DOM-preserving hydration — SSR DOM stays, event listeners attach in place

Scope-based cursor walks the existing SSR DOM during island hydration
instead of creating new elements and calling replaceChildren. The
hydration scope (sx-hydrating) propagates through define-library via
scope-push!/peek/pop!, solving the env isolation that broke the
previous set!-based approach.

Changes:
- adapter-dom.sx: hydrating?, hydrate-next-node, hydrate-enter/exit-element
  helpers. render-to-dom reuses text nodes. render-dom-element reuses
  elements by tag match, skips dom-append. reactive-text/cek-reactive-text
  reuse existing text nodes. render-dom-fragment/lake/marsh skip append.
  dispatch-render-form (if/when/cond) injects markers into existing DOM.
- boot.sx: hydrate-island pushes cursor scope, skips replaceChildren.
  On mismatch error, falls back to full re-render.

Result: zero DOM destruction, zero visual flash, event listeners
attached to original SSR elements. Stepper clicks verified working.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/static/wasm/sx/adapter-dom.sx

@@ -1,16 +1,69 @@
 (import (sx dom))
 (import (sx render))
 
-(define-library (web adapter-dom)
+(define-library
-  (export SVG_NS MATH_NS island-scope? contains-deref? dom-on render-to-dom render-dom-list render-dom-element render-dom-component render-dom-fragment render-dom-raw render-dom-unknown-component RENDER_DOM_FORMS render-dom-form? dispatch-render-form render-lambda-dom render-dom-island render-dom-lake render-dom-marsh reactive-text reactive-attr reactive-spread reactive-fragment render-list-item extract-key reactive-list bind-input *use-cek-reactive* enable-cek-reactive! cek-reactive-text cek-reactive-attr render-dom-portal render-dom-error-boundary)
+  (web adapter-dom)
+  (export
+    SVG_NS
+    MATH_NS
+    island-scope?
+    hydrating?
+    contains-deref?
+    dom-on
+    render-to-dom
+    render-dom-list
+    render-dom-element
+    render-dom-component
+    render-dom-fragment
+    render-dom-raw
+    render-dom-unknown-component
+    RENDER_DOM_FORMS
+    render-dom-form?
+    dispatch-render-form
+    render-lambda-dom
+    render-dom-island
+    render-dom-lake
+    render-dom-marsh
+    reactive-text
+    reactive-attr
+    reactive-spread
+    reactive-fragment
+    render-list-item
+    extract-key
+    reactive-list
+    bind-input
+    *use-cek-reactive*
+    enable-cek-reactive!
+    cek-reactive-text
+    cek-reactive-attr
+    render-dom-portal
+    render-dom-error-boundary)
   (begin
-
     (define SVG_NS "http://www.w3.org/2000/svg")
-
     (define MATH_NS "http://www.w3.org/1998/Math/MathML")
-
+    (define
-(define island-scope? (fn () (not (nil? (scope-peek "sx-island-scope")))))
+      island-scope?
-
+      (fn () (not (nil? (scope-peek "sx-island-scope")))))
+    (define hydrating? (fn () (not (nil? (scope-peek "sx-hydrating")))))
+    (define
+      hydrate-next-node
+      (fn
+        ()
+        (let
+          ((cursor (scope-peek "sx-hydrating")))
+          (when
+            cursor
+            (let
+              ((parent (dict-get cursor "parent"))
+                (idx (dict-get cursor "index")))
+              (let
+                ((child (host-call (host-get parent "childNodes") "item" idx)))
+                (dict-set! cursor "index" (+ idx 1))
+                child))))))
+    (define
+      hydrate-enter-element
+      (fn (el) (scope-push! "sx-hydrating" (dict "parent" el "index" 0))))
+    (define hydrate-exit-element (fn () (scope-pop! "sx-hydrating")))
     (begin
       (define *memo-cache* (dict))
       (define *cyst-counter* 0)
@@ -20,7 +73,6 @@
           ()
           (set! *cyst-counter* (+ *cyst-counter* 1))
           (str "sx-cyst-" *cyst-counter*))))
-
     (define
       contains-deref?
       (fn
@@ -37,7 +89,6 @@
                 (= (symbol-name (first expr)) "deref"))
               true
               (some contains-deref? expr))))))
-
     (define
       dom-on
       :effects (io)
@@ -59,7 +110,6 @@
                 (trampoline (call-lambda handler (list e)))
                 (run-post-render-hooks)))
             handler))))
-
     (define
       render-to-dom
       :effects (render)
@@ -75,13 +125,22 @@
           "raw-html"
           (dom-parse-html (raw-html-content expr))
           "string"
-      (create-text-node expr)
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node expr))
+            (create-text-node expr))
           "number"
-      (create-text-node (str expr))
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node (str expr)))
+            (create-text-node (str expr)))
           "symbol"
           (render-to-dom (trampoline (eval-expr expr env)) env ns)
           "keyword"
-      (create-text-node (keyword-name expr))
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node (keyword-name expr)))
+            (create-text-node (keyword-name expr)))
           "dom-node"
           expr
           "spread"
@@ -101,7 +160,6 @@
               (reactive-text expr)
               (create-text-node (str (deref expr))))
             (create-text-node (str expr))))))
-
     (define
       render-dom-list
       :effects (render)
@@ -136,7 +194,10 @@
                   (render-dom-element name args env ns)
                   (dispatch-render-form name expr env ns))
                 (and (env-has? env name) (macro? (env-get env name)))
-            (render-to-dom (expand-macro (env-get env name) args env) env ns)
+                (render-to-dom
+                  (expand-macro (env-get env name) args env)
+                  env
+                  ns)
                 (contains? HTML_TAGS name)
                 (render-dom-element name args env ns)
                 (and
@@ -156,7 +217,12 @@
                           ((skip (get state "skip")))
                           (if
                             skip
-                        (assoc state "skip" false "i" (inc (get state "i")))
+                            (assoc
+                              state
+                              "skip"
+                              false
+                              "i"
+                              (inc (get state "i")))
                             (if
                               (and
                                 (= (type-of arg) "keyword")
@@ -178,7 +244,10 @@
                               (assoc state "i" (inc (get state "i")))))))
                       (dict "i" 0 "skip" false)
                       args)
-                (dom-set-attr marker "data-sx-island" (component-name island))
+                    (dom-set-attr
+                      marker
+                      "data-sx-island"
+                      (component-name island))
                     (when
                       (not (empty-dict? kw-state))
                       (dom-set-attr
@@ -224,7 +293,6 @@
                     (when (not (spread? result)) (dom-append frag result))))
                 expr)
               frag)))))
-
     (define
       render-dom-element
       :effects (render)
@@ -232,7 +300,18 @@
         ((tag :as string) (args :as list) (env :as dict) (ns :as string))
         (let
           ((new-ns (cond (= tag "svg") SVG_NS (= tag "math") MATH_NS :else ns))
-        (el (dom-create-element tag new-ns)))
+            (el
+              (if
+                (hydrating?)
+                (let
+                  ((existing (hydrate-next-node)))
+                  (if
+                    (and
+                      existing
+                      (= (lower (or (host-get existing "tagName") "")) tag))
+                    (do (hydrate-enter-element existing) existing)
+                    (error (str "hydrate-mismatch:" tag))))
+                (dom-create-element tag new-ns))))
           (scope-push! "element-attrs" nil)
           (reduce
             (fn
@@ -296,7 +375,7 @@
                               (fn () (render-to-dom arg env new-ns)))
                             (spread? child)
                             nil
-                        :else (dom-append el child))))
+                            :else (when (not (hydrating?)) (dom-append el child)))))
                       (assoc state "i" (inc (get state "i"))))))))
