diff --git a/crates/agentic-core/src/storage/types/item.rs b/crates/agentic-core/src/storage/types/item.rs
index 9da2f44..85a5491 100644
--- a/crates/agentic-core/src/storage/types/item.rs
+++ b/crates/agentic-core/src/storage/types/item.rs
@@ -90,7 +90,8 @@ impl InOutItem {
                 InOutItem::Input(item) => Some(item),
                 InOutItem::Output(OutputItem::Message(msg)) => Some(InputItem::Message(msg.into())),
                 InOutItem::Output(OutputItem::Reasoning(r)) => Some(InputItem::Reasoning(r)),
-                InOutItem::Output(OutputItem::FunctionCall(_) | OutputItem::Unknown) => None,
+                InOutItem::Output(OutputItem::FunctionCall(f)) => Some(InputItem::FunctionCall(f)),
+                InOutItem::Output(OutputItem::Unknown) => None,
             })
             .collect()
     }
@@ -101,8 +102,8 @@ mod tests {
     use super::*;
     use crate::types::event::MessageStatus;
     use crate::types::io::{
-        InputContent, InputMessage, InputMessageContent, OutputMessage, OutputTextContent, ReasoningOutput,
-        ReasoningTextContent,
+        FunctionToolCall, InputContent, InputMessage, InputMessageContent, OutputMessage, OutputTextContent,
+        ReasoningOutput, ReasoningTextContent,
     };
 
     #[test]
@@ -161,11 +162,10 @@ mod tests {
                     InputMessageContent::Parts(parts) => {
                         assert_eq!(parts.len(), 1);
                         match &parts[0] {
-                            InputContent::Text(t) => {
-                                assert_eq!(t.type_, "output_text");
+                            InputContent::OutputText(t) => {
                                 assert_eq!(t.text, "answer");
                             }
-                            InputContent::Image(_) => panic!("expected text part"),
+                            _ => panic!("expected OutputText part"),
                         }
                     }
                     InputMessageContent::Text(_) => panic!("expected parts content"),
@@ -196,6 +196,25 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_into_input_items_preserves_function_calls() {
+        use crate::types::event::MessageStatus;
+        let fc = FunctionToolCall {
+            id: "fc_1".to_string(),
+            call_id: "call_abc".to_string(),
+            name: "my_tool".to_string(),
+            arguments: "{}".to_string(),
+            status: MessageStatus::Completed,
+        };
+        let items = vec![InOutItem::Output(OutputItem::FunctionCall(fc))];
+        let inputs = InOutItem::into_input_items(items);
+        assert_eq!(inputs.len(), 1);
+        assert!(matches!(inputs[0], InputItem::FunctionCall(_)));
+        if let InputItem::FunctionCall(f) = &inputs[0] {
+            assert_eq!(f.name, "my_tool");
+        }
+    }
+
     #[test]
     fn test_item_kind_serialization() {
         let kind = ItemKind::Input;
diff --git a/crates/agentic-core/src/types/io/input.rs b/crates/agentic-core/src/types/io/input.rs
index cfcbec9..f5df8e2 100644
--- a/crates/agentic-core/src/types/io/input.rs
+++ b/crates/agentic-core/src/types/io/input.rs
@@ -1,29 +1,36 @@
 use serde::{Deserialize, Serialize};
 
-use super::output::ReasoningOutput;
+use super::output::{FunctionToolCall, ReasoningOutput};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InputTextContent {
-    #[serde(rename = "type")]
-    pub type_: String,
     pub text: String,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InputImageContent {
-    #[serde(rename = "type")]
-    pub type_: String,
     pub image_url: Option<String>,
     pub detail: Option<String>,
 }
 
+/// Content item inside a message input.
+///
+/// Uses an internally-tagged enum — serde consumes `"type"` for the variant
+/// discriminant so the inner structs must NOT redeclare a `type_` field.
+/// `output_text` and `reasoning_text` reuse `InputTextContent` since they
+/// carry only a `text` field; they are preserved so vLLM sees the full history.
 #[derive(Debug, Clone, Serialize, Deserialize)]
-#[serde(tag = "type")]
+#[serde(tag = "type", rename_all = "snake_case")]
 pub enum InputContent {
-    #[serde(rename = "input_text")]
-    Text(InputTextContent),
-    #[serde(rename = "input_image")]
-    Image(InputImageContent),
+    InputText(InputTextContent),
+    InputImage(InputImageContent),
+    /// Assistant output text in rehydrated history.
+    OutputText(InputTextContent),
+    /// Reasoning step text in rehydrated history.
+    ReasoningText(InputTextContent),
+    /// Any other content type — drop silently.
+    #[serde(other)]
+    Unknown,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -50,6 +57,10 @@ pub struct FunctionToolResultMessage {
 pub enum InputItem {
     #[serde(rename = "message")]
     Message(InputMessage),
+    /// The model's tool invocation — appears in rehydrated history so vLLM sees
+    /// the full call/output pair across turns.
+    #[serde(rename = "function_call")]
+    FunctionCall(FunctionToolCall),
     #[serde(rename = "function_call_output")]
     FunctionCallOutput(FunctionToolResultMessage),
     #[serde(rename = "reasoning")]
diff --git a/crates/agentic-core/src/types/io/output.rs b/crates/agentic-core/src/types/io/output.rs
index 5925f06..fa4a85e 100644
--- a/crates/agentic-core/src/types/io/output.rs
+++ b/crates/agentic-core/src/types/io/output.rs
@@ -68,12 +68,7 @@ impl From<OutputMessage> for InputMessage {
         let parts = msg
             .content
             .into_iter()
-            .map(|c| {
-                InputContent::Text(InputTextContent {
-                    type_: c.type_,
-                    text: c.text,
-                })
-            })
+            .map(|c| InputContent::OutputText(InputTextContent { text: c.text }))
             .collect();
         Self {
             role: msg.role,
@@ -148,6 +143,7 @@ impl ReasoningTextContent {
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct ReasoningOutput {
+    #[serde(default)]
     pub id: String,
     #[serde(default)]
     pub content: Vec<ReasoningTextContent>,
diff --git a/crates/agentic-core/src/types/io/tools.rs b/crates/agentic-core/src/types/io/tools.rs
index 483604f..7e6f61b 100644
--- a/crates/agentic-core/src/types/io/tools.rs
+++ b/crates/agentic-core/src/types/io/tools.rs
@@ -1,9 +1,13 @@
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
+fn default_function_type() -> String {
+    "function".to_string()
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct FunctionTool {
-    #[serde(rename = "type")]
+    #[serde(rename = "type", default = "default_function_type")]
     pub type_: String,
     pub name: String,
     pub description: Option<String>,