refactor(server): plan 4 — document unreachable ?? default arms after single-row aggregates

3f Task 7's fix wave flagged a cluster of `row?.x ?? default` arms after
unqualified, ungrouped aggregate reads (MAX/COUNT/COALESCE(SUM,0)) as
"same class as OauthClients:147" but left them unexamined per-site. Decided
per site: document, don't delete — TypeScript still types
executeTakeFirst()'s result as `| undefined` even though SQL guarantees
exactly one row for these unqualified aggregates, so the optional chain
can't be removed without a non-null assertion (worse, not safer). Six
sites: JourneyEntries.repository.ts (maxSortOrderForDate JG42,
countStatsPlaces JG67), JourneyEntryPhotos.repository.ts
(maxSortOrderForEntry JG91), JourneyPhotos.repository.ts (maxSortOrder
JG88/JG99), VacayEntries.repository.ts (sumFraction VC1, sumCompFraction
VC2). No behavior change — comments only.

server/src/db/repositories/JourneyEntries.repository.ts

@@ -232,6 +232,14 @@ export class JourneyEntriesRepository extends TrekRepository<JourneyEntries> {
       .where('journey_id', '=', journeyId)
       .where('entry_date', '=', entryDate)
       .executeTakeFirst();
+    // Plan 4 Task 8b: `row?.` is unreachable — an unqualified, ungrouped
+    // `MAX(...)` always returns exactly one row (NULL `m` when nothing
+    // matches, never zero rows), so `executeTakeFirst()` can't actually miss
+    // here. Kept for type-shape symmetry with `executeTakeFirst()`'s
+    // `| undefined` return type (same accepted class as `OauthClients:147`
+    // — see that file's own docstring for the precedent), not dead by
+    // mistake. `row.m` itself genuinely can be `null` (no matching rows),
+    // so the `?? null` is real, not defensive filler.
     return row?.m ?? null;
   }
 
@@ -434,6 +442,11 @@ export class JourneyEntriesRepository extends TrekRepository<JourneyEntries> {
       .select((eb) => eb.fn.countAll<number>().as('n'))
       .where('jt.journey_id', '=', journeyId)
       .executeTakeFirst();
+    // Plan 4 Task 8b: both `row?.` AND `?? 0` are unreachable here — an
+    // unqualified, ungrouped `COUNT(*)` always returns exactly one row, and
+    // `COUNT` itself never returns `NULL` (zero matches is a real `0`, not
+    // an absent row). Kept for type-shape symmetry with `executeTakeFirst()`
+    // `| undefined` return type, same accepted class as `OauthClients:147`.
     return row?.n ?? 0;
   }
 

server/src/db/repositories/JourneyEntryPhotos.repository.ts

@@ -164,6 +164,11 @@ export class JourneyEntryPhotosRepository extends TrekRepository<JourneyEntryPho
       .select((eb) => eb.fn.max<number | null>('sort_order').as('m'))
       .where('entry_id', '=', entryId)
       .executeTakeFirst();
+    // Plan 4 Task 8b: `row?.` is unreachable — an unqualified, ungrouped
+    // `MAX(...)` always returns exactly one row, so `executeTakeFirst()`
+    // can't actually miss here. Kept for type-shape symmetry with
+    // `executeTakeFirst()`'s `| undefined` return type, same accepted class
+    // as `OauthClients:147`. `row.m` itself genuinely can be `null`.
     return row?.m ?? null;
   }
 

server/src/db/repositories/JourneyPhotos.repository.ts

@@ -233,6 +233,11 @@ export class JourneyPhotosRepository extends TrekRepository<JourneyPhotos> {
       .select((eb) => eb.fn.max<number | null>('sort_order').as('m'))
       .where('journey_id', '=', journeyId)
       .executeTakeFirst();
+    // Plan 4 Task 8b: `row?.` is unreachable — an unqualified, ungrouped
+    // `MAX(...)` always returns exactly one row, so `executeTakeFirst()`
+    // can't actually miss here. Kept for type-shape symmetry with
+    // `executeTakeFirst()`'s `| undefined` return type, same accepted class
+    // as `OauthClients:147`. `row.m` itself genuinely can be `null`.
     return row?.m ?? null;
   }
 

server/src/db/repositories/VacayEntries.repository.ts

@@ -46,6 +46,12 @@ export class VacayEntriesRepository extends TrekRepository<VacayEntries> {
       .where('date', '>=', start)
       .where('date', '<', end)
       .executeTakeFirst();
+    // Plan 4 Task 8b: both `row?.` AND `?? 0` are unreachable here — an
+    // unqualified, ungrouped `COALESCE(SUM(...), 0)` always returns exactly
+    // one row with a non-null value (the `COALESCE` already resolves the
+    // "no matching rows" case to `0` at the SQL level). Kept for type-shape
+    // symmetry with `executeTakeFirst()`'s `| undefined` return type, same
+    // accepted class as `OauthClients:147`.
     return row?.used ?? 0;
   }
 
@@ -60,6 +66,9 @@ export class VacayEntriesRepository extends TrekRepository<VacayEntries> {
       .where('date', '<', end)
       .where('kind', '=', 'comp')
       .executeTakeFirst();
+    // Plan 4 Task 8b: same unreachable `row?.`/`?? 0` shape as {@link
+    // sumFraction} above — `COALESCE(SUM(...), 0)` never returns a NULL
+    // value or a missing row for an unqualified, ungrouped aggregate.
     return row?.used ?? 0;
   }