             (dict "i" 0 "skip" false)
             args)
@@ -334,13 +413,15 @@
                 (keys spread-dict)))
             (scope-emitted "element-attrs"))
           (scope-pop! "element-attrs")
-      el)))
+          (do (when (hydrating?) (hydrate-exit-element)) el))))
-
     (define
       render-dom-component
       :effects (render)
       (fn
-    ((comp :as component) (args :as list) (env :as dict) (ns :as string))
+        ((comp :as component)
+          (args :as list)
+          (env :as dict)
+          (ns :as string))
         (let
           ((kwargs (dict)) (children (list)))
           (reduce
@@ -389,12 +470,16 @@
                   children)
                 (env-bind! local "children" child-frag)))
             (render-to-dom (component-body comp) local ns)))))
-
     (define
       render-dom-fragment
       :effects (render)
       (fn
         ((args :as list) (env :as dict) (ns :as string))
+        (if
+          (hydrating?)
+          (do
+            (for-each (fn (x) (render-to-dom x env ns)) args)
+            (create-fragment))
           (let
             ((frag (create-fragment)))
             (for-each
@@ -404,8 +489,7 @@
                   ((result (render-to-dom x env ns)))
                   (when (not (spread? result)) (dom-append frag result))))
               args)
-      frag)))
+            frag))))
-
     (define
       render-dom-raw
       :effects (render)
@@ -427,12 +511,10 @@
                   (dom-append frag (create-text-node (str val))))))
             args)
           frag)))
-
     (define
       render-dom-unknown-component
       :effects (render)
       (fn ((name :as string)) (error (str "Unknown component: " name))))
-
     (define
       RENDER_DOM_FORMS
       (list
@@ -459,12 +541,10 @@
         "scope"
         "provide"
         "cyst"))
-
     (define
       render-dom-form?
       :effects ()
       (fn ((name :as string)) (contains? RENDER_DOM_FORMS name)))
-
     (define
       dispatch-render-form
       :effects (render)
@@ -495,6 +575,21 @@
                             (list result)))
                         (dom-insert-after marker result))
                       (set! initial-result result)))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and
+                      initial-result
+                      (not (nil? initial-result))
+                      (not (spread? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result)
+                        (set! current-nodes (list initial-result)))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -510,7 +605,7 @@
                           (dom-child-nodes initial-result)
                           (list initial-result)))
                       (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (let
               ((cond-val (trampoline (eval-expr (nth expr 1) env))))
               (if
@@ -550,15 +645,41 @@
                           (dom-insert-after marker frag))))
                     (when
                       (trampoline (eval-expr (nth expr 1) env))
+                      (if
+                        (hydrating?)
+                        (let
+                          ((nodes (list)))
+                          (for-each
+                            (fn
+                              (i)
+                              (let
+                                ((result (render-to-dom (nth expr i) env ns)))
+                                (append! nodes result)))
+                            (range 2 (len expr)))
+                          (set! current-nodes nodes)
+                          (set! initial-result (first nodes)))
                         (let
                           ((frag (create-fragment)))
                           (for-each
                             (fn
                               (i)
-                        (dom-append frag (render-to-dom (nth expr i) env ns)))
+                              (dom-append
+                                frag
+                                (render-to-dom (nth expr i) env ns)))
                             (range 2 (len expr)))
                           (set! current-nodes (dom-child-nodes frag))
-                    (set! initial-result frag))))))
+                          (set! initial-result frag)))))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and initial-result (not (nil? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -566,7 +687,7 @@
                     ((frag (create-fragment)))
                     (dom-append frag marker)
                     (when initial-result (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (if
               (not (trampoline (eval-expr (nth expr 1) env)))
               (create-fragment)
@@ -617,6 +738,21 @@
                               (dom-child-nodes result)
                               (list result)))
                           (set! initial-result result)))))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and
+                      initial-result
+                      (not (nil? initial-result))
+                      (not (spread? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result)
+                        (set! current-nodes (list initial-result)))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -624,7 +760,7 @@
                     ((frag (create-fragment)))
                     (dom-append frag marker)
                     (when initial-result (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (let
               ((branch (eval-cond (rest expr) env)))
               (if branch (render-to-dom branch env ns) (create-fragment))))
@@ -670,7 +806,9 @@
               bindings)
             (when
               (> (len body) 1)
-          (for-each (fn (e) (trampoline (eval-expr e local))) (init body)))
+              (for-each
+                (fn (e) (trampoline (eval-expr e local)))
+                (init body)))
             (render-to-dom (last body) local ns))
           (or (= name "begin") (= name "do"))
           (if
@@ -771,7 +909,9 @@
                 (= (type-of (first rest-args)) "keyword")
                 (= (keyword-name (first rest-args)) "value"))
               (do
-            (set! scope-val (trampoline (eval-expr (nth rest-args 1) env)))
+                (set!
+                  scope-val
+                  (trampoline (eval-expr (nth rest-args 1) env)))
                 (set! body-exprs (slice rest-args 2)))
               (set! body-exprs rest-args))
             (scope-push! scope-name scope-val)
@@ -787,7 +927,9 @@
               (frag (create-fragment)))
             (scope-push! prov-name prov-val)
             (for-each
-          (fn (i) (dom-append frag (render-to-dom (nth expr i) env ns)))
+              (fn
+                (i)
+                (dom-append frag (render-to-dom (nth expr i) env ns)))
               (range 3 (len expr)))
             (scope-pop! prov-name)
             frag)
@@ -817,7 +959,6 @@
                   (dict-set! *memo-cache* cyst-key container)
                   container))))
           :else (render-to-dom (trampoline (eval-expr expr env)) env ns))))
-
     (define
       render-lambda-dom
       :effects (render)
@@ -829,12 +970,14 @@
             (fn (i p) (env-bind! local p (nth args i)))
             (lambda-params f))
           (render-to-dom (lambda-body f) local ns))))
-
     (define
       render-dom-island
       :effects (render mutation)
       (fn
-    ((island :as island) (args :as list) (env :as dict) (ns :as string))
+        ((island :as island)
+          (args :as list)
+          (env :as dict)
+          (ns :as string))
         (let
           ((kwargs (dict)) (children (list)))
           (reduce
@@ -878,19 +1021,22 @@
                   children)
                 (env-bind! local "children" child-frag)))
             (let
-          ((container (dom-create-element "span" nil)) (disposers (list)))
+              ((container (dom-create-element "span" nil))
+                (disposers (list)))
               (begin
                 (dom-set-attr container "data-sx-island" island-name)
                 (when
                   (not (empty-dict? kwargs))
-              (dom-set-attr container "data-sx-state" (sx-serialize kwargs))))
