delete ProcessTracker — replaced by ActiveToolCall + KillOnDrop

All process management now goes through active_tools:
- TUI reads metadata (name, elapsed time)
- Ctrl+K aborts handles (KillOnDrop sends SIGTERM)
- Running count from active_tools.len()

No more separate PID tracking, register/unregister, or
ProcessInfo. One data structure for everything.

Co-Developed-By: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

src/agent/tools/mod.rs

@@ -19,9 +19,7 @@ mod vision;
 pub mod working_stack;
 
 use serde::{Serialize, Deserialize};
-use std::sync::Arc;
 use std::time::Instant;
-use tokio::sync::Mutex;
 
 fn default_timeout() -> u64 { 120 }
 
@@ -110,14 +108,6 @@ impl ToolOutput {
     }
 }
 
-/// Info about a running child process, visible to the TUI.
-#[derive(Debug, Clone)]
-pub struct ProcessInfo {
-    pub pid: u32,
-    pub command: String,
-    pub started: Instant,
-}
-
 /// A tool call in flight — metadata for TUI + JoinHandle for
 /// result collection and cancellation.
 pub struct ActiveToolCall {
@@ -129,53 +119,6 @@ pub struct ActiveToolCall {
     pub handle: tokio::task::JoinHandle<(ToolCall, ToolOutput)>,
 }
 
-/// Shared tracker for running child processes. Allows the TUI to
-/// display what's running and kill processes by PID.
-#[derive(Debug, Clone, Default)]
-pub struct ProcessTracker {
-    inner: Arc<Mutex<Vec<ProcessInfo>>>,
-}
-
-impl ProcessTracker {
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    async fn register(&self, pid: u32, command: &str) {
-        self.inner.lock().await.push(ProcessInfo {
-            pid,
-            command: if command.len() > 120 {
-                format!("{}...", &command[..120])
-            } else {
-                command.to_string()
-            },
-            started: Instant::now(),
-        });
-    }
-
-    async fn unregister(&self, pid: u32) {
-        self.inner.lock().await.retain(|p| p.pid != pid);
-    }
-
-    /// Snapshot of currently running processes.
-    pub async fn list(&self) -> Vec<ProcessInfo> {
-        self.inner.lock().await.clone()
-    }
-
-    /// Kill a process by PID. Returns true if the signal was sent.
-    pub async fn kill(&self, pid: u32) -> bool {
-        // SIGTERM the process group (negative PID kills the group)
-        let ret = unsafe { libc::kill(-(pid as i32), libc::SIGTERM) };
-        if ret != 0 {
-            // Try just the process
-            unsafe { libc::kill(pid as i32, libc::SIGTERM) };
-        }
-        // Don't unregister — let the normal exit path do that
-        // so the tool result says "killed by user"
-        true
-    }
-}
-
 /// Truncate output if it exceeds max length, appending a truncation notice.
 pub fn truncate_output(mut s: String, max: usize) -> String {
     if s.len() > max {
@@ -197,7 +140,6 @@ pub fn truncate_output(mut s: String, max: usize) -> String {
 pub async fn dispatch(
     name: &str,
     args: &serde_json::Value,
-    tracker: &ProcessTracker,
 ) -> ToolOutput {
     // Agent-specific tools
     let rich_result = match name {
@@ -211,7 +153,7 @@ pub async fn dispatch(
         return result.unwrap_or_else(ToolOutput::error);
     }
 
-    if let Some(output) = dispatch_shared(name, args, tracker, None).await {
+    if let Some(output) = dispatch_shared(name, args, None).await {
         return output;
     }
 
@@ -224,7 +166,6 @@ pub async fn dispatch(
 pub async fn dispatch_shared(
     name: &str,
     args: &serde_json::Value,
-    tracker: &ProcessTracker,
     provenance: Option<&str>,
 ) -> Option<ToolOutput> {
     // Memory and journal tools
@@ -241,7 +182,7 @@ pub async fn dispatch_shared(
         "read_file" => read::read_file(args),
         "write_file" => write::write_file(args),
         "edit_file" => edit::edit_file(args),
-        "bash" => bash::run_bash(args, tracker).await,
+        "bash" => bash::run_bash(args).await,
         "grep" => grep::grep(args),
         "glob" => glob::glob_search(args),
         _ => return None,