web: re-boost swapped content from the [sx-boost] ancestor (fixes back-then-click full reload)

After a fragment swap, process-elements(target) -> process-boosted(target) only
boosted [sx-boost] containers that are DESCENDANTS of the swap target. But the
swap target (#content) is nested UNDER the boost wrapper (<div sx-boost="#content">
<div id="content">), so re-boosting scoped to the target found nothing — the
swapped-in links never got bound. Only the initial document-wide boot boost
worked, so: home->sub worked (home links boosted at boot), but Back restored the
home content unboosted, and the next click did a full page reload. (Post-page
links were unboosted too; Back just exposed it.)

process-boosted now ALSO boosts from the nearest [sx-boost] ANCESTOR of root
(dom-closest), so any swap target inside a boost scope gets its links rebound.
is-processed? guards keep it idempotent.

spa-check: the back-button test now clicks AGAIN after Back and asserts it's a
SPA nav (no full reload) — would have caught this. .sxbc regenerated.

Verified: spa-check 4/4 (incl. click-after-back).

web/orchestration.sx

@@ -714,9 +714,21 @@
       :effects (mutation io)
       (fn
         (root)
-        (for-each
-          (fn (container) (boost-descendants container))
-          (dom-query-all (or root (dom-body)) "[sx-boost]"))))
+        (do
+          ;; boost [sx-boost] containers WITHIN root (the document-scan case)
+          (for-each
+            (fn (container) (boost-descendants container))
+            (dom-query-all (or root (dom-body)) "[sx-boost]"))
+          ;; ALSO boost from the nearest [sx-boost] ANCESTOR of root: a swap
+          ;; target (e.g. #content) is nested under <div sx-boost>, so re-boosting
+          ;; scoped to the target alone never finds the marker, leaving the
+          ;; swapped-in links dead (full reload on the next click). is-processed?
+          ;; guards keep this idempotent.
+          (when
+            root
+            (let
+              ((anc (dom-closest root "[sx-boost]")))
+              (when anc (boost-descendants anc)))))))
     (define
       boost-descendants
       :effects (mutation io)