test: decouple R2/D1 bindings from wrangler.toml (forks that drop R2 keep green CI)

[poterpan]

Problem

R2 is optional in production — wrangler.toml's [[r2_buckets]] block carries a comment saying it can be removed, and env.ts types BUCKET? accordingly. But the Vitest pool read bindings straight from wrangler.toml (wrangler: { configPath: "./wrangler.toml" }). A fork that followed the "remove R2" instruction got env.BUCKET === undefined, and 10 storage-suite tests failed — even though the deployed Worker degraded gracefully.

Our own CI never caught this because the committed wrangler.toml keeps the R2 binding, so we never exercised the path we tell forkers to take. (Reported by a downstream fork; confirmed by reproducing locally.)

Fix

Declare the Worker's bindings (DB, BUCKET) via miniflare options in vitest.config.ts instead of relying on wrangler.toml for them:

miniflare: {
  bindings: { TEST_MIGRATIONS: migrations },
  d1Databases: ["DB"],
  r2Buckets: ["BUCKET"],
},

Rationale: binding shape is a code contract (src references env.DB/env.BUCKET), so the test harness should own it — not the deployment-specific, fork-editable wrangler.toml. compatibility_date/compatibility_flags + [vars] still come from wrangler.toml (preserves prod-fidelity). miniflare options take precedence over and merge with the wrangler config, so this is conflict-free when wrangler.toml also defines the bindings.

The R2-absent runtime path stays covered by the existing env.BUCKET = undefined tests (settle / retention / upload / admin). Added clarifying comments to smoke.test.ts and env.d.ts explaining why R2 is always present in tests.

Verification

Reproduced the fork's exact failure by commenting out [[r2_buckets]] locally:

• Pre-fix, R2 removed: 8 files / 10 tests fail (env.BUCKET undefined) — matches the fork's CI.
• Post-fix, R2 removed: 179/179 pass.
• Post-fix, R2 present (our config): 179/179 pass, typecheck clean.

Independent review (Codex) confirmed the diagnosis and that miniflare.r2Buckets is the correct option with safe merge semantics.