Effect v3 to v4 Migration

Drive an Effect v3 → v4 migration from the generated migration reference that ships in the Effect repo. Every rename, removal, and signature change is answered by upstream data — do not guess replacements.

Workflow

Work through these steps in order; each one is detailed in the section named.

1. Set up and validate the local checkouts — two shallow clones; verify any pre-existing .repos/effect before trusting it. See Setup: Local Checkouts.
2. Read MIGRATION.md and ls .repos/effect/migration/ for the background and guide index. See Reading Order.
3. Migrate package.json — remove consolidated packages, align every remaining Effect package on one v4 version. Do this before type-checking, or the first run drowns in unresolved-import noise from packages that no longer exist. See Repo-Level Changes.
4. Run the project's type-check (e.g. tsc --noEmit) to get the initial error inventory.
5. Iterate until the type-check is clean. For each error, resolve the API through the lookup discipline — search migration/v3-to-v4.md for the symbol, escalate per Reading Order — then fix the call site, delegating per-file fixes to sub-agents per Delegating to Sub-Agents. Never silence an error instead of resolving it; see Hard Prohibitions.
6. Finish — type-check clean; run tests and report their outcome honestly (not a gate); write the final summary. See Done Condition.

Setup: Local Checkouts

The migration is driven from two shallow, single-branch clones of the canonical Effect repo: