update(links): Relax link schemas to support domain-level identifier

This change updates all link schemas (START, END, RELATION, and embedded variants)
to allow references to either a CDEvent contextId, a domainId, or both.

Previously, links could only reference event context IDs. This limited
cross-system connectivity and encouraged embedding execution identifiers
in customData purely for graph reconstruction.

By allowing domainId alongside contextId:
- Links can represent relationships between domain executions
  (e.g., pipelinerun) as well as individual events.
- Connectivity metadata no longer needs to be embedded in event payloads.
- Chain-first modeling constraints are relaxed, enabling relation-first
  graph modeling.
- The change remains backward compatible.

At least one of contextId or domainId is now required for link endpoints.
AdditionalProperties are restricted to prevent schema drift.

This preserves existing semantics while improving flexibility and reducing
customData pollution.

Signed-off-by: xibz <bjp@apple.com>

Author: xibz

schemas/links/embeddedlinkend.json

@@ -15,6 +15,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [

schemas/links/embeddedlinkpath.json

@@ -15,6 +15,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [

schemas/links/embeddedlinkrelation.json

@@ -19,6 +19,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       }
     },

schemas/links/linkend.json

@@ -25,6 +25,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [
@@ -38,6 +42,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [

schemas/links/linkpath.json

@@ -22,6 +22,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [
@@ -34,6 +38,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [

schemas/links/linkrelation.json

@@ -28,6 +28,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [
@@ -41,6 +45,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [

schemas/links/linkstart.json

@@ -25,6 +25,10 @@
         "contextId": {
           "type": "string",
           "minLength": 1
+        },
+        "domainId": {
+          "type": "string",
+          "format": "uri-reference"
         }
       },
       "required": [