+                  (dom-set-attr
+                    container
+                    "data-sx-state"
+                    (sx-serialize kwargs))))
               (mark-processed! container "island-hydrated")
               (let
                 ((body-dom (with-island-scope (fn (disposable) (append! disposers disposable)) (fn () (render-to-dom (component-body island) local ns)))))
                 (dom-append container body-dom)
                 (dom-set-data container "sx-disposers" disposers)
                 container))))))
-
     (define
       render-dom-lake
       :effects (render)
@@ -927,13 +1073,16 @@
             (dict "i" 0 "skip" false)
             args)
           (let
-        ((el (dom-create-element lake-tag nil)))
+            ((el (if (hydrating?) (let ((existing (hydrate-next-node))) (if existing (do (hydrate-enter-element existing) existing) (dom-create-element lake-tag nil))) (dom-create-element lake-tag nil))))
             (dom-set-attr el "data-sx-lake" (or lake-id ""))
             (for-each
-          (fn (c) (dom-append el (render-to-dom c env ns)))
+              (fn
+                (c)
+                (let
+                  ((result (render-to-dom c env ns)))
+                  (when (not (hydrating?)) (dom-append el result))))
               children)
-        el))))
+            (do (when (hydrating?) (hydrate-exit-element)) el)))))
-
     (define
       render-dom-marsh
       :effects (render)
@@ -975,27 +1124,29 @@
             (dict "i" 0 "skip" false)
             args)
           (let
-        ((el (dom-create-element marsh-tag nil)))
+            ((el (if (hydrating?) (let ((existing (hydrate-next-node))) (if existing (do (hydrate-enter-element existing) existing) (dom-create-element marsh-tag nil))) (dom-create-element marsh-tag nil))))
             (dom-set-attr el "data-sx-marsh" (or marsh-id ""))
             (when
               marsh-transform
               (dom-set-data el "sx-marsh-transform" marsh-transform))
             (dom-set-data el "sx-marsh-env" env)
             (for-each
-          (fn (c) (dom-append el (render-to-dom c env ns)))
+              (fn
+                (c)
+                (let
+                  ((result (render-to-dom c env ns)))
+                  (when (not (hydrating?)) (dom-append el result))))
               children)
-        el))))
+            (do (when (hydrating?) (hydrate-exit-element)) el)))))
-
     (define
       reactive-text
       :effects (render mutation)
       (fn
         (sig)
         (let
-      ((node (create-text-node (str (deref sig)))))
+          ((node (if (hydrating?) (or (hydrate-next-node) (create-text-node (str (deref sig)))) (create-text-node (str (deref sig))))))
           (effect (fn () (dom-set-text-content node (str (deref sig)))))
           node)))
-
     (define
       reactive-attr
       :effects (render mutation)
@@ -1019,7 +1170,6 @@
                   (= val true)
                   (dom-set-attr el attr-name "")
                   :else (dom-set-attr el attr-name (str val)))))))))
-
     (define
       reactive-spread
       :effects (render mutation)
@@ -1044,7 +1194,9 @@
                       (filter (fn (c) (not (= c ""))) (split current " ")))
                     (kept
                       (filter
-                    (fn (c) (not (some (fn (pc) (= pc c)) prev-classes)))
+                        (fn
+                          (c)
+                          (not (some (fn (pc) (= pc c)) prev-classes)))
                         tokens)))
                   (if
                     (empty? kept)
@@ -1059,7 +1211,9 @@
                     ((attrs (spread-attrs result))
                       (cls-str (or (dict-get attrs "class") ""))
                       (new-classes
-                    (filter (fn (c) (not (= c ""))) (split cls-str " ")))
+                        (filter
+                          (fn (c) (not (= c "")))
+                          (split cls-str " ")))
                       (extra-keys
                         (filter (fn (k) (not (= k "class"))) (keys attrs))))
                     (set! prev-classes new-classes)
@@ -1079,8 +1233,9 @@
                       (fn (k) (dom-set-attr el k (str (dict-get attrs k))))
                       extra-keys)
                     (run-post-render-hooks))
-              (do (set! prev-classes (list)) (set! prev-extra-keys (list))))))))))
+                  (do
-
+                    (set! prev-classes (list))
+                    (set! prev-extra-keys (list))))))))))
     (define
       reactive-fragment
       :effects (render mutation)
@@ -1090,7 +1245,8 @@
           (env :as dict)
           (ns :as string))
         (let
-      ((marker (create-comment "island-fragment")) (current-nodes (list)))
+          ((marker (create-comment "island-fragment"))
+            (current-nodes (list)))
           (effect
             (fn
               ()
@@ -1103,7 +1259,6 @@
                   (set! current-nodes (dom-child-nodes frag))
                   (dom-insert-after marker frag)))))
           marker)))
-
     (define
       render-list-item
       :effects (render)
@@ -1113,7 +1268,6 @@
           (lambda? map-fn)
           (render-lambda-dom map-fn (list item) env ns)
           (render-to-dom (apply map-fn (list item)) env ns))))
-
     (define
       extract-key
       :effects (render)
@@ -1127,7 +1281,6 @@
             (let
               ((dk (dom-get-data node "key")))
               (if dk (str dk) (str "__idx_" index)))))))
-
     (define
       reactive-list
       :effects (render mutation)
@@ -1212,7 +1365,6 @@
                         (dom-append container rendered)))
                     items)))))
           container)))
-
     (define
       bind-input
       :effects (render mutation)
@@ -1220,7 +1372,8 @@
         (el (sig :as signal))
         (let
           ((input-type (lower (or (dom-get-attr el "type") "")))
-        (is-checkbox (or (= input-type "checkbox") (= input-type "radio"))))
+            (is-checkbox
+              (or (= input-type "checkbox") (= input-type "radio"))))
           (if
             is-checkbox
             (dom-set-prop el "checked" (deref sig))
@@ -1245,24 +1398,20 @@
                 is-checkbox
                 (reset! sig (dom-get-prop el "checked"))
                 (reset! sig (dom-get-prop el "value"))))))))
-
     (define *use-cek-reactive* true)
-
     (define enable-cek-reactive! (fn () (set! *use-cek-reactive* true)))
-
     (define
       cek-reactive-text
       :effects (render mutation)
       (fn
         (expr env)
         (let
-      ((node (create-text-node ""))
+          ((node (if (hydrating?) (or (hydrate-next-node) (create-text-node "")) (create-text-node "")))
             (update-fn (fn (val) (dom-set-text-content node (str val)))))
           (let
             ((initial (cek-run (make-cek-state expr env (list (make-reactive-reset-frame env update-fn true))))))
             (dom-set-text-content node (str initial))
             node))))
-
     (define
       cek-reactive-attr
       :effects (render mutation)
@@ -1278,7 +1427,6 @@
           (let
             ((initial (cek-run (make-cek-state expr env (list (make-reactive-reset-frame env update-fn true))))))
             (cek-call update-fn (list initial))))))
-
     (define
       render-dom-portal
       :effects (render)
@@ -1302,7 +1450,6 @@
                 (register-in-scope
                   (fn () (for-each (fn (n) (dom-remove n)) portal-nodes))))
               marker)))))
-
     (define
       render-dom-error-boundary
       :effects (render)
@@ -1342,10 +1489,7 @@
                     (let
                       ((fallback-dom (if (nil? fallback-fn) (let ((el (dom-create-element "div" nil))) (dom-set-attr el "class" "sx-render-error") (dom-set-attr el "style" "color:red;font-size:0.875rem;padding:0.5rem;border:1px solid red;border-radius:0.25rem;margin:0.5rem 0;") (dom-set-text-content el (str "Render error: " err)) el) (if (lambda? fallback-fn) (render-lambda-dom fallback-fn (list err retry-fn) env ns) (render-to-dom (apply fallback-fn (list err retry-fn)) env ns)))))
                       (dom-append container fallback-dom)))))))
-      container)))
+          container)))))
-
-
-))
 
