From 446a986fabd1329d6bbfcb5b4f8d7c30d2372e35 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Sat, 3 Oct 2026 23:43:29 +0000
Subject: [PATCH 1/5] internal(ci): Fail open on esmodule relevance and speed
 up rest legacy types

The esmodule relevance flag now uses a denylist of provably irrelevant
paths, so new inputs run the esmodule jobs by default. rest's legacy
types build uses scripts/build-legacy-types.sh (direct downlevel-dts,
d.ts-only copies) with --newer-overlays-last to keep its overlay order;
ts4.0/ts4.1 output is byte-identical (8.6s -> 4.5s locally).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EEcQdob4nGVuMq91oUHC2V
---
 .circleci/config.yml          |  5 +++--
 .cursor/rules/ci-config.mdc   |  4 ++--
 packages/rest/package.json    |  4 +---
 scripts/build-legacy-types.sh | 22 ++++++++++++++++++----
 4 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 06221312b2f3..374a1422ea6d 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -85,8 +85,9 @@ jobs:
             elif git -c core.quotePath=off diff --no-renames --name-only "${DIFF_RANGE}" > /tmp/ci-changed-files; then
               echo "Changed files:"
               cat /tmp/ci-changed-files
-              if ! grep -Eq \
-                '^(\.circleci/config\.yml|package\.json$|tsconfig[^/]*\.json$|babel\.config\.js$|\.yarnrc\.yml$|scripts/|yarn\.lock|examples/todo-app/|examples/github-app/|examples/normalizr-relationships/|packages/)' /tmp/ci-changed-files; then
+              # Denylist (fail open): only paths provably outside every esmodule
+              # job's inputs can skip them, so a new input dir runs by default.
+              if ! grep -Evq '^(website/|docs/|\.changeset/|\.cursor/|\.agents/|\.claude/|\.github/|\.vscode/|plans/|__tests__/|[^/]+\.md$|eslint\.config\.mjs$|jest\.config\.js$|examples/[^/]+\.md$|examples/(benchmark|benchmark-react|coin-app|nextjs|normalizr-github|normalizr-redux|test-bundlesize|vue-todo-app)/)' /tmp/ci-changed-files; then
                 echo "No relevant esmodule-related changes; downstream esmodule jobs will halt."
                 ESMODULE_RELEVANT=false
               fi
diff --git a/.cursor/rules/ci-config.mdc b/.cursor/rules/ci-config.mdc
index 490a6482dd4e..342924efefe1 100644
--- a/.cursor/rules/ci-config.mdc
+++ b/.cursor/rules/ci-config.mdc
@@ -10,9 +10,9 @@ alwaysApply: false
 
 - Jest `--maxWorkers` is pinned per job to the `resource_class` vCPU count (large = 4, medium = 2) because docker containers report the host's CPUs via `os.cpus()`. Exception: the ReactNative `unit_tests` run is deliberately uncapped — its suites are fake-timer-wait dominated and capping workers flakes 5s test timeouts.
 - Jobs halt via the `halt-unless-relevant-change` command based on flags computed once in `setup` (`.ci-esmodule-relevant`, `.ci-tests-relevant`) and transported via `save_cache`/`restore_cache` (keyed on `CIRCLE_SHA1`) so jobs can halt before paying `attach_workspace`. Missing/unreadable flags fail open (jobs run). On the default branch both flags are always true (a push may carry several commits). The diff uses `--no-renames` so moving a file out of a relevant dir still counts.
-  - `esmodule`: the path regex must cover every path the esmodule jobs build (currently `examples/todo-app`, `examples/github-app`, `examples/normalizr-relationships`, `packages/`, root `package.json`, root `tsconfig*.json`, `babel.config.js`, `.yarnrc.yml`, `scripts/`, `yarn.lock`, the config itself).
+  - `esmodule` (validate-esmodule-browser-build, esmodule-types*): a denylist, so new paths fail open. False only when every changed path is provably outside the esmodule jobs' inputs: the `tests` denylist plus `.vscode/`, `plans/`, root `__tests__/` (excluded by every `tsconfig.compile.json`), `eslint.config.mjs`, `jest.config.js`, `examples/*.md`, and examples the jobs never build (`benchmark`, `benchmark-react`, `coin-app`, `nextjs`, `normalizr-github`, `normalizr-redux`, `test-bundlesize`, `vue-todo-app`). Only add a path if no esmodule job (or the `setup` builds feeding them) reads it.
   - `tests` (lint, typecheck, unit_tests, node_matrix): false only when every changed path is docs/website/tooling (`website/`, `docs/`, `.changeset/`, `.cursor/`, `.agents/`, `.claude/`, `.github/`, root `*.md`), except `website/src/components/Playground/` (has unit tests). When both flags are false, `setup` halts before install.
-- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently.
+- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; rest passes `--newer-overlays-last` because its newer `src-*-types` must replace the downleveled lib files (endpoint/normalizr copy them before downleveling). Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it).
 - Never `git fetch --depth` the base branch in the relevance check: a shallow fetch severs the merge base and the three-dot diff fails.
 - Changing root `package.json` `workspaces` requires updating the `setup` job's workspace trimming step.
 
diff --git a/packages/rest/package.json b/packages/rest/package.json
index 2d66e7ee8eb6..3009c284831d 100644
--- a/packages/rest/package.json
+++ b/packages/rest/package.json
@@ -123,9 +123,7 @@
     "build:js:browser": "BROWSERSLIST_ENV=legacy yarn g:rollup",
     "build:bundle": "yarn g:runs build:js:\\* && echo '{\"type\":\"commonjs\"}' > dist/package.json",
     "build:clean": "yarn g:clean ts4.0 ts4.1 index.d.ts next.d.ts",
-    "build:legacy-types": "yarn g:runp build:legacy-types:4.0 build:legacy-types:4.1",
-    "build:legacy-types:4.0": "yarn g:downtypes lib ts4.0 --to=4.0 && yarn g:copy --up 1 ./src-4.1-types/**/*.d.ts ./ts4.0/ && yarn g:copy --up 1 ./src-4.0-types/**/*.d.ts ./ts4.0",
-    "build:legacy-types:4.1": "yarn g:downtypes lib ts4.1 --to=4.1 && yarn g:copy --up 1 ./src-4.1-types/**/*.d.ts ./ts4.1",
+    "build:legacy-types": "yarn g:legacy-types --newer-overlays-last 4.1 4.0",
     "build": "run build:lib && run build:legacy:lib && run build:bundle",
     "dev": "NODE_ENV=production BROWSERSLIST_ENV='2020' POLYFILL_TARGETS='chrome>88,safari>14' yarn g:babel --out-dir lib -w",
     "prepare": "run build:lib",
diff --git a/scripts/build-legacy-types.sh b/scripts/build-legacy-types.sh
index 9e5be7dab35c..97c292185b74 100755
--- a/scripts/build-legacy-types.sh
+++ b/scripts/build-legacy-types.sh
@@ -1,9 +1,17 @@
 #!/bin/bash
 set -e
 
+# --newer-overlays-last: copy earlier versions' custom types after the
+# downleveled lib instead of before, so they replace colliding lib files.
+newer_last=false
+if [ "$1" = "--newer-overlays-last" ]; then
+    newer_last=true
+    shift
+fi
+
 # Check if at least one directory is provided
 if [ $# -eq 0 ]; then
-    echo "Usage: $0 <version1> [version2] ..."
+    echo "Usage: $0 [--newer-overlays-last] <version1> [version2] ..."
     exit 1
 fi
 
@@ -22,17 +30,23 @@ copy_types() {
 
 # Custom types for a version also apply to every version listed after it,
 # so each output dir gets (in order): earlier versions' custom types, the
-# downleveled lib, then its own custom types. Each output dir only depends on
-# lib and src-*-types, so versions build concurrently.
+# downleveled lib, then its own custom types (with --newer-overlays-last, the
+# downleveled lib comes first). Each output dir only depends on lib and
+# src-*-types, so versions build concurrently.
 build_version() {
     local version="$1"
     shift
     mkdir -p "./ts$version"
+    if [ "$newer_last" = true ]; then
+        "$downlevel_dts" lib "ts$version" --to="$version"
+    fi
     for earlier in "$@"
     do
         copy_types "./src-$earlier-types" "./ts$version"
     done
-    "$downlevel_dts" lib "ts$version" --to="$version"
+    if [ "$newer_last" = false ]; then
+        "$downlevel_dts" lib "ts$version" --to="$version"
+    fi
     copy_types "./src-$version-types" "./ts$version"
 }
 

From 60e36284957a338c402d2d0bd3a04d261c2bcc3a Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Sun, 4 Oct 2026 02:37:03 +0000
Subject: [PATCH 2/5] internal(ci): Simplify legacy types overlay order and
 share docs-only paths

