diff --git a/hive-ag3nt/src/mcp.rs b/hive-ag3nt/src/mcp.rs
index 6c33ffea..edfcdfa8 100644
--- a/hive-ag3nt/src/mcp.rs
+++ b/hive-ag3nt/src/mcp.rs
@@ -102,6 +102,51 @@ impl From<hive_sh4re::Response> for SocketReply {
     }
 }
 
+/// Write (or remove) the status file in the agent's own `state/` directory.
+/// Called by both `AgentServer::set_status` and `ManagerServer::set_status`
+/// before dispatching the wire `SetStatus` request (which only triggers a
+/// dashboard rescan on the host side — file I/O moved here because the
+/// harness runs as the agent user and has write access to `state/`, whereas
+/// hive-c0re's `hive-core` user does not after the privsep migration).
+///
+/// Mirrors the validation in `hive-c0re::limits::check_status_text` so
+/// the file is never written with text the server would later reject (which
+/// would leave a stale invalid entry on disk).
+fn write_status_file(text: &str) -> Result<(), String> {
+    let trimmed = text.trim();
+    if !trimmed.is_empty() {
+        if trimmed.contains('\n') || trimmed.contains('\r') {
+            return Err(
+                "set_status text must be a single line — write multi-line context to \
+                 a file under your state/ dir and reference that path from the chip instead"
+                    .to_owned(),
+            );
+        }
+        // 200 chars mirrors STATUS_MAX_CHARS in hive-c0re/src/limits.rs.
+        // Keep in sync if that constant changes.
+        const STATUS_MAX_CHARS: usize = 200;
+        let len = trimmed.chars().count();
+        if len > STATUS_MAX_CHARS {
+            return Err(format!(
+                "set_status text too long ({len} chars, max {STATUS_MAX_CHARS}); trim to a short summary"
+            ));
+        }
+    }
+    let path = crate::paths::state_dir().join("hyperhive-status");
+    let result = if trimmed.is_empty() {
+        std::fs::remove_file(&path).or_else(|e| {
+            if e.kind() == std::io::ErrorKind::NotFound {
+                Ok(())
+            } else {
+                Err(e)
+            }
+        })
+    } else {
+        std::fs::write(&path, format!("{trimmed}\n"))
+    };
+    result.map_err(|e| format!("set_status write failed: {e}"))
+}
+
 /// Format helper for "send-like" tools (anything that expects an `Ok`).
 /// `tool` and `ok_msg` only appear in the result string; they don't change
 /// behavior.
@@ -763,6 +808,9 @@ impl AgentServer {
     )]
     async fn set_status(&self, Parameters(args): Parameters<SetStatusArgs>) -> String {
         run_tool_envelope("set_status", args.text.clone(), async move {
+            if let Err(e) = write_status_file(&args.text) {
+                return e;
+            }
             let (resp, retries) = self
                 .dispatch(hive_sh4re::AgentRequest::SetStatus { text: args.text })
                 .await;
@@ -1821,6 +1869,9 @@ impl ManagerServer {
     )]
     async fn set_status(&self, Parameters(args): Parameters<SetStatusArgs>) -> String {
         run_tool_envelope("set_status", args.text.clone(), async move {
+            if let Err(e) = write_status_file(&args.text) {
+                return e;
+            }
             let (resp, retries) = self
                 .dispatch(hive_sh4re::ManagerRequest::SetStatus { text: args.text })
                 .await;
diff --git a/hive-c0re/src/agent_server.rs b/hive-c0re/src/agent_server.rs
index 9dcf468e..3ff38bd9 100644
--- a/hive-c0re/src/agent_server.rs
+++ b/hive-c0re/src/agent_server.rs
@@ -239,29 +239,13 @@ pub(crate) async fn dispatch_shared(
             if let Err(message) = crate::limits::check_status_text(text) {
                 return Some(hive_sh4re::Response::Err { message });
             }
-            let path =
-                crate::coordinator::Coordinator::agent_notes_dir(agent).join("hyperhive-status");
-            let result = if text.trim().is_empty() {
-                std::fs::remove_file(&path).or_else(|e| {
-                    if e.kind() == std::io::ErrorKind::NotFound {
-                        Ok(())
-                    } else {
-                        Err(e)
-                    }
-                })
-            } else {
-                std::fs::write(&path, format!("{}\n", text.trim()))
-            };
-            match result {
-                Ok(()) => {
-                    let coord2 = Arc::clone(coord);
-                    tokio::spawn(async move { coord2.rescan_containers_and_emit().await });
-                    hive_sh4re::Response::Ok
-                }
-                Err(e) => hive_sh4re::Response::Err {
-                    message: format!("set_status write failed: {e}"),
-                },
-            }
+            // The harness writes the status file to its own `state/` dir
+            // before sending this request (it runs as the agent user, so
+            // it has write access). We just trigger a dashboard rescan so
+            // the new value is reflected immediately.
