chore: run the mock server from locked local tooling

[apcha-oai]

Summary

This is part of a series to reduce the SDK's dependency surface and make contributor tooling more predictable. It builds on the merged #3678.

• Lock the existing Steady 0.22.1 release and its platform packages in the repository's pnpm lockfile.
• Keep ./scripts/bootstrap followed by ./scripts/test working, including automatic mock-server startup, an existing server, TEST_API_BASE_URL, and both Pydantic test lanes.
• Run only the locally installed mock server. Missing tooling produces setup instructions instead of an on-demand npm download.

This completes the mock-tooling portion of #3116 using the current uv/pnpm setup.

[jbeckwith-oai]

Reviewed the complete stacked Steady mock-server migration against its exact parent. The tool and optional platform binaries are integrity-pinned; repository-local execution avoids downloads, preserves signal forwarding, readiness and failure cleanup, existing-server behavior, custom endpoints, and both Pydantic test lanes. No additional issue is introduced by this stacked change. The separate parent-PR devcontainer finding remains tracked on #3678.

[openai-sdks]

OkTest Summary

✅ 237/237 SDK tests passed in 11.701s for Python SDK PR #3679.

Test results — 42 files

Test	Result	Time
tests/chat-completions-complex-body.test.ts	✅ Passed	221ms
tests/chat-completions-create.test.ts	✅ Passed	345ms
tests/chat-completions-stream.test.ts	✅ Passed	129ms
tests/files-content-binary.test.ts	✅ Passed	226ms
tests/files-create-multipart.test.ts	✅ Passed	241ms
tests/files-list-pagination.test.ts	✅ Passed	157ms
tests/initialize-config.test.ts	✅ Passed	303ms
tests/instance-isolation.test.ts	✅ Passed	189ms
tests/models-list.test.ts	✅ Passed	218ms
tests/responses-background-lifecycle.test.ts	✅ Passed	278ms
tests/responses-body-method-errors.test.ts	✅ Passed	444ms
tests/responses-cancel-timeout.test.ts	✅ Passed	234ms
tests/responses-cancel.test.ts	✅ Passed	291ms
tests/responses-compact-retries.test.ts	✅ Passed	341ms
tests/responses-compact.test.ts	✅ Passed	282ms
tests/responses-create-advanced-stream.test.ts	✅ Passed	192ms
tests/responses-create-advanced.test.ts	✅ Passed	284ms
tests/responses-create-disconnect.test.ts	✅ Passed	1.111s
tests/responses-create-errors.test.ts	✅ Passed	259ms
tests/responses-create-malformed-api-responses.test.ts	✅ Passed	284ms
tests/responses-create-retries.test.ts	✅ Passed	410ms
tests/responses-create-stream-failures.test.ts	✅ Passed	125ms
tests/responses-create-stream-timeout.test.ts	✅ Passed	214ms
tests/responses-create-stream-wire.test.ts	✅ Passed	3.533s
tests/responses-create-stream.test.ts	✅ Passed	135ms
tests/responses-create-terminal-states.test.ts	✅ Passed	331ms
tests/responses-create-timeout.test.ts	✅ Passed	302ms
tests/responses-create.test.ts	✅ Passed	218ms
tests/responses-delete.test.ts	✅ Passed	234ms
tests/responses-input-items-errors.test.ts	✅ Passed	386ms
tests/responses-input-items-list.test.ts	✅ Passed	287ms
tests/responses-input-items-options.test.ts	✅ Passed	317ms
tests/responses-input-tokens-count-timeout.test.ts	✅ Passed	307ms
tests/responses-input-tokens-count.test.ts	✅ Passed	274ms
tests/responses-malformed-inputs.test.ts	✅ Passed	2.61s
tests/responses-not-found-errors.test.ts	✅ Passed	319ms
tests/responses-parse.test.ts	✅ Passed	421ms
tests/responses-retrieve-retries.test.ts	✅ Passed	363ms
tests/responses-retrieve.test.ts	✅ Passed	292ms
tests/responses-stored-method-errors.test.ts	✅ Passed	678ms
tests/retry-behavior.test.ts	✅ Passed	3.175s
tests/sdk-error-shape.test.ts	✅ Passed	410ms

View OkTest run #32274473270

_{SDK merge (0ec2f55f328f) · head (a5f7c3af1588) · base (3079be224c05) · OkTest (0ad95c429af9)}