Honor CAP REQ -cap and ignore unknown batch refs

Two compliance gaps surfaced by the chat.papo.im integration
suite:

  - CAP REQ :-echo-message previously matched no supported cap
    name (because of the leading '-'), so it was NAKed; even when
    a client sent a plain disable like above, papod silently kept
    the cap in the active set.  We now split each REQ token by
    the '-' prefix, mark it as :add or :remove, and update the
    client's cap set accordingly.  An REQ containing a mix of
    known and unknown caps is still NAKed atomically.

  - A message tagged with @batch=X referring to a batch that was
    never opened (e.g. because handle-batch-open! rejected the
    BATCH because of a missing target) used to fall through into
    normal command processing — so a malformed multiline batch
    would still deliver its inner PRIVMSG.  Per IRCv3 we now
    silently drop those messages instead.

1 files changed, 24 insertions, 10 deletions

diff --git a/src/papod.clj b/src/papod.clj
index d5b6f20..35b9b49 100644
--- a/src/papod.clj
+++ b/src/papod.clj
@@ -1502,12 +1502,23 @@
                         "draft/channel-rename"
                         "draft/extended-isupport"
                         "draft/metadata-2"
-                        "draft/typing"}]
-        (if-not (every? supported requested)
+                        "draft/typing"}
+            split (fn [c] (if (string/starts-with? c "-")
+                            [(subs c 1) :remove]
+                            [c :add]))
+            split-reqs (map split requested)
+            all-known? (every? (fn [[name _]]
+                                 (supported name))
+                               split-reqs)]
+        (if-not all-known?
           [(str ":" +server-name+ " CAP " nick
                 " NAK :" raw-args)]
-          (do (swap! client update :caps
-                     (fnil into #{}) requested)
+          (do (doseq [[name op] split-reqs]
+                (swap! client update :caps
+                  (fn [s]
+                    (case op
+                      :add    (conj (or s #{}) name)
+                      :remove (disj (or s #{}) name)))))
               [(str ":" +server-name+ " CAP " nick
                     " ACK :" raw-args)])))
 
@@ -4975,13 +4986,16 @@
                       (string/starts-with? c ":") (subs 1))))
         blank? (and content (empty? content))]
     (cond
-      ;; Tagged with a batch ID we don't know about, while
-      ;; another batch is open: protocol violation.
-      (and batch-tag (not in-batch) any-batch-open?)
+      ;; Tagged with a batch ID we don't know about: per IRCv3
+      ;; the message MUST be ignored (the batch was rejected or
+      ;; never existed).  We additionally clear any other open
+      ;; batches when one was open, since this is a sign the
+      ;; client got out of sync.
+      (and batch-tag (not in-batch))
       (do
-        (swap! client dissoc :batches)
-        [(str "FAIL BATCH MULTILINE_INVALID"
-              " :Batch tag does not match")])
+        (when any-batch-open?
+          (swap! client dissoc :batches))
+        [])
 
       ;; Concat tag on a blank message: invalid per spec.
       (and in-batch concat-tag? blank?)