test: launchd survive-collection execs the osascript child; pwsh probe traps and narrates

- test_source_launcher_publication: launchd ProgramArguments are `/usr/bin/osascript -e` since #71206;
  on Linux exec the child argv the script would spawn (minus the shell redirection tail).
- test_source_build_env: pwsh 7.6.5 on the Windows lane exits 0 without running the child; the probe
  now traps any terminating error (exit 97 + stack) and narrates each step to stderr.

tests/hermes_cli/test_source_launcher_publication.py

@@ -276,8 +276,11 @@ def _command_survives_generation_collection(tmp_path, monkeypatch, surface):
                 monkeypatch.setattr(gateway, "PROJECT_ROOT", repo)
                 if surface == "launchd":
                     import plistlib
+                    from tests.hermes_cli.test_gateway_service import _osascript_exec_argv
                     unit = gateway.generate_launchd_plist()
-                    command = plistlib.loads(unit.encode())["ProgramArguments"]
+                    # The job runs through osascript (#71206); exec the child it would spawn, minus the
+                    # `>> log 2>> log` tail that only means something to the shell.
+                    command = _osascript_exec_argv(plistlib.loads(unit.encode())["ProgramArguments"])[:-4]
                     args = ["gateway", "run", "--external-supervisor"]
                 else:
                     unit = gateway.generate_systemd_unit()

tests/scripts/test_source_build_env.py

@@ -89,10 +89,14 @@ console.log(JSON.stringify(process.env));
         script = tmp_path / "probe.ps1"
         script.write_text('''$ErrorActionPreference = 'Stop'
 [Console]::Error.WriteLine("probe start: $($PSVersionTable.PSVersion) assets=$env:ASSETS python=$env:PROBE_PYTHON")
+trap { [Console]::Error.WriteLine("probe trap: $_"); [Console]::Error.WriteLine($_.ScriptStackTrace); exit 97 }
 . (Join-Path $env:ASSETS 'source-build-env.ps1')
-Invoke-SourceBuild { & $env:PROBE_PYTHON -I -S $env:PROBE_SCRIPT; if ($LASTEXITCODE) { throw 'stamp failed' } }
+[Console]::Error.WriteLine("probe: asset sourced")
+Invoke-SourceBuild { & $env:PROBE_PYTHON -I -S $env:PROBE_SCRIPT; [Console]::Error.WriteLine("probe: child exit $LASTEXITCODE"); if ($LASTEXITCODE) { throw 'stamp failed' } }
+[Console]::Error.WriteLine("probe: stamp step done")
 try { Invoke-SourceBuild { throw 'child failure' }; throw 'lost exception' }
 catch { if ($_.Exception.Message -ne 'child failure') { throw } }
+[Console]::Error.WriteLine("probe: failure step done")
 & $env:PROBE_PYTHON -I -S -c 'import json, os; print(json.dumps(dict(os.environ)))'
 if ($LASTEXITCODE) { exit $LASTEXITCODE }
 ''', encoding="utf-8-sig")