[TheGreatAxios]

Summary

• Presence (who's-here, cursors, typing, Y.Doc co-editing) is dropped from Workbench entirely for now. The library is preserved upstream at corbitsdev/corbits-presence and returns, if it does, as its own re-pin.
• The artifact editor is now a plain single-user controlled textarea (ArtifactTextEditor), debounced-saved through a new PUT /api/tenants/:tenantId/artifacts/:artifactId route added to packages/artifacts-hub (uses @corbits/artifacts' existing writeArtifactVersion) — this is the only save path a doc-kind artifact ever gets now. Previously the only save path was presence's Y.Doc debounced snapshot persistence, which had no HTTP equivalent.
• Deleted packages/presence entirely, the hub's presence room registry/mount in apps/hub/src/index.ts, apps/web/src/presence/, and every @corbits/presence/yjs/y-protocols dependency.
• Regenerated tsconfig references and .changeset/config.json; shrank the report-error baseline for the deleted catch clauses.

Deleted tests

Per owner ruling, tests encoding the old co-edit/presence behavior were deleted rather than adapted:

• apps/hub/test/artifact-doc-persistence.test.ts (presence → writeArtifactVersion wiring)
• apps/hub/test/presence-mount.test.ts
• apps/web/test/use-presence-room.test.tsx
• apps/web/test/artifact-cursor-overlay.test.tsx
• packages/artifact-ui/test/artifact-text-editor.test.tsx (Y.Doc-based)
• packages/artifact-ui/src/y-text-diff.test.ts (and its source, y-text-diff.ts)
• packages/presence/** (whole package, tests included)
• Co-editing describe block in apps/web/test/canvas-column.test.tsx — replaced with a single-user equivalent covering the same read-only/editable/typing-saves behavior.
• save-state.test.ts's "editing" (co-editor) cases — the editing ArtifactSaveState kind is gone, replaced by saving.

What the artifact editor save path is now

ArtifactTextEditor (packages/artifact-ui) is a plain controlled <textarea>. On change it debounces 1s then calls onSave(content). The host (apps/web/src/shell/app-shell.tsx) wires that to saveArtifactContent (apps/web/src/shell/library-artifacts.ts), which does PUT /api/tenants/:tenantId/artifacts/:artifactId with { content }. That route (new, in packages/artifacts-hub/src/routes.ts) calls @corbits/artifacts' writeArtifactVersion and returns the updated row; the host renders "Saving…" / "Saved · vN" / "Unsaved changes" off the response.

Test plan

• bun run typecheck
• bun run lint
• bun run check:structural
• bun --cwd apps/hub test (DB-gated suites skip locally, no DATABASE_URL)
• bun --cwd apps/web test
• bun --cwd packages/artifact-ui test

[linear-code]

CL-8189