The bpg/proxmox provider has to reach london-a's API and node, which only
live on the tailnet, during plan and apply. Add a setup-tailnet composite
action (Tailscale via the CI OAuth client + the deploy SSH key in an agent)
and use it in the terraform plan/apply and validate workflows. Pin the
provider's node SSH address to london-a's Tailscale IP so it isn't reached
via the API-reported LAN address.
The SOPS install + version, the decrypt loop, the OpenTofu version, and
the Backblaze backend-credential extraction were copy-pasted across
terraform.yml (twice), validate-terraform.yml, and _deploy-core.yml.
A version bump meant editing the same string in up to four places and
was easy to do partially.
Pull them into three local composite actions so each is defined once:
- setup-tofu (pins OpenTofu version)
- sops-decrypt (installs SOPS, decrypts *.enc.* in place)
- tofu-backend-creds (exports Backblaze S3 creds to GITHUB_ENV)
Behaviour is unchanged; sops-decrypt also matches *.enc.env everywhere
(previously only _deploy-core did), which is a no-op in terraform/.
* ci: serialize infra runs and enable terraform state locking
Add concurrency guards to the terraform and deploy-on-merge workflows so
two merges in quick succession can't run against the same state or the
same hosts at once (queue, never cancel an in-flight run).
Enable native S3 state locking (use_lockfile) on the Backblaze B2 backend,
which needs OpenTofu 1.10+, so bump the CI tofu version 1.9.0 -> 1.10.10
and the required_version constraint to >= 1.10.0.
* ci: bump tofu to 1.10.10 in the validate workflow too
Missed this one in the last commit — the PR-time validate still pinned
1.9.0, which trips the new required_version >= 1.10.0 constraint.
* ci: drop use_lockfile — Backblaze B2 can't do native state locking
B2's S3 API returns 501 NotImplemented for the conditional PutObject that
use_lockfile relies on, so tofu plan/apply fails to acquire the lock.
Revert the lockfile and the 1.10 version bump it required; rely on the
concurrency guard to serialize applies instead. Left a note in the
backend block so this isn't re-attempted.
