diff --git a/src/tools/delegate-task/resolve-call-id.test.ts b/src/tools/delegate-task/resolve-call-id.test.ts
new file mode 100644
index 000000000..7b4da140e
--- /dev/null
+++ b/src/tools/delegate-task/resolve-call-id.test.ts
@@ -0,0 +1,40 @@
+import { describe, test, expect } from "bun:test"
+import { resolveCallID } from "./resolve-call-id"
+import type { ToolContextWithMetadata } from "./types"
+
+describe("resolveCallID", () => {
+  function makeCtx(overrides: Partial<ToolContextWithMetadata> = {}): ToolContextWithMetadata {
+    return {
+      sessionID: "ses_test",
+      messageID: "msg_test",
+      agent: "sisyphus",
+      abort: new AbortController().signal,
+      ...overrides,
+    }
+  }
+
+  test("#given callID is set #then returns callID", () => {
+    const ctx = makeCtx({ callID: "call_abc" })
+    expect(resolveCallID(ctx)).toBe("call_abc")
+  })
+
+  test("#given only callId is set #then returns callId", () => {
+    const ctx = makeCtx({ callId: "call_def" })
+    expect(resolveCallID(ctx)).toBe("call_def")
+  })
+
+  test("#given only call_id is set #then returns call_id", () => {
+    const ctx = makeCtx({ call_id: "call_ghi" })
+    expect(resolveCallID(ctx)).toBe("call_ghi")
+  })
+
+  test("#given callID and callId are both set #then prefers callID", () => {
+    const ctx = makeCtx({ callID: "preferred", callId: "fallback" })
+    expect(resolveCallID(ctx)).toBe("preferred")
+  })
+
+  test("#given no call ID variants are set #then returns undefined", () => {
+    const ctx = makeCtx()
+    expect(resolveCallID(ctx)).toBeUndefined()
+  })
+})
diff --git a/src/tools/delegate-task/resolve-call-id.ts b/src/tools/delegate-task/resolve-call-id.ts
new file mode 100644
index 000000000..cfa3b747e
--- /dev/null
+++ b/src/tools/delegate-task/resolve-call-id.ts
@@ -0,0 +1,5 @@
+import type { ToolContextWithMetadata } from "./types"
+
+export function resolveCallID(ctx: ToolContextWithMetadata): string | undefined {
+  return ctx.callID ?? ctx.callId ?? ctx.call_id
+}