dream: error-handling middleware (dream-catch) + status reason phrases + 15 tests

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

plans/dream-on-sx.md

@@ -92,6 +92,13 @@ with extensions + hardening below.
   in this worktree every `sx-tree` *edit* tool (`sx_replace_node`,
   `sx_replace_by_pattern`, `sx_insert_near`) raises a yojson `Expected string, got
   null` error — only `sx_write_file` works, so edits rewrite the whole file.
+- **2026-06-07 — Ext: error handling + status phrases** (`lib/dream/error.sx`, 15
+  tests, 282 total). `dream-status-text` / `dream-status-line` reason-phrase map (string
+  keys); `dream-status-page` renders a status page. `dream-catch` is a `guard`-based
+  middleware that turns a raised error into a 500 (`dream-catch-with on-error` for a
+  custom page receiving `(req e)`); normal responses pass through untouched, composes
+  around a router. (`guard` catches explicit `(error …)` raises; `e` stringifies to the
+  message.)
 
 ## Extensions (post-roadmap)
 
@@ -99,9 +106,9 @@ The five-types core is complete; these harden it toward a production HTTP front
 
 - [x] **Router HTTP correctness**: 405 Method Not Allowed + `Allow` header; automatic
       HEAD (serve the GET handler with an empty body).
-- [ ] **Status reason phrases** + `dream-status-text`.
+- [x] **Status reason phrases** + `dream-status-text` (`lib/dream/error.sx`).
 - [ ] **CORS middleware** (`dream-cors`).
-- [ ] **Error-handling middleware** (`dream-catch` / custom 404 + 500 templates).
+- [x] **Error-handling middleware** (`dream-catch` / custom 500 templates; `guard`-based).
 - [ ] **Signed session cookies** (the noted hardening — sign the sid).
 - [ ] **JSON helpers** (build from dict; parse to dict).
 - [ ] **Query/header convenience** (`dream-queries`, defaults).