feat(config): update system prompt for file referencing in responses

- remove old system prompt setting in configuration
- replace it with a hardcoded prompt including URI format examples
- modifies behavior to improve navigation and tooling integration

Author: aweis89

lua/opencode/config.lua

@@ -200,8 +200,6 @@ M.defaults = {
     on_done_thinking = nil,
     on_permission_requested = nil,
   },
-  -- Additional system prompt, used to customize assistant behavior (e.g., file reference formatting)
-  system_prompt = 'When referencing files in your responses, always use the file:// URI scheme (e.g., file://path/to/file.lua or file://path/to/file.lua:42 for a specific line). This helps with navigation and tooling integration.',
 }
 
 M.values = vim.deepcopy(M.defaults)

lua/opencode/core.lua

@@ -167,10 +167,8 @@ M.send_message = Promise.async(function(prompt, opts)
     state.current_mode = opts.agent
   end
 
-  -- Add system prompt if configured
-  if config.system_prompt and config.system_prompt ~= '' then
-    params.system = config.system_prompt
-  end
+  params.system =
+    'When referencing files in your responses, always use the file:// URI scheme (e.g., file://path/to/file.lua, file://path/to/file.lua:42 for a specific line, or file://path/to/file.lua:42-50 for a range). This helps with navigation and tooling integration.'
 
   params.parts = context.format_message(prompt, opts.context)
   M.before_run(opts)