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

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

lib/dream/error.sx

@@ -0,0 +1,41 @@
+;; lib/dream/error.sx — Dream-on-SX status phrases + error-handling middleware.
+;; dream-catch wraps a handler and turns a raised error into a 500 response (or a
+;; custom page). Depends on types.sx.
+
+;; ── status reason phrases ──────────────────────────────────────────
+(define dr/status-texts {:206 "Partial Content" :202 "Accepted" :422 "Unprocessable Entity" :400 "Bad Request" :302 "Found" :204 "No Content" :502 "Bad Gateway" :429 "Too Many Requests" :301 "Moved Permanently" :415 "Unsupported Media Type" :405 "Method Not Allowed" :303 "See Other" :401 "Unauthorized" :304 "Not Modified" :503 "Service Unavailable" :404 "Not Found" :308 "Permanent Redirect" :504 "Gateway Timeout" :416 "Range Not Satisfiable" :500 "Internal Server Error" :307 "Temporary Redirect" :201 "Created" :501 "Not Implemented" :409 "Conflict" :200 "OK" :410 "Gone" :403 "Forbidden"})
+
+(define
+  dream-status-text
+  (fn (status) (or (get dr/status-texts (str status)) "Unknown")))
+(define
+  dream-status-line
+  (fn (status) (str status " " (dream-status-text status))))
+
+;; ── error-handling middleware ──────────────────────────────────────
+(define
+  dream-default-error-page
+  (fn
+    (req e)
+    (dream-html-status
+      500
+      (str "<h1>" (dream-status-line 500) "</h1>"))))
+
+(define
+  dream-catch-with
+  (fn
+    (on-error)
+    (fn
+      (next)
+      (fn (req) (guard (e (true (on-error req e))) (next req))))))
+
+(define dream-catch (dream-catch-with dream-default-error-page))
+
+;; a fallback handler that renders a status page for any code
+(define
+  dream-status-page
+  (fn
+    (status)
+    (dream-html-status
+      status
+      (str "<h1>" (dream-status-line status) "</h1>"))))