Make inputDrvs JSON schema more precise

It now captures the stable non-recursive format (just an output set) and
the unstable recursive form for dynamic derivations.

doc/manual/source/protocols/json/schema/derivation-v3.yaml

@@ -103,6 +103,13 @@ properties:
       > ```
       >
       > specifies that this derivation depends on the `dev` output of `curl`, and the `out` output of `unzip`.
+    additionalProperties:
+      title: Store Path
+      description: |
+        A store path to a derivation, mapped to the outputs of that derivation.
+      oneOf:
+      - "$ref": "#/$defs/outputNames"
+      - "$ref": "#/$defs/dynamicOutputs"
 
   system:
     type: string
@@ -167,3 +174,28 @@ properties:
         title: Expected hash value
         description: |
           For fixed-output derivations, the expected content hash in base-16.
+
+  outputName:
+    type: string
+    title: Output name
+    description: Name of the derivation output to depend on
+
+  outputNames:
+    type: array
+    title: Output Names
+    description: Set of names of derivation outputs to depend on
+    items:
+      "$ref": "#/$defs/outputName"
+
+  dynamicOutputs:
+    type: object
+    title: Dynamic Outputs
+    description: |
+      **Experimental feature**: [`dynamic-derivations`](@docroot@/development/experimental-features.md#xp-feature-dynamic-derivations)
+
+      This recursive data type allows for depending on outputs of outputs.
+    properties:
+      outputs:
+        "$ref": "#/$defs/outputNames"
+      dynamicOutputs:
+          "$ref": "#/$defs/dynamicOutputs"