Fix flaky test_single_query_terminated_with_semicolon

[tconbeer]

Closes #1174

What are the key elements of this solution?

test_single_query_terminated_with_semicolon[sqlite] failed all three Windows retries in this run. The test focused the editor as soon as a results table was mounted. At that point Harlequin.load_tables could still be running, and its trailing results_viewer.focus() took focus back. The next ctrl+j then went to the Results Viewer, which doesn't bind it, so no second QuerySubmitted was posted.

• Adds wait_for_results(pilot, app, messages, count=n) to tests/functional_tests/helpers.py. It waits for the n-th ResultsFetched, then waits for results_viewer.loading to clear. The message hook fires before the handler runs, and loading clears in the same synchronous tail of load_tables that moves focus to the Results Viewer.
• In test_single_query_terminated_with_semicolon, uses it in place of wait_for_any_table and the two wait_for_workers calls. The test reads tab_count and moves focus right after those waits.
• Applies the same change to test_multiple_queries, which has the same wait → editor.focus() → ctrl+j pattern.

Why did you design your solution this way? Did you assess any alternatives? Are there tradeoffs?

It waits on the condition the test actually depends on, rather than a sleep or retry, per tests/waiting.py's conventions. I reproduced the race locally by injecting a 0.3s delay before ResultsFetched is posted and a 0.5s delay after add_pane in push_table. With those delays the old test failed every run with the CI error (timed out … waiting for 2 QuerySubmitted messages, saw 1), and the new test passed every run. The delays were not committed. test_multiple_queries didn't fail under those delays, so that change is preventive.

Does this PR require a change to Harlequin's docs?

• No.
• Yes, and I have opened a PR at tconbeer/harlequin-web.
• Yes; I haven't opened a PR, but the gist of the change is: ...

Did you add or update tests for this change?

• Yes.
• No, I believe tests aren't necessary.
• No, I need help with testing this change.

Please complete the following checklist:

• I have added an entry to CHANGELOG.md, under the [Unreleased] section heading. That entry references the issue closed by this PR. — Not added: test-only change, nothing user-facing.
• I acknowledge Harlequin's MIT license. I do not own my contribution.

Locally: pytest -m "not online" 2131 passed; ruff, mypy, and lint-imports clean.

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https://claude.ai/code/session_016SvJmAXqxMtxPYcygLwinH

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[tconbeer]

Windows-latest - 3.10 (job) failed during dependency install, before any test ran. uv couldn't fetch the pinned pytest-textual-snapshot git dependency (fatal: unable to access 'https://github.com/tconbeer/pytest-textual-snapshot.git/': Empty reply from server). This is a network error, not caused by this PR, and there is no fix to port. I'll re-run the failed job once, after the workflow run finishes (GitHub refuses a re-run while the run is in progress).

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