feat(cli): mirror Desktop mention delivery

crates/buzz-acp/src/base_prompt.md

@@ -40,6 +40,8 @@ For explicit changes to an existing personal agent, use `buzz agents draft-updat
 
 - Use the person's **exact full display name** after `@` (e.g., `@Will Pfleger`, not `@Will`). Partial names fail silently.
 - Do NOT format mentions with bold, italic, or backticks — it breaks notification delivery.
+- When you know intended recipient pubkeys, send readable `@Name` text and pass the identities separately in the same command: `buzz messages send ... --content "@Name ..." --mention <hex-or-npub>`. Repeat `--mention` for multiple recipients. Any explicit identity (`--mention` or `nostr:npub...`) permits unresolved or ambiguous `@Name` text as presentation-only; uniquely resolved member names still add their own recipients. Include a pubkey for every presentation-only name that should notify. The success JSON's `mention_pubkeys` comes from the signed event and is the delivery evidence; no follow-up verification command is needed.
+- Without `--mention`, the CLI resolves `@Name` against current channel members. It stops before sending on an unresolved/ambiguous name or a mentioned pubkey that is not a member. For a non-member, add them explicitly with `buzz channels add-member` only when authorized, then retry. Sending never changes membership automatically.
 - Only `@mention` when you need their attention. Don't mention in narrative (e.g., "coordinating with Duncan" — no `@`). Naming someone while talking *about* them is narrative — "waiting on @morgan", "until @morgan brings work", "I'll loop in @morgan later". Drop the `@`. Every mention sends a notification; a mention nobody needs to act on is a false alarm.
 
 ### Callback Mentions

crates/buzz-acp/src/lib.rs

@@ -3625,6 +3625,22 @@ mod agent_draft_prompt_tests {
         assert!(prompt.contains("single-quoted shell strings preserve `\\n` literally"));
         assert!(prompt.contains("buzz messages send ... --content -"));
     }
+
+    #[test]
+    fn shared_base_prompt_teaches_single_command_mentions_and_preflight() {
+        let prompt = include_str!("base_prompt.md");
+        assert!(prompt.contains("--mention <hex-or-npub>"));
+        assert!(prompt.contains("every presentation-only name that should notify"));
+        assert!(
+            prompt.contains("permits unresolved or ambiguous `@Name` text as presentation-only")
+        );
+        assert!(prompt.contains("success JSON's `mention_pubkeys`"));
+        assert!(prompt.contains("no follow-up verification command is needed"));
+        assert!(prompt.contains("stops before sending"));
+        assert!(prompt
+            .contains("add them explicitly with `buzz channels add-member` only when authorized"));
+        assert!(prompt.contains("never changes membership automatically"));
+    }
 }
 
 fn default_heartbeat_prompt() -> String {