Wires the project context into the Determinator row stack so a UPC INF
matter doesn't need to be hand-walked through five obvious cascade picks.
Auto-walk descends single-option chains as `is-prefilled` rows, the inbox
row vanishes for UPC matters (CMS implied), and the first prefilled row
carries the project reference inline ("aus Akte: HL-2024-001").
Backend: `internal/services/proceeding_mapping.go` adds
MapLitigationToFristenrechner — single source of truth for bridging the
litigation conceptual codes (INF / REV / APP / CCR / AMD / APM / OPP) onto
fristenrechner codes (UPC_INF / DE_INF / EPA_OPP / …). Ambiguous combos
(APP+DE, ZPO_CIVIL, AMD+DE) return ok=false; callers degrade to "no
narrowing" instead of guessing. Table-driven test covers every documented
mapping plus the ambiguous-degrade cases.
Frontend: `buildRowStack` filters cascade children by project context
along the proceeding axis (kebab segment lookup against the project's
fristenrechner code); auto-walks while filtered scope narrows to one;
caps depth via `cascadeAutoWalkStopAfter` after an "ändern" on a prefilled
row so the user lands at an active chip set without the auto-walk
re-engaging. Result panel narrows on the post-auto-walk effective slug,
not the URL slug. A one-time inline tooltip ("Diese Schritte ergeben sich
aus Ihrer Akte") surfaces when ≥2 rows render prefilled — dismissal flag
persists in localStorage.
Narrowing is purely additive: an Akte without a fristenrechner code
(11/11 live projects pre-Slice-5 were NULL) degrades to today's
forum-only behaviour. Slice 3 (mobile polish + search relocation) follows.
Refs: docs/design-determinator-row-cascade-2026-05-13.md §10 Slice 2 + §4 + §5.