[thekevinbot]

Part of #1042.

PR B1 of the one-function-per-file ratchet toward Kevin's chosen target of max_lines = 12. Pure refactor of two internals/checks probe packages; no testing-conventions.toml is touched — a separate PR sets the ceilings once every split has landed.

What moved

Both extension-load probes carry two functions over the threshold, so the gate flags run — the second function in the file — even though run is the orchestration entry point every checks/* package exposes and every caller imports. Per #1040, the fix is to move the holder instead:

Package	New module	Moved
internals/checks/src/checks/npm_binary_extension_load/	diagnose.py + diagnose_test.py	diagnose, STATIC_MARKER
internals/checks/src/checks/wheel_extension_load/	diagnose.py + diagnose_test.py	diagnose, STATIC_MARKER

STATIC_MARKER rides along because diagnose is its only consumer. gate.py picks the function back up with a relative from .diagnose import diagnose, so run is now first in each file and the callers (cli.py) are unchanged. The describe_diagnose cases were relocated out of each gate_test.py, not duplicated.

Second commit: unit lint reads a unit test's import of a sibling source module as an unmocked collaborator, so each gate_test.py now patches diagnose by string and asserts on the probe result handed to it. The rendered wording is asserted in the new diagnose_test.py files, which also gained one case pinning the literal SQLite error text ("Dynamic loading not supported") rather than routing the fixture through the constant.

Verification

internals/checks/src at max_lines = 12, testing-conventions@0.0.111 pinned, config copied to /tmp with the ceiling lowered (the repo config is deliberately untouched):

$ npx -y testing-conventions@0.0.111 unit one-function-per-file --language python --config /tmp/tc-12.toml internals/checks/src
internals/checks/src/checks/platforms_mirror/parse.py:96: `_row` runs 13 lines ...
internals/checks/src/checks/platforms_mirror/parse.py:139: `typescript_table` runs 15 lines ...
internals/checks/src/checks/preflight/matrix.py:118: `named` runs 14 lines ...
error: 3 function(s) sharing a file with another function over the 12-line threshold

Both files in this PR's scope report zero. The three remaining are PR B2's scope.

just preflight (full matrix, 47 pairs): 0 failing, 3 skipped (packaging, which needs a built artifact). unit mutation on the changed lines: no surviving mutants. Zero exemptions added.

Manual run

Ran both CLIs against an empty dist dir (skip path, exit 0), then the npm probe against a fake dirsql that writes the real SQLite error to stderr, which exercises the moved diagnose through run end to end:

$ dirsql-checks npm-binary-extension-load --dist-dir /tmp/fake
npm-binary-extension-load: the npm bundled-cli `dirsql` binary cannot load SQLite extensions
('Dynamic loading not supported'): it is statically linked (static-pie) ... See dirsql#762.
stdout=''
stderr='Error: Dynamic loading not supported\n'

Red/green

Does not apply — this is a behavior-preserving move, so there is no new behavior to turn a test red. The suite stayed green throughout (400 unit, 43 integration, 24 e2e).

E2E Verification

• Ran e2e suites locally for every affected SDK
• Python SDK e2e: N/A — no packages/python change
• TypeScript SDK e2e: N/A — no packages/ts change
• Rust core e2e (if applicable): N/A — no packages/rust change
• internals/checks/e2e-attestations/claude-tackle-1042-b1-extload.json receipt written (just e2e-attest-internals-checks)
• Command(s) run: cd internals/checks && uv run python -m pytest tests/e2e -x -q
• Result summary: 24 passed. The attest commit adds exactly one file and deletes none (checked per e2e attest silently deletes other branches' attestation receipts #1041).

Changelog / Migrations

• Not required — changelog_gate/decide.py scopes the gate to _ROOTS = ("packages", "plugins"), so internals/checks/** is outside it.
• Migration fragment not required — behavior-preserving, and every moved symbol is package-internal.

PARITY

No change. Neither function is part of any SDK's public surface; internals/checks is repo tooling and appears nowhere in PARITY.md.