diff --git a/staged/src-tauri/examples/acp_stream_probe.rs b/staged/src-tauri/examples/acp_stream_probe.rs
new file mode 100644
index 00000000..60dec1b5
--- /dev/null
+++ b/staged/src-tauri/examples/acp_stream_probe.rs
@@ -0,0 +1,219 @@
+use std::collections::HashMap;
+use std::path::PathBuf;
+use std::sync::{Arc, Mutex};
+
+use acp_client::{AcpDriver, AgentDriver, MessageWriter, Store};
+use anyhow::{anyhow, Result};
+use async_trait::async_trait;
+use tokio_util::sync::CancellationToken;
+
+struct NoopStore;
+
+#[async_trait]
+impl Store for NoopStore {
+    fn set_agent_session_id(&self, session_id: &str, agent_session_id: &str) -> Result<(), String> {
+        println!(
+            "[probe] set_agent_session_id: session_id={} agent_session_id={}",
+            session_id, agent_session_id
+        );
+        Ok(())
+    }
+}
+
+#[derive(Default)]
+struct ProbeState {
+    tool_call_counts: HashMap<String, usize>,
+    total_tool_calls: usize,
+    total_tool_title_updates: usize,
+    total_tool_results: usize,
+    assistant_chunks: usize,
+}
+
+struct ProbeWriter {
+    state: Arc<Mutex<ProbeState>>,
+}
+
+impl ProbeWriter {
+    fn new(state: Arc<Mutex<ProbeState>>) -> Self {
+        Self { state }
+    }
+
+    fn truncate(s: &str) -> String {
+        const MAX: usize = 180;
+        let mut out = String::new();
+        for (idx, ch) in s.chars().enumerate() {
+            if idx >= MAX {
+                out.push_str("...");
+                break;
+            }
+            out.push(ch);
+        }
+        out.replace('\n', "\\n")
+    }
+}
+
+#[async_trait]
+impl MessageWriter for ProbeWriter {
+    async fn append_text(&self, text: &str) {
+        let mut state = self.state.lock().expect("probe state lock poisoned");
+        state.assistant_chunks += 1;
+        println!(
+            "[probe] assistant_chunk #{}: {}",
+            state.assistant_chunks,
+            Self::truncate(text)
+        );
+    }
+
+    async fn finalize(&self) {
+        println!("[probe] finalize");
+    }
+
+    async fn record_tool_call(&self, tool_call_id: &str, title: &str) {
+        let mut state = self.state.lock().expect("probe state lock poisoned");
+        state.total_tool_calls += 1;
+        let count_for_id = *state
+            .tool_call_counts
+            .entry(tool_call_id.to_string())
+            .and_modify(|count| *count += 1)
+            .or_insert(1);
+        println!(
+            "[probe] tool_call #{} id={} seen_for_id={} title={}",
+            state.total_tool_calls,
+            tool_call_id,
+            count_for_id,
+            Self::truncate(title)
+        );
+    }
+
+    async fn update_tool_call_title(&self, tool_call_id: &str, title: &str) {
+        let mut state = self.state.lock().expect("probe state lock poisoned");
+        state.total_tool_title_updates += 1;
+        println!(
+            "[probe] tool_call_update #{} id={} title={}",
+            state.total_tool_title_updates,
+            tool_call_id,
+            Self::truncate(title)
+        );
+    }
+
+    async fn record_tool_result(&self, content: &str) {
+        let mut state = self.state.lock().expect("probe state lock poisoned");
+        state.total_tool_results += 1;
+        println!(
+            "[probe] tool_result #{}: {}",
+            state.total_tool_results,
+            Self::truncate(content)
+        );
+    }
+}
+
+fn print_usage() {
+    eprintln!(
+        "Usage:
+  cargo run --manifest-path src-tauri/Cargo.toml --example acp_stream_probe -- \\
+    --provider <provider-id> --workdir <path> --prompt <text>
+
+Defaults:
+  --provider codex
+  --workdir .
+  --prompt \"Run `echo hello` and summarize the output in one sentence.\""
+    );
+}
+
+fn parse_args() -> Result<(String, PathBuf, String)> {
+    let mut provider = "codex".to_string();
