feat(610): split the decision corpus into one YAML-frontmatter file per record

168 records -> docs/decisions/records/<area>/<topic>.md (163 active, 23 dirs) and
docs/decisions/archive/<area>/<topic>.md (5 archived). The filename IS the key,
so one-active-record-per-key becomes a filesystem property rather than a
validator check, and supersession becomes a `git mv`.

WHY: the monolith was a concurrency problem before an aesthetic one. A
3,900-line append target made parallel sessions collide -- PR #605 and PR #614
both hit append-vs-append conflicts during routine rebases, and hand-resolving
those inside the corpus is exactly the operation the rationale-rewrite guard
exists to police.

HOW IT IS VERIFIED: a ~170-file diff cannot be meaningfully read, so correctness
does not rest on reading it. The parser was taught BOTH formats first, so the
body-diff guard parses the old form at the merge-base and the new form at head --
the migration validates itself, no bypass. The proof is a field-level equivalence
harness: 168 records before and after, zero lost, zero gained, zero field
mismatches, zero rationale bodies differing. Reviewers should scrutinise the
harness; it is the actual evidence.

What measuring caught that reading would not have:

- ~500 lines sit OUTSIDE any record -- decisions.md's lifecycle schema and each
  topic file's preamble, mostly the only copy. Source files are kept and
  stripped, never deleted. They also cannot be filed per-area: topic files hold
  several areas and 4 of 23 areas span several files.
- Archive discovery was a non-recursive glob; after the split it found ZERO
  archived records, surfacing as four bogus "supersedes points to unknown key"
  errors rather than an obvious failure.
- ~32 live docs point into the corpus BY DATE, which the split dangles. Each
  stripped file now ends with a generated "Records formerly in this file" index,
  which also rescues the identical breadcrumbs in old issue comments.
- decisions.md's "In this file:" list was 97 same-file anchor bullets that the
  split makes WRONG, not merely stale. Dropped; the generated index replaces
  them with links that resolve.

The equivalence harness now runs against a checked-in FIXTURE, not the live
corpus. The earlier version migrated the real tree, which made it a one-shot:
the moment the migration landed there was nothing left to move and the tests
failed for reasons unrelated to the code. A fixture keeps them testing the
SCRIPT rather than the repo's current state.

Keys preserved verbatim, warts included: `sched` (12) and `scheduling` (1) remain
two directories for one concept. Renaming a key is not a move -- it changes
identity, breaks the equivalence proof, and invalidates MemPalace's per-key
drawers. Taxonomy normalisation is separate work.

refs #610

docs/decisions/records/sched/autotune-detailpanel-members.md

@@ -0,0 +1,38 @@
+---
+key: sched.autotune-detailpanel-members
+title: 2026-07-17 — Auto-Tune DetailPanel member list = live search-index roll-up, not EF enumeration (#384)
+status: active
+since: '2026-07-17'
+supersedes: none
+superseded-by: none
+rule: The Auto-Tune DetailPanel's per-channel content-source list is a live `ISearchIndex.Search` roll-up through the server-owned `AutoTuneAxisMap.GenerateQuery`, not an EF distinct+count query, so the preview matches exactly what the built channel's SmartCollection will contain.
+signals: 'Auto-Tune DetailPanel, search-index roll-up, SmartCollection fidelity · paths: `GET /api/v1/channels/auto-tune/members`, `MediaCollectionRepository.GetSmartCollectionItems` · issues: #384, #383, #69, #385, #386'
+mechanics: '`AutoTuneAxisMap.GenerateQuery`; `LibraryBrowseItemMapper.GetShows/GetMovies`; `PagedLibraryBrowseItemsResponseModel`'
+---
+
+The Auto-Tune DetailPanel (#383) shows, per proposed channel, the distinct **content sources** its
+generated SmartCollection resolves to (a genre channel's shows/movies), each weightable in the #385
+write path. `GET /api/v1/channels/auto-tune/members?axis=&value=` backs that list.
+
+**Why the search index, not an EF distinct+count query** — even though #69's *preview* enumeration uses
+EF (`PreviewAutoTuneChannelsHandler.EnumerateTvShows/…`). The created channel's playout is built from a
+**SmartCollection** whose members come from `ISearchIndex.Search` (`MediaCollectionRepository.GetSmartCollectionItems`).
+For the DetailPanel to faithfully preview *what the built channel will actually contain*, the member list
+must run the **same** query through the **same** index — so the handler calls the server-owned
+`AutoTuneAxisMap.GenerateQuery(axis, value)` (client never sends Lucene, per #69 PR1) and rolls the matching
+leaf items up to their distinct parents. #69's preview is a different granularity (enumerating candidate
+axis *values* with EF exact counts to drive the min-items threshold); this is enumerating the *members of one
+value*, where index-fidelity matters more than count-exactness. The two coexist deliberately.
+
+**Roll-up + shape.** Episode axes (TvShow/TvGenre) → distinct parent shows (Episode→Season→ShowId), with
+`ItemCount` = the **query-matching** episode count, not the show's total (a show contributes only its matching
+episodes to a genre channel). Movie-genre axis → the matching movies are themselves the sources. Both reuse
+the existing `PagedLibraryBrowseItemsResponseModel` / `LibraryBrowseItemResponseModel` DTOs and
+`LibraryBrowseItemMapper.GetShows/GetMovies` (no new schema), ordered by title then id, paged in memory
+(the distinct-source set is bounded — dozens for a genre). Search pulls up to the 10k cap
+`GetSmartCollectionItems` already uses; a value resolving to >10k leaf items could under-report sources past
+the cap — the same staleness bound the smart-collection path accepts. Read-only, catalog-read tier (no
+`[RequiresAuthentication]`), so a cold review sufficed. Sibling backend child #385 (write-path overrides +
+weights) and SPA child #386 remain open under the #383 milestone.
+
+---