Downlevel always runs first; --inherit-newer-overlays (rest) then applies
earlier versions' custom types. Without the flag those copies were always
overwritten by downlevel-dts, so endpoint/normalizr output is unchanged
(ts*/ byte-identical). The esmodule and tests relevance checks now share
one DOCS_ONLY path list.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EEcQdob4nGVuMq91oUHC2V
---
 .circleci/config.yml          |  6 ++++--
 .cursor/rules/ci-config.mdc   |  4 ++--
 packages/rest/package.json    |  2 +-
 scripts/build-legacy-types.sh | 36 +++++++++++++++--------------------
 4 files changed, 22 insertions(+), 26 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 374a1422ea6d..86d6393a13d2 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -85,15 +85,17 @@ jobs:
             elif git -c core.quotePath=off diff --no-renames --name-only "${DIFF_RANGE}" > /tmp/ci-changed-files; then
               echo "Changed files:"
               cat /tmp/ci-changed-files
+              # Docs/website/tooling paths; both flags below are denylists over it.
+              DOCS_ONLY='website/|docs/|\.changeset/|\.cursor/|\.agents/|\.claude/|\.github/|[^/]+\.md$'
               # Denylist (fail open): only paths provably outside every esmodule
               # job's inputs can skip them, so a new input dir runs by default.
-              if ! grep -Evq '^(website/|docs/|\.changeset/|\.cursor/|\.agents/|\.claude/|\.github/|\.vscode/|plans/|__tests__/|[^/]+\.md$|eslint\.config\.mjs$|jest\.config\.js$|examples/[^/]+\.md$|examples/(benchmark|benchmark-react|coin-app|nextjs|normalizr-github|normalizr-redux|test-bundlesize|vue-todo-app)/)' /tmp/ci-changed-files; then
+              if ! grep -Evq "^(${DOCS_ONLY}|\.vscode/|plans/|__tests__/|eslint\.config\.mjs$|jest\.config\.js$|examples/[^/]+\.md$|examples/(benchmark|benchmark-react|coin-app|nextjs|normalizr-github|normalizr-redux|test-bundlesize|vue-todo-app)/)" /tmp/ci-changed-files; then
                 echo "No relevant esmodule-related changes; downstream esmodule jobs will halt."
                 ESMODULE_RELEVANT=false
               fi
               # Docs/website/tooling-only changes can't affect lint, typecheck or
               # unit tests (Playground has unit tests, so it stays relevant).
-              if ! grep -Evq '^(website/|docs/|\.changeset/|\.cursor/|\.agents/|\.claude/|\.github/|[^/]+\.md$)' /tmp/ci-changed-files \
+              if ! grep -Evq "^(${DOCS_ONLY})" /tmp/ci-changed-files \
                 && ! grep -q '^website/src/components/Playground/' /tmp/ci-changed-files; then
                 echo "Only docs/website/tooling paths changed; test jobs will halt."
                 TESTS_RELEVANT=false
diff --git a/.cursor/rules/ci-config.mdc b/.cursor/rules/ci-config.mdc
index 342924efefe1..5db8838975a5 100644
--- a/.cursor/rules/ci-config.mdc
+++ b/.cursor/rules/ci-config.mdc
@@ -10,9 +10,9 @@ alwaysApply: false
 
 - Jest `--maxWorkers` is pinned per job to the `resource_class` vCPU count (large = 4, medium = 2) because docker containers report the host's CPUs via `os.cpus()`. Exception: the ReactNative `unit_tests` run is deliberately uncapped — its suites are fake-timer-wait dominated and capping workers flakes 5s test timeouts.
 - Jobs halt via the `halt-unless-relevant-change` command based on flags computed once in `setup` (`.ci-esmodule-relevant`, `.ci-tests-relevant`) and transported via `save_cache`/`restore_cache` (keyed on `CIRCLE_SHA1`) so jobs can halt before paying `attach_workspace`. Missing/unreadable flags fail open (jobs run). On the default branch both flags are always true (a push may carry several commits). The diff uses `--no-renames` so moving a file out of a relevant dir still counts.
-  - `esmodule` (validate-esmodule-browser-build, esmodule-types*): a denylist, so new paths fail open. False only when every changed path is provably outside the esmodule jobs' inputs: the `tests` denylist plus `.vscode/`, `plans/`, root `__tests__/` (excluded by every `tsconfig.compile.json`), `eslint.config.mjs`, `jest.config.js`, `examples/*.md`, and examples the jobs never build (`benchmark`, `benchmark-react`, `coin-app`, `nextjs`, `normalizr-github`, `normalizr-redux`, `test-bundlesize`, `vue-todo-app`). Only add a path if no esmodule job (or the `setup` builds feeding them) reads it.
+  - `esmodule` (validate-esmodule-browser-build, esmodule-types*): a denylist, so new paths fail open. False only when every changed path is provably outside the esmodule jobs' inputs: the shared `DOCS_ONLY` paths (also the `tests` denylist) plus `.vscode/`, `plans/`, root `__tests__/` (excluded by every `tsconfig.compile.json`), `eslint.config.mjs`, `jest.config.js`, `examples/*.md`, and examples the jobs never build (`benchmark`, `benchmark-react`, `coin-app`, `nextjs`, `normalizr-github`, `normalizr-redux`, `test-bundlesize`, `vue-todo-app`). Only add a path if no esmodule job (or the `setup` builds feeding them) reads it.
   - `tests` (lint, typecheck, unit_tests, node_matrix): false only when every changed path is docs/website/tooling (`website/`, `docs/`, `.changeset/`, `.cursor/`, `.agents/`, `.claude/`, `.github/`, root `*.md`), except `website/src/components/Playground/` (has unit tests). When both flags are false, `setup` halts before install.
-- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; rest passes `--newer-overlays-last` because its newer `src-*-types` must replace the downleveled lib files (endpoint/normalizr copy them before downleveling). Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it).
+- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; rest passes `--inherit-newer-overlays` so its `src-4.1-types` also apply to `ts4.0` (endpoint/normalizr don't pass it; each version gets only its own overlays). Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it).
 - Never `git fetch --depth` the base branch in the relevance check: a shallow fetch severs the merge base and the three-dot diff fails.
 - Changing root `package.json` `workspaces` requires updating the `setup` job's workspace trimming step.
 
diff --git a/packages/rest/package.json b/packages/rest/package.json
index 3009c284831d..63b837a0a850 100644
--- a/packages/rest/package.json
+++ b/packages/rest/package.json
@@ -123,7 +123,7 @@
     "build:js:browser": "BROWSERSLIST_ENV=legacy yarn g:rollup",
     "build:bundle": "yarn g:runs build:js:\\* && echo '{\"type\":\"commonjs\"}' > dist/package.json",
     "build:clean": "yarn g:clean ts4.0 ts4.1 index.d.ts next.d.ts",
-    "build:legacy-types": "yarn g:legacy-types --newer-overlays-last 4.1 4.0",
+    "build:legacy-types": "yarn g:legacy-types --inherit-newer-overlays 4.1 4.0",
     "build": "run build:lib && run build:legacy:lib && run build:bundle",
     "dev": "NODE_ENV=production BROWSERSLIST_ENV='2020' POLYFILL_TARGETS='chrome>88,safari>14' yarn g:babel --out-dir lib -w",
     "prepare": "run build:lib",
diff --git a/scripts/build-legacy-types.sh b/scripts/build-legacy-types.sh
index 97c292185b74..89e972517a49 100755
--- a/scripts/build-legacy-types.sh
+++ b/scripts/build-legacy-types.sh
@@ -1,17 +1,17 @@
 #!/bin/bash
 set -e
 
-# --newer-overlays-last: copy earlier versions' custom types after the
-# downleveled lib instead of before, so they replace colliding lib files.
-newer_last=false
-if [ "$1" = "--newer-overlays-last" ]; then
-    newer_last=true
+# --inherit-newer-overlays: custom types for a version also apply to every
+# version listed after it. Without it each version gets only its own.
+inherit=false
+if [ "$1" = "--inherit-newer-overlays" ]; then
+    inherit=true
     shift
 fi
 
 # Check if at least one directory is provided
 if [ $# -eq 0 ]; then
-    echo "Usage: $0 [--newer-overlays-last] <version1> [version2] ..."
+    echo "Usage: $0 [--inherit-newer-overlays] <version1> [version2] ..."
     exit 1
 fi
 
@@ -28,24 +28,18 @@ copy_types() {
     done
 }
 
-# Custom types for a version also apply to every version listed after it,
-# so each output dir gets (in order): earlier versions' custom types, the
-# downleveled lib, then its own custom types (with --newer-overlays-last, the
-# downleveled lib comes first). Each output dir only depends on lib and
-# src-*-types, so versions build concurrently.
+# Each output dir gets the downleveled lib, then (with --inherit-newer-overlays)
+# earlier versions' custom types, then its own. Each output dir only depends on
+# lib and src-*-types, so versions build concurrently.
 build_version() {
     local version="$1"
     shift
-    mkdir -p "./ts$version"
-    if [ "$newer_last" = true ]; then
-        "$downlevel_dts" lib "ts$version" --to="$version"
-    fi
-    for earlier in "$@"
-    do
-        copy_types "./src-$earlier-types" "./ts$version"
-    done
-    if [ "$newer_last" = false ]; then
-        "$downlevel_dts" lib "ts$version" --to="$version"
+    "$downlevel_dts" lib "ts$version" --to="$version"
+    if [ "$inherit" = true ]; then
+        for earlier in "$@"
+        do
+            copy_types "./src-$earlier-types" "./ts$version"
+        done
     fi
     copy_types "./src-$version-types" "./ts$version"
 }

