dream: forms (urlencoded) + stateless signed CSRF + 26 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/dream-on-sx.md

@@ -64,11 +64,11 @@ The five types: `request`, `response`, `handler = request -> response`, `middlew
       - `dream-flash-middleware` — single-request cookie store.
       - `dream-add-flash-message req category msg`.
       - `dream-flash-messages req` — returns list of `(category, msg)`.
-- [ ] **Forms + CSRF** in `lib/dream/form.sx`:
-      - `dream-form req` — returns `(Ok fields)` or `(Err :csrf-token-invalid)`.
-      - `dream-multipart req` — streaming multipart form data.
-      - CSRF middleware: stateless signed tokens, session-scoped.
-      - `dream-csrf-tag req` — returns hidden input fragment for SX templates.
+- [~] **Forms + CSRF** in `lib/dream/form.sx`:
+      - [x] `dream-form req` — returns `(Ok fields)` or `(Err :csrf-token-invalid)`.
+      - [ ] `dream-multipart req` — streaming multipart form data. *(next commit)*
+      - [x] CSRF middleware: stateless signed tokens, session-scoped.
+      - [x] `dream-csrf-tag req` — returns hidden input fragment for SX templates.
 - [ ] **WebSockets** in `lib/dream/websocket.sx`:
       - `dream-websocket handler` — upgrades request; handler `(fn (ws) ...)`.
       - `dream-send ws msg`, `dream-receive ws`, `dream-close ws`.
@@ -151,6 +151,19 @@ Confirm scope before starting; some of these may be addable as Dream-internal he
   PREVIOUS request's messages) / `dream-flash-of` (by category) / accessors. Cookie
   codec percent-escapes the `|`/`~`/`%` separators so categories/messages round-trip.
   Read-after-write verified across request boundaries incl. multi-category.
+- **2026-06-07 — Forms + CSRF (urlencoded)** (`lib/dream/form.sx`, 26 tests). Ok/Err
+  result values (`dream-ok`/`dream-err` + predicates/accessors). `dream-form-fields`
+  parses `application/x-www-form-urlencoded` with a full percent-decoder
+  (`%XX` via `char-from-code`, `+`→space). CSRF is stateless + signed + session-
+  scoped: token = `sid.signature`, verified by recomputing the signature and checking
+  the session id — no server storage. Signing is **injectable** (`dream-csrf-with`);
+  the default `dream-csrf-sign-default` is a pure-SX dual-base polynomial keyed hash
+  (NOT cryptographic — production should inject a host HMAC). `dream-csrf` attaches
+  context (needs the session middleware upstream for the sid); `dream-csrf-token` /
+  `dream-csrf-tag` (hidden input for templates); `dream-form` returns `Ok fields` or
+  `Err :csrf-token-invalid`; `dream-csrf-protect` auto-rejects unsafe methods (403)
+  lacking a valid token. Full session→csrf→form stack verified accept + reject.
+  Multipart deferred to the next commit.
 
 ## Blockers