Improve distinguishing user from agent edits (#34716)

We no longer rely on the `author` field to tell if a change was made by
the user or the agent. The `author` can be set to `User` in many
situations that are not really user-made edits, such as saving a file,
accepting a change, auto-formatting, and more. I started tracking and
fixing some of these cases, but found that inspecting changes in
`diff_base` is a more reliable method.

Also, we no longer show empty diffs. For example, if the user adds a
line and then removes the same line, the final diff is empty, even
though the buffer is marked as user-changed. Now we won't show such
edit.

There are still some issues to address:

- When a user edits within an unaccepted agent-written block, this
change becomes a part of the agent's edit. Rejecting this block will
lose user edits. It won't be displayed in project notifications, either.

- Accepting an agent block counts as a user-made edit.

- Agent start to call `project_notifications` tool after seeing enough
auto-calls.

Release Notes:

- N/A

crates/agent/src/thread.rs

@@ -47,7 +47,7 @@ use std::{
     time::{Duration, Instant},
 };
 use thiserror::Error;
-use util::{ResultExt as _, debug_panic, post_inc};
+use util::{ResultExt as _, post_inc};
 use uuid::Uuid;
 use zed_llm_client::{CompletionIntent, CompletionRequestStatus, UsageLimit};
 
@@ -1582,20 +1582,18 @@ impl Thread {
         model: Arc<dyn LanguageModel>,
         cx: &mut App,
     ) -> Option<PendingToolUse> {
-        let action_log = self.action_log.read(cx);
+        // Represent notification as a simulated `project_notifications` tool call
+        let tool_name = Arc::from("project_notifications");
+        let tool = self.tools.read(cx).tool(&tool_name, cx)?;
 
-        if !action_log.has_unnotified_user_edits() {
+        if !self.profile.is_tool_enabled(tool.source(), tool.name(), cx) {
             return None;
         }
 
-        // Represent notification as a simulated `project_notifications` tool call
-        let tool_name = Arc::from("project_notifications");
-        let Some(tool) = self.tools.read(cx).tool(&tool_name, cx) else {
-            debug_panic!("`project_notifications` tool not found");
-            return None;
-        };
-
-        if !self.profile.is_tool_enabled(tool.source(), tool.name(), cx) {
+        if self
+            .action_log
+            .update(cx, |log, cx| log.unnotified_user_edits(cx).is_none())
+        {
             return None;
         }