chore(lint): enable unicorn/consistent-existence-index-check

[HAYDEN-OAI]

• I understand that this repository is auto-generated and my pull request may not be merged

Changes being requested

• Remove the unicorn/consistent-existence-index-check compatibility exception from oxlint.config.ts.
• Normalize the 3 existing handwritten-code findIndex() existence checks to compare with -1.

Additional context & links

• Oxlint cleanup stack, part 63; stacked on chore(lint): enable no-new-wrappers #2141.
• Preserves generated-file exclusions and repository-specific import policy.

Validation

• pnpm lint
• pnpm exec tsc --pretty false
• pnpm exec vitest run --config vitest.config.mts --update=none

Stack

#2141
#2143 👈 this PR
#2144
#2145
#2146
#2147
#2148
#2149

[jbeckwith-oai]

The three rewrites are semantically equivalent because Array.prototype.findIndex returns only -1 or a nonnegative index, and the newly enabled rule now passes across the handwritten source. The immediate stacked diff is minimal, introduces no file-size or structural regression, and local lint, typecheck, focused emitter tests, and exact-head CI all pass.

[openai-sdks]

OkTest Summary

✅ 237/237 SDK tests passed in 11.796s for Node SDK PR #2143.

Test results — 42 files

Test	Result	Time
tests/chat-completions-complex-body.test.ts	✅ Passed	300ms
tests/chat-completions-create.test.ts	✅ Passed	284ms
tests/chat-completions-stream.test.ts	✅ Passed	252ms
tests/files-content-binary.test.ts	✅ Passed	194ms
tests/files-create-multipart.test.ts	✅ Passed	205ms
tests/files-list-pagination.test.ts	✅ Passed	228ms
tests/initialize-config.test.ts	✅ Passed	224ms
tests/instance-isolation.test.ts	✅ Passed	127ms
tests/models-list.test.ts	✅ Passed	197ms
tests/responses-background-lifecycle.test.ts	✅ Passed	266ms
tests/responses-body-method-errors.test.ts	✅ Passed	433ms
tests/responses-cancel-timeout.test.ts	✅ Passed	227ms
tests/responses-cancel.test.ts	✅ Passed	314ms
tests/responses-compact-retries.test.ts	✅ Passed	330ms
tests/responses-compact.test.ts	✅ Passed	342ms
tests/responses-create-advanced-stream.test.ts	✅ Passed	187ms
tests/responses-create-advanced.test.ts	✅ Passed	258ms
tests/responses-create-disconnect.test.ts	✅ Passed	1.222s
tests/responses-create-errors.test.ts	✅ Passed	286ms
tests/responses-create-malformed-api-responses.test.ts	✅ Passed	225ms
tests/responses-create-retries.test.ts	✅ Passed	340ms
tests/responses-create-stream-failures.test.ts	✅ Passed	329ms
tests/responses-create-stream-timeout.test.ts	✅ Passed	2.179s
tests/responses-create-stream-wire.test.ts	✅ Passed	2.454s
tests/responses-create-stream.test.ts	✅ Passed	112ms
tests/responses-create-terminal-states.test.ts	✅ Passed	280ms
tests/responses-create-timeout.test.ts	✅ Passed	230ms
tests/responses-create.test.ts	✅ Passed	259ms
tests/responses-delete.test.ts	✅ Passed	342ms
tests/responses-input-items-errors.test.ts	✅ Passed	260ms
tests/responses-input-items-list.test.ts	✅ Passed	178ms
tests/responses-input-items-options.test.ts	✅ Passed	163ms
tests/responses-input-tokens-count-timeout.test.ts	✅ Passed	272ms
tests/responses-input-tokens-count.test.ts	✅ Passed	260ms
tests/responses-malformed-inputs.test.ts	✅ Passed	2.239s
tests/responses-not-found-errors.test.ts	✅ Passed	347ms
tests/responses-parse.test.ts	✅ Passed	207ms
tests/responses-retrieve-retries.test.ts	✅ Passed	335ms
tests/responses-retrieve.test.ts	✅ Passed	308ms
tests/responses-stored-method-errors.test.ts	✅ Passed	807ms
tests/retry-behavior.test.ts	✅ Passed	3.089s
tests/sdk-error-shape.test.ts	✅ Passed	405ms

View OkTest run #31230061951

_{SDK merge (8001f75636d1) · head (c42ace32ba3d) · base (4051f9fa463a) · OkTest (91635c6a2723)}