diff --git a/src/agents/session-transcript-repair.test.ts b/src/agents/session-transcript-repair.test.ts
index ccc63ec7f..342c37e4f 100644
--- a/src/agents/session-transcript-repair.test.ts
+++ b/src/agents/session-transcript-repair.test.ts
@@ -1,6 +1,6 @@
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
 import { describe, expect, it } from "vitest";
-import { sanitizeToolUseResultPairing } from "./session-transcript-repair.js";
+import { isIncompleteToolCall, sanitizeToolUseResultPairing } from "./session-transcript-repair.js";
 
 describe("sanitizeToolUseResultPairing", () => {
   it("moves tool results directly after tool calls and inserts missing results", () => {
@@ -109,4 +109,201 @@ describe("sanitizeToolUseResultPairing", () => {
     expect(out.some((m) => m.role === "toolResult")).toBe(false);
     expect(out.map((m) => m.role)).toEqual(["user", "assistant"]);
   });
+
+  it("skips incomplete tool calls (partialJson, no arguments) and drops their synthetic results", () => {
+    // Simulates a terminated streaming response: the assistant message has a
+    // tool call with partialJson but no arguments, followed by a synthetic
+    // error toolResult inserted by session persistence.  The repair must skip
+    // the incomplete tool call entirely so no synthetic result is emitted, and
+    // the orphaned synthetic result is dropped.
+    const input = [
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "Let me write that file:" },
+          {
+            type: "toolCall",
+            id: "toolu_terminated",
+            name: "write",
+            partialJson: '{"path": "/tmp/test.md", "content": "# Hello',
+          },
+        ],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_terminated",
+        toolName: "write",
+        content: [
+          {
+            type: "text",
+            text: "[moltbot] missing tool result in session history; inserted synthetic error result for transcript repair.",
+          },
+        ],
+        isError: true,
+      },
+      { role: "user", content: "what happened?" },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+    // The incomplete tool call should be treated as having zero tool calls,
+    // so no toolResult should appear in the output.
+    expect(out.some((m) => m.role === "toolResult")).toBe(false);
+    expect(out.map((m) => m.role)).toEqual(["assistant", "user"]);
+  });
+
+  it("keeps complete tool calls even when partialJson is present", () => {
+    // A tool call that completed successfully may still carry partialJson
+    // from the streaming buffer.  It must be treated normally.
+    const input = [
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "toolCall",
+            id: "call_ok",
+            name: "read",
+            arguments: { path: "/tmp/test.md" },
+            partialJson: '{"path": "/tmp/test.md"}',
+          },
+        ],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "call_ok",
+        toolName: "read",
+        content: [{ type: "text", text: "file contents" }],
+        isError: false,
+      },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+    expect(out).toHaveLength(2);
+    expect(out[0]?.role).toBe("assistant");
+    expect(out[1]?.role).toBe("toolResult");
+  });
+
+  it("handles mixed complete and incomplete tool calls in one assistant message", () => {
+    // The assistant issued two parallel tool calls but was terminated during
+    // the second.  The first call completed and has a real result; the second
+    // is incomplete.  Only the first should be paired.
+    const input = [
+      {
+        role: "assistant",
+        content: [
+          { type: "toolCall", id: "call_done", name: "read", arguments: { path: "/a" } },
+          {
+            type: "toolCall",
+            id: "call_partial",
+            name: "write",
+            partialJson: '{"path": "/b", "content": "half...',
+          },
+        ],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "call_done",
+        toolName: "read",
+        content: [{ type: "text", text: "ok" }],
+        isError: false,
+      },
+      {
+        role: "toolResult",
+        toolCallId: "call_partial",
+        toolName: "write",
+        content: [{ type: "text", text: "[moltbot] synthetic" }],
+        isError: true,
+      },
+      { role: "user", content: "continue" },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+    const results = out.filter((m) => m.role === "toolResult");
+    // Only the completed tool call should have a result
+    expect(results).toHaveLength(1);
+    expect((results[0] as { toolCallId?: string }).toolCallId).toBe("call_done");
+    expect(out.map((m) => m.role)).toEqual(["assistant", "toolResult", "user"]);
+  });
+
+  it("handles incomplete tool call with empty arguments object", () => {
+    // Some providers set arguments to {} when the stream was interrupted
+    // before any argument parsing completed.
+    const input = [
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "toolCall",
+            id: "call_empty_args",
+            name: "exec",
+            arguments: {},
+            partialJson: '{"command": "ls',
+          },
+        ],
+      },
+      { role: "user", content: "?" },
+    ] satisfies AgentMessage[];
+
+    const out = sanitizeToolUseResultPairing(input);
+    expect(out.some((m) => m.role === "toolResult")).toBe(false);
+    expect(out.map((m) => m.role)).toEqual(["assistant", "user"]);
+  });
+});
+
+describe("isIncompleteToolCall", () => {
+  it("returns true for partialJson with no arguments", () => {
+    expect(
+      isIncompleteToolCall({
+        type: "toolCall",
+        id: "x",
+        name: "write",
+        partialJson: '{"path": "/tmp',
+      }),
+    ).toBe(true);
+  });
+
+  it("returns true for partialJson with empty arguments", () => {
+    expect(
+      isIncompleteToolCall({
+        type: "toolCall",
+        id: "x",
+        name: "exec",
+        arguments: {},
+        partialJson: '{"command": "ls',
+      }),
+    ).toBe(true);
+  });
+
+  it("returns false for complete tool call with partialJson", () => {
+    expect(
+      isIncompleteToolCall({
+        type: "toolCall",
+        id: "x",
+        name: "read",
+        arguments: { path: "/tmp/test" },
+        partialJson: '{"path": "/tmp/test"}',
+      }),
+    ).toBe(false);
+  });
+
+  it("returns false for tool call without partialJson", () => {
+    expect(
+      isIncompleteToolCall({
+        type: "toolCall",
+        id: "x",
+        name: "read",
+        arguments: { path: "/tmp/test" },
+      }),
+    ).toBe(false);
+  });
+
+  it("returns false when partialJson is empty string", () => {
+    expect(
+      isIncompleteToolCall({
+        type: "toolCall",
+        id: "x",
+        name: "read",
+        partialJson: "",
+      }),
+    ).toBe(false);
+  });
 });
diff --git a/src/agents/session-transcript-repair.ts b/src/agents/session-transcript-repair.ts
index d680beb4d..4ec30813b 100644
--- a/src/agents/session-transcript-repair.ts
+++ b/src/agents/session-transcript-repair.ts
@@ -5,6 +5,35 @@ type ToolCallLike = {
   name?: string;
 };
 