 ;; Re-export to global env
 (import (web adapter-dom))

shared/static/wasm/sx/boot.sx

@@ -330,13 +330,29 @@
                     (if (dict-has? kwargs p) (dict-get kwargs p) nil)))
                 (component-params comp))
               (let
-                ((body-dom (cek-try (fn () (with-island-scope (fn (disposable) (append! disposers disposable)) (fn () (render-to-dom (component-body comp) local nil)))) (fn (err) (log-warn (str "hydrate-island FAILED: " comp-name " — " err)) (let ((error-el (dom-create-element "div" nil))) (dom-set-attr error-el "class" "sx-island-error") (dom-set-attr error-el "style" "padding:8px;margin:4px 0;border:1px solid #ef4444;border-radius:4px;background:#fef2f2;color:#b91c1c;font-family:monospace;font-size:12px;white-space:pre-wrap") (dom-set-text-content error-el (str "Island error: " comp-name "\n" err)) error-el)))))
+                ((cursor (dict "parent" el "index" 0)))
-                (host-call el "replaceChildren" body-dom)
+                (scope-push! "sx-hydrating" cursor)
+                (cek-try
+                  (fn
+                    ()
+                    (with-island-scope
+                      (fn (disposable) (append! disposers disposable))
+                      (fn () (render-to-dom (component-body comp) local nil))))
+                  (fn
+                    (err)
+                    (scope-pop! "sx-hydrating")
+                    (log-warn
+                      (str "hydrate fallback: " comp-name " — " err))
+                    (let
+                      ((fallback (cek-try (fn () (with-island-scope (fn (d) (append! disposers d)) (fn () (render-to-dom (component-body comp) local nil)))) (fn (err2) (let ((e (dom-create-element "div" nil))) (dom-set-text-content e (str "Island error: " comp-name "\n" err2)) e)))))
+                      (host-call el "replaceChildren" fallback)
+                      nil)))
+                (scope-pop! "sx-hydrating")
                 (dom-set-data el "sx-disposers" disposers)
                 (set-timeout (fn () (process-elements el)) 0)
                 (log-info
                   (str
-                    "hydrated island: "
+                    "hydrated island: ~"
                     comp-name
                     " ("
                     (len disposers)

shared/static/wasm/sx/module-manifest.json

@@ -536,6 +536,7 @@
       "SVG_NS",
       "MATH_NS",
       "island-scope?",
+      "hydrating?",
       "contains-deref?",
       "dom-on",
       "render-to-dom",

web/adapter-dom.sx

@@ -1,16 +1,69 @@
 (import (sx dom))
 (import (sx render))
 
