feat(acp): propagate automatic reply context

Co-authored-by: npub1x4hk035p3p9q39a3fcrd2fe30lpkrhr5dwe0cqzzjphxyyh8m0gsq4vqap <356f67c681884a0897b14e06d527317fc361dc746bb2fc0042906e6212e7dbd1@buzz.block.builderlab.xyz>
Signed-off-by: npub1x4hk035p3p9q39a3fcrd2fe30lpkrhr5dwe0cqzzjphxyyh8m0gsq4vqap <356f67c681884a0897b14e06d527317fc361dc746bb2fc0042906e6212e7dbd1@buzz.block.builderlab.xyz>
(cherry picked from commit 1535e6e5b3a42d0bca12b18627c83ae1164f3275)
Signed-off-by: Michael Neale <michael.neale@gmail.com>

crates/buzz-cli/src/commands/messages.rs

@@ -480,6 +480,33 @@ pub struct SendMessageParams {
     pub files: Vec<String>,
 }
 
+fn reply_to_from_sources(
+    explicit: Option<String>,
+    env_value: Option<String>,
+    file_path: Option<&std::ffi::OsStr>,
+) -> Option<String> {
+    explicit
+        .or_else(|| {
+            env_value.and_then(|value| {
+                let value = value.trim();
+                (!value.is_empty()).then(|| value.to_owned())
+            })
+        })
+        .or_else(|| {
+            let path = file_path?;
+            let value = std::fs::read_to_string(path).ok()?;
+            (!value.trim().is_empty()).then(|| value.trim().to_owned())
+        })
+}
+
+fn automatic_reply_to(explicit: Option<String>) -> Option<String> {
+    reply_to_from_sources(
+        explicit,
+        std::env::var("BUZZ_REPLY_TO").ok(),
+        std::env::var_os("BUZZ_REPLY_TO_FILE").as_deref(),
+    )
+}
+
 pub async fn cmd_send_message(
     client: &BuzzClient,
     mut p: SendMessageParams,
@@ -490,6 +517,7 @@ pub async fn cmd_send_message(
     // bugs for agent and human users alike.
     p.content = read_or_stdin(&p.content)?;
     validate_content_size(&p.content)?;
+    p.reply_to = automatic_reply_to(p.reply_to);
     if let Some(ref r) = p.reply_to {
         validate_hex64(r)?;
     }
@@ -876,7 +904,9 @@ pub async fn dispatch(
 
 #[cfg(test)]
 mod tests {
-    use super::{find_root_from_tags, match_profiles_by_name, parse_member_pubkeys};
+    use super::{
+        find_root_from_tags, match_profiles_by_name, parse_member_pubkeys, reply_to_from_sources,
+    };
     use buzz_sdk::mentions::{
         extract_at_mentions_with_known, extract_at_names, match_names_to_profiles, MentionProfile,
     };
@@ -892,6 +922,53 @@ mod tests {
     const PK_VALID_B: &str = "c6237ef84fa537c78dcee78efd2d4e59f728859c7f194da42ac51ededfa0be05";
     const PK_VALID_C: &str = "f4a42a97e594b77bdbd8ee35191c8b28a94a4cb871d96f32921558275421fb68";
 
+    #[test]
+    fn explicit_reply_to_precedes_environment_and_file() {
+        let file = tempfile::NamedTempFile::new().unwrap();
+        std::fs::write(file.path(), ID_B).unwrap();
+        assert_eq!(
+            reply_to_from_sources(
+                Some(ID_A.into()),
+                Some(ID_B.into()),
+                Some(file.path().as_os_str()),
+            )
+            .as_deref(),
+            Some(ID_A)
+        );
+    }
+
+    #[test]
+    fn reply_to_environment_precedes_file() {
+        let file = tempfile::NamedTempFile::new().unwrap();
+        std::fs::write(file.path(), ID_A).unwrap();
+        assert_eq!(
+            reply_to_from_sources(
+                None,
+                Some(format!(" {ID_B}\n")),
+                Some(file.path().as_os_str()),
+            )
+            .as_deref(),
+            Some(ID_B)
+        );
+    }
+
+    #[test]
+    fn reply_to_file_is_fallback_and_empty_values_are_ignored() {
+        let file = tempfile::NamedTempFile::new().unwrap();
+        std::fs::write(file.path(), format!(" {ID_A}\n")).unwrap();
+        assert_eq!(
+            reply_to_from_sources(None, Some("  ".into()), Some(file.path().as_os_str()))
+                .as_deref(),
+            Some(ID_A)
+        );
+        std::fs::write(file.path(), "").unwrap();
+        assert_eq!(
+            reply_to_from_sources(None, None, Some(file.path().as_os_str())),
+            None
+        );
+        assert_eq!(reply_to_from_sources(None, None, None), None);
+    }
+
     #[test]
     fn root_marker_wins_over_reply_marker() {
         let tags = json!([