+/**
+ * Check whether a tool call block is incomplete (terminated mid-stream).
+ *
+ * When a streaming response is interrupted (`stopReason: "error"`,
+ * `errorMessage: "terminated"`), the assistant message may contain tool call
+ * blocks with only `partialJson` and no valid `arguments`.  These were never
+ * executed, so inserting a synthetic `toolResult` for them causes Anthropic's
+ * API to reject the request with "unexpected tool_use_id".
+ *
+ * We detect incompleteness by checking:
+ *   1. `partialJson` is present (streaming was in progress), AND
+ *   2. `arguments` is missing, empty, or not a non-empty object.
+ *
+ * If `arguments` is fully populated the call completed successfully and should
+ * be treated normally, even if `partialJson` happens to be set.
+ */
+function isIncompleteToolCall(block: Record<string, unknown>): boolean {
+  if (typeof block.partialJson !== "string" || !block.partialJson) return false;
+
+  const args = block.arguments;
+  // No arguments at all → incomplete
+  if (args === undefined || args === null) return true;
+  // Empty object {} → incomplete (arguments were not parsed)
+  if (typeof args === "object" && !Array.isArray(args) && Object.keys(args as object).length === 0)
+    return true;
+
+  return false;
+}
+
 function extractToolCallsFromAssistant(
   msg: Extract<AgentMessage, { role: "assistant" }>,
 ): ToolCallLike[] {
@@ -18,6 +47,10 @@ function extractToolCallsFromAssistant(
     if (typeof rec.id !== "string" || !rec.id) continue;
 
     if (rec.type === "toolCall" || rec.type === "toolUse" || rec.type === "functionCall") {
+      // Skip incomplete tool calls from terminated/errored streaming responses.
+      // These were never executed, so they must not receive a synthetic toolResult.
+      if (isIncompleteToolCall(rec as Record<string, unknown>)) continue;
+
       toolCalls.push({
         id: rec.id,
         name: typeof rec.name === "string" ? rec.name : undefined,
@@ -54,7 +87,7 @@ function makeMissingToolResult(params: {
   } as Extract<AgentMessage, { role: "toolResult" }>;
 }
 
-export { makeMissingToolResult };
+export { isIncompleteToolCall, makeMissingToolResult };
 
 export function sanitizeToolUseResultPairing(messages: AgentMessage[]): AgentMessage[] {
   return repairToolUseResultPairing(messages).messages;