+    let mut workdir = PathBuf::from(".");
+    let mut prompt = "Run `echo hello` and summarize the output in one sentence.".to_string();
+
+    let mut args = std::env::args().skip(1).peekable();
+    while let Some(arg) = args.next() {
+        match arg.as_str() {
+            "--provider" => {
+                provider = args
+                    .next()
+                    .ok_or_else(|| anyhow!("missing value for --provider"))?;
+            }
+            "--workdir" => {
+                workdir = PathBuf::from(
+                    args.next()
+                        .ok_or_else(|| anyhow!("missing value for --workdir"))?,
+                );
+            }
+            "--prompt" => {
+                prompt = args
+                    .next()
+                    .ok_or_else(|| anyhow!("missing value for --prompt"))?;
+            }
+            "--help" | "-h" => {
+                print_usage();
+                std::process::exit(0);
+            }
+            other => {
+                return Err(anyhow!("unknown argument: {other}"));
+            }
+        }
+    }
+
+    Ok((provider, workdir, prompt))
+}
+
+fn main() -> Result<()> {
+    let (provider, workdir, prompt) = parse_args()?;
+    println!("[probe] provider={provider} workdir={}", workdir.display());
+    println!("[probe] prompt={}", ProbeWriter::truncate(&prompt));
+
+    let rt = tokio::runtime::Builder::new_current_thread()
+        .enable_all()
+        .build()?;
+    let local = tokio::task::LocalSet::new();
+
+    local.block_on(&rt, async move {
+        let driver = AcpDriver::new(&provider).map_err(|e| anyhow!(e))?;
+        let store = Arc::new(NoopStore) as Arc<dyn Store>;
+        let state = Arc::new(Mutex::new(ProbeState::default()));
+        let writer = Arc::new(ProbeWriter::new(Arc::clone(&state))) as Arc<dyn MessageWriter>;
+        let cancel_token = CancellationToken::new();
+
+        let result = driver
+            .run(
+                "probe-session",
+                &prompt,
+                &workdir,
+                &store,
+                &writer,
+                &cancel_token,
+                None,
+            )
+            .await;
+
+        let state = state.lock().expect("probe state lock poisoned");
+        println!("[probe] result={result:?}");
+        println!(
+            "[probe] summary: assistant_chunks={} tool_calls={} tool_call_updates={} tool_results={}",
+            state.assistant_chunks,
+            state.total_tool_calls,
+            state.total_tool_title_updates,
+            state.total_tool_results
+        );
+
+        let mut duplicate_ids: Vec<(&String, &usize)> = state
+            .tool_call_counts
+            .iter()
+            .filter(|(_, count)| **count > 1)
+            .collect();
+        duplicate_ids.sort_by(|(a, _), (b, _)| a.cmp(b));
+
+        if duplicate_ids.is_empty() {
+            println!("[probe] duplicate_tool_call_ids=none");
+        } else {
+            println!("[probe] duplicate_tool_call_ids:");
+            for (id, count) in duplicate_ids {
+                println!("  - id={id} count={count}");
+            }
+        }
+
+        Ok::<(), anyhow::Error>(())
+    })?;
+
+    Ok(())
+}
diff --git a/staged/src-tauri/src/agent/writer.rs b/staged/src-tauri/src/agent/writer.rs
index b708b218..76e8c5e9 100644
--- a/staged/src-tauri/src/agent/writer.rs
+++ b/staged/src-tauri/src/agent/writer.rs
@@ -39,6 +39,11 @@ pub struct MessageWriter {
     last_flush_at: Mutex<Instant>,
     /// Maps external tool-call IDs → DB row IDs.
     tool_call_rows: Mutex<HashMap<String, i64>>,
+    /// DB row id of the currently streaming tool result.
+    ///
+    /// ACP can send multiple content updates for one tool call; we update
+    /// the same row instead of inserting duplicates.
+    current_tool_result_msg_id: Mutex<Option<i64>>,
 }
 
