Add workspace lifecycle management via task-complete callback

- Workspaces curl POST /webhook/task-complete/{name} when done
- Orchestrator deletes the workspace via Coder API on callback
- Active workspaces count toward concurrency limit
- GET /queue now shows active workspaces with elapsed time
- Coder template gains callback_url parameter
- TTL becomes a safety net, not the primary shutdown mechanism

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

coder/cloudflare-worker/main.tf

@@ -208,6 +208,15 @@ data "coder_parameter" "anthropic_api_key" {
   mutable      = false
 }
 
+data "coder_parameter" "callback_url" {
+  name         = "callback_url"
+  display_name = "Task Complete Callback URL"
+  description  = "URL to POST when task finishes (set by orchestrator)"
+  type         = "string"
+  default      = ""
+  mutable      = false
+}
+
 data "coder_parameter" "deploy_env" {
   name         = "deploy_env"
   display_name = "Deploy Environment"
@@ -443,6 +452,7 @@ resource "coder_agent" "main" {
     ISSUE_NUMBER      = data.coder_parameter.issue_number.value
     REPO_CLONE_URL    = data.coder_parameter.repo_clone_url.value
     DEPLOY_ENV        = data.coder_parameter.deploy_env.value
+    CALLBACK_URL      = data.coder_parameter.callback_url.value
   }
 
   startup_script = <<-EOT
@@ -519,6 +529,13 @@ resource "coder_agent" "main" {
       claude --print --dangerously-skip-permissions "/project:$TASK_TYPE $ARGS" 2>&1 | tee ~/task-output.log
 
       echo "Task completed. Output saved to ~/task-output.log"
+
+      # Notify orchestrator that the task is done
+      if [ -n "$CALLBACK_URL" ]; then
+        curl -s -X POST -H "Content-Type: application/json" \
+          -d '{"status":"complete"}' \
+          "$CALLBACK_URL" || echo "Callback failed (non-fatal)"
+      fi
     fi
   EOT
 }
@@ -657,6 +674,11 @@ resource "kubernetes_deployment_v1" "workspace" {
             value = data.coder_parameter.deploy_env.value
           }
 
+          env {
+            name  = "CALLBACK_URL"
+            value = data.coder_parameter.callback_url.value
+          }
+
           resources {
             requests = {
               cpu    = "${tonumber(data.coder_parameter.cpu.value) * 500}m"