feat: refine builder skill chip flows

docs/architecture.md

@@ -553,6 +553,24 @@ builder-ready only when each of its three assigned abilities has all three
 active Skill Chip definitions. Skill Chip mutations refresh readiness for
 focuses that reference both the previous and resulting ability.
 
+`specialization_ability_skill_chip_links` may pair two active abilities from the
+same specialization. Operators create each pair explicitly; the application does
+not infer compatibility from ability names, focus membership, or shared
+specialization. The pair is bidirectional, and an ability may belong to only one
+pair. This permits compatible abilities such as two Tactical Link variants to
+share definitions without making unrelated pairs such as two Smart Cover
+variants compatible. Archiving either ability removes the pair; restoring an
+ability does not recreate it.
+
+A linked ability can equip its own three definitions or its partner's three
+definitions, so each of its three Builder positions offers at most six choices.
+The loadout still equips three Skill Chips per ability and nine per focus.
+Ability-scoped primary values and 3-piece Talent outcomes bind to the ability
+that owns the equipped position, not the definition's original owner. Two-piece
+and 3-piece thresholds remain local to one equipped ability and never combine
+matching definitions across ability panels. ISAC audit snapshots and game-data
+transfers include the compatibility pair.
+
 Every equipped quality counts toward the two-piece threshold. After the loadout
 meets that threshold, only equipped High-end chips increase the interpolation
 step. For `h` High-end chips, where `h` is zero through three, a configured