[Bug]: Antigravity installation fails with generic error on CPUs without AVX (crashes with SIGILL)

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Run T3 Code on a machine whose CPU lacks AVX/AVX2 instruction sets (e.g., Intel Pentium Gold, Celeron, or legacy x86_64).
2. Configure WSL backend (or native host).
3. Navigate to Providers -> Antigravity.
4. Click to Install / Activate Antigravity provider.
5. Wait for the 682 MB download and archive extraction to complete.

Expected behavior

Either:
1. Pre-flight check: T3 Code checks CPU flags (avx/avx2) before downloading 682 MB and warns that Google Antigravity binary requires AVX instructions.
2. Clear validation error: If runtime validation fails due to SIGILL (signal 4 / exit code 132), UI clearly informs the user that the process crashed due to an illegal CPU instruction caused by missing AVX
support.

Actual behavior

T3 Code downloads the entire 682 MB archive, extracts it, attempts validation (`agy_acp_server.par --uid=`), crashes immediately on `SIGILL`, and surfaces only a generic message in UI:

> "The downloaded Antigravity runtime could not start in this environment."

Users assume archive corruption, file permission errors, or WSL communication glitches, repeatedly re-downloading ~682 MB.

Impact

Blocks work completely

Version or commit

v0.0.28

Environment

• OS: Windows 10/11 x64 with WSL2 backend (Ubuntu 22.04 LTS, kernel 6.18.33.2-microsoft-standard-WSL2) - CPU: Intel(R) Pentium(R) Gold G5400 @ 3.70GHz (flags: SSE4.1, SSE4.2; lacks AVX and AVX2) - Chipset: Intel B360

Logs or stack traces

From `server.trace.ndjson`:
    
    {
      "type": "effect-span",
      "name": "AntigravityInstallation.validate",
      "exit": {
        "_tag": "Failure",
        "cause": "AntigravityInstallationError: The downloaded Antigravity runtime could not start in this environment.\n [cause]: AcpTransportError: ACP transport operation read-process-exit-status failed.\n [cause]:
  PlatformError: Unknown: ChildProcess.exitCode (.../agy_acp_server.par --uid=)\n [cause]: Error: Process interrupted due to receipt of signal: 'SIGILL'"
      }
    }

  Kernel output (dmesg):

    agy_acp_server.par: potentially unexpected fatal signal 4.
    WSL (CaptureCrash): Capturing crash for pid: 1877, executable: .../agy_acp_server.par, signal: 4

Screenshots, recordings, or supporting files

No response

Workaround

None...

• Upgrade CPU to an AVX/AVX2 capable processor (e.g. Intel Core i3/i5/i7 8th/9th Gen on LGA1151 or AMD Ryzen).
• Run the runtime binary under Intel SDE emulator (sde64), though with significant performance penalty.
• Use alternative providers in T3 Code that do not require Google's AVX runtime binary.

Start in apps/server at AntigravityInstallation.validate and trace the agy_acp_server.par validation failure reported as SIGILL or exit code 132. Reproduce on a CPU without AVX/AVX2, then determine whether the completed work is a pre-flight warning, a clearer validation error, or both; verify that the UI identifies missing AVX support instead of suggesting a generic runtime failure.