diff --git a/crates/buzz-cli/src/commands/messages.rs b/crates/buzz-cli/src/commands/messages.rs
index 40a9ae80b56..33568fe76cf 100644
--- a/crates/buzz-cli/src/commands/messages.rs
+++ b/crates/buzz-cli/src/commands/messages.rs
@@ -561,6 +561,86 @@ fn match_profiles_by_name(events: &[serde_json::Value], name: &str) -> Vec<(Stri
     matches
 }
 
+/// Channel type recorded on the relay's kind:39000 discovery event (`t` tag).
+fn channel_type_from_metadata(event: &serde_json::Value) -> Option<&str> {
+    event
+        .get("tags")?
+        .as_array()?
+        .iter()
+        .find_map(|tag| {
+            let tag = tag.as_array()?;
+            (tag.first()?.as_str()? == "t").then(|| tag.get(1)?.as_str())
+        })
+        .flatten()
+}
+
+/// The single decision about which kind a `messages send` publishes.
+///
+/// Desktop's forum surface lists kind:45001 topics and kind:45003 comments; a
+/// kind:9 event in a forum channel is accepted by the relay and then never
+/// appears in the topic list, so the send looks successful while the content
+/// is invisible where people read it. Matching the channel's canonical surface
+/// is what removes that failure — which is also why `--broadcast` cannot
+/// quietly opt back into it.
+///
+/// `--broadcast` is stream-only. Two combinations are rejected rather than
+/// half-applied:
+///
+/// * an implicit forum send with `--broadcast` — publishing kind:9 there is
+///   the exact invisible-success this command is fixing, so it fails instead;
+/// * an explicit forum kind with `--broadcast` — `build_forum_post` and
+///   `build_forum_comment` take no broadcast argument, so the flag was being
+///   silently dropped.
+///
+/// `--kind 9 --broadcast` stays available as the explicit opt-out: the caller
+/// has said which kind they want, and kind:9 is what broadcast means.
+fn resolve_message_kind(
+    explicit: Option<u16>,
+    channel_type: Option<&str>,
+    is_reply: bool,
+    broadcast: bool,
+) -> Result<u16, CliError> {
+    let is_forum = channel_type == Some("forum");
+    match explicit {
+        Some(kind @ (45001 | 45003)) if broadcast => Err(CliError::Usage(format!(
+            "--broadcast is stream-only and does not apply to kind {kind}; drop --broadcast, or use --kind 9 --broadcast to post a broadcast stream message"
+        ))),
+        Some(kind @ (9 | 45001 | 45003)) => Ok(kind),
+        Some(kind) => Err(CliError::Usage(format!(
+            "--kind {kind} is not supported (use 9, 45001, or 45003)"
+        ))),
+        None if is_forum && broadcast => Err(CliError::Usage(
+            "--broadcast is stream-only, and this is a forum channel: a kind 9 event there is accepted by the relay but never listed on the forum surface. Drop --broadcast to post a forum topic or comment, or use --kind 9 --broadcast if the invisible stream message is really what you want."
+                .into(),
+        )),
+        None if is_forum && is_reply => Ok(45003),
+        None if is_forum => Ok(45001),
+        None => Ok(9),
+    }
+}
+
+/// Read a channel's type from its kind:39000 discovery event.
+///
+/// Returns `None` when the relay has no metadata for the channel or the event
+/// carries no `t` tag — the caller then keeps the stream default rather than
+/// failing a send over a missing discovery event.
+async fn resolve_channel_type(
+    client: &BuzzClient,
+    channel_id: &str,
+) -> Result<Option<String>, CliError> {
+    let filter = serde_json::json!({
+        "kinds": [39000],
+        "#d": [channel_id],
+        "limit": 1,
+    });
+    let raw = client.query(&filter).await?;
+    let events: Vec<serde_json::Value> = serde_json::from_str(&raw).unwrap_or_default();
+    Ok(events
+        .first()
+        .and_then(channel_type_from_metadata)
+        .map(str::to_owned))
+}
+
 pub struct SendMessageParams {
     pub channel_id: String,
     pub content: String,
@@ -610,6 +690,20 @@ pub async fn cmd_send_message(
         ));
     }
 
+    // Settle the kind before anything is uploaded. Every rejection above is a
+    // usage error the caller can fix and retry; deciding after the upload loop
+    // would leave the attachments on the relay with no event referencing them.
