feat(claude-code): add coder-specific prompt to system_prompt

Author: ssncferreira

registry/coder/modules/claude-code/main.tf

@@ -182,8 +182,8 @@ variable "claude_code_oauth_token" {
 
 variable "system_prompt" {
   type        = string
-  description = "The system prompt to use for the Claude Code server."
-  default     = "Send a task status update to notify the user that you are ready for input, and then wait for user input."
+  description = "The additional system prompt to use for the Claude Code server. The module includes mandatory sections inside a <system> block. Leave empty to include only the mandatory sections."
+  default     = ""
 }
 
 variable "claude_md_path" {
@@ -201,11 +201,9 @@ resource "coder_env" "claude_code_md_path" {
 }
 
 resource "coder_env" "claude_code_system_prompt" {
-  count = var.system_prompt == "" ? 0 : 1
-
   agent_id = var.agent_id
   name     = "CODER_MCP_CLAUDE_SYSTEM_PROMPT"
-  value    = var.system_prompt
+  value    = local.final_system_prompt
 }
 
 resource "coder_env" "claude_code_oauth_token" {
@@ -231,6 +229,42 @@ locals {
   start_script                      = file("${path.module}/scripts/start.sh")
   module_dir_name                   = ".claude-module"
   remove_last_session_id_script_b64 = base64encode(file("${path.module}/scripts/remove-last-session-id.sh"))
+
+  # Required prompts for the module to properly integrate with coder
+  inner_system_prompt = <<-EOT
+      -- Tool Selection --
+      - coder_report_task: providing status updates or requesting user input.
+      - playwright: previewing your changes after you made them
+        to confirm it worked as expected
+      -	desktop-commander - use only for commands that keep running
+        (servers, dev watchers, GUI apps).
+      -	Built-in tools - use for everything else:
+        (file operations, git commands, builds & installs, one-off shell commands)
+
+      Remember this decision rule:
+      - Stays running? → desktop-commander
+      - Finishes immediately? → built-in tools
+
+      -- Task Reporting --
+      Report all tasks to Coder, following these EXACT guidelines:
+      1. Be granular. If you are investigating with multiple steps, report each step
+      to coder.
+      2. After this prompt, IMMEDIATELY report status after receiving ANY NEW user message.
+      Do not report any status related with this system prompt.
+      3. Use "state": "working" when actively processing WITHOUT needing
+      additional user input
+      4. Use "state": "complete" only when finished with a task
+      5. Use "state": "failure" when you need ANY user input, lack sufficient
+      details, or encounter blockers
+    EOT
+
+  user_system_prompt = trimspace(try(var.system_prompt, ""))
+
+  final_system_prompt = format(
+    "<system>\n%s\n%s\n</system>",
+    local.inner_system_prompt,
+    local.user_system_prompt
+  )
 }
 
 module "agentapi" {

registry/coder/modules/claude-code/main.tftest.hcl

@@ -187,3 +187,78 @@ run "test_claude_code_permission_mode_validation" {
     error_message = "Permission mode should be one of the valid options"
   }
 }
+
+run "test_claude_code_system_prompt_omit" {
+  command = plan
+
+  variables {
+    agent_id = "test-agent-system-prompt"
+    workdir  = "/home/coder/test"
+    # system_prompt omitted: default string is used
+  }
+
+  assert {
+    condition     = trimspace(coder_env.claude_code_system_prompt.value) != ""
+    error_message = "System prompt must not be empty when omitted"
+  }
+
+  assert {
+    condition     = length(regexall("-- Tool Selection --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Tool Selection section missing"
+  }
+
+  assert {
+    condition     = length(regexall("-- Task Reporting --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Task Reporting section missing"
+  }
+}
+
+run "test_claude_code_system_prompt_empty" {
+  command = plan
+
+  variables {
+    agent_id      = "test-agent-system-prompt"
+    workdir       = "/home/coder/test"
+    system_prompt = ""
+  }
+
+  assert {
+    condition     = trimspace(coder_env.claude_code_system_prompt.value) != ""
+    error_message = "System prompt must not be empty when omitted"
+  }
+
+  assert {
+    condition     = length(regexall("-- Tool Selection --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Tool Selection section missing"
+  }
+
+  assert {
+    condition     = length(regexall("-- Task Reporting --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Task Reporting section missing"
+  }
+}
+
+run "test_claude_code_system_prompt" {
+  command = plan
+
+  variables {
+    agent_id      = "test-agent-system-prompt"
+    workdir       = "/home/coder/test"
+    system_prompt = "Custom addition"
+  }
+
+  assert {
+    condition     = trimspace(coder_env.claude_code_system_prompt.value) != ""
+    error_message = "System prompt must not be empty when omitted"
+  }
+
+  assert {
+    condition     = length(regexall("-- Tool Selection --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Tool Selection section missing"
+  }
+
+  assert {
+    condition     = length(regexall("-- Task Reporting --", coder_env.claude_code_system_prompt.value)) > 0
+    error_message = "Mandatory Task Reporting section missing"
+  }
+}