From 6ea3b1aa73b2af16ca0490f6e770c158c222b43b Mon Sep 17 00:00:00 2001
From: Oleksii Sholik <oleksii@sholik.dev>
Date: Tue, 12 May 2026 12:30:54 +0300
Subject: [PATCH 1/2] Pending tool results in Anthropic API contract violation
 when runtime restarts

---
 packages/agents-runtime/src/timeline-context.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/packages/agents-runtime/src/timeline-context.ts b/packages/agents-runtime/src/timeline-context.ts
index 13d88452e5..c1c48b15db 100644
--- a/packages/agents-runtime/src/timeline-context.ts
+++ b/packages/agents-runtime/src/timeline-context.ts
@@ -153,6 +153,14 @@ export function defaultProjection(
             toolCallId: runItem.key,
             isError: runItem.status === `failed`,
           })
+        } else {
+          // Tool was interrupted (crashed mid-execution) - synthesize error result
+          messages.push({
+            role: `tool_result`,
+            content: `Tool execution was interrupted before completion (status: ${runItem.status})`,
+            toolCallId: runItem.key,
+            isError: true,
+          })
         }
       }
 

From 113584d1b2591f184f20dbebbd3f104f2207ab68 Mon Sep 17 00:00:00 2001
From: Oleksii Sholik <oleksii@sholik.dev>
Date: Tue, 12 May 2026 12:31:58 +0300
Subject: [PATCH 2/2] Add changeset for pending tool result fix

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 .changeset/fix-pending-tool-on-restart.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/fix-pending-tool-on-restart.md

diff --git a/.changeset/fix-pending-tool-on-restart.md b/.changeset/fix-pending-tool-on-restart.md
new file mode 100644
index 0000000000..21576b868f
--- /dev/null
+++ b/.changeset/fix-pending-tool-on-restart.md
@@ -0,0 +1,5 @@
+---
+'@electric-ax/agents-runtime': patch
+---
+
+Fix Anthropic API contract violation when an agent restart leaves a tool call without a result. The timeline projection now synthesizes a synthetic error tool_result for interrupted tool calls so every tool_use has a matching tool_result.