-(define-library (web adapter-dom)
+(define-library
-  (export SVG_NS MATH_NS island-scope? contains-deref? dom-on render-to-dom render-dom-list render-dom-element render-dom-component render-dom-fragment render-dom-raw render-dom-unknown-component RENDER_DOM_FORMS render-dom-form? dispatch-render-form render-lambda-dom render-dom-island render-dom-lake render-dom-marsh reactive-text reactive-attr reactive-spread reactive-fragment render-list-item extract-key reactive-list bind-input *use-cek-reactive* enable-cek-reactive! cek-reactive-text cek-reactive-attr render-dom-portal render-dom-error-boundary)
+  (web adapter-dom)
+  (export
+    SVG_NS
+    MATH_NS
+    island-scope?
+    hydrating?
+    contains-deref?
+    dom-on
+    render-to-dom
+    render-dom-list
+    render-dom-element
+    render-dom-component
+    render-dom-fragment
+    render-dom-raw
+    render-dom-unknown-component
+    RENDER_DOM_FORMS
+    render-dom-form?
+    dispatch-render-form
+    render-lambda-dom
+    render-dom-island
+    render-dom-lake
+    render-dom-marsh
+    reactive-text
+    reactive-attr
+    reactive-spread
+    reactive-fragment
+    render-list-item
+    extract-key
+    reactive-list
+    bind-input
+    *use-cek-reactive*
+    enable-cek-reactive!
+    cek-reactive-text
+    cek-reactive-attr
+    render-dom-portal
+    render-dom-error-boundary)
   (begin
-
     (define SVG_NS "http://www.w3.org/2000/svg")
-
     (define MATH_NS "http://www.w3.org/1998/Math/MathML")
-
+    (define
-(define island-scope? (fn () (not (nil? (scope-peek "sx-island-scope")))))
+      island-scope?
-
+      (fn () (not (nil? (scope-peek "sx-island-scope")))))
+    (define hydrating? (fn () (not (nil? (scope-peek "sx-hydrating")))))
+    (define
+      hydrate-next-node
+      (fn
+        ()
+        (let
+          ((cursor (scope-peek "sx-hydrating")))
+          (when
+            cursor
+            (let
+              ((parent (dict-get cursor "parent"))
+                (idx (dict-get cursor "index")))
+              (let
+                ((child (host-call (host-get parent "childNodes") "item" idx)))
+                (dict-set! cursor "index" (+ idx 1))
+                child))))))
+    (define
+      hydrate-enter-element
+      (fn (el) (scope-push! "sx-hydrating" (dict "parent" el "index" 0))))
+    (define hydrate-exit-element (fn () (scope-pop! "sx-hydrating")))
     (begin
       (define *memo-cache* (dict))
       (define *cyst-counter* 0)
@@ -20,7 +73,6 @@
           ()
           (set! *cyst-counter* (+ *cyst-counter* 1))
           (str "sx-cyst-" *cyst-counter*))))
-
     (define
       contains-deref?
       (fn
@@ -37,7 +89,6 @@
                 (= (symbol-name (first expr)) "deref"))
               true
               (some contains-deref? expr))))))
-
     (define
       dom-on
       :effects (io)
@@ -59,7 +110,6 @@
                 (trampoline (call-lambda handler (list e)))
                 (run-post-render-hooks)))
             handler))))
-
     (define
       render-to-dom
       :effects (render)
@@ -75,13 +125,22 @@
           "raw-html"
           (dom-parse-html (raw-html-content expr))
           "string"
-      (create-text-node expr)
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node expr))
+            (create-text-node expr))
           "number"
-      (create-text-node (str expr))
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node (str expr)))
+            (create-text-node (str expr)))
           "symbol"
           (render-to-dom (trampoline (eval-expr expr env)) env ns)
           "keyword"
-      (create-text-node (keyword-name expr))
+          (if
+            (hydrating?)
+            (or (hydrate-next-node) (create-text-node (keyword-name expr)))
+            (create-text-node (keyword-name expr)))
           "dom-node"
           expr
           "spread"
@@ -101,7 +160,6 @@
               (reactive-text expr)
               (create-text-node (str (deref expr))))
             (create-text-node (str expr))))))
-
     (define
       render-dom-list
       :effects (render)
@@ -136,7 +194,10 @@
                   (render-dom-element name args env ns)
                   (dispatch-render-form name expr env ns))
                 (and (env-has? env name) (macro? (env-get env name)))
-            (render-to-dom (expand-macro (env-get env name) args env) env ns)
+                (render-to-dom
+                  (expand-macro (env-get env name) args env)
+                  env
+                  ns)
                 (contains? HTML_TAGS name)
                 (render-dom-element name args env ns)
                 (and
@@ -156,7 +217,12 @@
                           ((skip (get state "skip")))
                           (if
                             skip
-                        (assoc state "skip" false "i" (inc (get state "i")))
+                            (assoc
+                              state
+                              "skip"
+                              false
+                              "i"
+                              (inc (get state "i")))
                             (if
                               (and
                                 (= (type-of arg) "keyword")
@@ -178,7 +244,10 @@
                               (assoc state "i" (inc (get state "i")))))))
                       (dict "i" 0 "skip" false)
                       args)
-                (dom-set-attr marker "data-sx-island" (component-name island))
+                    (dom-set-attr
+                      marker
+                      "data-sx-island"
+                      (component-name island))
                     (when
                       (not (empty-dict? kw-state))
                       (dom-set-attr
@@ -224,7 +293,6 @@
                     (when (not (spread? result)) (dom-append frag result))))
                 expr)
               frag)))))
-
     (define
       render-dom-element
       :effects (render)
@@ -232,7 +300,18 @@
         ((tag :as string) (args :as list) (env :as dict) (ns :as string))
         (let
           ((new-ns (cond (= tag "svg") SVG_NS (= tag "math") MATH_NS :else ns))
-        (el (dom-create-element tag new-ns)))
+            (el
+              (if
+                (hydrating?)
+                (let
+                  ((existing (hydrate-next-node)))
+                  (if
+                    (and
+                      existing
+                      (= (lower (or (host-get existing "tagName") "")) tag))
+                    (do (hydrate-enter-element existing) existing)
+                    (error (str "hydrate-mismatch:" tag))))
+                (dom-create-element tag new-ns))))
           (scope-push! "element-attrs" nil)
           (reduce
             (fn
@@ -296,7 +375,7 @@
                               (fn () (render-to-dom arg env new-ns)))
                             (spread? child)
                             nil
-                        :else (dom-append el child))))
+                            :else (when (not (hydrating?)) (dom-append el child)))))
                       (assoc state "i" (inc (get state "i"))))))))
             (dict "i" 0 "skip" false)
             args)
@@ -334,13 +413,15 @@
                 (keys spread-dict)))
             (scope-emitted "element-attrs"))
           (scope-pop! "element-attrs")
-      el)))
+          (do (when (hydrating?) (hydrate-exit-element)) el))))
-
     (define
       render-dom-component
       :effects (render)
       (fn
-    ((comp :as component) (args :as list) (env :as dict) (ns :as string))
+        ((comp :as component)
+          (args :as list)
+          (env :as dict)
+          (ns :as string))
         (let
           ((kwargs (dict)) (children (list)))
           (reduce
@@ -389,12 +470,16 @@
                   children)
                 (env-bind! local "children" child-frag)))
             (render-to-dom (component-body comp) local ns)))))
-
     (define
       render-dom-fragment
       :effects (render)
       (fn
