Introduce a new StreamingEditFileTool (#29733)

This pull request introduces a new tool for streaming edits. The
short-term goal is for this tool to replace the existing `EditFileTool`,
but we want to get this out the door as soon as possible so that we can
start testing it.

`StreamingEditFileTool` is mutually exclusive with `EditFileTool`. It
will be enabled by default for anyone who has the `agent-stream-edits`
feature flag, as well as people that set `assistant.stream_edits` to
`true` in their settings.

### Implementation

Streaming is achieved by requesting a completion while the `edit_file`
tool gets called. We invoke the model by taking the existing
conversation with the agent and appending a prompt specifically tailored
for editing. In that prompt, we ask the model to produce a stream of
`<old_text>`/`<new_text>` tags. As the model streams text in, we
incrementally parse it and start editing as soon as we can.

### Evals

Note that, as part of this pull request, I also defined some new evals
that I used to drive the behavior of the recursive LLM call. To run
them, use this command:

```bash
cargo test --package=assistant_tools --features eval -- eval_extract_handle_command_output
```

Or comment out the `#[cfg_attr(not(feature = "eval"), ignore)]` macro.

I recommend running them one at a time, because right now we don't
really have a way of orchestrating of all these evals. I think we should
invest into that effort once the new agent panel goes live.

Release Notes:

- N/A

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Oleksiy Syvokon <oleksiy.syvokon@gmail.com>

crates/assistant_tools/src/assistant_tools.rs

@@ -7,6 +7,7 @@ mod create_directory_tool;
 mod create_file_tool;
 mod delete_path_tool;
 mod diagnostics_tool;
+mod edit_agent;
 mod edit_file_tool;
 mod fetch_tool;
 mod find_path_tool;
@@ -19,7 +20,9 @@ mod read_file_tool;
 mod rename_tool;
 mod replace;
 mod schema;
+mod streaming_edit_file_tool;
 mod symbol_info_tool;
+mod templates;
 mod terminal_tool;
 mod thinking_tool;
 mod ui;
@@ -27,14 +30,19 @@ mod web_search_tool;
 
 use std::sync::Arc;
 
+use assistant_settings::AssistantSettings;
 use assistant_tool::ToolRegistry;
 use copy_path_tool::CopyPathTool;
+use feature_flags::{AgentStreamEditsFeatureFlag, FeatureFlagAppExt};
 use gpui::App;
 use http_client::HttpClientWithUrl;
 use language_model::LanguageModelRegistry;
 use move_path_tool::MovePathTool;
+use settings::{Settings, SettingsStore};
 use web_search_tool::WebSearchTool;
 
+pub(crate) use templates::*;
+
 use crate::batch_tool::BatchTool;
 use crate::code_action_tool::CodeActionTool;
 use crate::code_symbols_tool::CodeSymbolsTool;
@@ -52,6 +60,7 @@ use crate::now_tool::NowTool;
 use crate::open_tool::OpenTool;
 use crate::read_file_tool::ReadFileTool;
 use crate::rename_tool::RenameTool;
+use crate::streaming_edit_file_tool::StreamingEditFileTool;
 use crate::symbol_info_tool::SymbolInfoTool;
 use crate::terminal_tool::TerminalTool;
 use crate::thinking_tool::ThinkingTool;
@@ -71,7 +80,6 @@ pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
     registry.register_tool(CreateFileTool);
     registry.register_tool(CopyPathTool);
     registry.register_tool(DeletePathTool);
-    registry.register_tool(EditFileTool);
     registry.register_tool(SymbolInfoTool);
     registry.register_tool(CodeActionTool);
     registry.register_tool(MovePathTool);
@@ -88,6 +96,12 @@ pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
     registry.register_tool(ThinkingTool);
     registry.register_tool(FetchTool::new(http_client));
 
+    register_edit_file_tool(cx);
+    cx.observe_flag::<AgentStreamEditsFeatureFlag, _>(|_, cx| register_edit_file_tool(cx))
+        .detach();
+    cx.observe_global::<SettingsStore>(register_edit_file_tool)
+        .detach();
+
     cx.subscribe(
         &LanguageModelRegistry::global(cx),
         move |registry, event, cx| match event {
@@ -108,6 +122,19 @@ pub fn init(http_client: Arc<HttpClientWithUrl>, cx: &mut App) {
     .detach();
 }
 
+fn register_edit_file_tool(cx: &mut App) {
+    let registry = ToolRegistry::global(cx);
+
+    registry.unregister_tool(EditFileTool);
+    registry.unregister_tool(StreamingEditFileTool);
+
+    if AssistantSettings::get_global(cx).stream_edits(cx) {
+        registry.register_tool(StreamingEditFileTool);
+    } else {
+        registry.register_tool(EditFileTool);
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -146,6 +173,7 @@ mod tests {
     #[gpui::test]
     fn test_builtin_tool_schema_compatibility(cx: &mut App) {
         settings::init(cx);
+        AssistantSettings::register(cx);
 
         let client = Client::new(
             Arc::new(FakeSystemClock::new()),