free legacy soft-deleted workflow names

[elias-ba]

Description

A one-off release task to free the names of workflows soft-deleted before merges renamed on delete. They still hold their original name, which the uniqueness rule uses to block a later merge from recreating it (~900 such workflows in prod). #4842 stops new ones forming; this clears the existing ones.

Lightning.Release.backfill_deleted_workflow_names/1 (via bin/backfill_deleted_workflow_names) renames each to name_del, reusing the app's existing logic. Idempotent, with a dry_run: true option.

Validation steps

In iex -S mix, seed a few soft-deleted workflows including a collision:

alias Lightning.Repo
alias Lightning.Projects.Project
alias Lightning.Workflows.Workflow

now = DateTime.utc_now() |> DateTime.truncate(:second)
project = Repo.insert!(%Project{name: "backfill-demo"})

# never-renamed soft-deletes
Repo.insert!(%Workflow{project_id: project.id, name: "Patient Sync", deleted_at: now})
Repo.insert!(%Workflow{project_id: project.id, name: "Report", deleted_at: now})
# collision: "Report_del" is already taken
Repo.insert!(%Workflow{project_id: project.id, name: "Report_del", deleted_at: now})
# control: a live workflow, should stay untouched
Repo.insert!(%Workflow{project_id: project.id, name: "Live One"})

Then:

1. Lightning.Release.backfill_deleted_workflow_names(dry_run: true) reports the count and writes nothing.
2. Lightning.Release.backfill_deleted_workflow_names() frees the names: Patient Sync becomes Patient Sync_del, Report becomes Report_del1 (since Report_del is taken), Live One is untouched.
3. Re-running returns {:ok, 0}.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.4%. Comparing base (bc12040) to head (a02428b).

Additional details and impacted files

@@                   Coverage Diff                   @@
##           sandbox-merge-followups   #4844   +/-   ##
=======================================================
  Coverage                     90.4%   90.4%           
=======================================================
  Files                          444     444           
  Lines                        22632   22632           
=======================================================
  Hits                         20453   20453           
  Misses                        2179    2179           

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[github-actions]

Security Review ✅

• S0 (project scoping): N/A — the only data-touching change is a release-time operator task (lib/lightning/release.ex:80) invoked via bin/backfill_deleted_workflow_names; it intentionally scans all soft-deleted workflows, and the collision lookup in Workflows.resolve_name_for_pending_deletion/1 already filters by project_id (lib/lightning/workflows.ex:779).
• S1 (authorization): N/A — no new LiveView events, controller actions, or channel handlers; the new entrypoint is a shell wrapper requiring operator/release-image access, and the sandbox log change at lib/lightning/projects/sandboxes.ex:214-235 does not alter any auth gate.
• S2 (audit trail): PASS — the rename is a corrective backfill on rows whose original soft-delete was already audited via Audit.marked_for_deletion in Workflows.mark_for_deletion/3 (lib/lightning/workflows.ex:725), so no new state-transition audit is required for the operator-time name freeing.

[elias-ba]

Closing this. The team's conclusion is that the real fix is the missing workflow purge lifecycle (#4163), not a one-off backfill. Renaming the existing rows just patches one symptom (merge name collisions); #4163 will purge soft-deleted workflows properly once their history has aged out under the project's retention, and can weigh the partial-index option that removes the rename approach altogether. Folding the intent into #4163 rather than shipping the bandaid.