Phase 7c + 7d: optimistic data updates and offline mutation queue

7c — Optimistic Data Updates:
- orchestration.sx: optimistic-cache-update/revert/confirm + submit-mutation
- pages.py: mount_action_endpoint at /sx/action/<name> for client mutations
- optimistic-demo.sx: live demo with todo list, pending/confirmed/reverted states
- helpers.py: demo data + add-demo-item action handler

7d — Offline Data Layer:
- orchestration.sx: connectivity tracking, offline-queue-mutation, offline-sync,
  offline-aware-mutation (routes online→submit, offline→queue)
- offline-demo.sx: live demo with notes, connectivity indicator, sync timeline
- helpers.py: offline demo data

Also updates plans.sx: marks Phase 7 fully complete (all 6 sub-phases 7a-7f).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sx/optimistic-demo.sx

@@ -0,0 +1,81 @@
+;; Optimistic update demo — exercises Phase 7c client-side predicted mutations.
+;;
+;; This page shows a todo list with optimistic add/remove.
+;; Mutations are predicted client-side, sent to server, and confirmed/reverted.
+;;
+;; Open browser console and look for:
+;;   "sx:optimistic confirmed" — server accepted the mutation
+;;   "sx:optimistic reverted"  — server rejected, data rolled back
+
+(defcomp ~optimistic-demo-content (&key items server-time)
+  (div :class "space-y-8"
+    (div :class "border-b border-stone-200 pb-6"
+      (h1 :class "text-2xl font-bold text-stone-900" "Optimistic Updates")
+      (p :class "mt-2 text-stone-600"
+        "This page tests Phase 7c optimistic data mutations. Items are updated "
+        "instantly on the client, then confirmed or reverted when the server responds."))
+
+    ;; Server metadata
+    (div :class "rounded-lg border border-stone-200 bg-white p-6 space-y-3"
+      (h2 :class "text-lg font-semibold text-stone-800" "Current state")
+      (dl :class "grid grid-cols-2 gap-2 text-sm"
+        (dt :class "font-medium text-stone-600" "Server time")
+        (dd :class "font-mono text-stone-900" server-time)
+        (dt :class "font-medium text-stone-600" "Item count")
+        (dd :class "text-stone-900" (str (len items)))))
+
+    ;; Item list
+    (div :class "space-y-3"
+      (h2 :class "text-lg font-semibold text-stone-800" "Items")
+      (div :id "optimistic-items" :class "space-y-2"
+        (map (fn (item)
+          (div :class "flex items-center justify-between rounded border border-stone-100 bg-white p-3"
+            (div :class "flex items-center gap-3"
+              (span :class "flex-none rounded-full bg-violet-100 text-violet-700 w-6 h-6 flex items-center justify-center text-xs font-bold"
+                (str (get item "id")))
+              (span :class "text-stone-900" (get item "label")))
+            (span :class "text-xs px-2 py-0.5 rounded-full"
+              :class (case (get item "status")
+                "confirmed" "bg-green-100 text-green-700"
+                "pending" "bg-amber-100 text-amber-700"
+                "reverted" "bg-red-100 text-red-700"
+                :else "bg-stone-100 text-stone-500")
+              (get item "status"))))
+          items))
+
+      ;; Add button — triggers optimistic mutation
+      (div :class "pt-2"
+        (button :class "px-4 py-2 bg-violet-500 text-white rounded hover:bg-violet-600 text-sm"
+                :sx-post "/sx/action/add-demo-item"
+                :sx-target "#main-panel"
+                :sx-vals "{\"label\": \"New item\"}"
+          "Add item (optimistic)")))
+
+    ;; How it works
+    (div :class "space-y-4"
+      (h2 :class "text-lg font-semibold text-stone-800" "How it works")
+      (div :class "space-y-2"
+        (map-indexed
+          (fn (i step)
+            (div :class "flex items-start gap-3 rounded border border-stone-100 bg-white p-3"
+              (span :class "flex-none rounded-full bg-stone-100 text-stone-700 w-6 h-6 flex items-center justify-center text-xs font-bold"
+                (str (+ i 1)))
+              (div
+                (div :class "font-medium text-stone-900" (get step "label"))
+                (div :class "text-sm text-stone-500" (get step "detail")))))
+          (list
+            (dict :label "Predict" :detail "Client applies mutator function to cached data immediately")
+            (dict :label "Snapshot" :detail "Pre-mutation data saved in _optimistic-snapshots for rollback")
+            (dict :label "Re-render" :detail "Page content re-evaluated and swapped with predicted data")
+            (dict :label "Submit" :detail "Mutation sent to server via POST /sx/action/<name>")
+            (dict :label "Confirm or revert" :detail "Server responds — cache updated with truth, or reverted to snapshot")))))
+
+    ;; How to verify
+    (div :class "rounded-lg border border-amber-200 bg-amber-50 p-4 text-sm space-y-2"
+      (p :class "font-semibold text-amber-800" "How to verify")
+      (ol :class "list-decimal list-inside text-amber-700 space-y-1"
+        (li "Open the browser console (F12)")
+        (li "Navigate to this page from another isomorphism page")
+        (li "Click \"Add item\" — item appears instantly with \"pending\" status")
+        (li "Watch console for " (code :class "bg-amber-100 px-1 rounded" "sx:optimistic confirmed"))
+        (li "Item status changes to \"confirmed\" when server responds")))))