Roll out SSH deployment archives using releases and an atomic current symlink

[shyim]

Parent: #1553 (under #1009).

User story

As a developer using SSH hosting, I want to activate an existing archive through a versioned release directory, so that preparation can finish before the running application's code is switched.

Dependencies and current status

#1554 provides deployment creation; archives produced by deployment package archive are also valid inputs. An implementation exists in the current working branch; review and merge are pending.

Acceptance criteria

• project deployment rollout <local-archive> -e <environment> uses the supplied archive without rebuilding it.
• for deployment situations/commands,ssh.directory is an absolute path ending in /current; releases, shared and CLI metadata are siblings beneath its parent.
• Validate archive paths, entry types and contained symlinks locally; verify the uploaded archive checksum before extraction.
• Hold a remote process-owned deployment lock across upload, preparation and activation. Concurrent attempts fail clearly.
• Create a unique release, link the default shared runtime paths, run Deployment Helper, ensure install.lock, and run pre-rollout system checks before activation.
• Respect existing releases and shared data. Refuse to replace a real current directory or silently migrate data out of a live release.
• Atomically rename a prepared symlink onto current; repeated rollout of the same deployment creates a distinct rollout reference.
• Failed preparation preserves current. Client disconnect before activation authorization cannot cause a later switch; a lost connection during activation reports that the active release must be inspected.
• Retain old/failed releases and useful rollout metadata; remove owned temporary uploads and release the lock on failure.
• Send helper output to stderr and print the successful rollout reference to stdout.
• Document PHP/tar/Deployment Helper prerequisites and the distinction between atomic activation and full zero downtime.
• Exercise the actual remote PHP preparation script with local SSH fixtures, covering repeat rollout, shared-data preservation, helper/check failures, corrupt uploads, locking and disconnect handling.

Out of scope

Configurable shared-path lists (separate child issue), history/rollback commands, database rollback, automatic pruning, and universal worker/OPcache restart behavior.

Readiness checklist

• Acceptance criteria are defined.
• Backward compatibility: deployment commands remain experimental behind the deployment build tag.
• User-facing help/documentation reviewed.
• Tests added or adjusted and reviewed.