diff --git a/crates/focus-core/src/provider.rs b/crates/focus-core/src/provider.rs
index 3424476..4da072f 100644
--- a/crates/focus-core/src/provider.rs
+++ b/crates/focus-core/src/provider.rs
@@ -276,15 +276,33 @@ impl ProviderEventReducer {
         out
     }
 
-    /// 在 `index`（provider 局部索引，映射到一个新内容槽）处打开工具调用块。
+    /// 在 `index`（provider 局部索引，映射到一个新内容槽）处打开工具调用块，
+    /// 使用指定的调用 id（API 提供的真实 id）。
     /// Open a tool-call block at `index` (provider-local index, mapped to a
-    /// new content slot).
-    pub fn tool_call_start(&mut self, index: usize, name: &str) -> Vec<StreamEvent> {
+    /// new content slot), using the given call id (the API's real id).
+    ///
+    /// 使用 API 的真实 id 至关重要：跨多轮工具调用时，若每轮都从 `call_0`
+    /// 重新生成，回放历史时 id 会冲突，导致 API 无法配对 function_call 与
+    /// function_call_output。空 id 时退回自动生成。
+    /// Using the API's real id matters: across multiple tool-using turns,
+    /// re-generating `call_0` every turn collides on replay, breaking the
+    /// function_call ↔ function_call_output pairing. Empty ids fall back to
+    /// auto-generated ones.
+    pub fn tool_call_start_with_id(
+        &mut self,
+        index: usize,
+        name: &str,
+        id: &str,
+    ) -> Vec<StreamEvent> {
         let mut out = Vec::new();
         if let Some(ev) = self.ensure_started() {
             out.push(ev);
         }
-        let call_id = format!("call_{}", self.tool_call_pos.len());
+        let call_id = if id.is_empty() {
+            format!("call_{}", self.tool_call_pos.len())
+        } else {
+            id.to_string()
+        };
         self.content.push(ContentBlock::ToolCall(ToolCall {
             id: call_id,
             name: name.to_string(),
@@ -300,6 +318,14 @@ impl ProviderEventReducer {
         out
     }
 
+    /// 在 `index`（provider 局部索引，映射到一个新内容槽）处打开工具调用块，
+    /// 自动生成调用 id。
+    /// Open a tool-call block at `index` (provider-local index, mapped to a
+    /// new content slot) with an auto-generated call id.
+    pub fn tool_call_start(&mut self, index: usize, name: &str) -> Vec<StreamEvent> {
+        self.tool_call_start_with_id(index, name, "")
+    }
+
     /// 向 `index` 处的工具调用追加部分 JSON 参数（按 provider 局部索引寻址）。
     /// Append partial JSON arguments to the tool call at `index` (addressed by
     /// the provider-local index).
diff --git a/crates/focus-core/tests/provider_tests.rs b/crates/focus-core/tests/provider_tests.rs
index 98b5d17..4140108 100644
--- a/crates/focus-core/tests/provider_tests.rs
+++ b/crates/focus-core/tests/provider_tests.rs
@@ -92,3 +92,18 @@ fn reducer_thinking_then_text() {
         .iter()
         .any(|e| matches!(e, StreamEvent::ThinkingEnd { .. })));
 }
+
+/// 工具调用 id 可显式指定（API 真实 id），空时退回自动生成。
+/// Tool-call ids can be set explicitly (the API's real id); empty falls back
+/// to auto-generation.
+#[test]
+fn reducer_tool_call_id_override() {
+    let mut r = ProviderEventReducer::new("m");
+    let _ = r.tool_call_start_with_id(0, "shell", "call_00_realId");
+    let _ = r.tool_call_start_with_id(1, "read", "");
+    let msg = r.finish().expect("final message");
+    let tc0 = msg.content[0].as_tool_call().expect("call 0");
+    let tc1 = msg.content[1].as_tool_call().expect("call 1");
+    assert_eq!(tc0.id, "call_00_realId");
+    assert_eq!(tc1.id, "call_1");
+}
diff --git a/crates/focus-providers/src/openai.rs b/crates/focus-providers/src/openai.rs
index 79f3f35..07d76bf 100644
--- a/crates/focus-providers/src/openai.rs
+++ b/crates/focus-providers/src/openai.rs
@@ -650,7 +650,13 @@ impl OpenAiTurn {
                             if let Some(f) = tc.get("function") {
                                 if let Some(name) = f.get_str("name") {
                                     if !name.is_empty() && self.seen_calls.insert(idx) {
-                                        for ev in self.reducer.tool_call_start(idx, name) {
+                                        // 用 API 的真实 id（跨回合唯一）。
+                                        // Use the API's real id (unique across
+                                        // turns).
+                                        let call_id = tc.get_str("id").unwrap_or("");
+                                        for ev in
+                                            self.reducer.tool_call_start_with_id(idx, name, call_id)
+                                        {
                                             if !common::send(tx, ev) {
                                                 return Ok(false);
                                             }
@@ -709,8 +715,12 @@ impl OpenAiTurn {
                         "function_call" => {
                             let idx = json.get_num("output_index").unwrap_or(0.0) as usize;
                             let name = item.get_str("name").unwrap_or("").to_string();
+                            // 用 API 的真实 call_id（跨回合唯一，回放时避免冲突）。
+                            // Use the API's real call_id (unique across turns,
+                            // avoiding collisions on replay).
+                            let call_id = item.get_str("call_id").unwrap_or("");
                             if !name.is_empty() {
-                                for e in self.reducer.tool_call_start(idx, &name) {
+                                for e in self.reducer.tool_call_start_with_id(idx, &name, call_id) {
                                     if !common::send(tx, e) {
                                         return Ok(false);
                                     }
diff --git a/crates/focus-providers/tests/openai_tests.rs b/crates/focus-providers/tests/openai_tests.rs
index 0a6df6c..83edd9a 100644
--- a/crates/focus-providers/tests/openai_tests.rs
+++ b/crates/focus-providers/tests/openai_tests.rs
@@ -686,6 +686,12 @@ fn real_log_captures_reasoning_and_tools() {
     let cmd2 = tc2.arguments.get_str("command").unwrap_or("");
     assert!(cmd2.contains("find"), "got: {}", cmd2);
 
