feat(macos): support agent environment hints

refs https://github.com/ogulcancelik/herdr/discussions/679

1 files changed, 72 insertions, 11 deletions

diff --git a/src/platform/macos.rs b/src/platform/macos.rs
index 70eea7ec..f35fd1eb 100644
--- a/src/platform/macos.rs
+++ b/src/platform/macos.rs
@@ -842,6 +842,33 @@ fn process_argv(pid: u32) -> Option<Vec<String>> {
     procargs2_argv(&buf)
 }
 
+/// 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 buf = kern_procargs2(pid)?;
+    super::parse_agent_env_hint(procargs2_env(&buf)?)
+}
+
+fn procargs2_argv_start(rest: &[u8]) -> Option<usize> {
+    let exec_end = rest.iter().position(|&byte| byte == 0)?;
+    let mut pos = exec_end;
+    while pos < rest.len() && rest[pos] == 0 {
+        pos += 1;
+    }
+    (pos < rest.len()).then_some(pos)
+}
+
+fn skip_nul_strings(bytes: &[u8], start: usize, count: usize) -> Option<usize> {
+    let mut current = start;
+    for _ in 0..count {
+        let end = bytes.get(current..)?.iter().position(|&byte| byte == 0)?;
+        current = current.checked_add(end)?.checked_add(1)?;
+    }
+    Some(current)
+}
+
 fn procargs2_argv(buf: &[u8]) -> Option<Vec<String>> {
     if buf.len() < 4 {
         return None;
@@ -852,19 +879,10 @@ fn procargs2_argv(buf: &[u8]) -> Option<Vec<String>> {
         return None;
     }
 
-    // Layout: [argc: i32] [exec_path\0] [padding\0...] [argv[0]\0] [argv[1]\0] ... [env\0] ...
+    // Layout: [argc: i32] [exec_path\0] [padding\0...] [argv[0]\0] ... [env\0] ...
     let rest = &buf[4..];
-    let exec_end = rest.iter().position(|&b| b == 0)?;
-    let mut pos = exec_end;
-    while pos < rest.len() && rest[pos] == 0 {
-        pos += 1;
-    }
-    if pos >= rest.len() {
-        return None;
-    }
-
+    let mut current = procargs2_argv_start(rest)?;
     let mut argv = Vec::with_capacity(argc as usize);
-    let mut current = pos;
     for _ in 0..argc {
         if current >= rest.len() {
             return None;
@@ -884,6 +902,22 @@ fn procargs2_argv(buf: &[u8]) -> Option<Vec<String>> {
     Some(argv)
 }
 
+fn procargs2_env(buf: &[u8]) -> Option<&[u8]> {
+    if buf.len() < 4 {
+        return None;
+    }
+
+    let argc = i32::from_ne_bytes([buf[0], buf[1], buf[2], buf[3]]);
+    if argc < 1 {
+        return None;
+    }
+
+    let rest = &buf[4..];
+    let argv_start = procargs2_argv_start(rest)?;
+    let env_start = skip_nul_strings(rest, argv_start, argc as usize)?;
+    rest.get(env_start..)
+}
+
 /// Get the current working directory of a process.
 ///
 /// Uses `proc_pidinfo(PROC_PIDVNODEPATHINFO)` to read `pvi_cdir.vip_path`.
@@ -1068,6 +1102,33 @@ mod tests {
     }
 
     #[test]
+    fn procargs2_env_reads_agent_hint_after_argv() {
+        let buf = build_procargs2(
+            "/opt/homebrew/bin/nono",
+            &["nono", "run", "HERDR_AGENT=codex", "--", "claude"],
+            &["PATH=/usr/bin", "HERDR_AGENT=claude", "TERM=xterm-256color"],
+        );
+
+        let env = procargs2_env(&buf).expect("expected env block");
+        assert_eq!(
+            crate::platform::parse_agent_env_hint(env),
+            Some(crate::detect::Agent::Claude)
+        );
+    }
+
+    #[test]
+    fn procargs2_env_does_not_treat_argv_as_environment() {
+        let buf = build_procargs2(
+            "/opt/homebrew/bin/nono",
+            &["nono", "run", "HERDR_AGENT=claude"],
+            &["PATH=/usr/bin"],
+        );
+
+        let env = procargs2_env(&buf).expect("expected env block");
+        assert_eq!(crate::platform::parse_agent_env_hint(env), None);
+    }
+
+    #[test]
     fn terminal_bundle_identifier_maps_known_terminal_env() {
         assert_eq!(
             terminal_bundle_identifier_from_env(Some("ghostty"), None, false, false),