         ((args :as list) (env :as dict) (ns :as string))
+        (if
+          (hydrating?)
+          (do
+            (for-each (fn (x) (render-to-dom x env ns)) args)
+            (create-fragment))
           (let
             ((frag (create-fragment)))
             (for-each
@@ -404,8 +489,7 @@
                   ((result (render-to-dom x env ns)))
                   (when (not (spread? result)) (dom-append frag result))))
               args)
-      frag)))
+            frag))))
-
     (define
       render-dom-raw
       :effects (render)
@@ -427,12 +511,10 @@
                   (dom-append frag (create-text-node (str val))))))
             args)
           frag)))
-
     (define
       render-dom-unknown-component
       :effects (render)
       (fn ((name :as string)) (error (str "Unknown component: " name))))
-
     (define
       RENDER_DOM_FORMS
       (list
@@ -459,12 +541,10 @@
         "scope"
         "provide"
         "cyst"))
-
     (define
       render-dom-form?
       :effects ()
       (fn ((name :as string)) (contains? RENDER_DOM_FORMS name)))
-
     (define
       dispatch-render-form
       :effects (render)
@@ -495,6 +575,21 @@
                             (list result)))
                         (dom-insert-after marker result))
                       (set! initial-result result)))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and
+                      initial-result
+                      (not (nil? initial-result))
+                      (not (spread? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result)
+                        (set! current-nodes (list initial-result)))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -510,7 +605,7 @@
                           (dom-child-nodes initial-result)
                           (list initial-result)))
                       (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (let
               ((cond-val (trampoline (eval-expr (nth expr 1) env))))
               (if
@@ -550,15 +645,41 @@
                           (dom-insert-after marker frag))))
                     (when
                       (trampoline (eval-expr (nth expr 1) env))
+                      (if
+                        (hydrating?)
+                        (let
+                          ((nodes (list)))
+                          (for-each
+                            (fn
+                              (i)
+                              (let
+                                ((result (render-to-dom (nth expr i) env ns)))
+                                (append! nodes result)))
+                            (range 2 (len expr)))
+                          (set! current-nodes nodes)
+                          (set! initial-result (first nodes)))
                         (let
                           ((frag (create-fragment)))
                           (for-each
                             (fn
                               (i)
-                        (dom-append frag (render-to-dom (nth expr i) env ns)))
+                              (dom-append
+                                frag
+                                (render-to-dom (nth expr i) env ns)))
                             (range 2 (len expr)))
                           (set! current-nodes (dom-child-nodes frag))
-                    (set! initial-result frag))))))
+                          (set! initial-result frag)))))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and initial-result (not (nil? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -566,7 +687,7 @@
                     ((frag (create-fragment)))
                     (dom-append frag marker)
                     (when initial-result (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (if
               (not (trampoline (eval-expr (nth expr 1) env)))
               (create-fragment)
@@ -617,6 +738,21 @@
                               (dom-child-nodes result)
                               (list result)))
                           (set! initial-result result)))))))
+              (if
+                (hydrating?)
+                (do
+                  (when
+                    (and
+                      initial-result
+                      (not (nil? initial-result))
+                      (not (spread? initial-result)))
+                    (let
+                      ((parent (dom-parent initial-result)))
+                      (when
+                        parent
+                        (host-call parent "insertBefore" marker initial-result)
+                        (set! current-nodes (list initial-result)))))
+                  marker)
                 (if
                   (spread? initial-result)
                   initial-result
@@ -624,7 +760,7 @@
                     ((frag (create-fragment)))
                     (dom-append frag marker)
                     (when initial-result (dom-append frag initial-result))
-              frag)))
+                    frag))))
             (let
               ((branch (eval-cond (rest expr) env)))
               (if branch (render-to-dom branch env ns) (create-fragment))))
@@ -670,7 +806,9 @@
               bindings)
             (when
               (> (len body) 1)
-          (for-each (fn (e) (trampoline (eval-expr e local))) (init body)))
+              (for-each
+                (fn (e) (trampoline (eval-expr e local)))
+                (init body)))
             (render-to-dom (last body) local ns))
           (or (= name "begin") (= name "do"))
           (if
@@ -771,7 +909,9 @@
                 (= (type-of (first rest-args)) "keyword")
                 (= (keyword-name (first rest-args)) "value"))
               (do
-            (set! scope-val (trampoline (eval-expr (nth rest-args 1) env)))
+                (set!
+                  scope-val
+                  (trampoline (eval-expr (nth rest-args 1) env)))
                 (set! body-exprs (slice rest-args 2)))
               (set! body-exprs rest-args))
             (scope-push! scope-name scope-val)
@@ -787,7 +927,9 @@
               (frag (create-fragment)))
             (scope-push! prov-name prov-val)
             (for-each
-          (fn (i) (dom-append frag (render-to-dom (nth expr i) env ns)))
+              (fn
+                (i)
+                (dom-append frag (render-to-dom (nth expr i) env ns)))
               (range 3 (len expr)))
             (scope-pop! prov-name)
             frag)
@@ -817,7 +959,6 @@
                   (dict-set! *memo-cache* cyst-key container)
                   container))))
           :else (render-to-dom (trampoline (eval-expr expr env)) env ns))))
-
     (define
       render-lambda-dom
       :effects (render)
@@ -829,12 +970,14 @@
             (fn (i p) (env-bind! local p (nth args i)))
             (lambda-params f))
           (render-to-dom (lambda-body f) local ns))))
-
     (define
       render-dom-island
       :effects (render mutation)
       (fn
-    ((island :as island) (args :as list) (env :as dict) (ns :as string))
+        ((island :as island)
+          (args :as list)
+          (env :as dict)
+          (ns :as string))
         (let
           ((kwargs (dict)) (children (list)))
           (reduce
@@ -878,19 +1021,22 @@
                   children)
                 (env-bind! local "children" child-frag)))
             (let
-          ((container (dom-create-element "span" nil)) (disposers (list)))
+              ((container (dom-create-element "span" nil))
+                (disposers (list)))
               (begin
                 (dom-set-attr container "data-sx-island" island-name)
                 (when
                   (not (empty-dict? kwargs))
-              (dom-set-attr container "data-sx-state" (sx-serialize kwargs))))
+                  (dom-set-attr
+                    container
+                    "data-sx-state"
+                    (sx-serialize kwargs))))
               (mark-processed! container "island-hydrated")
               (let