 impl MessageWriter {
@@ -50,6 +55,7 @@ impl MessageWriter {
             current_text: Mutex::new(String::new()),
             last_flush_at: Mutex::new(Instant::now()),
             tool_call_rows: Mutex::new(HashMap::new()),
+            current_tool_result_msg_id: Mutex::new(None),
         }
     }
 
@@ -87,6 +93,14 @@ impl MessageWriter {
     /// to maintain correct message ordering.
     pub async fn record_tool_call(&self, tool_call_id: &str, title: &str) {
         self.finalize().await;
+        *self.current_tool_result_msg_id.lock().await = None;
+
+        // Some providers may resend ToolCall for the same ID while streaming.
+        // Treat those as updates to the existing row.
+        if let Some(&row_id) = self.tool_call_rows.lock().await.get(tool_call_id) {
+            let _ = self.store.update_message_content(row_id, title);
+            return;
+        }
 
         match self
             .store
@@ -112,9 +126,19 @@ impl MessageWriter {
 
     /// Record the result/output of a tool call.
     pub async fn record_tool_result(&self, content: &str) {
-        let _ = self
+        let mut current_result_id = self.current_tool_result_msg_id.lock().await;
+        if let Some(id) = *current_result_id {
+            let _ = self.store.update_message_content(id, content);
+            return;
+        }
+
+        match self
             .store
-            .add_session_message(&self.session_id, MessageRole::ToolResult, content);
+            .add_session_message(&self.session_id, MessageRole::ToolResult, content)
+        {
+            Ok(id) => *current_result_id = Some(id),
+            Err(e) => log::error!("Failed to insert tool_result message: {e}"),
+        }
     }
 
     // =====================================================================
@@ -181,3 +205,52 @@ impl acp_client::MessageWriter for MessageWriter {
         self.record_tool_result(content).await
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+    use std::sync::Arc;
+
+    use super::MessageWriter;
+    use crate::store::{MessageRole, Session, Store};
+
+    fn setup_writer() -> (Arc<Store>, String, MessageWriter) {
+        let store = Arc::new(Store::in_memory().expect("in-memory store"));
+        let session = Session::new_running("test prompt", Path::new("."));
+        store.create_session(&session).expect("create session");
+        let writer = MessageWriter::new(session.id.clone(), Arc::clone(&store));
+        (store, session.id, writer)
+    }
+
+    #[tokio::test]
+    async fn record_tool_result_updates_existing_row_for_streaming_updates() {
+        let (store, session_id, writer) = setup_writer();
+
+        writer.record_tool_call("tc-1", "Run echo hello").await;
+        writer.record_tool_result("first chunk").await;
+        writer.record_tool_result("second chunk").await;
+
+        let messages = store
+            .get_session_messages(&session_id)
+            .expect("query messages");
+        assert_eq!(messages.len(), 2);
+        assert_eq!(messages[0].role, MessageRole::ToolCall);
+        assert_eq!(messages[1].role, MessageRole::ToolResult);
+        assert_eq!(messages[1].content, "second chunk");
+    }
+
+    #[tokio::test]
+    async fn record_tool_call_same_id_updates_instead_of_inserting() {
+        let (store, session_id, writer) = setup_writer();
+
+        writer.record_tool_call("tc-dup", "Run first title").await;
+        writer.record_tool_call("tc-dup", "Run updated title").await;
+
+        let messages = store
+            .get_session_messages(&session_id)
+            .expect("query messages");
+        assert_eq!(messages.len(), 1);
+        assert_eq!(messages[0].role, MessageRole::ToolCall);
+        assert_eq!(messages[0].content, "Run updated title");
+    }
+}