tvOS: formalize the XCUITest agent validation loop on tvOS 27

[jlipworth]

Parent umbrella: #182

Goal

Make the existing deterministic tvOS XCUITest loop the documented, repeatable agent validation path on Xcode/tvOS 27.

Current foundation

• Credential-free browse, player, season, and keyboard fixtures.
• LabstreamTVUITests uses semantic targets and XCUIRemote.
• tvOS intentionally excludes downloads.

Acceptance

• The current tvOS 27 runtime executes the fixture launch/navigation and player suites under the repository's one-simulator lease.
• A named wrapper preserves result bundles, screenshots/logs, and machine-readable pass/fail.
• Documentation explicitly chooses XCUITest/XCUIRemote rather than iOS-only Device Interaction.
• Failures cleanly distinguish product defects, runtime limitations, and human gates.

[jlipworth]

The named credential-free tvOS agent wrapper is now exercised on tvOS 27.

• scripts/agent-tvos-run.sh fixture-home-semantic --allow-simulator passed 2/2 using semantic XCTest targets plus XCUIRemote for launch and Home-to-detail/back.
• Evidence includes video, start/end screenshots, bounded logs, .xcresult, exported attachments, test-summary.json, and run.json; local bundle: artifacts/agent-platform-runs/20260812T202501Z-tvos-fixture-home-semantic.
• LabstreamTVUITests.xctestplan now isolates UI execution from unrelated hosted sources that cannot belong to tvOS's no-download compile boundary.

The deterministic local-player assertions also passed (1/1: reveal playback chrome, close player), but current Xcode 27 remained stuck finalizing the test log after the suite completed. The wrapper now has a 90-second process-group bound and reports exit 2 / blocked / xcodebuild-test-log-finalization-timeout rather than hanging or claiming an incomplete result bundle as passed. Local blocker evidence: artifacts/agent-platform-runs/20260812T202546Z-tvos-fixture-player-basic.

Implementation commits on the issue branch: db7ffb87, c0ca86f8, f24412c0.

[jlipworth]

Integrated locally into main through f24412c0. The isolated tvOS UI test plan and named XCUITest/XCUIRemote Home/navigation evidence wrapper pass with complete artifacts. The local-player assertions also pass, while Xcode 27 may hang during test-log finalization; the wrapper now bounds that phase and reports a structured tooling block. Canonical tvOS and testing documentation records this distinction.

Publication status: local main only; not yet pushed to origin/main. Leaving open until publication and final supported-scope review.