Devcontainers: As a side-effect of deleting agents, it's possible for the stats collector to become sad

[mafredri]

I did not investigate how this state was achieved, but it happened in my dev environment and it seems plausible that customer could trigger it as well.

[API] 2025-06-10 14:27:13.146 [erro]  coderd.workspaceapps.stats_collector: failed to flush workspace app stats ...
[API] error= report workspace app stats from backlog failed:
[API] github.com/coder/coder/v2/coderd/workspaceapps.(*StatsCollector).flush
[API] /home/coder/coder/coderd/workspaceapps/stats.go:263
[API] - insert workspace app stats failed:
[API] github.com/coder/coder/v2/coderd/workspacestats.(*Reporter).ReportAppStats
[API] /home/coder/coder/coderd/workspacestats/reporter.go:116
[API] - execute transaction:
[API] github.com/coder/coder/v2/coderd/database.(*sqlQuerier).runTx
[API] /home/coder/coder/coderd/database/db.go:213
[API] - pq: insert or update on table "workspace_app_stats" violates foreign key constraint "workspace_app_stats_agent_id_fkey"

Steps to reproduce (somewhat unknown but potentially some or all of these):

1. Run workspace with devcontainer and sub agents
2. Recreate devcontainer but fail to delete sub agent (inject/stop race)
3. Restart workspace
4. Recreate devcontainer
5. Potentially observe the above in coderd logs

[mafredri]

Same problem, but from the other side:

error= delete existing subagent failed:
               github.com/coder/coder/v2/agent/agentcontainers.(*API).maybeInjectSubAgentIntoContainerLocked
                   /home/coder/coder/agent/agentcontainers/api.go:1091
             - pq: update or delete on table "workspace_agents" violates foreign key constraint "workspace_app_stats_agent_id_fkey" on table "workspace_app_stats"
                storj.io/drpc/drpcwire.UnmarshalError:26
                storj.io/drpc/drpcstream.(*Stream).HandlePacket:224
                storj.io/drpc/drpcmanager.(*Manager).manageReader:247