STA-1716 reported that a packaged `orca serve` could become the single-instance owner after the desktop app exits, leaving Dock/Finder unable to restore a window — and that forcing a reopen made the headless process hydrate a renderer that interrupted and DUPLICATED live agent sessions.
Verification against main found every criterion already fixed (#8646 for desktop promotion and the fail-closed CLI, #12212 for duplicate serve activation, #12574 + #9729 for the resume/ownership guards). The genuine gap was criterion 6: the ticket's own automated regression never existed. An existing reliability gate asserted PTY identity survives promotion, but nothing asserted what the incident was actually about — how many agents the promoted renderer resumes.
This adds that coverage: a unit/service-level journey that drives the real single-instance lock, activation gate, settle and focus paths, then runs the real resume logic against a store seeded as a renderer freshly mounted inside the serve process, asserting zero duplicate resumes.
`settleServeDesktopActivation` moved from `index.ts` into its own module with identical semantics, so the test drives the real decision rather than re-implementing it — the earlier repro had to mirror that logic locally, which is the "test passes without running the scenario" failure mode.
Proven to be a real oracle: breaking each guard individually turns it red, and reverting the pre-#12574 pane form reproduces the incident exactly (two duplicate `codex resume` tabs).
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