Fixes #1886.

Root cause

The ClickHouse driver guessed whether a query returns data by taking the first token of the SQL, split on a literal space character. SELECT on its own line yields the token SELECT\n, and a leading -- or /* */ comment yields --, so both misclassified a real SELECT. The misclassified path discarded the HTTP response body without reading it and returned empty columns, which the app renders as "Query executed successfully" with no grid. The same guess also gated the streaming export path, so exports of comment-prefixed queries wrote empty files.

This is the bug class the ClickHouse JDBC maintainers fixed in clickhouse-java#2784: client-side statement classification must never make server-returned rows disappear.

Fix

Stop classifying the query text. Every request now pins the output format out of band and the response decides what to show:

• default_format=TabSeparatedWithNamesAndTypes and wait_end_of_query=1 go on the URL, never appended to the SQL. Appending FORMAT X to the SQL text was also independently broken: a trailing -- comment swallowed it silently and a user-written FORMAT clause produced a double-FORMAT syntax error. Verified against a live ClickHouse 26.7 server.
• Body in the pinned format: parse as TSV. Zero rows still carry the two header lines, so an empty result shows a grid with real columns instead of a success message.
• Empty body: no result set. Affected rows now come from the X-ClickHouse-Summary header's written_rows, so INSERT stops reporting 0 rows affected.
• Body in a different format (the user wrote their own FORMAT clause, detected via the X-ClickHouse-Format response header): the raw output is shown in a single column instead of being dropped.
• http_write_exception_in_output_format=0 is sent only to servers on 23.8 or later, gated through ClickHouseCapabilities, because older servers reject unknown settings.
• The streaming export request uses default_format=JSONEachRow instead of string concatenation, closing the same hole there.

The response classification and TSV parsing moved into TableProPluginKit as ClickHouseResponseClassifier so the shipped code is unit-testable. ClickHouseConnectionTests now tests that shipped code instead of a private copy of the unescape function.

ABI

scripts/check-pluginkit-abi.sh main reports an additive-only diff: one new public type, nothing removed or changed. No PluginKit version bump. ClickHouse is a bundled plugin, so this ships with the next app release.

Testing

• 33 unit tests across ClickHouseResponseClassifierTests (new), ClickHouseCapabilitiesTests (new), and ClickHouseConnectionTests; xcodebuild test passes.
• Test shapes taken from real bug reports in other clients: leading comment, SELECT on its own line, zero-row result vs no result set, user FORMAT clause, malformed and oversized bodies, row-cap truncation.
• swiftlint lint --strict clean on changed files.

Follow-up filed separately: #1895 (statement scanner turns a trailing comment after the last semicolon into a phantom statement).