Revert "Simplify inline assist to avoid spurious xml in completions (… (#16231)

…#16184)"

This reverts commit c3edbd7d9a, which
caused a regression that leaked chatter into inline assist replacements
and <rewrite_this> tags into insertions.

Release Notes:

- N/A

assets/prompts/content_prompt.hbs

@@ -1,41 +1,52 @@
+Here's a text file that I'm going to ask you to make an edit to.
+
 {{#if language_name}}
-File language: {{language_name}}
+The file is in {{language_name}}.
 {{/if}}
 
+You need to rewrite a portion of it.
+
+The section you'll need to edit is marked with <rewrite_this></rewrite_this> tags.
+
 <document>
 {{{document_content}}}
 </document>
 
 {{#if is_truncated}}
-Note: Context around the relevant section has been truncated for brevity.
+The context around the relevant section has been truncated (possibly in the middle of a line) for brevity.
 {{/if}}
 
-Editing instructions:
-1. Rewrite the section marked with <rewrite_this></rewrite_this> tags based on this prompt:
+Rewrite the section of {{content_type}} in <rewrite_this></rewrite_this> tags based on the following prompt:
+
 <prompt>
 {{{user_prompt}}}
 </prompt>
 
-2. Within <rewrite_this></rewrite_this>, make changes only in these subsections:
-   {{#if has_insertion}}
-   - Insert text where marked with <insert_here></insert_here> tags
-   {{/if}}
-   {{#if has_replacement}}
-   - Edit text surrounded by <edit_here></edit_here> tags
-   {{/if}}
+Here's the section to edit based on that prompt again for reference:
+
+<rewrite_this>
+{{{rewrite_section}}}
+</rewrite_this>
+
+You'll rewrite this entire section, but you will only make changes within certain subsections.
+
+{{#if has_insertion}}
+Insert text anywhere you see it marked with with <insert_here></insert_here> tags. Do not include <insert_here> tags in your output.
+{{/if}}
+{{#if has_replacement}}
+Edit edit text that you see surrounded with <edit_here></edit_here> tags. Do not include <edit_here> tags in your output.
+{{/if}}
 
-3. Section to edit:
 <rewrite_this>
 {{{rewrite_section_with_selections}}}
 </rewrite_this>
 
-4. Guidelines:
-   - Only make changes necessary to fulfill the prompt
-   - Preserve all surrounding {{content_type}}
-   - Maintain the original indentation level
-   - Rewrite the entire section, even if no changes are needed
-   - Do not include <rewrite_this>, <insert_here>, or <edit_here> tags in your output
+Only make changes that are necessary to fulfill the prompt, leave everything else as-is. All surrounding {{content_type}} will be preserved. Do not output the <rewrite_this></rewrite this> tags or anything outside of them.
 
-Output format:
-Immediately start with the following, ensuring no leading whitespace:
-```{{REWRITTEN_CODE}}```
+Start at the indentation level in the original file in the rewritten {{content_type}}. Don't stop until you've rewritten the entire section, even if you have no more changes to make. Always write out the whole section with no unnecessary elisions.
+
+Immediately start with the following format with no remarks:
+
+```
+\{{REWRITTEN_CODE}}
+```