From 202acbddd39dfe99937731293617c75b0172a8cd Mon Sep 17 00:00:00 2001
From: Nathaniel Tucker <me@ntucker.me>
Date: Sat, 3 Oct 2026 23:17:40 -0400
Subject: [PATCH 3/5] fix(types): Apply newer legacy type overlays to older TS
 outputs (#4138)

* fix(types): Apply newer legacy type overlays to older TS outputs

endpoint and normalizr legacy outputs (ts4.2, ts4.0, ts3.4) now inherit
every newer version's src-*-types overlay, as rest already did. This
replaces the TS 5.4 NoInfer builtin with the NI<T> = T fallback for
TS < 4.8 consumers.

normalizr re-exports memo types by name instead of `export type *`
(TS 5.0 syntax that downlevel-dts leaves as is).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MpCgcZt8G8R5KARZ7z5CKE

* docs(blog): Note legacy TypeScript types fix

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MpCgcZt8G8R5KARZ7z5CKE

---------

Co-authored-by: Claude <noreply@anthropic.com>
---
 .changeset/legacy-ts-noinfer.md            | 22 ++++++++++++++++++
 .cursor/rules/ci-config.mdc                |  2 +-
 packages/normalizr/src/index.ts            |  7 +++++-
 packages/rest/package.json                 |  2 +-
 scripts/build-legacy-types.sh              | 27 ++++++++--------------
 website/blog/2026-10-03-v0.19-batch-set.md |  1 +
 6 files changed, 40 insertions(+), 21 deletions(-)
 create mode 100644 .changeset/legacy-ts-noinfer.md

diff --git a/.changeset/legacy-ts-noinfer.md b/.changeset/legacy-ts-noinfer.md
new file mode 100644
index 000000000000..d27ac8b61936
--- /dev/null
+++ b/.changeset/legacy-ts-noinfer.md
@@ -0,0 +1,22 @@
+---
+'@data-client/endpoint': patch
+'@data-client/normalizr': patch
+'@data-client/rest': patch
+'@data-client/graphql': patch
+'@data-client/react': patch
+'@data-client/vue': patch
+---
+
+Fix types for TypeScript 4.x when `skipLibCheck` is off
+
+TypeScript 4.0 through 4.7 no longer report `Cannot find name 'NoInfer'` from `@data-client/endpoint` or `@data-client/normalizr`, and TypeScript 4.0 through 4.9 no longer report `Only named exports may use 'export type'` from `@data-client/normalizr`.
+
+```ts
+import { Entity } from '@data-client/endpoint';
+import { normalize } from '@data-client/normalizr';
+
+// Before (TypeScript 4.7, skipLibCheck: false):
+//   error TS2304: Cannot find name 'NoInfer'.
+//   error TS1383: Only named exports may use 'export type'.
+// After: no errors
+```
diff --git a/.cursor/rules/ci-config.mdc b/.cursor/rules/ci-config.mdc
index 5db8838975a5..9da0cac5e476 100644
--- a/.cursor/rules/ci-config.mdc
+++ b/.cursor/rules/ci-config.mdc
@@ -12,7 +12,7 @@ alwaysApply: false
 - Jobs halt via the `halt-unless-relevant-change` command based on flags computed once in `setup` (`.ci-esmodule-relevant`, `.ci-tests-relevant`) and transported via `save_cache`/`restore_cache` (keyed on `CIRCLE_SHA1`) so jobs can halt before paying `attach_workspace`. Missing/unreadable flags fail open (jobs run). On the default branch both flags are always true (a push may carry several commits). The diff uses `--no-renames` so moving a file out of a relevant dir still counts.
   - `esmodule` (validate-esmodule-browser-build, esmodule-types*): a denylist, so new paths fail open. False only when every changed path is provably outside the esmodule jobs' inputs: the shared `DOCS_ONLY` paths (also the `tests` denylist) plus `.vscode/`, `plans/`, root `__tests__/` (excluded by every `tsconfig.compile.json`), `eslint.config.mjs`, `jest.config.js`, `examples/*.md`, and examples the jobs never build (`benchmark`, `benchmark-react`, `coin-app`, `nextjs`, `normalizr-github`, `normalizr-redux`, `test-bundlesize`, `vue-todo-app`). Only add a path if no esmodule job (or the `setup` builds feeding them) reads it.
   - `tests` (lint, typecheck, unit_tests, node_matrix): false only when every changed path is docs/website/tooling (`website/`, `docs/`, `.changeset/`, `.cursor/`, `.agents/`, `.claude/`, `.github/`, root `*.md`), except `website/src/components/Playground/` (has unit tests). When both flags are false, `setup` halts before install.
-- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; rest passes `--inherit-newer-overlays` so its `src-4.1-types` also apply to `ts4.0` (endpoint/normalizr don't pass it; each version gets only its own overlays). Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it).
+- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; each `ts<version>/` gets the downleveled `lib`, then every newer version's `src-*-types` overlay, then its own. Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it) unless it intentionally changes published types (then add a changeset).
 - Never `git fetch --depth` the base branch in the relevance check: a shallow fetch severs the merge base and the three-dot diff fails.
 - Changing root `package.json` `workspaces` requires updating the `setup` job's workspace trimming step.
 
diff --git a/packages/normalizr/src/index.ts b/packages/normalizr/src/index.ts
index 3eb4d4da9619..3c6ac4bce05f 100644
--- a/packages/normalizr/src/index.ts
+++ b/packages/normalizr/src/index.ts
@@ -19,7 +19,12 @@ export type {
 export type { NI } from './NoInfer.js';
 export * from './endpoint/types.js';
 export * from './interface.js';
-export type * from './memo/types.js';
+export type {
+  EntityCache,
+  EndpointsCache,
+  DenormGetEntity,
+  IMemoPolicy,
+} from './memo/types.js';
 export * from './Expiry.js';
 export { INVALID } from './denormalize/symbol.js';
 export { validateQueryKey } from './buildQueryKey.js';
diff --git a/packages/rest/package.json b/packages/rest/package.json
index 63b837a0a850..5faf4e204233 100644
--- a/packages/rest/package.json
+++ b/packages/rest/package.json
@@ -123,7 +123,7 @@
     "build:js:browser": "BROWSERSLIST_ENV=legacy yarn g:rollup",
     "build:bundle": "yarn g:runs build:js:\\* && echo '{\"type\":\"commonjs\"}' > dist/package.json",
     "build:clean": "yarn g:clean ts4.0 ts4.1 index.d.ts next.d.ts",
-    "build:legacy-types": "yarn g:legacy-types --inherit-newer-overlays 4.1 4.0",
+    "build:legacy-types": "yarn g:legacy-types 4.1 4.0",
     "build": "run build:lib && run build:legacy:lib && run build:bundle",
     "dev": "NODE_ENV=production BROWSERSLIST_ENV='2020' POLYFILL_TARGETS='chrome>88,safari>14' yarn g:babel --out-dir lib -w",
     "prepare": "run build:lib",
diff --git a/scripts/build-legacy-types.sh b/scripts/build-legacy-types.sh
index 89e972517a49..b54f85420c51 100755
--- a/scripts/build-legacy-types.sh
+++ b/scripts/build-legacy-types.sh
@@ -1,17 +1,9 @@
 #!/bin/bash
 set -e
 
-# --inherit-newer-overlays: custom types for a version also apply to every
-# version listed after it. Without it each version gets only its own.
-inherit=false
-if [ "$1" = "--inherit-newer-overlays" ]; then
-    inherit=true
-    shift
-fi
-
 # Check if at least one directory is provided
 if [ $# -eq 0 ]; then
-    echo "Usage: $0 [--inherit-newer-overlays] <version1> [version2] ..."
+    echo "Usage: $0 <version1> [version2] ..."
     exit 1
 fi
 
