diff --git a/src/agent.rs b/src/agent.rs
index 0b144b73..f5b1fa03 100644
--- a/src/agent.rs
+++ b/src/agent.rs
@@ -193,6 +193,7 @@ pub struct Implementation {
 }
 
 impl Implementation {
+    #[must_use]
     pub fn new(name: impl Into<String>, version: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -297,6 +298,7 @@ impl AuthenticateResponse {
 pub struct AuthMethodId(pub Arc<str>);
 
 impl AuthMethodId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -393,6 +395,7 @@ pub struct AuthMethodAgent {
 }
 
 impl AuthMethodAgent {
+    #[must_use]
     pub fn new(id: impl Into<AuthMethodId>, name: impl Into<String>) -> Self {
         Self {
             id: id.into(),
@@ -456,6 +459,7 @@ pub struct AuthMethodEnvVar {
 
 #[cfg(feature = "unstable_auth_methods")]
 impl AuthMethodEnvVar {
+    #[must_use]
     pub fn new(
         id: impl Into<AuthMethodId>,
         name: impl Into<String>,
@@ -473,8 +477,8 @@ impl AuthMethodEnvVar {
 
     /// Optional link to a page where the user can obtain their credentials.
     #[must_use]
-    pub fn link(mut self, link: impl Into<String>) -> Self {
-        self.link = Some(link.into());
+    pub fn link(mut self, link: impl IntoOption<String>) -> Self {
+        self.link = link.into_option();
         self
     }
 
@@ -554,6 +558,7 @@ fn is_false(v: &bool) -> bool {
 #[cfg(feature = "unstable_auth_methods")]
 impl AuthEnvVar {
     /// Creates a new auth env var.
+    #[must_use]
     pub fn new(name: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -566,8 +571,8 @@ impl AuthEnvVar {
 
     /// Human-readable label for this variable, displayed in client UI.
     #[must_use]
-    pub fn label(mut self, label: impl Into<String>) -> Self {
-        self.label = Some(label.into());
+    pub fn label(mut self, label: impl IntoOption<String>) -> Self {
+        self.label = label.into_option();
         self
     }
 
@@ -634,6 +639,7 @@ pub struct AuthMethodTerminal {
 
 #[cfg(feature = "unstable_auth_methods")]
 impl AuthMethodTerminal {
+    #[must_use]
     pub fn new(id: impl Into<AuthMethodId>, name: impl Into<String>) -> Self {
         Self {
             id: id.into(),
@@ -702,6 +708,7 @@ pub struct NewSessionRequest {
 }
 
 impl NewSessionRequest {
+    #[must_use]
     pub fn new(cwd: impl Into<PathBuf>) -> Self {
         Self {
             cwd: cwd.into(),
@@ -850,6 +857,7 @@ pub struct LoadSessionRequest {
 }
 
 impl LoadSessionRequest {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, cwd: impl Into<PathBuf>) -> Self {
         Self {
             mcp_servers: vec![],
@@ -994,6 +1002,7 @@ pub struct ForkSessionRequest {
 
 #[cfg(feature = "unstable_session_fork")]
 impl ForkSessionRequest {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, cwd: impl Into<PathBuf>) -> Self {
         Self {
             session_id: session_id.into(),
@@ -1153,6 +1162,7 @@ pub struct ResumeSessionRequest {
 
 #[cfg(feature = "unstable_session_resume")]
 impl ResumeSessionRequest {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, cwd: impl Into<PathBuf>) -> Self {
         Self {
             session_id: session_id.into(),
@@ -1507,6 +1517,7 @@ pub struct SessionInfo {
 
 #[cfg(feature = "unstable_session_list")]
 impl SessionInfo {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, cwd: impl Into<PathBuf>) -> Self {
         Self {
             session_id: session_id.into(),
@@ -1609,6 +1620,7 @@ pub struct SessionMode {
 }
 
 impl SessionMode {
+    #[must_use]
     pub fn new(id: impl Into<SessionModeId>, name: impl Into<String>) -> Self {
         Self {
             id: id.into(),
@@ -1644,6 +1656,7 @@ impl SessionMode {
 pub struct SessionModeId(pub Arc<str>);
 
