[Refactor] Add test-utils guardrails and convert remaining stragglers

[zoomote]

Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

Related GitHub Issue

N/A: Phase 4 test-utils rollout guardrails.

Description

Adds lightweight guardrails so the Phase 3 test-utils migration cannot regress, per the initiative plan's Phase 4:

• src/eslint.config.mjs: no-restricted-syntax error on vi.clearAllMocks() / vitest.clearAllMocks() scoped to the converted extension lanes (api/providers/__tests__, core/config/__tests__, services/code-index/**/__tests__, integrations/terminal/**/__tests__), pointing authors at src/test-utils/reset.
• webview-ui/eslint.config.mjs: no-restricted-imports error on importing QueryClientProvider in component specs (src/components/**/__tests__/**/*.tsx), pointing authors at renderWithExtensionState. Scoped to .tsx component specs intentionally — .ts hook specs keep local renderHook wrappers because they pass a specific QueryClient instance to the hook.
• PR template: new "Test Helpers (test changes only)" checklist item: shared helpers only for mechanical duplication; test intent stays visible.

Two stragglers found while verifying the guardrail are converted here so the rules land green:

• CustomModesManager.spec.ts: 9 remaining direct vi.clearAllMocks() call sites missed by [Refactor] Reuse shared CustomModesManager test helpers #1190 (helper was already imported).
• useSelectedModel.spec.ts / useZooGatewayRouterModelsSync.spec.ts: hand-rolled new QueryClient({ queries: { retry: false } }) replaced with the shared createTestQueryClient().

Both rules were probe-tested: a temporary offending file in each lane errors with the intended message.

This is a test-and-lint-config-only change with no intended runtime or user-facing behavior change.

Test Procedure

• Probe files confirmed each rule errors correctly (removed after verification)
• pnpm exec vitest run core/config/__tests__/CustomModesManager.spec.ts from src (48 tests passed)
• pnpm exec vitest run src/components/ui/hooks/__tests__/useZooGatewayRouterModelsSync.spec.ts src/components/ui/hooks/__tests__/useSelectedModel.spec.ts from webview-ui (48 + 42 tests passed)
• pnpm test (extension: 445 files, 7,355 tests; webview: 145 files, 1,643 tests)
• pnpm lint
• pnpm check-types
• ESLint prune check on touched extension files passes with --max-warnings=0; src/eslint-suppressions.json unchanged.

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Test Helpers (test changes only): Shared test helpers (src/test-utils/, @/utils/test-utils) are used only for mechanical duplication; test intent and scenario-specific mocks remain visible.
• Visual Snapshot (UI changes only): Not applicable; this is a test-only refactor with no rendered UI change.
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Visual Snapshots

Not applicable; no product UI changed.

Videos (interaction / animation only)

Not applicable; no product interaction changed.

Documentation Updates

• No documentation updates are required.
• Yes, documentation updates are required.

Additional Notes

No changesets were added. Author self-review found no behavior or scope regressions. The .tsx scoping of the webview rule is deliberate; hook specs that need a specific QueryClient instance keep local renderHook wrappers but now share createTestQueryClient().

Get in Touch

Mention @roomote on this PR for follow-up requests.

[zoomote]

Author self-review summary:

• Scope: 6 files, 60 insertions / 18 deletions — two scoped ESLint rules, one PR-template checklist item, and three straggler conversions so the rules land green.
• Both rules probe-tested: a temporary offending file per lane produced the intended error message, then was removed.
• Extension rule is scoped to exactly the four converted lanes; the shared helper module itself sits outside the globs, and the base config has no conflicting no-restricted-syntax.
• Webview rule is deliberately .tsx-only: .ts hook specs pass a specific QueryClient instance to renderHook, so they keep local wrappers but now share createTestQueryClient() (noted in a config comment).
• Validation: 48 + 42 focused tests on touched specs; full pnpm test (extension 445 files / 7,355 tests; webview 145 files / 1,643 tests); pnpm lint; pnpm check-types; suppressions file content-identical to HEAD.
• No production code, docs-site changes, or changesets. Visual proof not applicable.

Per initiative policy, not approving this Roomote-authored PR — leaving review to a human maintainer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!