@@ -28,19 +20,18 @@ copy_types() {
     done
 }
 
-# Each output dir gets the downleveled lib, then (with --inherit-newer-overlays)
-# earlier versions' custom types, then its own. Each output dir only depends on
-# lib and src-*-types, so versions build concurrently.
+# Versions are listed newest first, and custom types for a version also apply
+# to every version listed after it. So each output dir gets the downleveled lib,
+# then earlier versions' custom types, then its own. Each output dir only
+# depends on lib and src-*-types, so versions build concurrently.
 build_version() {
     local version="$1"
     shift
     "$downlevel_dts" lib "ts$version" --to="$version"
-    if [ "$inherit" = true ]; then
-        for earlier in "$@"
-        do
-            copy_types "./src-$earlier-types" "./ts$version"
-        done
-    fi
+    for earlier in "$@"
+    do
+        copy_types "./src-$earlier-types" "./ts$version"
+    done
     copy_types "./src-$version-types" "./ts$version"
 }
 
diff --git a/website/blog/2026-10-03-v0.19-batch-set.md b/website/blog/2026-10-03-v0.19-batch-set.md
index 77d20541c40c..86180b75057b 100644
--- a/website/blog/2026-10-03-v0.19-batch-set.md
+++ b/website/blog/2026-10-03-v0.19-batch-set.md
@@ -19,6 +19,7 @@ import StackBlitz from '@site/src/components/StackBlitz';
 - Vue [useSuspense()](/vue/api/useSuspense) and [useLive()](/vue/api/useLive) keep the previous data while new arguments load, instead of returning `undefined` ([#4131](https://github.com/reactive/data-client/pull/4131))
 - Vue [useSuspense()](/vue/api/useSuspense), [useDLE()](/vue/api/useDLE) and [useFetch()](/vue/api/useFetch) no longer refetch stale data on every store update, so a `controller.set()` is not overwritten ([#4134](https://github.com/reactive/data-client/pull/4134))
 - Vue [useDLE()](/vue/api/useDLE) and [useCache()](/vue/api/useCache) keep expired `invalidIfStale` data through unrelated store updates instead of getting stuck loading ([#4142](https://github.com/reactive/data-client/pull/4142))
+- Fix `Cannot find name 'NoInfer'` and `export type` errors on TypeScript 4.x with `skipLibCheck` off ([#4138](https://github.com/reactive/data-client/pull/4138))
 
 {/* truncate */}
 

From 182344b63c50709b4d23b6bf65c41ee8ba3b30b3 Mon Sep 17 00:00:00 2001
From: Nathaniel Tucker <me@ntucker.me>
Date: Sat, 3 Oct 2026 23:57:12 -0400
Subject: [PATCH 4/5] fix(types): Fix endpoint/rest legacy type errors with
 skipLibCheck off (#4140)

* fix(types): Apply newer legacy type overlays to older TS outputs

endpoint and normalizr legacy outputs (ts4.2, ts4.0, ts3.4) now inherit
every newer version's src-*-types overlay, as rest already did. This
replaces the TS 5.4 NoInfer builtin with the NI<T> = T fallback for
TS < 4.8 consumers.

normalizr re-exports memo types by name instead of `export type *`
(TS 5.0 syntax that downlevel-dts leaves as is).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MpCgcZt8G8R5KARZ7z5CKE

* docs(blog): Note legacy TypeScript types fix

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MpCgcZt8G8R5KARZ7z5CKE

* fix(types): Fix endpoint/rest legacy type errors with skipLibCheck off

- TS 4.0: unroll RemoveArray and approximate PartialArray (recursive
  conditional types need 4.1) in new src-4.0-types overlays
- TS <4.2: rewrite `abstract new` to `new` in the downleveled output and
  drop the stale src-4.0-types Entity/EntityTypes copies
- TS 4.2: ConstructorInstance<> replaces InstanceType<> on abstract TBase
- TS 4.2-4.4: UnionInstance Args is unconstrained
- TS 4.0-4.5: rest getPage narrows paginationField with Extract<>
- CI: esmodule-types also typechecks a skipLibCheck: false consumer

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AMEHZGboXdMFRkF4D2ktki

* docs(blog): Link #4140 in v0.19 notes

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AMEHZGboXdMFRkF4D2ktki

* refactor(types): Isolate recursive tuple types so the 4.0 overlay is one small file

- RemoveArray and PartialArray move to tupleTypes.ts; the src-4.0-types
  overlay replaces only that module instead of copying endpointTypes/utility
- Legacy build only rewrites files that contain `abstract new (`
- libcheck typetest skips TypeScript's own lib checks
- Split the legacy types bullet in ci-config.mdc

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AMEHZGboXdMFRkF4D2ktki

* internal: Resolve leftover merge conflict in ci-config rule

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AMEHZGboXdMFRkF4D2ktki

* internal: Resolve leftover merge conflict in build-legacy-types.sh

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AMEHZGboXdMFRkF4D2ktki

---------

Co-authored-by: Claude <noreply@anthropic.com>
---
 .changeset/legacy-ts-endpoint-libcheck.md     |  30 ++++
 .circleci/config.yml                          |   2 +
 .cursor/rules/ci-config.mdc                   |   7 +-
 .../todo-app/tsconfig.typetest-libcheck.json  |  16 ++
 examples/todo-app/typetest-libcheck.ts        |  44 +++++
 .../src-4.0-types/schemas/Entity.d.ts         |  45 -----
 .../src-4.0-types/schemas/EntityTypes.d.ts    | 164 ------------------
 .../endpoint/src-4.0-types/tupleTypes.d.ts    |  14 ++
 .../endpoint/src-4.2-types/endpointTypes.d.ts |   7 +-
 packages/endpoint/src/endpointTypes.ts        |   8 +-
 packages/endpoint/src/schema.d.ts             |   4 +-
 packages/endpoint/src/schemas/EntityMixin.ts  |   9 +-
 packages/endpoint/src/schemas/EntityRecord.ts |   8 +-
 packages/endpoint/src/schemas/EntityTypes.ts  |  14 +-
 packages/endpoint/src/tupleTypes.ts           |  16 ++
 packages/endpoint/src/utility.ts              |   7 +-
 packages/rest/src/RestEndpointTypes.ts        |   3 +-
 scripts/build-legacy-types.sh                 |  15 +-
 website/blog/2026-10-03-v0.19-batch-set.md    |   1 +
 19 files changed, 170 insertions(+), 244 deletions(-)
 create mode 100644 .changeset/legacy-ts-endpoint-libcheck.md
 create mode 100644 examples/todo-app/tsconfig.typetest-libcheck.json
 create mode 100644 examples/todo-app/typetest-libcheck.ts
 delete mode 100644 packages/endpoint/src-4.0-types/schemas/Entity.d.ts
 delete mode 100644 packages/endpoint/src-4.0-types/schemas/EntityTypes.d.ts
 create mode 100644 packages/endpoint/src-4.0-types/tupleTypes.d.ts
 create mode 100644 packages/endpoint/src/tupleTypes.ts

diff --git a/.changeset/legacy-ts-endpoint-libcheck.md b/.changeset/legacy-ts-endpoint-libcheck.md
new file mode 100644
index 000000000000..6fde9e1a81a8
--- /dev/null
+++ b/.changeset/legacy-ts-endpoint-libcheck.md
@@ -0,0 +1,30 @@
+---
+'@data-client/endpoint': patch
+'@data-client/rest': patch
+'@data-client/graphql': patch
+---
+
+Fix more TypeScript 4.x errors when `skipLibCheck` is off
+
+[Entity](https://dataclient.io/rest/api/Entity), [Endpoint](https://dataclient.io/rest/api/Endpoint), [Union](https://dataclient.io/rest/api/Union) and [RestEndpoint](https://dataclient.io/rest/api/RestEndpoint) declarations no longer report errors on TypeScript 4.0 through 4.5. On TypeScript 4.0 and 4.1, an `Entity` can be an `Endpoint` schema again.
+
+```ts
+import { Endpoint, Entity, schema } from '@data-client/endpoint';
+
+class User extends Entity {
+  id = '';
+  type = 'users';
+}
+const getUser = new Endpoint(
+  (id: string) => fetch(`/users/${id}`).then(res => res.json()),
+  { schema: User },
+);
+const feed = new schema.Union({ users: User }, 'type');
+
+// Before (TypeScript 4.0, skipLibCheck: false):
+//   error TS2456: Type alias 'RemoveArray' circularly references itself.
+//   error TS2322: Type 'typeof User' is not assignable to type 'EntityInterface<any>'.
+// Before (TypeScript 4.2):
+//   error TS2344: Type 'TBase' does not satisfy the constraint 'new (...args: any) => any'.
+// After: no errors
+```
diff --git a/.circleci/config.yml b/.circleci/config.yml
index 86d6393a13d2..b42b06379396 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -329,6 +329,8 @@ jobs:
             fi
             yarn run tsc --project examples/todo-app/tsconfig.typetest.json
             yarn run tsc --project examples/github-app/tsconfig.typetest.json
+            # skipLibCheck: false, so the legacy typesVersions outputs get checked too
+            yarn run tsc --project examples/todo-app/tsconfig.typetest-libcheck.json
 
