Foundation for the EIC-based terminal handler (#1528). The tenant's
workspace-server needs to map workspace_id → EC2 instance_id to open
an SSH session, but CPProvisioner.Start returned the instance id only
for logging — it was never written anywhere. This PR adds the column
and writes it at provision time.
Scope kept intentionally small: no terminal code yet. The follow-up
PR will consume this column from the terminal handler.
What's here:
- migrations/038_workspace_instance_id — nullable TEXT column on
workspaces, partial index on non-null for fast lookup
- workspace_provision.go — UPDATE after CPProvisioner.Start; failure
logs but doesn't fail provisioning (row just lacks instance_id and
terminal falls back to the existing not-reachable error)
- docs/infra/workspace-terminal.md — full design for the terminal
flow: EIC vs SSM comparison, IAM policy JSON, SG rules, key
lifetime, failure modes, rollout checklist
Refs: #1528
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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