diff --git a/.changeset/23768-datasources-default-host-reserved.md b/.changeset/23768-datasources-default-host-reserved.md
new file mode 100644
index 00000000000..249058a77d2
--- /dev/null
+++ b/.changeset/23768-datasources-default-host-reserved.md
@@ -0,0 +1,9 @@
+---
+'@objectstack/skills': patch
+---
+
+docs(skills): the `objectstack-data` datasources rule states that `default` is host-reserved — the host connects it from `OS_DATABASE_URL`, and a stack that declares a datasource named `default` is refused (#23768)
+
+Clause-②: no
+
+`skills/objectstack-data/rules/datasources.md`'s opening paragraph read "Most apps need only the `default` datasource; declare more to read/write a separate or external database." "Declare more" implied that `default` is declared too, and a stack whose `datasources` collection carries an entry named `default` is refused at `defineStack`, `os validate`, publish and boot: the host declares and connects `default` itself. The sentence is replaced by the rule the spec and runtime hold: `default` is host-reserved, the host connects it from `OS_DATABASE_URL`, a stack that declares a datasource named `default` is refused, and a datasource is declared under its own name only to read/write a separate or external database. The added words are paid for inside the same file by deleting two restatements of the field reference: "`external` settings are required when `schemaMode !== 'managed'`" (the schema refuses the omission itself) and "Set `autoConnect: true` to force a live connection" (the auto-connect list two lines above already names it). No behaviour changes; nothing an author writes changes.
diff --git a/skills/objectstack-data/rules/datasources.md b/skills/objectstack-data/rules/datasources.md
index 4e8310862bc..f39634a1381 100644
--- a/skills/objectstack-data/rules/datasources.md
+++ b/skills/objectstack-data/rules/datasources.md
@@ -2,8 +2,10 @@
 
 A **datasource** (`defineDatasource`, a `*.datasource.ts` metadata file) is a
 connection to a data store. Objects route to one via their `datasource` field
-(default: `'default'`). Most apps need only the `default` datasource; declare more
-to read/write a **separate** or **external** database.
+(default: `'default'`). `default` is host-reserved: the host connects it from
+`OS_DATABASE_URL`, and a stack that declares a datasource named `default` is
+refused. Declare a datasource under its own name only to read/write a
+**separate** or **external** database.
 
 Full field reference: `node_modules/@objectstack/spec/src/data/datasource.zod.ts`.
 
@@ -15,8 +17,6 @@ Full field reference: `node_modules/@objectstack/spec/src/data/datasource.zod.ts
 | `external` | A mature external DB ObjectStack does **not** own; DDL forbidden; boot mismatch **fails**. |
 | `validate-only` | Like `external`, but a mismatch **warns** instead of failing boot. |
 
-`external` settings are **required** when `schemaMode !== 'managed'`.
-
 ## Federated (external) objects
 
 An object on an external datasource binds to its remote table via `external`:
@@ -55,7 +55,7 @@ objects' read metadata registered **automatically at boot** — no `onEnable` /
 4. a **`datasourceMapping` rule routes at least one object to it**.
 
 A `managed` datasource that nothing routes to stays **metadata-only** — visible but
-not connected. Set `autoConnect: true` to force a live connection.
+not connected.
 
 ⚠️ A `datasourceMapping` rule is **routing, not a hint**. A rule pointing at a
 datasource that cannot be connected fails the boot, and a query against a mapped