   esmodule-types-latest:
     executor: node
diff --git a/.cursor/rules/ci-config.mdc b/.cursor/rules/ci-config.mdc
index 9da0cac5e476..3283a70bfe87 100644
--- a/.cursor/rules/ci-config.mdc
+++ b/.cursor/rules/ci-config.mdc
@@ -12,7 +12,12 @@ alwaysApply: false
 - Jobs halt via the `halt-unless-relevant-change` command based on flags computed once in `setup` (`.ci-esmodule-relevant`, `.ci-tests-relevant`) and transported via `save_cache`/`restore_cache` (keyed on `CIRCLE_SHA1`) so jobs can halt before paying `attach_workspace`. Missing/unreadable flags fail open (jobs run). On the default branch both flags are always true (a push may carry several commits). The diff uses `--no-renames` so moving a file out of a relevant dir still counts.
   - `esmodule` (validate-esmodule-browser-build, esmodule-types*): a denylist, so new paths fail open. False only when every changed path is provably outside the esmodule jobs' inputs: the shared `DOCS_ONLY` paths (also the `tests` denylist) plus `.vscode/`, `plans/`, root `__tests__/` (excluded by every `tsconfig.compile.json`), `eslint.config.mjs`, `jest.config.js`, `examples/*.md`, and examples the jobs never build (`benchmark`, `benchmark-react`, `coin-app`, `nextjs`, `normalizr-github`, `normalizr-redux`, `test-bundlesize`, `vue-todo-app`). Only add a path if no esmodule job (or the `setup` builds feeding them) reads it.
   - `tests` (lint, typecheck, unit_tests, node_matrix): false only when every changed path is docs/website/tooling (`website/`, `docs/`, `.changeset/`, `.cursor/`, `.agents/`, `.claude/`, `.github/`, root `*.md`), except `website/src/components/Playground/` (has unit tests). When both flags are false, `setup` halts before install.
-- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`) build inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path. In CI it builds only endpoint/normalizr/rest outputs for TS >= 4.0 (`LEGACY_MIN_TS=4.0`), since the oldest TS in the `esmodule-types` matrix is 4.0; release builds (`build:types`) still emit every version. `scripts/build-legacy-types.sh` builds each TS version concurrently; each `ts<version>/` gets the downleveled `lib`, then every newer version's `src-*-types` overlay, then its own. Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it) unless it intentionally changes published types (then add a changeset).
+- Legacy TS types (`ci:build:legacy-types`, consumed by `esmodule-types`):
+  - Built inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path.
+  - In CI only endpoint/normalizr/rest outputs for TS >= 4.0 are built (`LEGACY_MIN_TS=4.0`, the oldest TS in the `esmodule-types` matrix); release builds (`build:types`) still emit every version.
+  - `scripts/build-legacy-types.sh` builds each TS version concurrently; each `ts<version>/` gets the downleveled `lib` (with `abstract new` rewritten to `new` below 4.2, which `downlevel-dts` misses), then every newer version's `src-*-types` overlay, then its own. Keep overlays to small single-purpose modules (like `NoInfer.ts`, `tupleTypes.ts`) so whole-file copies can't go stale.
+  - `esmodule-types` also runs `examples/todo-app/tsconfig.typetest-libcheck.json` (`skipLibCheck: false`, `types: []`) so errors inside the legacy outputs fail CI; the other typetests use `skipLibCheck: true`.
+  - Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it) unless it intentionally changes published types (then add a changeset).
 - Never `git fetch --depth` the base branch in the relevance check: a shallow fetch severs the merge base and the three-dot diff fails.
 - Changing root `package.json` `workspaces` requires updating the `setup` job's workspace trimming step.
 
