chore: upgrade to Effect 4.0.0 and Alchemy 2.0.0-beta.80

[K-Mistele]

Moves fold from the Effect 4.0.0 release candidate (rc.112) to the stable 4.0.0 release. Alchemy beta.80 requires effect@^4.0.0, so it moves with it; @effect/tsgo goes to 0.48.0.

Versions

Package	Before	After
effect, @effect/platform-node, @effect/platform-bun, @effect/vitest	4.0.0-rc.112	4.0.0
alchemy	2.0.0-beta.76	2.0.0-beta.80
@effect/tsgo	0.47.0	0.48.0

What 4.0.0 required

• Module paths: effect/unstable/* became effect/* (effect/http, effect/ai, effect/cli, ...). This is most of the diff.
• Renames:
  • Config.string / Config.redacted → Config.String / Config.Redacted.
  • CLI Flag constructors became PascalCase, with choice → Literals and integer → Int.
  • Schema.isStartsWith → Schema.isStartingWith.
  • LanguageModel.Service → LanguageModel.LanguageModel.
  • FileSystem.Size → ByteSize.bytes.
  • effect/Encoding → Base64 / Base64Url from effect/encoding.
• Vendored AI providers (effect-ai-openai, effect-ai-anthropic, effect-ai-openai-compat): upstream's rc.112 → 4.0.0 changes were applied with a three-way merge, keeping the HumanLayer delta listed in each UPSTREAM.md. Each UPSTREAM.md and the openai-compat checksums now pin 4.0.0. The openai-compat files in UPSTREAM.sha256 were checked to match the 4.0.0 tarball byte for byte.

Choices worth a look

• unstableApiUsage is off in tsconfig.json and .oxlintrc.jsonc. 4.0.0 marks effect/ai, effect/http and the other moved modules as unstable. fold is built on them, and the new diagnostic produced about 1,500 warnings and failed the declaration build.

• makeBrandedId has one type assertion. Schema.brand now accepts only a single literal brand name. makeBrandedId computes the name at runtime, from brand or the prefix, so it asserts the overload's literal type once, with a SAFETY: comment. Brands are type-only at runtime in 4.0.0, and the public API is unchanged.

• AnyTool in ToolsetService.ts. In 4.0.0, a tool's parameter-encoding services reach streamText, and its handler services reach the handler's start. With Tool.Any both come out as unknown. AnyTool states that fold's tool schemas need no services and its handlers need only the per-call services. ToolsetService.handle now declares those services on the outer effect too; ToolRuntime already provides them there.

• A flaky test, fixed. In 4.0.0, FileSystem.stat reads file times in nanoseconds and drops the fraction of a millisecond. The session-summary fast-path test reset a log's time from Node's statSync, and utimesSync can store that a hair early. Effect then read the previous millisecond, about half the time, and the cache missed. It failed 4 times in 10 here and 0 in 10 on main. The test now sets the time half a millisecond past the recorded one, and passed 20 of 20. Production code isn't affected, because the cache compares Effect's readings with each other.

Checks

bun run typecheck, bun run lint, bun run format:check and bun run test all pass locally:

• fold-core: 331 tests
• fold-agent: 273
• fold-cli: 119
• fold-codex: 44
• examples and the other packages: the rest

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