backfill: database handles are published on globalThis #625

#385 wires the backfill modules to the database through globals:

// src/db.ts
;(globalThis as any).__lens_prisma = prisma
;(globalThis as any).__lens_pgPool = pgPool

// src/backfill/gaps.ts
function getPrisma() { return (globalThis as any).__lens_prisma }

Why it was done this way, and it is a real constraint. src/backfill/gaps.ts must not import ../db at module load. Several suites mock ../config only partially, and importing db.ts evaluates config.db.url at load time — so an eager import makes unrelated tests fail with Cannot read properties of undefined (reading 'url'). The globals are a decoupling seam, not laziness.

Why it is still worth changing. src/db.ts runs in the API process, not just the CLI, so every request handler shares a process where a live Prisma client and pg pool are reachable as globalThis.__lens_prisma by any code at all — including a dependency that never imported them. It is also untyped on both ends, so a refactor of db.ts will not surface here.

What I tried and why it is not a quick fix. I attempted two versions while merging and reverted both:

1. Importing the handles in gaps.ts with the global as an override — breaks 6 suites on the load-time config.db.url evaluation described above.
2. Moving the installation into scripts/backfill.ts and making the accessors throw when absent — breaks 33 suites, because the API routes reach gaps.ts without installing anything.

So it needs a deliberate approach rather than an in-flight patch. Options worth weighing:

• Make src/db.ts lazy — build the client on first use rather than at module load — which removes the reason for the seam entirely and is probably the real fix.
• Pass the handles in as arguments to the backfill functions, so the dependency is explicit and the tests inject rather than mock.
• Keep the seam but confine it: a small src/backfill/handles.ts with typed getters and a setter, so at least it is typed, greppable and not on globalThis.

Not urgent — the current arrangement works and the feature is live. Worth doing before anything else starts reading those globals, because every new reader makes it harder to remove.