diff --git a/examples/todo-app/tsconfig.typetest-libcheck.json b/examples/todo-app/tsconfig.typetest-libcheck.json
new file mode 100644
index 000000000000..3104ec65ec61
--- /dev/null
+++ b/examples/todo-app/tsconfig.typetest-libcheck.json
@@ -0,0 +1,16 @@
+{
+  // Standalone so it type-checks only @data-client declarations (and their deps)
+  // on every TypeScript in the esmodule-types matrix.
+  "compilerOptions": {
+    "target": "es2020",
+    "module": "esnext",
+    "lib": ["dom", "esnext"],
+    "moduleResolution": "node",
+    "strict": true,
+    "skipLibCheck": false,
+    "skipDefaultLibCheck": true,
+    "types": [],
+    "noEmit": true
+  },
+  "files": ["typetest-libcheck.ts"]
+}
diff --git a/examples/todo-app/typetest-libcheck.ts b/examples/todo-app/typetest-libcheck.ts
new file mode 100644
index 000000000000..ff7a12505085
--- /dev/null
+++ b/examples/todo-app/typetest-libcheck.ts
@@ -0,0 +1,44 @@
+// Type-checks published declarations (including legacy typesVersions outputs)
+// with skipLibCheck: false; see tsconfig.typetest-libcheck.json
+import { Endpoint, Entity, schema } from '@data-client/endpoint';
+import { denormalize, MemoCache, normalize } from '@data-client/normalizr';
+import { resource, RestEndpoint } from '@data-client/rest';
+
+class User extends Entity {
+  id = '';
+  name = '';
+  type = 'users';
+}
+class Post extends Entity {
+  id = '';
+  title = '';
+  author = User.fromJS();
+  static schema = { author: User };
+}
+
+const getUser = new Endpoint(
+  (id: string) => Promise.resolve({ id, name: 'a', type: 'users' }),
+  { schema: User },
+);
+const twoArgs = new Endpoint((a: string, b: number) =>
+  Promise.resolve({ id: a, title: String(b) }),
+);
+const bound = twoArgs.bind(null, 'x');
+bound(5);
+// @ts-expect-error
+bound('wrong');
+
+const feed = new schema.Union({ users: User }, 'type');
+const PostResource = resource({
+  path: '/posts/:id',
+  schema: Post,
+  paginationField: 'cursor',
+});
+PostResource.getList.getPage({ cursor: 'a' });
+const search = new RestEndpoint({ path: '/search' });
+
+const memo = new MemoCache();
+const { result, entities } = normalize(Post, { id: '1', title: 'hi' });
+denormalize(Post, result, entities);
+
+export { getUser, feed, search, memo };
diff --git a/packages/endpoint/src-4.0-types/schemas/Entity.d.ts b/packages/endpoint/src-4.0-types/schemas/Entity.d.ts
deleted file mode 100644
index eb14bb91a7fe..000000000000
--- a/packages/endpoint/src-4.0-types/schemas/Entity.d.ts
+++ /dev/null
@@ -1,45 +0,0 @@
-// we just removed instances of 'abstract new'
-import { AbstractInstanceType } from '../normal.js';
-declare const Entity_base: import("./EntityTypes.js").IEntityClass<new (...args: any[]) => {
-    pk(parent?: any, key?: string, args?: readonly any[]): string | number | undefined;
-}> & (new (...args: any[]) => {
-    pk(parent?: any, key?: string, args?: readonly any[]): string | number | undefined;
-});
-/**
- * Entity defines a single (globally) unique object.
- * @see https://dataclient.io/rest/api/Entity
- */
-export default abstract class Entity extends Entity_base {
-    /** Control how automatic schema validation is handled
-     *
-     * `undefined`: Defaults - throw error in worst offense
-     * 'warn': only ever warn
-     * 'silent': Don't bother with processing at all
-     *
-     * Note: this only applies to non-nested members.
-     */
-    protected static automaticValidation?: 'warn' | 'silent';
-    /** Factory method to convert from Plain JS Objects.
-     *
-     * @see https://dataclient.io/rest/api/Entity#fromJS
-     * @param [props] Plain Object of properties to assign.
-     */
-    static fromJS: <T extends typeof Entity>(this: T, props?: Partial<AbstractInstanceType<T>>) => AbstractInstanceType<T>;
-    /**
-     * A unique identifier for each Entity
-     *
-     * @see https://dataclient.io/rest/api/Entity#pk
-     * @param [value] POJO of the entity or subset used
-     * @param [parent] When normalizing, the object which included the entity
-     * @param [key] When normalizing, the key where this entity was found
-     * @param [args] ...args sent to Endpoint
-     */
-    static pk: <T extends typeof Entity>(this: T, value: Partial<AbstractInstanceType<T>>, parent?: any, key?: string, args?: any[]) => string | number | undefined;
-    /** Do any transformations when first receiving input
-     *
-     * @see https://dataclient.io/rest/api/Entity#process
-     */
-    static process(input: any, parent: any, key: string | undefined, args: any[]): any;
-    static denormalize: <T extends typeof Entity>(this: T, input: any, args: readonly any[], unvisit: (schema: any, input: any) => any) => AbstractInstanceType<T>;
-}
-export {};
diff --git a/packages/endpoint/src-4.0-types/schemas/EntityTypes.d.ts b/packages/endpoint/src-4.0-types/schemas/EntityTypes.d.ts
deleted file mode 100644
index f5e6cb83d627..000000000000
--- a/packages/endpoint/src-4.0-types/schemas/EntityTypes.d.ts
+++ /dev/null
@@ -1,164 +0,0 @@
-// we just removed instances of 'new'
-import type { Schema, IQueryDelegate } from '../interface.js';
-import { AbstractInstanceType } from '../normal.js';
-/**
- * Entity defines a single (globally) unique object.
- * @see https://dataclient.io/rest/api/EntityMixin
- */
-export interface IEntityClass<TBase extends Constructor = any> {
-    toJSON(): {
-        name: string;
-        schema: {
-            [k: string]: Schema;
-        };
-        key: string;
-    };
-    /** Defines nested entities
-     *
-     * @see https://dataclient.io/rest/api/Entity#schema
-     */
-    schema: {
-        [k: string]: Schema;
-    };
-    /** Returns the globally unique identifier for the static Entity
-     *
-     * @see https://dataclient.io/rest/api/Entity#key
-     */
-    key: string;
-    /** Defines indexes to enable lookup by
-     *
-     * @see https://dataclient.io/rest/api/Entity#indexes
-     */
-    indexes?: readonly string[] | undefined;
-    maxEntityDepth?: number | undefined;
-    /**
-     * A unique identifier for each Entity
-     *
-     * @see https://dataclient.io/rest/api/Entity#pk
-     * @param [value] POJO of the entity or subset used
-     * @param [parent] When normalizing, the object which included the entity
-     * @param [key] When normalizing, the key where this entity was found
-     * @param [args] ...args sent to Endpoint
-     */
-    pk<T extends (new (...args: any[]) => IEntityInstance & InstanceType<TBase>) & IEntityClass & TBase>(this: T, value: Partial<AbstractInstanceType<T>>, parent?: any, key?: string, args?: any[]): string | number | undefined;
-    /** Return true to merge incoming data; false keeps existing entity
-     *
-     * @see https://dataclient.io/docs/api/Entity#shouldUpdate
-     */
-    shouldUpdate(existingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, incomingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, existing: any, incoming: any): boolean;
-    /** Determines the order of incoming entity vs entity already in store
-     *
-     * @see https://dataclient.io/docs/api/Entity#shouldReorder
-     * @returns true if incoming entity should be first argument of merge()
-     */
-    shouldReorder(existingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, incomingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, existing: any, incoming: any): boolean;
-    /** Creates new instance copying over defined values of arguments
-     *
-     * @see https://dataclient.io/docs/api/Entity#merge
-     */
-    merge(existing: any, incoming: any): any;
-    /** Run when an existing entity is found in the store
-     *
-     * @see https://dataclient.io/docs/api/Entity#mergeWithStore
-     */
-    mergeWithStore(existingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, incomingMeta: {
-        date: number;
-        fetchedAt: number;
-    }, existing: any, incoming: any): any;
-    /** Run when an existing entity is found in the store
-     *
-     * @see https://dataclient.io/docs/api/Entity#mergeMetaWithStore
-     */
-    mergeMetaWithStore(existingMeta: {
-        expiresAt: number;
-        date: number;
-        fetchedAt: number;
-    }, incomingMeta: {
-        expiresAt: number;
-        date: number;
-        fetchedAt: number;
-    }, existing: any, incoming: any): {
-        expiresAt: number;
-        date: number;
-        fetchedAt: number;
-    };
-    /** Factory method to convert from Plain JS Objects.
-     *
-     * @param [props] Plain Object of properties to assign.
-     */
-    fromJS<T extends (new (...args: any[]) => IEntityInstance & InstanceType<TBase>) & IEntityClass & TBase>(this: T, props?: Partial<AbstractInstanceType<T>>): AbstractInstanceType<T>;
-    /** Called when denormalizing an entity to create an instance when 'valid'
-     *
-     * @param [props] Plain Object of properties to assign.
-     * @see https://dataclient.io/rest/api/Entity#createIfValid
-     */
-    createIfValid<T extends (new (...args: any[]) => IEntityInstance & InstanceType<TBase>) & IEntityClass & TBase>(this: T, props: Partial<AbstractInstanceType<T>>): AbstractInstanceType<T> | undefined;
-    /** Do any transformations when first receiving input
-     *
-     * @see https://dataclient.io/rest/api/Entity#process
-     */
-    process(input: any, parent: any, key: string | undefined, args: any[]): any;
-    normalize(input: any, parent: any, key: string | undefined, args: any[], visit: (...args: any) => any, snapshot: {
-        getEntity: any;
-        setEntity: any;
-    }): any;
-    /** Do any transformations when first receiving input
-     *
-     * @see https://dataclient.io/rest/api/Entity#validate
-     */
-    validate(processedEntity: any): string | undefined;
-    /** Builds a key access the entity without endpoint results
-     *
-     * @see https://dataclient.io/rest/api/Entity#queryKey
-     */
-    queryKey(args: readonly any[], unvisit: any, delegate: IQueryDelegate): any;
-    denormalize<T extends (new (...args: any[]) => IEntityInstance & InstanceType<TBase>) & IEntityClass & TBase>(this: T, input: any, args: readonly any[], unvisit: (schema: any, input: any) => any): AbstractInstanceType<T>;
-    /** All instance defaults set */
-    readonly defaults: any;
-}
-export interface IEntityInstance {
-    /**
-     * A unique identifier for each Entity
-     *
-     * @param [parent] When normalizing, the object which included the entity
-     * @param [key] When normalizing, the key where this entity was found
-     * @param [args] ...args sent to Endpoint
-     */
-    pk(parent?: any, key?: string, args?: readonly any[]): string | number | undefined;
-}
-export type Constructor = new (...args: any[]) => {};
-export type IDClass = new (...args: any[]) => {
-    id: string | number | undefined;
-};
-export type PKClass = new (...args: any[]) => {
-    pk(parent?: any, key?: string, args?: readonly any[]): string | number | undefined;
-};
-type ValidSchemas<TInstance> = {
-    [k in keyof TInstance]?: Schema;
-};
-export type EntityOptions<TInstance extends {}> = {
-    readonly schema?: ValidSchemas<TInstance>;
-    readonly pk?: ((value: TInstance, parent?: any, key?: string) => string | number | undefined) | keyof TInstance;
-    readonly key?: string;
-} & {
-    readonly [K in Extract<keyof IEntityClass, 'process' | 'merge' | 'expiresAt' | 'createIfValid' | 'mergeWithStore' | 'validate' | 'shouldReorder' | 'shouldUpdate'>]?: IEntityClass<new (...args: any[]) => TInstance>[K];
-};
-export interface RequiredPKOptions<TInstance extends {}> extends EntityOptions<TInstance> {
-    readonly pk: ((value: TInstance, parent?: any, key?: string) => string | number | undefined) | keyof TInstance;
-}
-export {};
diff --git a/packages/endpoint/src-4.0-types/tupleTypes.d.ts b/packages/endpoint/src-4.0-types/tupleTypes.d.ts
new file mode 100644
index 000000000000..0f74f0cdd61d
--- /dev/null
+++ b/packages/endpoint/src-4.0-types/tupleTypes.d.ts
@@ -0,0 +1,14 @@
+// Recursive conditional types need TypeScript 4.1, so these are approximated
+
+export type PartialArray<A> = A extends any[] ? Partial<A> : never;
+
+/** Removes Rem's length worth of leading elements from Orig (up to 3) */
+export type RemoveArray<Orig extends any[], Rem extends any[]> =
+  Rem extends [] ? Orig
+  : Rem extends [any] ?
+    Orig extends [any, ...infer R] ? R : never
+  : Rem extends [any, any] ?
+    Orig extends [any, any, ...infer R] ? R : never
+  : Rem extends [any, any, any] ?
+    Orig extends [any, any, any, ...infer R] ? R : never
+  : any[];
diff --git a/packages/endpoint/src-4.2-types/endpointTypes.d.ts b/packages/endpoint/src-4.2-types/endpointTypes.d.ts
index a2ed418c4898..d697ee2a4c26 100644
--- a/packages/endpoint/src-4.2-types/endpointTypes.d.ts
+++ b/packages/endpoint/src-4.2-types/endpointTypes.d.ts
@@ -7,6 +7,7 @@ import type {
   FetchFunction,
   PartialParameters,
 } from './types.js';
+import type { RemoveArray } from './tupleTypes.js';
 export interface EndpointOptions<
   F extends FetchFunction = FetchFunction,
   S extends Schema | undefined = undefined,
@@ -156,11 +157,5 @@ export interface ExtendableEndpointConstructor {
   ): EndpointInstanceInterface<F, S, M> & E;
   readonly prototype: Function;
 }
-type RemoveArray<Orig extends any[], Rem extends any[]> =
-  Rem extends [any, ...infer RestRem] ?
-    Orig extends [any, ...infer RestOrig] ?
-      RemoveArray<RestOrig, RestRem>
-    : never
-  : Orig;
 export {};
 //# sourceMappingURL=endpointTypes.d.ts.map
diff --git a/packages/endpoint/src/endpointTypes.ts b/packages/endpoint/src/endpointTypes.ts
index ee90dcd47b1f..1c7fe5a67a64 100644
--- a/packages/endpoint/src/endpointTypes.ts
+++ b/packages/endpoint/src/endpointTypes.ts
@@ -5,6 +5,7 @@ import type {
   FetchFunction,
   PartialParameters,
 } from './types.js';
+import type { RemoveArray } from './tupleTypes.js';
 
