Shared-home CLI reproduction | BEFORE
Linux x86_64; built CLI; fresh synthetic HOME; no copied database.
Host A: isolated PID + network + UTS namespaces; hostname evidence-host-a.
Host B: normal PID/network namespace; same home files.
Server A is live; recorded PID=1, port=39555, hostname=<absent>.
Local PID 1 exists; server A loopback is unreachable from host B.

$ t3 pair --base-dir "$HOME/.t3"
[21:50:52.700] ERROR (#2): NoRunningServerError: No running T3 Code server found.
  checked $HOME/.t3/userdata/server-runtime.json
  checked $HOME/.t3/dev/server-runtime.json
Start one with `t3 serve --base-dir $HOME/.t3`, or connect this machine with T3 Connect: `t3 connect --base-dir $HOME/.t3`.
    at file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:9270:16
    at pair.discoverPairTarget (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:9390:24)
    at pair.discoverPairTarget (definition) (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:9238:28)
[exit 1]

$ t3 serve --base-dir "$HOME/.t3" --port 39556
[21:50:53.411] ERROR (#2): ServerAlreadyRunningError: A T3 Code server already owns $HOME/.t3/userdata. Stop that server, or use a separate T3 home and pair with it, then retry. No server was stopped. server-owner.sqlite is the ownership lock; do not delete it while a server is running.
    at catch (file://<checkout>/apps/server/dist/relayTracing-tvcolmCh.mjs:9016:43)
    at file://<checkout>/apps/server/dist/Schema-znhrSbG8.mjs:10527:18
    at acquireServerOwnership (file://<checkout>/apps/server/dist/server-C2Az9RMb.mjs:53088:27)
    at acquireServerOwnership (definition) (file://<checkout>/apps/server/dist/relayTracing-tvcolmCh.mjs:8984:32)
    at server.runServerCommand (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:10286:363)
    at server.runServerCommand (definition) (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:10257:26)
[exit 78]

$ t3 up --base-dir "$HOME/.t3-hostB" --yes --headless

ERROR
  The T3 Code service on this machine serves $HOME/.t3, not $HOME/.t3-hostB. Pass --base-dir '$HOME/.t3' to manage it, or run `t3 service uninstall --base-dir '$HOME/.t3'` first to move it; both data directories are kept.
[exit 1]
Synthetic unit unchanged: True. No uninstall executed.

$ t3 __service-launcher (same shared T3 home)
[21:50:54.219] ERROR (#2): ServerAlreadyRunningError: A T3 Code server already owns $HOME/.t3/userdata. Stop that server, or use a separate T3 home and pair with it, then retry. No server was stopped. server-owner.sqlite is the ownership lock; do not delete it while a server is running.
    at catch (file://<checkout>/apps/server/dist/relayTracing-tvcolmCh.mjs:9016:43)
    at file://<checkout>/apps/server/dist/Schema-znhrSbG8.mjs:10527:18
    at acquireServerOwnership (file://<checkout>/apps/server/dist/server-C2Az9RMb.mjs:53088:27)
    at acquireServerOwnership (definition) (file://<checkout>/apps/server/dist/relayTracing-tvcolmCh.mjs:8984:32)
    at server.runServerCommand (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:10286:363)
    at server.runServerCommand (definition) (file://<checkout>/apps/server/dist/binCli-CooXn26B.mjs:10257:26)
[service-launcher] Another T3 Code server owns this T3 home. Stop it, then restart this service.
[capture driver stopped the process it started]
Server A still alive after all commands: True.