docs(rfd): Indicate deletes in diffs (#441)

* Added file-delete.mdx

* add json example

* Clean up

* Update website

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

Author: anna239

docs/docs.json

@@ -119,7 +119,8 @@
               "rfds/rust-sdk-v1",
               "rfds/logout-method",
               "rfds/session-delete",
-              "rfds/message-id"
+              "rfds/message-id",
+              "rfds/diff-delete"
             ]
           },
           {

docs/rfds/diff-delete.mdx

@@ -0,0 +1,78 @@
+---
+title: "Represent deleted files in diff"
+---
+
+Author(s): [anna239](https://github.com/benbrandt)
+
+## Elevator pitch
+
+> What are you proposing to change?
+
+Add flag `deleted` to [Diff](https://agentclientprotocol.com/protocol/tool-calls#diffs) entity type for the case of a deleted file.
+
+## Status quo
+
+> How do things work today and what problems does this cause? Why would we change things?
+
+Currently, in Diff entity type `newText` is not nullable, so it's not possible to distinguish between a deleted file and empty file.
+
+## What we propose to do about it
+
+> What are you proposing to improve the situation?
+
+Add flag `deleted` to [Diff](https://agentclientprotocol.com/protocol/tool-calls#diffs) entity type for the case of a deleted file.
+
+**Current structure (cannot distinguish deleted file from empty file):**
+
+```json
+{
+  "type": "diff",
+  "path": "/home/user/project/src/config.json",
+  "oldText": "{\n  \"debug\": false\n}",
+  "newText": ""
+}
+```
+
+**Proposed structure with `deleted` flag:**
+
+```json
+{
+  "type": "diff",
+  "path": "/home/user/project/src/config.json",
+  "oldText": "{\n  \"debug\": false\n}",
+  "newText": "",
+  "deleted": true
+}
+```
+
+Note: we would ideally make newText nullable, but that would break existing clients.
+
+## Shiny future
+
+> How will things will play out once this feature exists?
+
+It is possible for the agent to distinguish between a deleted file and an empty file.
+
+## Implementation details and plan
+
+> Tell me more about your implementation. What is your detailed implementation plan?
+
+Adding the new field will be a non-breaking change, and clients that update can better distinguish between deleted and empty files.
+
+## Frequently asked questions
+
+> What questions have arisen over the course of authoring this document or during subsequent discussions?
+
+**Do we need to represent moved files?**
+
+An agent could represent that with a deleted file at the old path and a new file at the new path.
+
+We need to rework the entire diff structure to handle more cases, and binary files, but in the meantime this provides a stop-gap until we can implement a more comprehensive solution.
+
+### What alternative approaches did you consider, and why did you settle on this one?
+
+We considered making newText nullable, but that would break existing clients.
+
+## Revision history
+
+2026-02-20: Initial draft

docs/updates.mdx

@@ -4,6 +4,13 @@ description: Updates and announcements about the Agent Client Protocol
 rss: true
 ---
 
+<Update label="February 20, 2025" tags={["RFD"]}>
+## Delete in Diff RFD moves to Draft stage
+
+The RFD for indicating whether a diff resulted in a file deletion has been moved to Draft stage. Please review the [RFD](./rfds/diff-delete) for more information on the current proposal and provide feedback as work on the implementation begins.
+
+</Update>
+
 <Update label="February 18, 2025" tags={["Governance"]}>
 ## Sergey Ignatov is now a Lead Maintainer