 export interface EndpointOptions<
   F extends FetchFunction = FetchFunction,
@@ -191,10 +192,3 @@ type IfAny<T, Y, N> = 0 extends 1 & T ? Y : N;
 type IfTypeScriptLooseNull<Y, N> = 1 | undefined extends 1 ? Y : N;
 
 type OnlyFirst<A extends unknown[]> = A extends [] ? [] : [A[0]];
-
-type RemoveArray<Orig extends any[], Rem extends any[]> =
-  Rem extends [any, ...infer RestRem] ?
-    Orig extends [any, ...infer RestOrig] ?
-      RemoveArray<RestOrig, RestRem>
-    : never
-  : Orig;
diff --git a/packages/endpoint/src/schema.d.ts b/packages/endpoint/src/schema.d.ts
index 65cbc15ca970..0ea1c195ff23 100644
--- a/packages/endpoint/src/schema.d.ts
+++ b/packages/endpoint/src/schema.d.ts
@@ -228,8 +228,8 @@ export interface UnionConstructor {
  */
 export interface UnionInstance<
   Choices extends EntityMap = any,
-  Args extends EntityFields<AbstractInstanceType<Choices[keyof Choices]>> =
-    EntityFields<AbstractInstanceType<Choices[keyof Choices]>>,
+  // unconstrained: TypeScript 4.2-4.4 can't prove UnionConstructor's Args satisfy EntityFields
+  Args = EntityFields<AbstractInstanceType<Choices[keyof Choices]>>,
 > {
   readonly _hoistable: true;
   define(definition: Schema): void;
diff --git a/packages/endpoint/src/schemas/EntityMixin.ts b/packages/endpoint/src/schemas/EntityMixin.ts
index b28fd9d3bdc1..6944f9ed89b9 100644
--- a/packages/endpoint/src/schemas/EntityMixin.ts
+++ b/packages/endpoint/src/schemas/EntityMixin.ts
@@ -13,6 +13,7 @@ import type {
   RequiredPKOptions,
   IDClass,
   Constructor,
+  ConstructorInstance,
   PKClass,
 } from './EntityTypes.js';
 
@@ -22,24 +23,24 @@ import type {
  */
 export default function EntityMixin<TBase extends PKClass>(
   Base: TBase,
-  opt?: EntityOptions<InstanceType<TBase>>,
+  opt?: EntityOptions<ConstructorInstance<TBase>>,
 ): IEntityClass<TBase> & TBase;
 
 // id is in Instance, so we default to that as pk
 export default function EntityMixin<TBase extends IDClass>(
   Base: TBase,
-  opt?: EntityOptions<InstanceType<TBase>>,
+  opt?: EntityOptions<ConstructorInstance<TBase>>,
 ): IEntityClass<TBase> & TBase & (new (...args: any[]) => IEntityInstance);
 
 // pk was specified in options, so we don't need to redefine
 export default function EntityMixin<TBase extends Constructor>(
   Base: TBase,
-  opt: RequiredPKOptions<InstanceType<TBase>>,
+  opt: RequiredPKOptions<ConstructorInstance<TBase>>,
 ): IEntityClass<TBase> & TBase & (new (...args: any[]) => IEntityInstance);
 
 export default function EntityMixin<TBase extends Constructor>(
   Base: TBase,
-  options: EntityOptions<InstanceType<TBase>> = {},
+  options: EntityOptions<ConstructorInstance<TBase>> = {},
 ) {
   /**
    * Entity defines a single (globally) unique object.
diff --git a/packages/endpoint/src/schemas/EntityRecord.ts b/packages/endpoint/src/schemas/EntityRecord.ts
index 43bb81f79eaa..fb646451a62b 100644
--- a/packages/endpoint/src/schemas/EntityRecord.ts
+++ b/packages/endpoint/src/schemas/EntityRecord.ts
@@ -1,6 +1,10 @@
-import { Constructor, EntityOptions } from './EntityTypes.js';
+import {
+  Constructor,
+  ConstructorInstance,
+  EntityOptions,
+} from './EntityTypes.js';
 
 export default function EntityRecord<TBase extends Constructor>(
   Base: TBase,
-  options: EntityOptions<InstanceType<TBase>> = {},
+  options: EntityOptions<ConstructorInstance<TBase>> = {},
 ) {}
diff --git a/packages/endpoint/src/schemas/EntityTypes.ts b/packages/endpoint/src/schemas/EntityTypes.ts
index 592a71a7fc91..89187468b3a3 100644
--- a/packages/endpoint/src/schemas/EntityTypes.ts
+++ b/packages/endpoint/src/schemas/EntityTypes.ts
@@ -53,7 +53,7 @@ export interface IEntityClass<TBase extends Constructor = any> {
   pk<
     T extends (abstract new (
       ...args: any[]
-    ) => IEntityInstance & InstanceType<TBase>) &
+    ) => IEntityInstance & ConstructorInstance<TBase>) &
       IEntityClass &
       TBase,
   >(
@@ -136,7 +136,7 @@ export interface IEntityClass<TBase extends Constructor = any> {
   fromJS<
     T extends (abstract new (
       ...args: any[]
-    ) => IEntityInstance & InstanceType<TBase>) &
+    ) => IEntityInstance & ConstructorInstance<TBase>) &
       IEntityClass &
       TBase,
   >(
@@ -151,7 +151,7 @@ export interface IEntityClass<TBase extends Constructor = any> {
   createIfValid<
     T extends (abstract new (
       ...args: any[]
-    ) => IEntityInstance & InstanceType<TBase>) &
+    ) => IEntityInstance & ConstructorInstance<TBase>) &
       IEntityClass &
       TBase,
   >(
@@ -182,7 +182,7 @@ export interface IEntityClass<TBase extends Constructor = any> {
   denormalize<
     T extends (abstract new (
       ...args: any[]
-    ) => IEntityInstance & InstanceType<TBase>) &
+    ) => IEntityInstance & ConstructorInstance<TBase>) &
       IEntityClass &
       TBase,
   >(
@@ -209,6 +209,12 @@ export interface IEntityInstance {
 }
 
 export type Constructor = abstract new (...args: any[]) => {};
+/** InstanceType<> for abstract constructor types, which TypeScript 4.2's InstanceType rejects
+ *
+ * Unlike AbstractInstanceType<>, this resolves constructor type aliases (not just classes)
+ */
+export type ConstructorInstance<T extends abstract new (...args: any) => any> =
+  T extends abstract new (...args: any) => infer R ? R : any;
 export type IDClass = abstract new (...args: any[]) => {
   id: string | number | undefined;
 };
diff --git a/packages/endpoint/src/tupleTypes.ts b/packages/endpoint/src/tupleTypes.ts
new file mode 100644
index 000000000000..fe387f31dff9
--- /dev/null
+++ b/packages/endpoint/src/tupleTypes.ts
@@ -0,0 +1,16 @@
+// Recursive conditional types need TypeScript 4.1; src-4.0-types overlays this file
+
+export type PartialArray<A> =
+  A extends [] ? []
+  : A extends [infer F] ? [F] | []
+  : A extends [infer F, ...infer Rest] ? [F] | [F, ...PartialArray<Rest>]
+  : A extends (infer T)[] ? T[]
+  : never;
+
+/** Removes Rem's length worth of leading elements from Orig */
+export type RemoveArray<Orig extends any[], Rem extends any[]> =
+  Rem extends [any, ...infer RestRem] ?
+    Orig extends [any, ...infer RestOrig] ?
+      RemoveArray<RestOrig, RestRem>
+    : never
+  : Orig;
diff --git a/packages/endpoint/src/utility.ts b/packages/endpoint/src/utility.ts
index 3dc9a49b10c5..9f73d47e6849 100644
--- a/packages/endpoint/src/utility.ts
+++ b/packages/endpoint/src/utility.ts
@@ -8,12 +8,7 @@ export type EndpointParam<E> =
 export type ResolveType<E extends (...args: any) => any> =
   ReturnType<E> extends Promise<infer R> ? R : never;
 
-export type PartialArray<A> =
-  A extends [] ? []
-  : A extends [infer F] ? [F] | []
-  : A extends [infer F, ...infer Rest] ? [F] | [F, ...PartialArray<Rest>]
-  : A extends (infer T)[] ? T[]
-  : never;
+export type { PartialArray } from './tupleTypes.js';
 