                 ((body-dom (with-island-scope (fn (disposable) (append! disposers disposable)) (fn () (render-to-dom (component-body island) local ns)))))
                 (dom-append container body-dom)
                 (dom-set-data container "sx-disposers" disposers)
                 container))))))
-
     (define
       render-dom-lake
       :effects (render)
@@ -927,13 +1073,16 @@
             (dict "i" 0 "skip" false)
             args)
           (let
-        ((el (dom-create-element lake-tag nil)))
+            ((el (if (hydrating?) (let ((existing (hydrate-next-node))) (if existing (do (hydrate-enter-element existing) existing) (dom-create-element lake-tag nil))) (dom-create-element lake-tag nil))))
             (dom-set-attr el "data-sx-lake" (or lake-id ""))
             (for-each
-          (fn (c) (dom-append el (render-to-dom c env ns)))
+              (fn
+                (c)
+                (let
+                  ((result (render-to-dom c env ns)))
+                  (when (not (hydrating?)) (dom-append el result))))
               children)
-        el))))
+            (do (when (hydrating?) (hydrate-exit-element)) el)))))
-
     (define
       render-dom-marsh
       :effects (render)
@@ -975,27 +1124,29 @@
             (dict "i" 0 "skip" false)
             args)
           (let
-        ((el (dom-create-element marsh-tag nil)))
+            ((el (if (hydrating?) (let ((existing (hydrate-next-node))) (if existing (do (hydrate-enter-element existing) existing) (dom-create-element marsh-tag nil))) (dom-create-element marsh-tag nil))))
             (dom-set-attr el "data-sx-marsh" (or marsh-id ""))
             (when
               marsh-transform
               (dom-set-data el "sx-marsh-transform" marsh-transform))
             (dom-set-data el "sx-marsh-env" env)
             (for-each
-          (fn (c) (dom-append el (render-to-dom c env ns)))
+              (fn
+                (c)
+                (let
+                  ((result (render-to-dom c env ns)))
+                  (when (not (hydrating?)) (dom-append el result))))
               children)
-        el))))
+            (do (when (hydrating?) (hydrate-exit-element)) el)))))
-
     (define
       reactive-text
       :effects (render mutation)
       (fn
         (sig)
         (let
-      ((node (create-text-node (str (deref sig)))))
+          ((node (if (hydrating?) (or (hydrate-next-node) (create-text-node (str (deref sig)))) (create-text-node (str (deref sig))))))
           (effect (fn () (dom-set-text-content node (str (deref sig)))))
           node)))
-
     (define
       reactive-attr
       :effects (render mutation)
@@ -1019,7 +1170,6 @@
                   (= val true)
                   (dom-set-attr el attr-name "")
                   :else (dom-set-attr el attr-name (str val)))))))))
-
     (define
       reactive-spread
       :effects (render mutation)
@@ -1044,7 +1194,9 @@
                       (filter (fn (c) (not (= c ""))) (split current " ")))
                     (kept
                       (filter
-                    (fn (c) (not (some (fn (pc) (= pc c)) prev-classes)))
+                        (fn
+                          (c)
+                          (not (some (fn (pc) (= pc c)) prev-classes)))
                         tokens)))
                   (if
                     (empty? kept)
@@ -1059,7 +1211,9 @@
                     ((attrs (spread-attrs result))
                       (cls-str (or (dict-get attrs "class") ""))
                       (new-classes
-                    (filter (fn (c) (not (= c ""))) (split cls-str " ")))
+                        (filter
+                          (fn (c) (not (= c "")))
+                          (split cls-str " ")))
                       (extra-keys
                         (filter (fn (k) (not (= k "class"))) (keys attrs))))
                     (set! prev-classes new-classes)
@@ -1079,8 +1233,9 @@
                       (fn (k) (dom-set-attr el k (str (dict-get attrs k))))
                       extra-keys)
                     (run-post-render-hooks))
-              (do (set! prev-classes (list)) (set! prev-extra-keys (list))))))))))
+                  (do
-
+                    (set! prev-classes (list))
+                    (set! prev-extra-keys (list))))))))))
     (define
       reactive-fragment
       :effects (render mutation)
@@ -1090,7 +1245,8 @@
           (env :as dict)
           (ns :as string))
         (let
-      ((marker (create-comment "island-fragment")) (current-nodes (list)))
+          ((marker (create-comment "island-fragment"))
+            (current-nodes (list)))
           (effect
             (fn
               ()
@@ -1103,7 +1259,6 @@
                   (set! current-nodes (dom-child-nodes frag))
                   (dom-insert-after marker frag)))))
           marker)))
-
     (define
       render-list-item
       :effects (render)
@@ -1113,7 +1268,6 @@
           (lambda? map-fn)
           (render-lambda-dom map-fn (list item) env ns)
           (render-to-dom (apply map-fn (list item)) env ns))))
-
     (define
       extract-key
       :effects (render)
@@ -1127,7 +1281,6 @@
             (let
               ((dk (dom-get-data node "key")))
               (if dk (str dk) (str "__idx_" index)))))))
-
     (define
       reactive-list
       :effects (render mutation)
@@ -1212,7 +1365,6 @@
                         (dom-append container rendered)))
                     items)))))
           container)))
-
     (define
       bind-input
       :effects (render mutation)
@@ -1220,7 +1372,8 @@
         (el (sig :as signal))
         (let
           ((input-type (lower (or (dom-get-attr el "type") "")))
-        (is-checkbox (or (= input-type "checkbox") (= input-type "radio"))))
+            (is-checkbox
+              (or (= input-type "checkbox") (= input-type "radio"))))
           (if
             is-checkbox
             (dom-set-prop el "checked" (deref sig))
@@ -1245,24 +1398,20 @@
                 is-checkbox
                 (reset! sig (dom-get-prop el "checked"))
                 (reset! sig (dom-get-prop el "value"))))))))
-
     (define *use-cek-reactive* true)
-
     (define enable-cek-reactive! (fn () (set! *use-cek-reactive* true)))
-
     (define
       cek-reactive-text
       :effects (render mutation)
       (fn
         (expr env)
         (let
-      ((node (create-text-node ""))
+          ((node (if (hydrating?) (or (hydrate-next-node) (create-text-node "")) (create-text-node "")))
             (update-fn (fn (val) (dom-set-text-content node (str val)))))
           (let
             ((initial (cek-run (make-cek-state expr env (list (make-reactive-reset-frame env update-fn true))))))
             (dom-set-text-content node (str initial))
             node))))
-
     (define
       cek-reactive-attr
       :effects (render mutation)
@@ -1278,7 +1427,6 @@
           (let
             ((initial (cek-run (make-cek-state expr env (list (make-reactive-reset-frame env update-fn true))))))
             (cek-call update-fn (list initial))))))
-
     (define
       render-dom-portal
       :effects (render)
@@ -1302,7 +1450,6 @@
                 (register-in-scope
                   (fn () (for-each (fn (n) (dom-remove n)) portal-nodes))))
               marker)))))
-
     (define
       render-dom-error-boundary
       :effects (render)
@@ -1342,10 +1489,7 @@
                     (let
                       ((fallback-dom (if (nil? fallback-fn) (let ((el (dom-create-element "div" nil))) (dom-set-attr el "class" "sx-render-error") (dom-set-attr el "style" "color:red;font-size:0.875rem;padding:0.5rem;border:1px solid red;border-radius:0.25rem;margin:0.5rem 0;") (dom-set-text-content el (str "Render error: " err)) el) (if (lambda? fallback-fn) (render-lambda-dom fallback-fn (list err retry-fn) env ns) (render-to-dom (apply fallback-fn (list err retry-fn)) env ns)))))
                       (dom-append container fallback-dom)))))))
-      container)))
+          container)))))
-
-
-))
 
