feat(dogfood): clean up named Docker volumes and Go build cache cron (#23026)

Docker keeps named volumes around, even if they're dangling. During
development users generate a lot of named coder- volumes and the like.
These are now cleaned on shutdown once they are 30 days old.

For long running workspaces, go build cache also accumulates, so now
we clean these up via cron as well. All cache older than 2 days is wiped
and the cron schedule is based on workspace ID to distribute the load.

dogfood/coder/main.tf

@@ -37,6 +37,11 @@ locals {
   repo_base_dir  = data.coder_parameter.repo_base_dir.value == "~" ? "/home/coder" : replace(data.coder_parameter.repo_base_dir.value, "/^~\\//", "/home/coder/")
   repo_dir       = replace(try(module.git-clone[0].repo_dir, ""), "/^~\\//", "/home/coder/")
   container_name = "coder-${data.coder_workspace_owner.me.name}-${lower(data.coder_workspace.me.name)}"
+
+  // Derive a stable per-workspace hour and minute from the workspace ID
+  // so that cache cleanup crons don't all hit the filesystem at once.
+  cache_cleanup_hour   = parseint(substr(data.coder_workspace.me.id, 0, 2), 16) % 24
+  cache_cleanup_minute = parseint(substr(data.coder_workspace.me.id, 2, 2), 16) % 60
 }
 
 data "coder_workspace_preset" "pittsburgh" {
@@ -616,6 +621,17 @@ resource "coder_agent" "dev" {
     #   - all build cache
     docker system prune -a -f
 
+    # Remove dangling named volumes that are older than KEEP_DAYS. Using
+    # 30 here as a conservative default (vacation, holidays, etc.).
+    KEEP_DAYS=30
+    docker volume ls -qf dangling=true \
+      | xargs -r docker volume inspect \
+      | jq -r --argjson days "$KEEP_DAYS" '.[] | select(.CreatedAt != null) | ((now - (.CreatedAt | fromdateiso8601)) / 86400 | floor) as $a | select($a >= $days) | "\($a)\t\(.Name)"' \
+      | while IFS=$'\t' read -r age name; do
+      echo "Removing volume $name ($age d)"
+      docker volume rm "$name" >/dev/null
+    done
+
     # Stop the Docker service to prevent errors during workspace destroy.
     sudo service docker stop
   EOT
@@ -641,6 +657,26 @@ resource "coder_script" "install-deps" {
   EOT
 }
 
+resource "coder_script" "go-cache-cleanup-cron" {
+  agent_id     = coder_agent.dev.id
+  display_name = "Go Build Cache Cleanup Cron"
+  icon         = "${data.coder_workspace.me.access_url}/emojis/1f9f9.png" // 🧹
+  cron         = "0 ${local.cache_cleanup_minute} ${local.cache_cleanup_hour} * * *"
+  script       = <<-EOT
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    cache_dir=$(go env GOCACHE)
+    echo "Cleaning Go build cache entries not used in the last 2 days..."
+    before=$(du -s "$cache_dir" 2>/dev/null | awk '{print $1}')
+    find "$cache_dir" -type f -mtime +2 -delete
+    find "$cache_dir" -type d -empty -delete
+    after=$(du -s "$cache_dir" 2>/dev/null | awk '{print $1}')
+    freed=$(( (before - after) / 1024 ))
+    echo "Freed $${freed}MB from Go build cache."
+  EOT
+}
+
 resource "coder_devcontainer" "coder" {
   count            = data.coder_parameter.devcontainer_autostart.value ? data.coder_workspace.me.start_count : 0
   agent_id         = coder_agent.dev.id