PR 19486: isolated systemd user service proof
Synthetic values only; fixture server children use the production launcher.

BEFORE (origin/main 45ad47df22):
{"phase":"before restart","observations":[{"phase":"active","version":"1.0.0"},{"phase":"trial","version":"1.1.0"},{"phase":"committed","version":"1.1.0"}]}
Failed to reset failed state of unit t3-takeover-ssh-relay-09-202775.service: Unit t3-takeover-ssh-relay-09-202775.service not loaded.
node:internal/modules/run_main:107
    triggerUncaughtException(
    ^

AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:

  assert(first.every(row => row.value === 'initial'))

    at file:///tmp/ssh-relay-remote-09/service-systemd-proof.mjs:59:3 {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '==',
  diff: 'simple'
}

Node.js v24.21.0

AFTER (dc0f483069):
{"phase":"before restart","observations":[{"phase":"active","value":"initial","version":"1.0.0"},{"phase":"trial","value":"initial","version":"1.1.0"},{"phase":"committed","value":"initial","version":"1.1.0"}]}
{
  "manager": "real systemd user transient unit",
  "unit": "t3-takeover-ssh-relay-09-206619.service",
  "observations": [
    {
      "phase": "active",
      "value": "initial",
      "version": "1.0.0"
    },
    {
      "phase": "trial",
      "value": "initial",
      "version": "1.1.0"
    },
    {
      "phase": "committed",
      "value": "initial",
      "version": "1.1.0"
    },
    {
      "phase": "restarted",
      "value": "changed",
      "version": "1.1.0"
    }
  ],
  "update": "committed",
  "filePreserved": true,
  "limits": "Fixture server children; actual t3 service install and launchd not exercised"
}
Failed to reset failed state of unit t3-takeover-ssh-relay-09-206619.service: Unit t3-takeover-ssh-relay-09-206619.service not loaded.

Transient units and isolated state removed. No canonical t3code.service was changed.
Actual service installation and macOS launchd not verified live.