 impl SessionModeId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -1718,6 +1731,7 @@ impl SetSessionModeResponse {
 pub struct SessionConfigId(pub Arc<str>);
 
 impl SessionConfigId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -1731,6 +1745,7 @@ impl SessionConfigId {
 pub struct SessionConfigValueId(pub Arc<str>);
 
 impl SessionConfigValueId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -1744,6 +1759,7 @@ impl SessionConfigValueId {
 pub struct SessionConfigGroupId(pub Arc<str>);
 
 impl SessionConfigGroupId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -2143,6 +2159,7 @@ pub struct McpServerHttp {
 }
 
 impl McpServerHttp {
+    #[must_use]
     pub fn new(name: impl Into<String>, url: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -2192,6 +2209,7 @@ pub struct McpServerSse {
 }
 
 impl McpServerSse {
+    #[must_use]
     pub fn new(name: impl Into<String>, url: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -2243,6 +2261,7 @@ pub struct McpServerStdio {
 }
 
 impl McpServerStdio {
+    #[must_use]
     pub fn new(name: impl Into<String>, command: impl Into<PathBuf>) -> Self {
         Self {
             name: name.into(),
@@ -2298,6 +2317,7 @@ pub struct EnvVariable {
 }
 
 impl EnvVariable {
+    #[must_use]
     pub fn new(name: impl Into<String>, value: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -2337,6 +2357,7 @@ pub struct HttpHeader {
 }
 
 impl HttpHeader {
+    #[must_use]
     pub fn new(name: impl Into<String>, value: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -2690,6 +2711,7 @@ pub struct ModelId(pub Arc<str>);
 
 #[cfg(feature = "unstable_session_model")]
 impl ModelId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -2723,6 +2745,7 @@ pub struct ModelInfo {
 
 #[cfg(feature = "unstable_session_model")]
 impl ModelInfo {
+    #[must_use]
     pub fn new(model_id: impl Into<ModelId>, name: impl Into<String>) -> Self {
         Self {
             model_id: model_id.into(),
diff --git a/src/client.rs b/src/client.rs
index 76844bfa..c58f9f98 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -448,6 +448,7 @@ pub struct AvailableCommand {
 }
 
 impl AvailableCommand {
+    #[must_use]
     pub fn new(name: impl Into<String>, description: impl Into<String>) -> Self {
         Self {
             name: name.into(),
@@ -502,6 +503,7 @@ pub struct UnstructuredCommandInput {
 }
 
 impl UnstructuredCommandInput {
+    #[must_use]
     pub fn new(hint: impl Into<String>) -> Self {
         Self {
             hint: hint.into(),
@@ -596,6 +598,7 @@ pub struct PermissionOption {
 }
 
 impl PermissionOption {
+    #[must_use]
     pub fn new(
         option_id: impl Into<PermissionOptionId>,
         name: impl Into<String>,
@@ -629,6 +632,7 @@ impl PermissionOption {
 pub struct PermissionOptionId(pub Arc<str>);
 
 impl PermissionOptionId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -772,6 +776,7 @@ pub struct WriteTextFileRequest {
 }
 
 impl WriteTextFileRequest {
+    #[must_use]
     pub fn new(
         session_id: impl Into<SessionId>,
         path: impl Into<PathBuf>,
@@ -860,6 +865,7 @@ pub struct ReadTextFileRequest {
 }
 
 impl ReadTextFileRequest {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, path: impl Into<PathBuf>) -> Self {
         Self {
             session_id: session_id.into(),
@@ -913,6 +919,7 @@ pub struct ReadTextFileResponse {
 }
 
 impl ReadTextFileResponse {
+    #[must_use]
     pub fn new(content: impl Into<String>) -> Self {
         Self {
             content: content.into(),
@@ -941,6 +948,7 @@ impl ReadTextFileResponse {
 pub struct TerminalId(pub Arc<str>);
 
 impl TerminalId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -985,6 +993,7 @@ pub struct CreateTerminalRequest {
 }
 
 impl CreateTerminalRequest {
+    #[must_use]
     pub fn new(session_id: impl Into<SessionId>, command: impl Into<String>) -> Self {
         Self {
             session_id: session_id.into(),
@@ -1145,6 +1154,7 @@ pub struct TerminalOutputResponse {
 }
 
