feat(config): support multiple custom instruction files

Add `instruction_files` option to configuration, allowing users to specify
multiple custom instruction files to be loaded from the current working
directory. The prompt resolution logic now iterates over all configured
instruction files and includes their contents if present.

This makes it easier to manage and extend custom Copilot instructions
across different projects.

lua/CopilotChat/config.lua

@@ -43,6 +43,7 @@
 ---@field log_level 'trace'|'debug'|'info'|'warn'|'error'|'fatal'?
 ---@field proxy string?
 ---@field allow_insecure boolean?
+---@field instruction_files table<int, string>?
 ---@field selection 'visual'|'unnamed'|nil
 ---@field chat_autocomplete boolean?
 ---@field log_path string?
@@ -105,6 +106,12 @@ return {
   proxy = nil, -- [protocol://]host[:port] Use this proxy
   allow_insecure = false, -- Allow insecure server connections
 
+  -- Instruction files to look for in current working directory
+  instruction_files = {
+    '.github/copilot-instructions.md',
+    'AGENTS.MD',
+  },
+
   selection = 'visual', -- Selection source
   chat_autocomplete = true, -- Enable chat autocompletion (when disabled, requires manual `mappings.complete` trigger)
 

lua/CopilotChat/prompts.lua

@@ -12,16 +12,22 @@ local WORD_WITH_INPUT_UNQUOTED = WORD .. ':?([^%s`]*)'
 
 --- Find custom instructions in the current working directory.
 ---@param cwd string
+---@param config CopilotChat.config.Config
 ---@return table
-local function find_custom_instructions(cwd)
+local function find_custom_instructions(cwd, config)
   local out = {}
-  local copilot_instructions_path = vim.fs.joinpath(cwd, '.github', 'copilot-instructions.md')
-  local copilot_instructions = files.read_file(copilot_instructions_path)
-  if copilot_instructions then
-    table.insert(out, {
-      filename = copilot_instructions_path,
-      content = vim.trim(copilot_instructions),
-    })
+  local files_to_check = {}
+  for _, relpath in ipairs(config.instruction_files or {}) do
+    table.insert(files_to_check, vim.fs.joinpath(cwd, relpath))
+  end
+  for _, path in ipairs(files_to_check) do
+    local content = files.read_file(path)
+    if content then
+      table.insert(out, {
+        filename = path,
+        content = vim.trim(content),
+      })
+    end
   end
   return out
 end
@@ -314,7 +320,7 @@ function M.resolve_prompt(prompt, config)
     end
 
     local custom_instructions = vim.trim(require('CopilotChat.instructions.custom_instructions'))
-    for _, instruction in ipairs(find_custom_instructions(source.cwd())) do
+    for _, instruction in ipairs(find_custom_instructions(source.cwd(), config)) do
       config.system_prompt = vim.trim(config.system_prompt)
         .. '\n'
         .. custom_instructions:gsub('{FILENAME}', instruction.filename):gsub('{CONTENT}', instruction.content)