Phase 7c+7d: cache invalidation + offline data layer

7c: Client data cache management via element attributes
(sx-cache-invalidate) and response headers (SX-Cache-Invalidate,
SX-Cache-Update). Programmatic API: invalidate-page-cache,
invalidate-all-page-cache, update-page-cache.

7d: Service Worker (sx-sw.js) with IndexedDB for offline-capable
data caching. Network-first for /sx/data/ and /sx/io/, stale-while-
revalidate for /static/. Cache invalidation propagates from
in-memory cache to SW via postMessage.

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

shared/sx/ref/orchestration.sx

@@ -195,6 +195,10 @@
       ;; Triggers (before swap)
       (dispatch-trigger-events el (get resp-headers "trigger"))
 
+      ;; Cache directives — process before navigation so cache is
+      ;; ready when the target page loads.
+      (process-cache-directives el resp-headers text)
+
       (cond
         ;; Redirect
         (get resp-headers "redirect")
@@ -589,6 +593,76 @@
       {"data" data "ts" (now-ms)})))
 
 
+;; --------------------------------------------------------------------------
+;; Client-side routing — cache management
+;; --------------------------------------------------------------------------
+
+(define invalidate-page-cache
+  (fn (page-name)
+    ;; Clear cached data for a page. Removes all cache entries whose key
+    ;; matches page-name (exact) or starts with "page-name:" (with params).
+    ;; Also notifies the service worker to clear its IndexedDB entries.
+    (for-each
+      (fn (k)
+        (when (or (= k page-name) (starts-with? k (str page-name ":")))
+          (dict-set! _page-data-cache k nil)))
+      (keys _page-data-cache))
+    (sw-post-message {"type" "invalidate" "page" page-name})
+    (log-info (str "sx:cache invalidate " page-name))))
+
+(define invalidate-all-page-cache
+  (fn ()
+    ;; Clear all cached page data and notify service worker.
+    (set! _page-data-cache (dict))
+    (sw-post-message {"type" "invalidate" "page" "*"})
+    (log-info "sx:cache invalidate *")))
+
+(define update-page-cache
+  (fn (page-name data)
+    ;; Replace cached data for a page with server-provided data.
+    ;; Uses a bare page-name key (no params) — the server knows the
+    ;; canonical data shape for the page.
+    (let ((cache-key (page-data-cache-key page-name (dict))))
+      (page-data-cache-set cache-key data)
+      (log-info (str "sx:cache update " page-name)))))
+
+(define process-cache-directives
+  (fn (el resp-headers response-text)
+    ;; Process cache invalidation and update directives from both
+    ;; element attributes and response headers.
+    ;;
+    ;; Element attributes (set by component author):
+    ;;   sx-cache-invalidate="page-name"   — clear page cache on success
+    ;;   sx-cache-invalidate="*"           — clear all page caches
+    ;;
+    ;; Response headers (set by server):
+    ;;   SX-Cache-Invalidate: page-name    — clear page cache
+    ;;   SX-Cache-Update: page-name        — replace cache with response data
+
+    ;; 1. Element-level invalidation
+    (let ((el-invalidate (dom-get-attr el "sx-cache-invalidate")))
+      (when el-invalidate
+        (if (= el-invalidate "*")
+          (invalidate-all-page-cache)
+          (invalidate-page-cache el-invalidate))))
+
+    ;; 2. Response header invalidation
+    (let ((hdr-invalidate (get resp-headers "cache-invalidate")))
+      (when hdr-invalidate
+        (if (= hdr-invalidate "*")
+          (invalidate-all-page-cache)
+          (invalidate-page-cache hdr-invalidate))))
+
+    ;; 3. Response header cache update (server pushes fresh data)
+    ;; parse-sx-data is a platform-provided function that parses SX text
+    ;; into a data value (returns nil on parse error).
+    (let ((hdr-update (get resp-headers "cache-update")))
+      (when hdr-update
+        (let ((data (parse-sx-data response-text)))
+          (when data
+            (update-page-cache hdr-update data)))))))
+
+
 ;; --------------------------------------------------------------------------
 ;; Client-side routing
 ;; --------------------------------------------------------------------------
@@ -1061,6 +1135,8 @@
 ;;   (resolve-page-data name params cb) → void; resolves data for a named page.
 ;;     Platform decides transport (HTTP, cache, IPC, etc). Calls (cb data-dict)
 ;;     when data is available. params is a dict of URL/route parameters.
+;;   (parse-sx-data text)             → parsed SX data value, or nil on error.
+;;     Used by cache update to parse server-provided data in SX format.
 ;;
 ;; From boot.sx:
 ;;   _page-routes                   → list of route entries
@@ -1080,4 +1156,8 @@
 ;;   (csrf-token)                   → string
 ;;   (cross-origin? url)            → boolean
 ;;   (now-ms)                       → timestamp ms
+;;
+;; === Cache management ===
+;;   (parse-sx-data text)             → parsed SX data value, or nil on error
+;;   (sw-post-message msg)            → void; post message to active service worker
 ;; --------------------------------------------------------------------------