 ;; Re-export to global env
 (import (web adapter-dom))

web/boot.sx

@@ -330,13 +330,29 @@
                     (if (dict-has? kwargs p) (dict-get kwargs p) nil)))
                 (component-params comp))
               (let
-                ((body-dom (cek-try (fn () (with-island-scope (fn (disposable) (append! disposers disposable)) (fn () (render-to-dom (component-body comp) local nil)))) (fn (err) (log-warn (str "hydrate-island FAILED: " comp-name " — " err)) (let ((error-el (dom-create-element "div" nil))) (dom-set-attr error-el "class" "sx-island-error") (dom-set-attr error-el "style" "padding:8px;margin:4px 0;border:1px solid #ef4444;border-radius:4px;background:#fef2f2;color:#b91c1c;font-family:monospace;font-size:12px;white-space:pre-wrap") (dom-set-text-content error-el (str "Island error: " comp-name "\n" err)) error-el)))))
+                ((cursor (dict "parent" el "index" 0)))
-                (host-call el "replaceChildren" body-dom)
+                (scope-push! "sx-hydrating" cursor)
+                (cek-try
+                  (fn
+                    ()
+                    (with-island-scope
+                      (fn (disposable) (append! disposers disposable))
+                      (fn () (render-to-dom (component-body comp) local nil))))
+                  (fn
+                    (err)
+                    (scope-pop! "sx-hydrating")
+                    (log-warn
+                      (str "hydrate fallback: " comp-name " — " err))
+                    (let
+                      ((fallback (cek-try (fn () (with-island-scope (fn (d) (append! disposers d)) (fn () (render-to-dom (component-body comp) local nil)))) (fn (err2) (let ((e (dom-create-element "div" nil))) (dom-set-text-content e (str "Island error: " comp-name "\n" err2)) e)))))
+                      (host-call el "replaceChildren" fallback)
+                      nil)))
+                (scope-pop! "sx-hydrating")
                 (dom-set-data el "sx-disposers" disposers)
                 (set-timeout (fn () (process-elements el)) 0)
                 (log-info
                   (str
-                    "hydrated island: "
+                    "hydrated island: ~"
                     comp-name
                     " ("
                     (len disposers)