingMergeTree, whose multiple parameters really are positional and correctly comma-separated.

Fix

Wrap multiple sum columns in a tuple; pass a single column directly.

ENGINE = SummingMergeTree((`Clicks`, `Impressions`))   -- multiple
ENGINE = SummingMergeTree(`Clicks`)                    -- single (unchanged)

Verified empirically against ClickHouse 26.6: the tuple form creates successfully, the comma form fails.

Why it wasn't caught (and how this closes the gap)

Engine DDL was only covered by string-comparison unit tests — and SummingMergeTree_multiple_columns actually asserted the invalid SQL as correct. No test ever executed the generated CREATE TABLE against a real server, so the two engines with round-trip integration coverage (MergeTree, ReplacingMergeTree) worked while the rest were unverified.

This PR adds engine-argument round-trip integration tests (EnsureCreated against a real ClickHouse container) for:

• SummingMergeTree — single and multiple columns (regression guard)
• CollapsingMergeTree
• VersionedCollapsingMergeTree
• AggregatingMergeTree

Invalid engine DDL now fails the build. I also audited every other engine's arg generation and verified each form against a live server — SummingMergeTree was the only one affected; the rest emit valid DDL (Graphite only needs a server-side rollup config, which is not a syntax issue).

Tests

All 91 tests in MigrationIntegrationTests + MigrationSqlGeneratorTests pass.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes ClickHouse DDL generation for SummingMergeTree when configured with multiple sum columns by emitting a single tuple parameter (instead of an invalid comma-separated argument list), and adds integration coverage to ensure engine clauses round-trip successfully against a real ClickHouse server.

Changes:

• Update migrations SQL generation to wrap multi-column SummingMergeTree sum columns in a tuple, while keeping single-column behavior unchanged.
• Correct/extend unit tests to assert the tuple form for multi-column SummingMergeTree and add a single-column test.
• Add new integration tests that execute EnsureCreatedAsync for several MergeTree-family engines to catch invalid engine DDL at runtime.
• Document the fix in CHANGELOG.md and RELEASENOTES.md.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/EFCore.ClickHouse.Tests/MigrationSqlGeneratorTests.cs	Updates the existing unit assertion for multi-column SummingMergeTree and adds a single-column test case.
test/EFCore.ClickHouse.Tests/MigrationIntegrationTests.cs	Adds engine-argument round-trip integration tests validating CREATE TABLE succeeds and engine clauses are persisted as expected.
src/EFCore.ClickHouse/Migrations/ClickHouseMigrationsSqlGenerator.cs	Fixes SummingMergeTree engine argument emission: tuple-wraps multiple sum columns.
RELEASENOTES.md	Notes the SummingMergeTree multi-column DDL bug fix in the unreleased section.
CHANGELOG.md	Notes the SummingMergeTree multi-column DDL bug fix in the unreleased section.

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