+    let channel_type = match p.kind {
+        Some(_) => None,
+        None => resolve_channel_type(client, &p.channel_id).await?,
+    };
+    let kind = resolve_message_kind(
+        p.kind,
+        channel_type.as_deref(),
+        p.reply_to.is_some(),
+        p.broadcast,
+    )?;
+
     // Upload files and build imeta tags
     let mut media_tags: Vec<Vec<String>> = Vec::new();
     let mut media_content = String::new();
@@ -643,12 +737,12 @@ pub async fn cmd_send_message(
 
     let mention_refs: Vec<&str> = mention_pubkeys.iter().map(String::as_str).collect();
 
-    let builder = match p.kind {
-        Some(45001) => {
+    let builder = match kind {
+        45001 => {
             buzz_sdk::build_forum_post(channel_uuid, &final_content, &mention_refs, &media_tags)
                 .map_err(|e| CliError::Other(format!("build_forum_post failed: {e}")))?
         }
-        Some(45003) => {
+        45003 => {
             let tr = thread_ref.as_ref().ok_or_else(|| {
                 CliError::Usage("--reply-to is required for forum comments (kind 45003)".into())
             })?;
@@ -661,7 +755,7 @@ pub async fn cmd_send_message(
             )
             .map_err(|e| CliError::Other(format!("build_forum_comment failed: {e}")))?
         }
-        None | Some(9) => buzz_sdk::build_message(
+        9 => buzz_sdk::build_message(
             channel_uuid,
             &final_content,
             thread_ref.as_ref(),
@@ -670,9 +764,12 @@ pub async fn cmd_send_message(
             &media_tags,
         )
         .map_err(|e| CliError::Other(format!("build_message failed: {e}")))?,
-        Some(k) => {
-            return Err(CliError::Usage(format!(
-                "--kind {k} is not supported (use 9, 45001, or 45003)"
+        // `resolve_message_kind` is the only source of `kind` and returns
+        // nothing else; an unsupported `--kind` is rejected there, before any
+        // upload.
+        other => {
+            return Err(CliError::Other(format!(
+                "internal: unhandled message kind {other}"
             )))
         }
     };
@@ -1373,3 +1470,116 @@ mod tests {
         assert_eq!(match_profiles_by_name(&events, "Aaron").len(), 1);
     }
 }
+
+#[cfg(test)]
+mod default_kind_tests {
+    use super::{channel_type_from_metadata, resolve_message_kind};
+
+    /// `resolve_message_kind` with no explicit `--kind` and no `--broadcast`.
+    fn implicit(channel_type: Option<&str>, is_reply: bool) -> u16 {
+        resolve_message_kind(None, channel_type, is_reply, false).expect("must resolve")
+    }
+
+    fn metadata(tags: serde_json::Value) -> serde_json::Value {
+        serde_json::json!({ "kind": 39000, "tags": tags })
+    }
+
+    #[test]
+    fn reads_the_channel_type_from_the_t_tag() {
+        let event = metadata(serde_json::json!([
+            ["d", "2cf6cfd0-b917-4ea0-b2d8-a29dea949b77"],
+            ["closed"],
+            ["t", "forum"],
+        ]));
+        assert_eq!(channel_type_from_metadata(&event), Some("forum"));
+    }
+
+    #[test]
+    fn missing_t_tag_reads_as_unknown() {
+        let event = metadata(serde_json::json!([["d", "x"], ["closed"]]));
+        assert_eq!(channel_type_from_metadata(&event), None);
+    }
+
+    #[test]
+    fn forum_root_defaults_to_a_topic() {
+        assert_eq!(implicit(Some("forum"), false), 45001);
+    }
+
+    #[test]
+    fn forum_reply_defaults_to_a_comment() {
+        assert_eq!(implicit(Some("forum"), true), 45003);
+    }
+
+    #[test]
+    fn stream_and_dm_keep_kind_nine() {
+        for channel_type in [Some("stream"), Some("dm"), Some("workflow"), None] {
+            assert_eq!(implicit(channel_type, false), 9);
+            assert_eq!(implicit(channel_type, true), 9);
+        }
+    }
+
+    #[test]
+    fn an_explicit_kind_wins_over_the_channel_type() {
+        assert_eq!(
+            resolve_message_kind(Some(9), Some("forum"), false, false).unwrap(),
+            9
+        );
+        assert_eq!(
+            resolve_message_kind(Some(45001), Some("stream"), false, false).unwrap(),
+            45001
+        );
+    }
+
+    #[test]
+    fn an_implicit_forum_broadcast_is_rejected() {
+        // Publishing kind 9 into a forum is the invisible success this command
+        // is fixing, so --broadcast there must fail rather than fall back.
