Add MCP server (v1 read-only): toggle, per-pane gate, panel UI

src-tauri/src/pty.rs

@@ -2,7 +2,7 @@
 //! through portable-pty, reads its output on a background thread, and
 //! forwards chunks to the frontend as `pane://{id}/data` events.
 
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::io::{Read, Write};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
@@ -52,6 +52,41 @@ pub enum SpawnSpec {
 /// the SSH prompt.
 type SharedWriter = Arc<Mutex<Box<dyn Write + Send>>>;
 
+/// Per-pane scrollback ring exposed to the MCP server. Capped — we drop the
+/// oldest bytes when full. `seq` is a monotonic byte counter that wraps at
+/// u64; the MCP `read_pane` tool uses it for incremental polling and the
+/// `wait_for_idle` tool uses it to detect silence.
+pub const PANE_RING_CAPACITY: usize = 256 * 1024;
+
+pub struct PaneRing {
+    buf: VecDeque<u8>,
+    seq: u64,
+}
+
+impl PaneRing {
+    fn new() -> Self {
+        Self {
+            buf: VecDeque::with_capacity(PANE_RING_CAPACITY),
+            seq: 0,
+        }
+    }
+
+    fn push(&mut self, bytes: &[u8]) {
+        for &b in bytes {
+            if self.buf.len() == PANE_RING_CAPACITY {
+                self.buf.pop_front();
+            }
+            self.buf.push_back(b);
+        }
+        self.seq = self.seq.wrapping_add(bytes.len() as u64);
+    }
+
+    /// Snapshot: current contents (oldest-first) + the seq counter.
+    pub fn snapshot(&self) -> (Vec<u8>, u64) {
+        (self.buf.iter().copied().collect(), self.seq)
+    }
+}
+
 /// What we keep alive for each spawned PTY.
 ///
 /// `master` stays in scope to keep the PTY alive; we never write through it
@@ -63,6 +98,9 @@ struct PaneHandle {
     writer: SharedWriter,
     #[allow(dead_code)]
     child: Box<dyn portable_pty::Child + Send + Sync>,
+    /// Same Arc the reader thread appends into; the MCP server reads via
+    /// {@link PtyManager::ring}.
+    ring: Arc<Mutex<PaneRing>>,
 }
 
 pub struct PtyManager {
@@ -127,6 +165,7 @@ impl PtyManager {
             .take_writer()
             .context("take_writer failed")?;
         let writer: SharedWriter = Arc::new(Mutex::new(writer_raw));
+        let ring: Arc<Mutex<PaneRing>> = Arc::new(Mutex::new(PaneRing::new()));
 
         let id = self.next_id.fetch_add(1, Ordering::Relaxed);
 
@@ -136,14 +175,18 @@ impl PtyManager {
                 master: pair.master,
                 writer: writer.clone(),
                 child,
+                ring: ring.clone(),
             },
         );
 
         // Reader thread: pump bytes -> base64 -> emit. Also handles the
-        // password-prompt autotype state machine if `saved_password` is set.
+        // password-prompt autotype state machine if `saved_password` is set,
+        // and pushes raw bytes into the per-pane scrollback ring for the
+        // MCP server to read.
         let app_for_reader = app.clone();
         let event_name = format!("pane://{id}/data");
         let writer_for_reader = writer.clone();
+        let ring_for_reader = ring.clone();
         std::thread::spawn(move || {
             let mut buf = [0u8; 8192];
             let mut pw_state = PasswordState::from(saved_password);
@@ -159,6 +202,9 @@ impl PtyManager {
                         // on the renderer; pw_state mutates here.
                         pw_state.observe(&buf[..n], &writer_for_reader, id);
 
+                        // Mirror bytes into the scrollback ring (MCP source).
+                        ring_for_reader.lock().push(&buf[..n]);
+
                         let chunk_b64 = B64.encode(&buf[..n]);
                         if let Err(e) =
                             app_for_reader.emit(&event_name, DataChunk { b64: chunk_b64 })
@@ -217,6 +263,13 @@ impl PtyManager {
         }
         Ok(())
     }
+
+    /// Borrow the per-pane scrollback ring. Returns None if the pane has
+    /// been killed. The Arc lets callers hold the ring even after the
+    /// PaneHandle is dropped (reader thread will stop pushing into it).
+    pub fn ring(&self, id: PaneId) -> Option<Arc<Mutex<PaneRing>>> {
+        self.panes.lock().get(&id).map(|p| p.ring.clone())
+    }
 }
 
 #[derive(Serialize, Clone)]