Reworks the language server's document-state lifecycle from eager, defensive reparse to invalidate-on-change + lazily materialize-on-read, synchronously, and moves diagnostics from push to LSP 3.17 pull (textDocument/diagnostic). Implements the lsp-document-state spec committed as this PR's first commit (projects/lsp-document-state/).

didChange  ──▶  version bump only (free from TextDocuments; no parse)
read req   ──▶  await project load (only while uncached; config eval is async)
            ──▶  ensureCurrent(project, uri)   (SYNC: reparse iff version changed)
            ──▶  derive (completion / diagnostics / tokens / folding)

Changes

• Lazy lifecycle (src/project-artifacts.ts, src/server.ts): ensureCurrent(project, uri) is the single synchronous materialize-on-read seam. CachedDocument carries the last-parsed version; a read at an unchanged version does zero parsing, and an edit-then-immediate-read costs exactly one parse. currentDocumentArtifact — the per-request whole-document text compare + defensive reparse — is deleted; completion, semantic tokens, and folding all read through the one per-project cache. Config reloads invalidate() cached versions so the fast path stays sound across prisma-next.config.ts changes. TextDocuments is retained as the text mirror / lifecycle / version source.
• Pull diagnostics with push fallback (src/server.ts): when the client advertises textDocument.diagnostic, the server advertises diagnosticProvider and serves full reports through ensureCurrent; didOpen/didChange become invalidate-only (no eager publish), and config/watched-file changes send workspace/diagnostic/refresh (gated on refreshSupport) instead of republishing. Clients without pull support keep the previous eager push behavior unchanged. Exactly one transport is ever active per client — structurally, since every push site is gated on the same capability flag. Flags ship as { interFileDependencies: false, workspaceDiagnostics: false } with a scope comment: this reflects the current single-input implementation, not a property of PSL, and flips with the future multi-input symbol table.
• Report builder seam: buildDocumentDiagnosticReport(project, uri) is project-scoped so the future multi-file table can attach relatedDocuments additively — no rewrite needed.

Why

• Every edit previously parsed twice (eager publish + currentDocumentArtifact's per-request reparse with an O(n) whole-text compare) to dodge a stale-buffer race the LSP spec's didChange ordering guarantee already rules out. Freshness is now keyed on the monotonic version that TextDocuments maintains anyway.
• The server is single-threaded: there is no await between reading the buffer and deriving from it, so a derived result is always internally consistent for one version — tsserver's version-keyed lazy recompute fits; rust-analyzer-style snapshots/cancellation are unnecessary. Async stays confined to project/config resolution (executable prisma-next.config.ts, cached and de-duped).
• Dropping eager compute on change is only safe once diagnostics are pull-served, which is why lifecycle and transport land together as one slice.

Validation

• Package gates: pnpm --filter @prisma-next/language-server test (187 tests, incl. no-reparse-at-unchanged-version, one-parse edit-then-complete, pull/push capability gating, refresh semantics), typecheck, lint; playground typecheck/lint.
• Workspace: pnpm build, pnpm typecheck, pnpm lint:deps clean. (pnpm test:packages locally red only in mongo-runtime/CLI tests that fail identically on main — mongod-less machine.)
• Manual QA: headless end-to-end run over the real playground WebSocket bridge (pull report with parse error, zero publishDiagnostics to the pull client, post-edit pull correct, tokens/folding healthy) — script + report under projects/lsp-document-state/manual-qa*. Visual Monaco-marker check (Part B) pending a browser run.

Non-goals

Removing TextDocuments, the multi-input project-wide symbol table, multi-project membership, interFileDependencies: true / workspace/diagnostic, and any behavioral change to completion/semantic-tokens/folding beyond their data source. See projects/lsp-document-state/spec.md § Non-goals.