Replace cl-isaac with ironclad for connection ID generation

[bhw-foss]

I ran into this issue with sbcl declaim safety 2 and patched my project by overriding clog-connection::random-hex-string. Claude's diagnosis is below.

The bug

cl-isaac's rand32 unconditionally decfs its randcnt slot
(declared (unsigned-byte 32)) before checking whether the
256-word ISAAC block is exhausted:

(defun rand32 (ctx)
  (let ((c (isaac-ctx-randcnt ctx)))
    (decf (isaac-ctx-randcnt ctx))       ; <- unconditional, underflows 0 -> -1
    (if (zerop c)
        (progn (generate-next-isaac-block ctx)
               (setf (isaac-ctx-randcnt ctx) 255)
               (aref (isaac-ctx-randrsl ctx) 255))
        (aref (isaac-ctx-randrsl ctx) (isaac-ctx-randcnt ctx)))))

cl-isaac compiles its own isaac-32.lisp under (safety 2) (set in
make.lisp), so SBCL's typed-slot writer raises TYPE-ERROR on the
underflow, unwinding rand32 before the (if (zerop c) ...) reset
branch ever runs. randcnt stays at 0 and the PRNG is permanently
wedged — every subsequent call traps in the same place.

How it manifests in CLOG

clog-connection::random-hex-string throws inside
handle-new-connection. The surrounding handler-case swallows the
error, the WebSocket upgrade completes, but the
(websocket-driver:send connection "clog['connection_id']='…'") and
the on-connect thread spawn never run — so the server sends 0 bytes
after the 101 handshake and the browser sits on an unbootstrapped body
forever. Restarting "fixes" it briefly because *isaac-ctx* is
restored from the save-lisp-and-die image with a non-zero randcnt;
after one ISAAC block (~256 connections) it wedges again.

Upstream is unresponsive — issue and PR open since 2023:

• The value -1 is not of type (UNSIGNED-BYTE 64) when setting slot CL-ISAAC::RANDCNT of structure CL-ISAAC:ISAAC64-CTX thephoeron/cl-isaac#12
• Error "The value -1 is not of type (UNSIGNED-BYTE 64) when setting slot CL-ISAAC::RANDCNT of structure CL-ISAAC:ISAAC64-CTX". thephoeron/cl-isaac#13

The fix

CLOG already called ironclad:byte-array-to-hex-string +
ironclad:random-data on the Windows branch of random-hex-string,
and cl-pass (already a direct dep) pulls ironclad in transitively.
This PR:

• drops cl-isaac from clog.asd and declares ironclad explicitly,
• removes the *isaac-ctx* defparameter (not exported — verified
  against the defsection @clog-connection export list),
• collapses random-hex-string to a single platform-agnostic body
  using the existing ironclad codepath.

Output contract is preserved: 32 lowercase hex chars (16 octets from
ironclad's default OS PRNG — /dev/urandom on Unix,
CryptGenRandom on Windows).

Verification

Loaded :clog clean in SBCL 2.5.2, then:

(every (lambda (s) (= 32 (length s)))
       (loop repeat 10000 collect (clog-connection:random-hex-string)))
;; => T

— would have wedged the old cl-isaac path after ~256 calls under
(safety 2).