fix(cli): fix prompt issue in mcp configure claude-code (coder#17599)

* Updates default Coder prompt.
* Skips the directions to report tasks if the pre-requisites are not
available (agent token and app slug).
* Adds the capability to override the default Coder prompt via
`CODER_MCP_CLAUDE_CODER_PROMPT`.

Author: johnstcn

cli/exp_mcp.go

@@ -114,6 +114,7 @@ func (*RootCmd) mcpConfigureClaudeCode() *serpent.Command {
 		claudeConfigPath string
 		claudeMDPath     string
 		systemPrompt     string
+		coderPrompt      string
 		appStatusSlug    string
 		testBinaryName   string
 
@@ -176,8 +177,27 @@ func (*RootCmd) mcpConfigureClaudeCode() *serpent.Command {
 			}
 			cliui.Infof(inv.Stderr, "Wrote config to %s", claudeConfigPath)
 
+			// Determine if we should include the reportTaskPrompt
+			var reportTaskPrompt string
+			if agentToken != "" && appStatusSlug != "" {
+				// Only include the report task prompt if both agent token and app
+				// status slug are defined. Otherwise, reporting a task will fail
+				// and confuse the agent (and by extension, the user).
+				reportTaskPrompt = defaultReportTaskPrompt
+			}
+
+			// If a user overrides the coder prompt, we don't want to append
+			// the report task prompt, as it then becomes the responsibility
+			// of the user.
+			actualCoderPrompt := defaultCoderPrompt
+			if coderPrompt != "" {
+				actualCoderPrompt = coderPrompt
+			} else if reportTaskPrompt != "" {
+				actualCoderPrompt += "\n\n" + reportTaskPrompt
+			}
+
 			// We also write the system prompt to the CLAUDE.md file.
-			if err := injectClaudeMD(fs, systemPrompt, claudeMDPath); err != nil {
+			if err := injectClaudeMD(fs, actualCoderPrompt, systemPrompt, claudeMDPath); err != nil {
 				return xerrors.Errorf("failed to modify CLAUDE.md: %w", err)
 			}
 			cliui.Infof(inv.Stderr, "Wrote CLAUDE.md to %s", claudeMDPath)
@@ -222,6 +242,14 @@ func (*RootCmd) mcpConfigureClaudeCode() *serpent.Command {
 				Value:       serpent.StringOf(&systemPrompt),
 				Default:     "Send a task status update to notify the user that you are ready for input, and then wait for user input.",
 			},
+			{
+				Name:        "coder-prompt",
+				Description: "The coder prompt to use for the Claude Code server.",
+				Env:         "CODER_MCP_CLAUDE_CODER_PROMPT",
+				Flag:        "claude-coder-prompt",
+				Value:       serpent.StringOf(&coderPrompt),
+				Default:     "", // Empty default means we'll use defaultCoderPrompt from the variable
+			},
 			{
 				Name:        "app-status-slug",
 				Description: "The app status slug to use when running the Coder MCP server.",
@@ -567,22 +595,25 @@ func configureClaude(fs afero.Fs, cfg ClaudeConfig) error {
 }
 
 var (
-	coderPrompt = `YOU MUST REPORT YOUR STATUS IMMEDIATELY AFTER EACH USER MESSAGE.
-INTERRUPT READING FILES OR ANY OTHER TOOL CALL IF YOU HAVE NOT REPORTED A STATUS YET.
-You MUST use the mcp__coder__coder_report_task function with all required parameters:
-- summary: Short description of what you're doing
-- link: A relevant link for the status
-- done: Boolean indicating if the task is complete (true/false)
-- emoji: Relevant emoji for the status
-- need_user_attention: Boolean indicating if the task needs user attention (true/false)
-WHEN TO REPORT (MANDATORY):
-1. IMMEDIATELY after receiving ANY user message, before any other actions
-2. After completing any task
-3. When making significant progress
-4. When encountering roadblocks
-5. When asking questions
-6. Before and after using search tools or making code changes
-FAILING TO REPORT STATUS PROPERLY WILL RESULT IN INCORRECT BEHAVIOR.`
+	defaultCoderPrompt = `You are a helpful Coding assistant. Aim to autonomously investigate
+and solve issues the user gives you and test your work, whenever possible.
+Avoid shortcuts like mocking tests. When you get stuck, you can ask the user
+but opt for autonomy.`
+
+	defaultReportTaskPrompt = `YOU MUST REPORT ALL TASKS TO CODER.
+When reporting tasks, you MUST follow these EXACT instructions:
+- IMMEDIATELY report status after receiving ANY user message.
+- Be granular. If you are investigating with multiple steps, report each step to coder.
+
+Task state MUST be one of the following:
+- Use "state": "working" when actively processing WITHOUT needing additional user input.
+- Use "state": "complete" only when finished with a task.
+- Use "state": "failure" when you need ANY user input, lack sufficient details, or encounter blockers.
+
+Task summaries MUST:
+- Include specifics about what you're doing.
+- Include clear and actionable steps for the user.
+- Be less than 160 characters in length.`
 
 	// Define the guard strings
 	coderPromptStartGuard  = "<coder-prompt>"
@@ -591,7 +622,7 @@ FAILING TO REPORT STATUS PROPERLY WILL RESULT IN INCORRECT BEHAVIOR.`
 	systemPromptEndGuard   = "</system-prompt>"
 )
 
-func injectClaudeMD(fs afero.Fs, systemPrompt string, claudeMDPath string) error {
+func injectClaudeMD(fs afero.Fs, coderPrompt, systemPrompt, claudeMDPath string) error {
 	_, err := fs.Stat(claudeMDPath)
 	if err != nil {
 		if !os.IsNotExist(err) {