docs: require the pnpm catalog for shared deps + enable catalogMode

.changeset/assist-field-group-reset.md

@@ -1,5 +1,5 @@
 ---
-'@sanity/assist': patch
+"@sanity/assist": patch
 ---
 
 Keep the document's selected field group from resetting while editing AI Assist instructions. The instruction inspector no longer overwrites the host document pane's `path` param, so working with AI Assist inputs preserves the active field group tab.

AGENTS.md

@@ -436,6 +436,16 @@ pnpm add lodash-es
 pnpm add lodash
 ```
 
+**Catalog shared dependencies**
+
+When a dependency is used by more than one package (two or more), manage its version in the pnpm [catalog](https://pnpm.io/catalogs) instead of repeating a literal range in each `package.json`:
+
+1. Add the dependency and its version range to the default `catalog:` in `pnpm-workspace.yaml`.
+2. Reference it from each `package.json` as `"dep-name": "catalog:"`.
+3. Shared studio peers (`react`, `react-dom`, `sanity`, `styled-components`) use the named `peer` catalog (`catalog:peer`) — see above. For other cases where one package must stay on a different major than the rest, add a named catalog and reference it with `catalog:<name>`.
+
+Leave niche one-off peers and `workspace:` protocol deps as they are. `pnpm add` runs with `catalogMode: prefer` (set in `pnpm-workspace.yaml`), so adding a dependency that already exists in a catalog reuses the catalog version automatically. pnpm has no built-in "used N times" enforcement, so apply this rule whenever you add or move shared dependencies.
+
 ### Formatting
 
 We use [oxfmt](https://oxc.rs/docs/formatter.html):

pnpm-workspace.yaml

@@ -83,6 +83,8 @@ catalogs:
     sanity: ^5 || ^6.0.0-0
     styled-components: ^6.1
 
+# When running `pnpm add`, reuse a dependency's catalog version automatically if
+# it already exists in a catalog, so shared deps stay aligned on a single version.
 catalogMode: prefer
 dedupeDirectDeps: true