agent: Truncate bash tool output (#28291)

The bash tool will now truncate its output to 8192 bytes (or the last
newline before that).

We also added a global limit for any tool that produces a clearly large
output that wouldn't fit the context window.

Release Notes:

- agent: Truncate bash tool output

---------

Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/agent/src/thread.rs

@@ -1487,6 +1487,7 @@ impl Thread {
                             tool_use_id.clone(),
                             tool_name,
                             output,
+                            cx,
                         );
 
                         cx.emit(ThreadEvent::ToolFinished {
@@ -1831,7 +1832,7 @@ impl Thread {
         ));
 
         self.tool_use
-            .insert_tool_output(tool_use_id.clone(), tool_name, err);
+            .insert_tool_output(tool_use_id.clone(), tool_name, err, cx);
 
         cx.emit(ThreadEvent::ToolFinished {
             tool_use_id,