+        let err = resolve_message_kind(None, Some("forum"), false, true).unwrap_err();
+        let msg = err.to_string();
+        assert!(msg.contains("stream-only"), "unexpected error: {msg}");
+        assert!(
+            msg.contains("--kind 9 --broadcast"),
+            "error must name the opt-out: {msg}"
+        );
+    }
+
+    #[test]
+    fn an_explicit_forum_kind_with_broadcast_is_rejected() {
+        // build_forum_post / build_forum_comment take no broadcast argument,
+        // so honouring both is impossible — the flag used to be dropped.
+        for kind in [45001u16, 45003] {
+            let err = resolve_message_kind(Some(kind), Some("forum"), true, true).unwrap_err();
+            assert!(
+                err.to_string().contains("stream-only"),
+                "kind {kind} must reject --broadcast: {err}"
+            );
+        }
+    }
+
+    #[test]
+    fn an_explicit_stream_broadcast_is_the_opt_out() {
+        // Even in a forum channel: the caller named the kind.
+        assert_eq!(
+            resolve_message_kind(Some(9), Some("forum"), false, true).unwrap(),
+            9
+        );
+    }
+
+    #[test]
+    fn broadcast_does_not_change_a_stream_channel() {
+        assert_eq!(
+            resolve_message_kind(None, Some("stream"), false, true).unwrap(),
+            9
+        );
+        assert_eq!(resolve_message_kind(None, None, true, true).unwrap(), 9);
+    }
+
+    #[test]
+    fn an_unsupported_kind_is_rejected_before_anything_is_uploaded() {
+        let err = resolve_message_kind(Some(1), None, false, false).unwrap_err();
+        assert!(
+            err.to_string().contains("not supported"),
+            "unexpected error: {err}"
+        );
+    }
+}
diff --git a/crates/buzz-cli/src/lib.rs b/crates/buzz-cli/src/lib.rs
index 2b041da57b5..535adf2b473 100644
--- a/crates/buzz-cli/src/lib.rs
+++ b/crates/buzz-cli/src/lib.rs
@@ -380,13 +380,15 @@ pub enum MessagesCmd {
         /// Message text — supports @mentions and markdown. Use '-' to read from stdin.
         #[arg(long)]
         content: String,
-        /// Nostr event kind (default: channel default)
+        /// Nostr event kind. Defaults to the channel's canonical kind:
+        /// 45001 for a forum topic, 45003 for a forum reply, 9 otherwise.
         #[arg(long)]
         kind: Option<u16>,
         /// Event ID to reply to (creates a thread)
         #[arg(long)]
         reply_to: Option<String>,
-        /// Also publish to the Nostr network
+        /// Also publish to the Nostr network. Stream-only (kind 9): rejected
+        /// in a forum channel and with --kind 45001/45003.
         #[arg(long, default_value_t = false)]
         broadcast: bool,
         /// Attach file(s) — uploads and includes as imeta tags