feat(sandbox): add JS Dockerfile snapshots

[Mukil Loganathan (langchain-infra)]

Summary

• Add JS SandboxClient.createSnapshotFromDockerfile(...) while keeping the existing Docker-image createSnapshot(...) signature unchanged.
• Upload local Docker build contexts to temporary builder sandboxes, run BuildKit, and capture the built sandbox-local image through the snapshot API.
• Extend JS capture snapshot options with Docker image export fields and re-export the new Dockerfile snapshot options type.

Release Note

JS SDK sandbox clients can now build snapshots from a local Dockerfile context.

Test Plan

• rtk pnpm test -- src/tests/sandbox.test.ts
• rtk pnpm exec oxfmt --check src/sandbox/client.ts src/sandbox/types.ts src/sandbox/index.ts src/tests/sandbox.test.ts
• rtk pnpm exec oxlint src/sandbox/client.ts src/sandbox/types.ts src/sandbox/index.ts src/tests/sandbox.test.ts
• rtk pnpm run check:types
• rtk pnpm run build
• Prod JS e2e with builder snapshot 55d870c0-1d0f-48fe-aa8b-c10f543a17f1: built Dockerfile, captured ready snapshot b1ef5128-b2af-4f63-9a56-275e02cc054b, deleted test snapshot.

[github-actions]

JS perf benchmark

Lower is better. Noisy on shared runners — treat as a signal, not a gate.

Base64-heavy payload

Single large base64 string per message — the shape the worker-offload path is optimized for.
Payload: 2511.2 KB in / 5.2 KB out, 100 runs.

metric	main	this PR	delta
Wall time (ms)	1878.73	1752.92	-6.7%
createRun total (ms)	74.48	78.08	+4.8%
createRun p50 (ms)	0.60	0.48	-19.5%
createRun p95 (ms)	0.80	0.82	+2.3%
createRun p99 (ms)	26.27	25.35	-3.5%
createRun max (ms)	26.27	25.35	-3.5%
updateRun total (ms)	42.20	43.31	+2.6%
updateRun p95 (ms)	0.72	1.01	+40.9%
loop lag total (ms)	1146.15	799.13	-30.3%
loop lag p50 (ms)	0.10	0.10	-0.7%
loop lag p95 (ms)	4.59	3.60	-21.6%
loop lag p99 (ms)	39.70	10.64	-73.2%
loop lag max (ms)	147.70	114.22	-22.7%

Structural payload

Many small strings across a wide/nested object graph. Should bypass worker offload and use sync flush.
Payload: 1239.5 KB in / 13.3 KB out, 100 runs.

metric	main	this PR	delta
Wall time (ms)	1453.59	1512.05	+4.0%
createRun total (ms)	395.47	440.61	+11.4%
createRun p50 (ms)	3.46	3.50	+1.1%
createRun p95 (ms)	6.82	6.00	-12.0%
createRun p99 (ms)	9.57	39.12	+308.6%
createRun max (ms)	9.57	39.12	+308.6%
updateRun total (ms)	39.37	40.96	+4.0%
updateRun p95 (ms)	0.63	0.69	+8.9%
loop lag total (ms)	1003.14	1060.11	+5.7%
loop lag p50 (ms)	0.07	0.08	+11.1%
loop lag p95 (ms)	4.75	4.83	+1.7%
loop lag p99 (ms)	122.17	120.78	-1.1%
loop lag max (ms)	166.17	162.40	-2.3%