[build-tools] Fix Argent tool server state discovery

[sjchmiela]

Why

Argent now writes per-install tool-server state files such as ~/.argent/tool-server-<hash>.json. The remote session step only watched the legacy tool-server.json, so it could time out even when the newly launched tool server was running.

How

• expose the PID of detached processes
• add a process ancestry helper that works on macOS and Linux
• run Argent in the foreground beneath the detached bunx process and pass --force
• scan legacy and hashed Argent state files, selecting only the state whose PID descends from the launched bunx process
• validate the state schema includes the tool-server PID
• cover legacy, hashed, matching, and unrelated state files

Test Plan

• yarn workspace @expo/build-tools jest-unit packages/build-tools/src/steps/functions/__tests__/startArgentRemoteSession.test.ts --runInBand
• yarn workspace @expo/build-tools build
• yarn workspace @expo/worker build
• yarn workspace eas-cli build
• yarn workspace @expo/build-tools typecheck
• yarn lint
• yarn fmt:check

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[github-actions]

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File Patterns	Mentions
**/*	@douglowder

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[codecov]

Codecov Report

❌ Patch coverage is 73.91304% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.67%. Comparing base (6d02728) to head (94396e8).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ls/src/steps/functions/startArgentRemoteSession.ts	70.97%	9 Missing ⚠️
packages/build-tools/src/utils/processes.ts	85.72%	2 Missing ⚠️
...ld-tools/src/steps/utils/remoteDeviceRunSession.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3997      +/-   ##
==========================================
+ Coverage   59.67%   59.67%   +0.01%     
==========================================
  Files         940      941       +1     
  Lines       41260    41318      +58     
  Branches     8666     8675       +9     
==========================================
+ Hits        24617    24654      +37     
- Misses      16549    16570      +21     
  Partials       94       94              

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