diff --git a/crates/fabric-core/src/agent_execution.rs b/crates/fabric-core/src/agent_execution.rs
index 7f9780f4c..5f8111c2c 100644
--- a/crates/fabric-core/src/agent_execution.rs
+++ b/crates/fabric-core/src/agent_execution.rs
@@ -239,7 +239,7 @@ fn agent_run_result_schema(schema: &mut Schema) {
                     "properties": {"status": {"const": "succeeded"}},
                     "required": ["status"]
                 },
-                "then": {"not": {"required": ["error"]}}
+                "then": {"properties": {"error": {"type": "null"}}}
             }
         ]),
     );
diff --git a/crates/fabric-core/src/schema.rs b/crates/fabric-core/src/schema.rs
index 39812e50f..83a399336 100644
--- a/crates/fabric-core/src/schema.rs
+++ b/crates/fabric-core/src/schema.rs
@@ -447,6 +447,15 @@ mod tests {
             "output": null,
             "error": {"code": "target_error", "message": "target failed"}
         })));
+        assert!(validator.is_valid(&serde_json::json!({
+            "status": "succeeded",
+            "output": null
+        })));
+        assert!(validator.is_valid(&serde_json::json!({
+            "status": "succeeded",
+            "output": null,
+            "error": null
+        })));
         for path in [
             " \t",
             "nested/../output",
diff --git a/docs/adapter-contract/results.md b/docs/adapter-contract/results.md
index 145245ce0..cde614ff2 100644
--- a/docs/adapter-contract/results.md
+++ b/docs/adapter-contract/results.md
@@ -31,10 +31,10 @@ Use the generated
 [`AgentRunResult` JSON Schema](https://github.com/NVIDIA/NeMo-Fabric/blob/main/schemas/adapter-contract/agent-run-result.schema.json)
 for exact fields and constraints.
 
-A failed result must contain `error`. A succeeded result must not contain
-`error`. Do not infer status from arbitrary fields in `output`. Exactly one
-terminal result is produced for an invocation, and its status is immutable
-once returned.
+A failed result must contain `error`. A succeeded result can omit `error` or
+set it to `null`; it must not contain a non-null error. Do not infer status
+from arbitrary fields in `output`. Exactly one terminal result is produced for
+an invocation, and its status is immutable once returned.
 
 ## Failure Classes
 
diff --git a/schemas/adapter-contract/agent-run-result.schema.json b/schemas/adapter-contract/agent-run-result.schema.json
index c6ac4081e..94704b106 100644
--- a/schemas/adapter-contract/agent-run-result.schema.json
+++ b/schemas/adapter-contract/agent-run-result.schema.json
@@ -199,10 +199,10 @@
         ]
       },
       "then": {
-        "not": {
-          "required": [
-            "error"
-          ]
+        "properties": {
+          "error": {
+            "type": "null"
+          }
         }
       }
     }
diff --git a/typescript/adapter-contract/schemas/agent-run-result.schema.json b/typescript/adapter-contract/schemas/agent-run-result.schema.json
index c6ac4081e..94704b106 100644
--- a/typescript/adapter-contract/schemas/agent-run-result.schema.json
+++ b/typescript/adapter-contract/schemas/agent-run-result.schema.json
@@ -199,10 +199,10 @@
         ]
       },
       "then": {
-        "not": {
-          "required": [
-            "error"
-          ]
+        "properties": {
+          "error": {
+            "type": "null"
+          }
         }
       }
     }
diff --git a/typescript/adapter-contract/scripts/generate.mjs b/typescript/adapter-contract/scripts/generate.mjs
index a0a117dac..ef796c27e 100644
--- a/typescript/adapter-contract/scripts/generate.mjs
+++ b/typescript/adapter-contract/scripts/generate.mjs
@@ -282,10 +282,10 @@ export type AgentRunResult =
   | AgentRunFailed
   | AgentRunCancelled;
 
-/** Successful terminal result. Successful results cannot carry an error. */
+/** Successful terminal result. Successful results can carry only a null error. */
 export interface AgentRunSucceeded extends AgentRunResultCommon {
   status: "succeeded";
-  error?: never;
+  error?: null;
 }
 
 /** Failed terminal result. Failed results must carry a non-null error. */
diff --git a/typescript/adapter-contract/scripts/projection-guards.mjs b/typescript/adapter-contract/scripts/projection-guards.mjs
index b6dd7de99..b009e6541 100644
--- a/typescript/adapter-contract/scripts/projection-guards.mjs
+++ b/typescript/adapter-contract/scripts/projection-guards.mjs
@@ -19,7 +19,7 @@ const supportedRunResultConditionals = [
       properties: { status: { const: "succeeded" } },
       required: ["status"],
     },
-    then: { not: { required: ["error"] } },
+    then: { properties: { error: { type: "null" } } },
   },
 ];
 
diff --git a/typescript/adapter-contract/src/generated/agent-run-result.ts b/typescript/adapter-contract/src/generated/agent-run-result.ts
index 43a604ebb..db771c8f7 100644
--- a/typescript/adapter-contract/src/generated/agent-run-result.ts
+++ b/typescript/adapter-contract/src/generated/agent-run-result.ts
@@ -12,10 +12,10 @@ export type AgentRunResult =
   | AgentRunFailed
   | AgentRunCancelled;
 
-/** Successful terminal result. Successful results cannot carry an error. */
+/** Successful terminal result. Successful results can carry only a null error. */
 export interface AgentRunSucceeded extends AgentRunResultCommon {
   status: "succeeded";
-  error?: never;
+  error?: null;
 }
 
 /** Failed terminal result. Failed results must carry a non-null error. */
diff --git a/typescript/adapter-contract/test/execution.test.ts b/typescript/adapter-contract/test/execution.test.ts
index 0cb4fdfab..e658dd874 100644
--- a/typescript/adapter-contract/test/execution.test.ts
+++ b/typescript/adapter-contract/test/execution.test.ts
@@ -19,6 +19,7 @@ const requests: AgentRunRequest[] = [
 
 const results: AgentRunResult[] = [
   { output: null, status: "succeeded" },
+  { error: null, output: null, status: "succeeded" },
   {
     error: { code: "target_error", message: "target failed" },
     output: { partial: true },