Replace api.updateSnapshot - #64204

Replaces latest-snapshot state with explicit snapshot creation and derivation, adding synthetic-program lifecycle support and branded project IDs.

Changes:

• Adds createSnapshot, Snapshot.update, and LSP snapshot retrieval.
• Supports creating, removing, and ensuring synthetic programs.
• Updates protocols, generators, caches, and tests for the new model.

Files not reviewed (1)

• tsc/internal/project/project_stringer_generated.go: Generated file

• Files reviewed: 29/32 changed files
• Comments generated: 3
• Review effort level: Balanced

Files not reviewed (1)

• tsc/internal/project/project_stringer_generated.go: Generated file

Suppressed comments (1)

tsc/internal/api/session.go:1245

• The same pre-request filtering breaks close-and-reopen for files: when a currently owned file appears in both lists, OpenFiles is removed here and CloseFiles is retained below, leaving the file closed. Independent snapshot reconciliation processes closes before opens, so the two APIs now produce different final states for the same change set. Compute both deltas from a temporary open-file state so the reopen wins.

	for uri := range apiRequest.OpenFiles.Keys() {
		path := s.toPath(uri.FileName())
		if s.openFiles.Has(path) {
			apiRequest.OpenFiles.Delete(uri)
		} else {

• Files reviewed: 31/34 changed files
• Comments generated: 2
• Review effort level: Balanced

Files not reviewed (1)

• tsc/internal/project/project_stringer_generated.go: Generated file

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

tsc/internal/project/projectcollectionbuilder.go:310

• Unknown project IDs are silently ignored because DidRequestProject returns without indicating whether it found anything. Consequently, ensurePrograms can report success even though the requested program is absent (for example, when an ID from an unrelated snapshot is supplied). Validate every requested ID against this snapshot and return a client error when one is missing.

• Files reviewed: 33/36 changed files
• Comments generated: 2
• Review effort level: Balanced

Files not reviewed (1)

• tsc/internal/project/project_stringer_generated.go: Generated file

• Files reviewed: 34/37 changed files
• Comments generated: 2
• Review effort level: Balanced

• Files reviewed: 38/40 changed files
• Comments generated: 3
• Review effort level: Balanced

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

packages/typescript/src/api/async/api.ts:511

• ensurePrograms: true only updates projects already present in the base snapshot; it does not perform the file-to-project discovery that the removed temporary-snapshot endpoint performed via Documents. Consequently, calling this helper for a file whose configured/inferred project is not already loaded leaves the callback snapshot with no project for that file. Open the file in this derived snapshot (which is disposed immediately afterward), or add a targeted ensure-file operation.

• Files reviewed: 38/40 changed files
• Comments generated: 1
• Review effort level: Balanced

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

tsc/internal/project/projectcollectionbuilder.go:360

• An unknown or stale ID in ensurePrograms is silently ignored because DidRequestProject has no failure result. The request then succeeds without ensuring the named program, contrary to this operation's contract; validate that each ID resolves in this snapshot and return a client error when it does not.

tsc/internal/api/session.go:1253

• createPrograms is decoded as a slice of pointers, so a wire request containing createPrograms: [null] reaches this dereference and panics instead of returning a client error. Reject nil entries before reading RootFiles.

	for i, programParams := range changes.CreatePrograms {
		rootFileNames := make([]string, len(programParams.RootFiles))

• Files reviewed: 38/40 changed files
• Comments generated: 2
• Review effort level: Balanced

Suppressed comments (2)

Previously missed (2) — in code that hasn't changed since the last review.

tsc/internal/project/projectcollectionbuilder.go:360

• Unknown IDs in ensurePrograms are silently ignored by DidRequestProject, so updating an unrelated/root snapshot with an ID from another snapshot succeeds even though the requested program is absent and cannot be ensured. Reject IDs not present in this builder, consistent with reconfigure/remove validation.
  packages/typescript/src/api/async/api.ts:375
• The overloads do not accept an explicit undefined or a CreateSnapshotParams | undefined variable, although the implementation and the documented changes? API make the parameter optional. Expose an optional-parameter overload rather than only a zero-argument overload.

• Files reviewed: 38/40 changed files
• Comments generated: 1
• Review effort level: Balanced