[typespec-ts] Revert #3938 (migrate generated configs to eng/tsconfigs pattern) and its two dependents

[maorleger]

Resolves #3964

The TL;DR is that since v0.53.0, SDK Validation has been broken for any TypeSpec-based PR in azure-rest-api-specs because the generated warp.config.yml references ./config/tsconfig.src.*.json files that don't actually get emitted on the "update existing package" code path. That's the path SDK automation usually hits, so this affects everyone.

I went back and forth on whether to take #3967 (which patches the symptom by adding the missing builders to the update path) or to just revert the whole thing. I landed on revert for two reasons:

1. The pre-feat: migrate generated configs to eng/tsconfigs pattern #3938 design was strictly simpler — one builder (buildTsSrcConfig), one template, repo-root ../../../tsconfig.src.*.json references, single linear code path. No new-vs-update fork to keep in sync, and known-good for both new and existing packages.
2. The eng/tsconfigs alignment goal of feat: migrate generated configs to eng/tsconfigs pattern #3938 is worth doing, but I think it should be reattempted with a cleaner design (single linear path + the consistency test [typespec-ts] Fix missing config/ tsconfig files when updating existing packages #3967 added). That feels safer as a follow-up than as a fast-follow on top of an already-broken release.

I'm open to hearing if there's a reason to keep the #3938 design — but for now this gets us back to a healthy place.

What this PR reverts

Three commits, in dependency order:

Commit	PR	Why reverted
679311a5	#3943 — Do not generate React Native build targets by default	Depends on #3938's split warp targets
813fd759	#3938 — migrate generated configs to eng/tsconfigs pattern	Root cause
ab712bd0	#3941 — stop generating vitest.esm.config.ts	Depends on #3938's removal of buildVitestConfig("esm")

All 11 unrelated commits between #3938 and HEAD (version bumps, real bug fixes, spector tests, the RestError re-export, etc.) are kept as-is.

Conflict resolution notes

Reverting #3938 surfaced 5 conflicts in regenerated test fixtures under packages/typespec-test/test/.../generated/. They were all about NodeReadableStream (added by #3938) vs RestError/isRestError (added later by unrelated #3930). I kept the RestError/isRestError exports and dropped the NodeReadableStream type alias — that matches what the reverted emitter would actually produce.

Validation

I built the emitter from this branch and ran an end-to-end pipeline (tsp compile → pnpm turbo build against a local azure-sdk-for-js) for both code paths:

Spec	Path	Result
cognitiveservices/CognitiveServices.Management (Azure/azure-rest-api-specs#41922)	Update existing package — the case that's failing on main	✅ 19/19 turbo tasks
scvmm/ScVmm.Management (deleted the existing SDK package first to force the new path)	New package	✅ 19/19 turbo tasks

I also spot-checked the generated warp.config.yml and it's back to ../../../tsconfig.src.*.json — no ./config/ indirection.

Follow-up

• Re-attempt the eng/tsconfigs alignment with a single linear builder path (no new-vs-update fork) and the consistency test from [typespec-ts] Fix missing config/ tsconfig files when updating existing packages #3967.
• I noticed two other regression classes while testing this branch (orphan subpath exports in warp.config.yml for modular operation groups, and raw NodeJS.* types leaking into RLC browser code). Those are unrelated to feat: migrate generated configs to eng/tsconfigs pattern #3938 and I'll file separate issues.

[maorleger]

Doing the migration for all packages moves 3000+ files of unnecessary config changes. That's not really great, and we want to simplify all this if we can. I think reverting this change and revisiting with a fresh perspective is the right choice but feel free to disagree!

[JialinHuang803]

"#3943 — Do not generate React Native build targets by default" may not relate to #3938 because the react-native build target has been existing in the warp.config since it was introduced in the codegen based on #3802.

And we need to revert the changes on the packages in the sdk repo. Please correct me if my understanding is wrong.

[maorleger]

"#3943 — Do not generate React Native build targets by default" may not relate to #3938 because the react-native build target has been existing in the warp.config since it was introduced in the codegen based on #3802.

And we need to revert the changes on the packages in the sdk repo. Please correct me if my understanding is wrong.

Sorry I forgot to close this, you're quite right on both counts - and Jeremy did end up migrating the entire repo so this PR is not even needed. Closing 👍