Point a dead copier at its fix: name the best target one reorder away

JCA.best_copy_target scans the board for copyable jokers (same truth
test as copy_source: blueprint_compat must be true, debuffed excluded,
other copiers excluded) and prefers the ones the database marks
copy_target. When a Blueprint or Brainstorm reports anything but 'ok',
the tooltip now adds the reorder that revives it: 'Fix: slot this just
left of Baron' / 'Fix: make Baron your leftmost joker'. Explanation,
not verdict, so learning mode keeps it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

main.lua

@@ -421,6 +421,30 @@ local function tag_labels(tag_set)
     return labels
 end
 
+-- When a copier is copying nothing (or something it cannot use), the fix is a
+-- reorder -- so name the best target actually on the board. Copyable means the
+-- same thing it means in copy_source: blueprint_compat tested for TRUTH, not
+-- debuffed, and not another copier (suggesting a copier would re-ask the same
+-- question one slot over). Jokers the database marks copy_target are preferred;
+-- the leftmost candidate wins a tie so the suggestion is stable across hovers.
+-- Returns the card and whether it carried the copy_target tag.
+function JCA.best_copy_target(copier)
+    if not (G.jokers and G.jokers.cards) then return nil end
+    local best, best_prime
+    for _, c in ipairs(G.jokers.cards) do
+        if c ~= copier and is_joker(c) and not c.debuff
+            and not COPIERS[c.config.center.key]
+            and c.config.center.blueprint_compat then
+            local entry = JCA.db[c.config.center.key]
+            local prime = not not (entry and entry.gives.copy_target)
+            if not best or (prime and not best_prime) then
+                best, best_prime = c, prime
+            end
+        end
+    end
+    return best, best_prime
+end
+
 -- Build gaps: what the current board is shopping for. A tag is a gap when
 -- some owned joker wants it and no OTHER owned joker gives it (same rule as
 -- scoring and theme discovery: a joker cannot feed itself). The reverse -- a
@@ -574,6 +598,18 @@ local function tooltip_rows(card)
                     and 'Copying nothing - it IS the leftmost joker'
                     or 'Copying nothing - no joker to its right', G.C.RED)
             end
+
+            -- A dead copier usually has a live fix one reorder away. This is
+            -- an explanation of the mechanic, so learning mode keeps it.
+            if status ~= 'ok' then
+                local best = JCA.best_copy_target(card)
+                if best then
+                    local bname = name_of(best.config.center.key)
+                    text_row(key == 'j_brainstorm'
+                        and ('Fix: make ' .. bname .. ' your leftmost joker')
+                        or ('Fix: slot this just left of ' .. bname), G.C.GREEN)
+                end
+            end
         end
 
         -- Ceremonial Dagger. This one is about to eat a joker, permanently, at the