+            let coord2 = Arc::clone(coord);
+            tokio::spawn(async move { coord2.rescan_containers_and_emit().await });
+            hive_sh4re::Response::Ok
         }
         hive_sh4re::Request::GetAgentMeta { name } => {
             let target = name.as_deref().unwrap_or(agent);
diff --git a/hive-c0re/src/container_view.rs b/hive-c0re/src/container_view.rs
index b327f8e9..e0ca2679 100644
--- a/hive-c0re/src/container_view.rs
+++ b/hive-c0re/src/container_view.rs
@@ -303,7 +303,17 @@ fn auth_failed_sentinel(name: &str) -> bool {
 pub fn read_agent_status(name: &str) -> (Option<String>, Option<i64>) {
     let path = Coordinator::agent_notes_dir(name).join("hyperhive-status");
     let meta = std::fs::metadata(&path).ok();
-    let s = std::fs::read_to_string(&path).ok();
+    // Read at most STATUS_MAX_CHARS * 4 + 2 bytes: 4 is the max UTF-8 byte
+    // width per char, +2 for the trailing newline. Guards against a
+    // pathologically large file written outside the harness validation path.
+    let s = {
+        use std::io::Read as _;
+        std::fs::File::open(&path).ok().and_then(|f| {
+            let cap = (crate::limits::STATUS_MAX_CHARS * 4 + 2) as u64;
+            let mut buf = String::new();
+            f.take(cap).read_to_string(&mut buf).ok().map(|_| buf)
+        })
+    };
     let text = s
         .as_deref()
         .map(str::trim)
diff --git a/hive-c0re/src/limits.rs b/hive-c0re/src/limits.rs
index 06b68a03..da61ac7a 100644
--- a/hive-c0re/src/limits.rs
+++ b/hive-c0re/src/limits.rs
@@ -48,6 +48,9 @@ pub fn check_size(label: &str, body: &str) -> Result<(), String> {
 /// payload. Cap at 200 chars to fit the chip plus a little
 /// descriptive padding without forcing the operator to read a
 /// scrolling chunk.
+/// NOTE: `hive-ag3nt/src/mcp.rs::write_status_file` mirrors this constant
+/// client-side so invalid text is caught before the file is written.
+/// Keep in sync if this value changes.
 pub const STATUS_MAX_CHARS: usize = 200;
 
 /// Validate a `set_status` payload. Single-line + bounded so
diff --git a/hive-sh4re/src/lib.rs b/hive-sh4re/src/lib.rs
index ec51197a..7d4f0f75 100644
--- a/hive-sh4re/src/lib.rs
+++ b/hive-sh4re/src/lib.rs
@@ -441,8 +441,9 @@ pub enum Request {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         agent: Option<String>,
     },
-    /// Set a free-text status string visible on the dashboard. Persisted
-    /// to `{state_dir}/hyperhive-status` so it survives harness restarts.
+    /// Set a free-text status string visible on the dashboard. The harness
+    /// writes `{state_dir}/hyperhive-status` locally before sending this
+    /// request; hive-c0re just triggers a dashboard rescan on receipt.
     /// Pass an empty string to clear the status.
     SetStatus { text: String },
     /// Fetch identity + status for an agent. `name = None` =