test(381): golden coverage for Sequential (YAML) playout builder; document Scripted deferral

Extends the #163 PlayoutBuildGoldenTests in-memory net to the Sequential (YAML)
builder: a committed fixture (Goldens/Fixtures/sequential-schedule.yml) with two
`count: 2` instructions over one chronological collection, built via
SequentialPlayoutBuilder over the pinned window. The count/all/duration handlers
do UTC-only arithmetic off the caller-supplied start, so the case is
TZ-independent (passes, not skips, under a non-UTC TZ) and needs no Assume guard.
Non-vacuity: a fixture count tweak flips the golden + the contiguity assertion.

Scripted is deliberately excluded from the golden net — ScriptedPlayoutBuilder
shells out via Cli.Wrap to an external process that drives SchedulingEngine over
HTTP, which no in-memory golden can characterize. Recorded as the Done-when
"documented decision" arm in docs/decisions.md
(testing.scripted-playout-golden-deferred) + docs/testing.md; the scripted
integration harness is tracked as follow-up #563.

fixes #381

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/decisions.md

@@ -3473,3 +3473,31 @@ enabled`) because `/iptv/*` does not accept the SPA's `ctv-session` cookie and n
 for the browser. #552 closed that: the SPA now mints a short-lived token and appends it as
 `?access_token=`, so this projection no longer inspects JWT status at all. See
 `security.iptv-browser-token`.
+## 2026-07-22 — Sequential (YAML) playout gets a golden; Scripted is excluded from the golden net by construction (#381)
+
+`key: testing.scripted-playout-golden-deferred` · `status: active` · `since: 2026-07-22` · `supersedes: none` · `superseded-by: none`
+**Rule:** The `PlayoutBuildGoldenTests` in-memory golden net covers Sequential (YAML) as of #381, but Scripted playout is deliberately excluded from it — Scripted shells out to an external process that calls back over HTTP, which no in-memory golden can characterize; its integration harness is tracked separately.
+**Signals:** why is there no scripted golden; SequentialPlayoutBuilder golden; scripted playout is not deterministic in-process; Cli.Wrap external process; SchedulingEngine HTTP callback · paths: `ErsatzTV.Core.Tests/Scheduling/Goldens/PlayoutBuildGoldenTests.cs`, `ErsatzTV.Core.Tests/Scheduling/Goldens/Fixtures/sequential-schedule.yml`, `ErsatzTV.Core/Scheduling/ScriptedScheduling/ScriptedPlayoutBuilder.cs`, `ErsatzTV.Core/Scheduling/YamlScheduling/SequentialPlayoutBuilder.cs` · issues: #381, #163, #563
+**Mechanics:** docs/testing.md → Golden-file nets
+
+**Sequential (YAML) is golden-able and TZ-independent.** `SequentialPlayoutBuilder` reads a YAML schedule
+file (`Playout.ScheduleFile`) rather than a `ProgramSchedule`/Block calendar, but it is still a pure
+in-process build: content resolves from an in-memory-SQLite `Collection` by name, and the `count`/`all`/
+`duration` handlers do UTC-only arithmetic off the caller-supplied `start`. So the `Sequential_yaml` case
+uses the exact same harness as Classic/Block — a committed input fixture
+(`Goldens/Fixtures/sequential-schedule.yml`) with two `count: 2` instructions over one `chronological`
+collection — and needs **no** `Assume`/TZ guard (verified: it passes, not skips, under a non-UTC `TZ`,
+unlike Block). The fixture deliberately avoids the local-time-of-day handlers (`wait_until`, `pad_to_next`,
+`pad_until`) and shuffle order, which would reintroduce TZ- or seed-dependence. The builder checks the
+file via the injected `IFileSystem` but reads bytes with the static `System.IO.File`, so the test commits a
+real fixture on disk and stubs only `IFileSystem.File.Exists`; the JSON-schema validator is stubbed (it
+loads its schema from a runtime cache folder, irrelevant to characterizing builder output).
+
+**Scripted is not golden-able.** `ScriptedPlayoutBuilder` builds nothing in-process: it `Cli.Wrap`-executes
+an external script process that drives `SchedulingEngine` over `http://localhost:{Settings.UiPort}`. An
+external-process + HTTP-callback flow cannot be pinned by the in-memory golden harness (shared SQLite, no
+I/O, deterministic clock). The deterministic core the scripts drive (`SchedulingEngine`) is in-process and
+unit-testable — there is a seed `SchedulingEngineTests` — but the scripted *builder* is process orchestration
+plus HTTP transport, i.e. integration-test territory. Rather than force a golden onto it, the scripted
+integration harness is deferred to **#563**; this is the Done-when-sanctioned "documented decision" arm of
+#381, not an omission.