feat(coder/modules/agentapi): add state persistence support (#736)

AgentAPI can now save and restore conversation state across workspace
restarts. The module exports env vars (AGENTAPI_STATE_FILE,
AGENTAPI_SAVE_STATE, AGENTAPI_LOAD_STATE, AGENTAPI_PID_FILE) that the
binary reads directly. No consumer module changes needed.

New variables: enable_state_persistence (default false),
state_file_path, pid_file_path. State and PID files default to
$HOME/<module_dir_name>/.

Requires agentapi >= v0.12.0. A shared version_at_least function in
lib.sh gates the env var exports and SIGUSR1 in the shutdown script.
Old binaries get a warning and graceful skip.

Shutdown script now does SIGUSR1 (state save), log snapshot capture
(existing, now fault-tolerant via subshell), then SIGTERM with wait.

Closes coder/internal#1257
Refs coder/internal#1256
Refs #696

Author: mafredri

registry/coder/modules/agentapi/README.md

@@ -16,7 +16,7 @@ The AgentAPI module is a building block for modules that need to run an AgentAPI
 ```tf
 module "agentapi" {
   source  = "registry.coder.com/coder/agentapi/coder"
-  version = "2.1.1"
+  version = "2.2.0"
 
   agent_id             = var.agent_id
   web_app_slug         = local.app_slug
@@ -62,6 +62,33 @@ module "agentapi" {
 }
 ```
 
+## State Persistence
+
+AgentAPI can save and restore conversation state across workspace restarts.
+This is disabled by default and requires agentapi binary >= v0.12.0.
+
+State and PID files are stored in `$HOME/<module_dir_name>/` alongside other
+module files (e.g. `$HOME/.claude-module/agentapi-state.json`).
+
+To enable:
+
+```tf
+module "agentapi" {
+  # ... other config
+  enable_state_persistence = true
+}
+```
+
+To override file paths:
+
+```tf
+module "agentapi" {
+  # ... other config
+  state_file_path = "/custom/path/state.json"
+  pid_file_path   = "/custom/path/agentapi.pid"
+}
+```
+
 ## For module developers
 
 For a complete example of how to use this module, see the [Goose module](https://github.com/coder/registry/blob/main/registry/coder/modules/goose/main.tf).

registry/coder/modules/agentapi/agentapi.tftest.hcl

@@ -0,0 +1,108 @@
+mock_provider "coder" {}
+
+variables {
+  agent_id             = "test-agent"
+  web_app_icon         = "/icon/test.svg"
+  web_app_display_name = "Test"
+  web_app_slug         = "test"
+  cli_app_display_name = "Test CLI"
+  cli_app_slug         = "test-cli"
+  start_script         = "echo test"
+  module_dir_name      = ".test-module"
+}
+
+run "default_values" {
+  command = plan
+
+  assert {
+    condition     = var.enable_state_persistence == false
+    error_message = "enable_state_persistence should default to false"
+  }
+
+  assert {
+    condition     = var.state_file_path == ""
+    error_message = "state_file_path should default to empty string"
+  }
+
+  assert {
+    condition     = var.pid_file_path == ""
+    error_message = "pid_file_path should default to empty string"
+  }
+
+  # Verify start script contains state persistence ARG_ vars.
+  assert {
+    condition     = can(regex("ARG_ENABLE_STATE_PERSISTENCE", coder_script.agentapi.script))
+    error_message = "start script should contain ARG_ENABLE_STATE_PERSISTENCE"
+  }
+
+  assert {
+    condition     = can(regex("ARG_STATE_FILE_PATH", coder_script.agentapi.script))
+    error_message = "start script should contain ARG_STATE_FILE_PATH"
+  }
+
+  assert {
+    condition     = can(regex("ARG_PID_FILE_PATH", coder_script.agentapi.script))
+    error_message = "start script should contain ARG_PID_FILE_PATH"
+  }
+
+  # Verify shutdown script contains PID-related ARG_ vars.
+  assert {
+    condition     = can(regex("ARG_PID_FILE_PATH", coder_script.agentapi_shutdown.script))
+    error_message = "shutdown script should contain ARG_PID_FILE_PATH"
+  }
+
+  assert {
+    condition     = can(regex("ARG_MODULE_DIR_NAME", coder_script.agentapi_shutdown.script))
+    error_message = "shutdown script should contain ARG_MODULE_DIR_NAME"
+  }
+
+  assert {
+    condition     = can(regex("ARG_ENABLE_STATE_PERSISTENCE", coder_script.agentapi_shutdown.script))
+    error_message = "shutdown script should contain ARG_ENABLE_STATE_PERSISTENCE"
+  }
+}
+
+run "state_persistence_disabled" {
+  command = plan
+
+  variables {
+    enable_state_persistence = false
+  }
+
+  assert {
+    condition     = var.enable_state_persistence == false
+    error_message = "enable_state_persistence should be false"
+  }
+
+  # Even when disabled, the ARG_ vars should still be in the script
+  # (the shell script handles the conditional logic).
+  assert {
+    condition     = can(regex("ARG_ENABLE_STATE_PERSISTENCE='false'", coder_script.agentapi.script))
+    error_message = "start script should contain ARG_ENABLE_STATE_PERSISTENCE='false'"
+  }
+}
+
+run "custom_paths" {
+  command = plan
+
+  variables {
+    state_file_path = "/custom/state.json"
+    pid_file_path   = "/custom/agentapi.pid"
+  }
+
+  assert {
+    condition     = can(regex("/custom/state.json", coder_script.agentapi.script))
+    error_message = "start script should contain custom state_file_path"
+  }
+
+  assert {
+    condition     = can(regex("/custom/agentapi.pid", coder_script.agentapi.script))
+    error_message = "start script should contain custom pid_file_path"
+  }
+
+  # Verify custom paths also appear in shutdown script.
+  assert {
+    condition     = can(regex("/custom/agentapi.pid", coder_script.agentapi_shutdown.script))
+    error_message = "shutdown script should contain custom pid_file_path"
+  }
+}