+    // 调用 id 必须保留 API 的真实 id（跨回合唯一，回放不冲突）。
+    // Call ids must keep the API's real ids (unique across turns, no replay
+    // collisions).
+    assert_eq!(tc1.id, "call_00_wyQ");
+    assert_eq!(tc2.id, "call_01_wUr");
+
     // usage 映射：input / output / cache-read。
     // Usage mapping: input / output / cache-read.
     assert_eq!(msg.usage.input_tokens, 850);
@@ -825,8 +831,9 @@ fn agent_multi_turn_replays_reasoning() {
         "got: {}",
         text
     );
-    // function_call 与 function_call_output 的 call_id 一致。
-    // The function_call and function_call_output call ids match.
+    // function_call 与 function_call_output 的 call_id 一致，且为 API 的真实 id。
+    // The function_call and function_call_output call ids match, using the
+    // API's real ids.
     let fc = input
         .iter()
         .find(|i| i.get_str("type") == Some("function_call"))
@@ -836,4 +843,27 @@ fn agent_multi_turn_replays_reasoning() {
         .find(|i| i.get_str("type") == Some("function_call_output"))
         .expect("function_call_output item");
     assert_eq!(fc.get_str("call_id"), fco.get_str("call_id"));
+    assert_eq!(fc.get_str("call_id"), Some("call_00_wyQ"));
+
+    // 第 3 个请求（回放两轮历史）：两轮的 call_id 不得冲突（回归：此前每轮
+    // 都从 call_0 重新生成导致跨回合撞号）。
+    // The third request (replaying two turns): call ids across turns must not
+    // collide (regression: ids used to restart at call_0 every turn).
+    let body3: focus_json::JsonValue =
+        focus_json::parse(&String::from_utf8_lossy(&reqs[2].body)).unwrap();
+    let input3 = body3.get_arr("input").expect("input items");
+    let call_ids: Vec<&str> = input3
+        .iter()
+        .filter(|i| i.get_str("type") == Some("function_call"))
+        .filter_map(|i| i.get_str("call_id"))
+        .collect();
+    let mut unique: Vec<&str> = call_ids.clone();
+    unique.sort();
+    unique.dedup();
+    assert_eq!(
+        unique.len(),
+        call_ids.len(),
+        "call ids must be unique across turns, got {:?}",
+        call_ids
+    );
 }