Run Expo serve-sim under EAS supervision

[szdziedzic]

Why

EAS Simulator currently launches the production-only serve-sim-szdziedzic fork and depends on its private tunnel flags and Tunnel: stdout format. The official @expo/serve-sim package is now published, but it is not a safe drop-in until EAS owns the production concerns that do not belong in the OSS server.

Coordinated serve-sim change: expo/serve-sim#36

That PR must merge and be published to npm's latest dist-tag before this change is rolled out, because the currently published package must contain the readiness/encoder startup contract.

How

• always install @expo/serve-sim@latest instead of using the personal fork or a hard-coded package version
• translate the VM-safe production streaming policy to the official CLI flags: explicit WebRTC/VP8, 1280px, 60 fps, 3 Mbps, and MJPEG fallback quality 0.55
• allocate a loopback port, launch serve-sim, and poll its stable /readyz endpoint instead of scraping stdout
• keep Cloudflare TURN discovery in EAS and pass the resulting ICE arguments to serve-sim
• make EAS own ngrok setup, the auth token, high-entropy tunnel hostname, and lifecycle
• return explicit cleanup handles for ngrok and detached processes, and stop preview resources from every remote-session caller

This is intentionally split across repositories: serve-sim owns generic streaming/readiness primitives; EAS owns infrastructure, credentials, policy, versioning, and supervision.

Test Plan

• yarn build — all 13 monorepo targets passed, including @expo/build-tools
• all directly affected suites outside the sandbox — 24 tests passed
• focused final suites plus build-tools typecheck — 15 tests passed
• yarn fmt:check
• yarn lint — 0 errors (13 unrelated existing warnings)
• the broader build-tools unit run reached 918 passing tests; its 10 failures were local sandbox restrictions around npm access, process inspection, and macOS keychain creation. The affected process-inspection suite passes outside the sandbox.
• end-to-end verified the coordinated serve-sim build negotiated VP8 and delivered live 589×1280 video while applying the requested 60 fps / 3 Mbps sender policy

Rollout order

1. Merge Add supervised stream startup contract serve-sim#36.
2. Publish and verify that npm's latest dist-tag contains the coordinated serve-sim changes.
3. Exercise this draft in an EAS Simulator staging session.
4. Merge this PR to switch production off serve-sim-szdziedzic.

[codecov]

Codecov Report

❌ Patch coverage is 31.70732% with 84 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.25%. Comparing base (6fa71f8) to head (cc0a823).

Files with missing lines	Patch %	Lines
...ld-tools/src/steps/utils/remoteDeviceRunSession.ts	35.49%	58 Missing and 2 partials ⚠️
...c/steps/functions/startAgentDeviceRemoteSession.ts	0.00%	13 Missing and 3 partials ⚠️
.../src/steps/functions/startServeSimRemoteSession.ts	0.00%	6 Missing ⚠️
...ls/src/steps/functions/startArgentRemoteSession.ts	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4114      +/-   ##
==========================================
- Coverage   62.27%   62.25%   -0.02%     
==========================================
  Files         994      994              
  Lines       44735    44820      +85     
  Branches     9412     9425      +13     
==========================================
+ Hits        27854    27897      +43     
- Misses      15434    15474      +40     
- Partials     1447     1449       +2     

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[github-actions]

✅ Thank you for adding the changelog entry!

[sjchmiela]

This is weird to me. Shouldn't serve-sim pick a port itself? Or, couldn't we just assign a well known port to serve-sim?

[szdziedzic]

serve-sim can choose/scan for a port, but EAS needs to know the selected port to poll /readyz and configure ngrok. I allocated one in EAS to avoid parsing serve-sim output. That said, since the runner is single-tenant and only starts one serve-sim instance, using a well-known port like 3200 is simpler. I can switch this to a constant.