dream: signed session cookies (tamper-evident sid) + 11 tests

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

plans/dream-on-sx.md

@@ -112,6 +112,13 @@ with extensions + hardening below.
   `dream-json-body` (parse request body). GOTCHA: `number?` is unreliable in this env —
   used `(= (type-of v) "number")`; `parse-float` handles decimals. Multi-key dict
   encode order follows `keys` (non-deterministic) so tests assert via parse round-trip.
+- **2026-06-07 — Ext: signed session cookies** (`lib/dream/session.sx`, session suite
+  30→41, 340 total). The default store uses guessable sids (`s1`, `s2`), so
+  `dream-sessions-signed backend secret` signs the cookie value (`sid.signature`) and
+  rejects any cookie whose signature doesn't verify — a forged plaintext `s1` or a
+  wrong-secret cookie yields a fresh session instead of a hijack. `dream-cookie-sign` /
+  `dream-cookie-unsign` (keyed hash; same not-cryptographic caveat — inject a host HMAC
+  in production). Plain `dream-sessions` unchanged for the no-secret case.
 
 ## Extensions (post-roadmap)
 
@@ -122,7 +129,7 @@ The five-types core is complete; these harden it toward a production HTTP front
 - [x] **Status reason phrases** + `dream-status-text` (`lib/dream/error.sx`).
 - [x] **CORS middleware** (`dream-cors`).
 - [x] **Error-handling middleware** (`dream-catch` / custom 500 templates; `guard`-based).
-- [ ] **Signed session cookies** (the noted hardening — sign the sid).
+- [x] **Signed session cookies** (`dream-sessions-signed` — tamper-evident sid).
 - [x] **JSON helpers** (encode + recursive-descent parse, pure SX).
 - [ ] **Query/header convenience** (`dream-queries`, defaults).
 - [ ] **`api.sx` facade + README** — single load point listing the public surface.