fix: support agent env hints

refs #679

related #699

2 files changed, 43 insertions, 0 deletions

diff --git a/src/platform/linux.rs b/src/platform/linux.rs
index 9a44d02e..3cf643e5 100644
--- a/src/platform/linux.rs
+++ b/src/platform/linux.rs
@@ -124,6 +124,26 @@ pub fn process_cwd(pid: u32) -> Option<PathBuf> {
     std::fs::read_link(format!("/proc/{pid}/cwd")).ok()
 }
 
+/// Read a Herdr agent identity hint from a process environment.
+pub fn process_agent_hint(pid: u32) -> Option<crate::detect::Agent> {
+    if pid == 0 {
+        return None;
+    }
+    let environ = std::fs::read(format!("/proc/{pid}/environ")).ok()?;
+    parse_agent_env_hint(&environ)
+}
+
+fn parse_agent_env_hint(environ: &[u8]) -> Option<crate::detect::Agent> {
+    for record in environ.split(|&byte| byte == 0) {
+        let Some(value) = record.strip_prefix(b"HERDR_AGENT=") else {
+            continue;
+        };
+        let value = std::str::from_utf8(value).ok()?;
+        return crate::detect::parse_agent_label(value);
+    }
+    None
+}
+
 pub fn session_processes(child_pid: u32) -> Vec<u32> {
     let Some(session_id) = process_session_id(child_pid) else {
         return Vec::new();
@@ -490,6 +510,24 @@ mod tests {
     }
 
     #[test]
+    fn parse_agent_env_hint_accepts_known_agents() {
+        assert_eq!(
+            parse_agent_env_hint(b"PATH=/bin\0HERDR_AGENT=claude\0TERM=xterm\0"),
+            Some(crate::detect::Agent::Claude)
+        );
+        assert_eq!(
+            parse_agent_env_hint(b"HERDR_AGENT=codex"),
+            Some(crate::detect::Agent::Codex)
+        );
+    }
+
+    #[test]
+    fn parse_agent_env_hint_ignores_missing_or_unknown_agents() {
+        assert_eq!(parse_agent_env_hint(b"PATH=/bin\0TERM=xterm\0"), None);
+        assert_eq!(parse_agent_env_hint(b"HERDR_AGENT=not-an-agent\0"), None);
+    }
+
+    #[test]
     fn clipboard_commands_prefer_wayland_when_available() {
         let _guard = env_lock().lock().unwrap();
         unsafe {
diff --git a/src/platform/mod.rs b/src/platform/mod.rs
index ec9a497f..0b5f9ecb 100644
--- a/src/platform/mod.rs
+++ b/src/platform/mod.rs
@@ -121,6 +121,11 @@ mod fallback;
 #[cfg(not(any(target_os = "linux", target_os = "macos", target_os = "windows")))]
 pub use fallback::*;
 
+#[cfg(not(target_os = "linux"))]
+pub fn process_agent_hint(_pid: u32) -> Option<crate::detect::Agent> {
+    None
+}
+
 #[cfg(not(target_os = "macos"))]
 #[derive(Debug)]
 pub(crate) struct InputSourceRestore;