diff --git a/plans/host-spa.md b/plans/host-spa.md
index c7533fd9..67d19698 100644
--- a/plans/host-spa.md
+++ b/plans/host-spa.md
@@ -43,6 +43,20 @@ graceful degradation to plain server-rendered pages with no JS.
   WASM kernel (sx.rose-ash.com avoids this because its Docker image ships a
   consistent bundle and it navigates via client-router page-routes, not boost).
 
+## Rebuild attempt (2026-06-28) — FAILED, reverted
+
+Tried it: `dune build browser/sx_browser.bc.wasm.js` succeeded (with many
+`integer-overflow` warnings — "generated code might be incorrect"), and
+`node hosts/ocaml/browser/compile-modules.js shared/static/wasm` recompiled all
+35 `.sxbc` cleanly. But the freshly-built kernel **crashes on init** in the
+browser: `Fatal error: exception Invalid_argument("Char.chr")` — so `SxKernel`
+never initialises (worse than before). The integer-overflow truncation during
+wasm codegen is the likely culprit (a SHA/char constant). Reverted
+`shared/static/wasm/` to the main-worktree bundle (which boots cleanly —
+verified SxKernel + data-sx-ready). So a naive in-worktree rebuild is NOT the
+fix; the wasm build itself needs investigating (wasm_of_ocaml version? the merged
+sx-vm-extensions/resolver changes interacting with codegen?).
+
 ## Next step — rebuild a consistent WASM bundle
 
 `scripts/sx-build-all.sh` does: build the browser wasm target → sync web `.sx`