 // workaround for https://github.com/microsoft/TypeScript/issues/29919
 export type PartialParameters<T extends (...args: any[]) => any> =
diff --git a/packages/rest/src/RestEndpointTypes.ts b/packages/rest/src/RestEndpointTypes.ts
index 7e0e163a1503..e1efe25e1ff9 100644
--- a/packages/rest/src/RestEndpointTypes.ts
+++ b/packages/rest/src/RestEndpointTypes.ts
@@ -166,7 +166,8 @@ export interface RestInstance<
     O['paginationField'] extends string ?
       PaginationFieldEndpoint<
         F & { schema: S; sideEffect: M } & O,
-        O['paginationField']
+        // TypeScript <4.6 doesn't narrow O['paginationField'] here
+        Extract<O['paginationField'], string>
       >
     : undefined
   : undefined;
diff --git a/scripts/build-legacy-types.sh b/scripts/build-legacy-types.sh
index b54f85420c51..b20fd0596dd2 100755
--- a/scripts/build-legacy-types.sh
+++ b/scripts/build-legacy-types.sh
@@ -20,6 +20,11 @@ copy_types() {
     done
 }
 
+# True when version $1 is older than version $2.
+version_lt() {
+    [ "$1" != "$2" ] && [ "$(printf '%s\n' "$1" "$2" | sort -V | head -1)" = "$1" ]
+}
+
 # Versions are listed newest first, and custom types for a version also apply
 # to every version listed after it. So each output dir gets the downleveled lib,
 # then earlier versions' custom types, then its own. Each output dir only
@@ -28,6 +33,13 @@ build_version() {
     local version="$1"
     shift
     "$downlevel_dts" lib "ts$version" --to="$version"
+    # downlevel-dts keeps `abstract new` constructor types, which need TS 4.2
+    if version_lt "$version" 4.2; then
+        grep -rl --include='*.d.ts' 'abstract new (' "ts$version" | while IFS= read -r file
+        do
+            perl -pi -e 's/abstract new \(/new (/g' "$file"
+        done
+    fi
     for earlier in "$@"
     do
         copy_types "./src-$earlier-types" "./ts$version"
@@ -37,8 +49,7 @@ build_version() {
 
 # LEGACY_MIN_TS skips outputs no consumer reads (CI's oldest tested TS).
 below_min() {
-    [ -n "$LEGACY_MIN_TS" ] && [ "$1" != "$LEGACY_MIN_TS" ] \
-        && [ "$(printf '%s\n' "$1" "$LEGACY_MIN_TS" | sort -V | head -1)" = "$1" ]
+    [ -n "$LEGACY_MIN_TS" ] && version_lt "$1" "$LEGACY_MIN_TS"
 }
 
 pids=()
diff --git a/website/blog/2026-10-03-v0.19-batch-set.md b/website/blog/2026-10-03-v0.19-batch-set.md
index 86180b75057b..484ea6cb623d 100644
--- a/website/blog/2026-10-03-v0.19-batch-set.md
+++ b/website/blog/2026-10-03-v0.19-batch-set.md
@@ -20,6 +20,7 @@ import StackBlitz from '@site/src/components/StackBlitz';
 - Vue [useSuspense()](/vue/api/useSuspense), [useDLE()](/vue/api/useDLE) and [useFetch()](/vue/api/useFetch) no longer refetch stale data on every store update, so a `controller.set()` is not overwritten ([#4134](https://github.com/reactive/data-client/pull/4134))
 - Vue [useDLE()](/vue/api/useDLE) and [useCache()](/vue/api/useCache) keep expired `invalidIfStale` data through unrelated store updates instead of getting stuck loading ([#4142](https://github.com/reactive/data-client/pull/4142))
 - Fix `Cannot find name 'NoInfer'` and `export type` errors on TypeScript 4.x with `skipLibCheck` off ([#4138](https://github.com/reactive/data-client/pull/4138))
+- Fix `Entity`, `Endpoint`, `Union` and `RestEndpoint` type errors on TypeScript 4.0–4.5 with `skipLibCheck` off ([#4140](https://github.com/reactive/data-client/pull/4140))
 
 {/* truncate */}
 

From 479badb7017ba884cc7dbdbcdfd08d58bdb72325 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Sun, 4 Oct 2026 15:14:53 +0000
Subject: [PATCH 5/5] internal(ci): Harden legacy types script and libcheck
 lib/ on latest TS

version_lt compares major.minor in bash instead of relying on sort -V
(a missing -V silently skipped the abstract new rewrite), and the
abstract new grep no longer fails the build under pipefail when nothing
matches. esmodule-types-latest also runs the skipLibCheck: false
typetest so lib/ is checked on the newest compiler.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EEcQdob4nGVuMq91oUHC2V
---
 .circleci/config.yml          | 2 ++
 .cursor/rules/ci-config.mdc   | 2 +-
 scripts/build-legacy-types.sh | 7 ++++---
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index b42b06379396..3054a37e5956 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -355,6 +355,8 @@ jobs:
             yarn run tsc --project examples/todo-app/tsconfig.typetest.json --exactOptionalPropertyTypes true
             yarn run tsc --project examples/github-app/tsconfig.typetest.json --exactOptionalPropertyTypes true
             yarn run tsc --project examples/todo-app/tsconfig.typetest41.json --exactOptionalPropertyTypes true
+            # skipLibCheck: false on lib/ too (TS 7 removed moduleResolution node)
+            yarn run tsc --project examples/todo-app/tsconfig.typetest-libcheck.json --moduleResolution bundler
 
   validate-esmodule-browser-build:
     executor: node
diff --git a/.cursor/rules/ci-config.mdc b/.cursor/rules/ci-config.mdc
index 3283a70bfe87..4b743b6e8a04 100644
--- a/.cursor/rules/ci-config.mdc
+++ b/.cursor/rules/ci-config.mdc
@@ -16,7 +16,7 @@ alwaysApply: false
   - Built inside `setup` (`ci:build:setup:esmodule`) only when the esmodule flag is set; there is no separate job, to keep a job hop off the critical path.
   - In CI only endpoint/normalizr/rest outputs for TS >= 4.0 are built (`LEGACY_MIN_TS=4.0`, the oldest TS in the `esmodule-types` matrix); release builds (`build:types`) still emit every version.
   - `scripts/build-legacy-types.sh` builds each TS version concurrently; each `ts<version>/` gets the downleveled `lib` (with `abstract new` rewritten to `new` below 4.2, which `downlevel-dts` misses), then every newer version's `src-*-types` overlay, then its own. Keep overlays to small single-purpose modules (like `NoInfer.ts`, `tupleTypes.ts`) so whole-file copies can't go stale.
-  - `esmodule-types` also runs `examples/todo-app/tsconfig.typetest-libcheck.json` (`skipLibCheck: false`, `types: []`) so errors inside the legacy outputs fail CI; the other typetests use `skipLibCheck: true`.
+  - `esmodule-types` also runs `examples/todo-app/tsconfig.typetest-libcheck.json` (`skipLibCheck: false`, `types: []`) so errors inside the legacy outputs fail CI, and `esmodule-types-latest` runs it with `--moduleResolution bundler` (TS 7 removed `node`) to cover `lib/`; the other typetests use `skipLibCheck: true`.
   - Any change to legacy types building must leave `ts*/` output byte-identical to master (diff it) unless it intentionally changes published types (then add a changeset).
 - Never `git fetch --depth` the base branch in the relevance check: a shallow fetch severs the merge base and the three-dot diff fails.
 - Changing root `package.json` `workspaces` requires updating the `setup` job's workspace trimming step.
diff --git a/scripts/build-legacy-types.sh b/scripts/build-legacy-types.sh
index b20fd0596dd2..6a4b1c560f10 100755
--- a/scripts/build-legacy-types.sh
+++ b/scripts/build-legacy-types.sh
@@ -20,9 +20,10 @@ copy_types() {
     done
 }
 
-# True when version $1 is older than version $2.
+# True when major.minor version $1 is older than $2 (pure bash, no `sort -V`).
 version_lt() {
-    [ "$1" != "$2" ] && [ "$(printf '%s\n' "$1" "$2" | sort -V | head -1)" = "$1" ]
+    local a_major="${1%%.*}" a_minor="${1#*.}" b_major="${2%%.*}" b_minor="${2#*.}"
+    (( a_major < b_major || (a_major == b_major && a_minor < b_minor) ))
 }
 
 # Versions are listed newest first, and custom types for a version also apply
@@ -35,7 +36,7 @@ build_version() {
     "$downlevel_dts" lib "ts$version" --to="$version"
     # downlevel-dts keeps `abstract new` constructor types, which need TS 4.2
     if version_lt "$version" 4.2; then
-        grep -rl --include='*.d.ts' 'abstract new (' "ts$version" | while IFS= read -r file
+        { grep -rl --include='*.d.ts' 'abstract new (' "ts$version" || true; } | while IFS= read -r file
         do
             perl -pi -e 's/abstract new \(/new (/g' "$file"
         done