 impl TerminalOutputResponse {
+    #[must_use]
     pub fn new(output: impl Into<String>, truncated: bool) -> Self {
         Self {
             output: output.into(),
diff --git a/src/content.rs b/src/content.rs
index 7760ba56..123982bb 100644
--- a/src/content.rs
+++ b/src/content.rs
@@ -75,6 +75,7 @@ pub struct TextContent {
 }
 
 impl TextContent {
+    #[must_use]
     pub fn new(text: impl Into<String>) -> Self {
         Self {
             annotations: None,
@@ -128,6 +129,7 @@ pub struct ImageContent {
 }
 
 impl ImageContent {
+    #[must_use]
     pub fn new(data: impl Into<String>, mime_type: impl Into<String>) -> Self {
         Self {
             annotations: None,
@@ -181,6 +183,7 @@ pub struct AudioContent {
 }
 
 impl AudioContent {
+    #[must_use]
     pub fn new(data: impl Into<String>, mime_type: impl Into<String>) -> Self {
         Self {
             annotations: None,
@@ -280,6 +283,7 @@ pub struct TextResourceContents {
 }
 
 impl TextResourceContents {
+    #[must_use]
     pub fn new(text: impl Into<String>, uri: impl Into<String>) -> Self {
         Self {
             mime_type: None,
@@ -326,6 +330,7 @@ pub struct BlobResourceContents {
 }
 
 impl BlobResourceContents {
+    #[must_use]
     pub fn new(blob: impl Into<String>, uri: impl Into<String>) -> Self {
         Self {
             blob: blob.into(),
@@ -380,6 +385,7 @@ pub struct ResourceLink {
 }
 
 impl ResourceLink {
+    #[must_use]
     pub fn new(name: impl Into<String>, uri: impl Into<String>) -> Self {
         Self {
             annotations: None,
diff --git a/src/error.rs b/src/error.rs
index 5fb94a16..22a98bff 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -54,6 +54,7 @@ impl Error {
     /// Creates a new error with the given code and message.
     ///
     /// The code parameter can be an `ErrorCode` constant or a tuple of (code, message).
+    #[must_use]
     pub fn new(code: i32, message: impl Into<String>) -> Self {
         Error {
             code: code.into(),
@@ -152,6 +153,7 @@ impl Error {
     /// Converts a standard error into an internal JSON-RPC error.
     ///
     /// The error's string representation is included as additional data.
+    #[must_use]
     pub fn into_internal_error(err: impl std::error::Error) -> Self {
         Error::internal_error().data(err.to_string())
     }
diff --git a/src/ext.rs b/src/ext.rs
index ab8c22d0..c89b6b5d 100644
--- a/src/ext.rs
+++ b/src/ext.rs
@@ -30,6 +30,7 @@ pub struct ExtRequest {
 }
 
 impl ExtRequest {
+    #[must_use]
     pub fn new(method: impl Into<Arc<str>>, params: Arc<RawValue>) -> Self {
         Self {
             method: method.into(),
@@ -71,6 +72,7 @@ pub struct ExtNotification {
 }
 
 impl ExtNotification {
+    #[must_use]
     pub fn new(method: impl Into<Arc<str>>, params: Arc<RawValue>) -> Self {
         Self {
             method: method.into(),
diff --git a/src/lib.rs b/src/lib.rs
index 63805a38..b38e7411 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -100,6 +100,7 @@ use std::{
 pub struct SessionId(pub Arc<str>);
 
 impl SessionId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
diff --git a/src/plan.rs b/src/plan.rs
index 6d6bc0d1..60d75083 100644
--- a/src/plan.rs
+++ b/src/plan.rs
@@ -82,6 +82,7 @@ pub struct PlanEntry {
 }
 
 impl PlanEntry {
+    #[must_use]
     pub fn new(
         content: impl Into<String>,
         priority: PlanEntryPriority,
diff --git a/src/rpc.rs b/src/rpc.rs
index 5bdfa08d..eb5aeb97 100644
--- a/src/rpc.rs
+++ b/src/rpc.rs
@@ -72,6 +72,7 @@ pub enum Response<Result> {
 }
 
 impl<R> Response<R> {
+    #[must_use]
     pub fn new(id: impl Into<RequestId>, result: Result<R>) -> Self {
         match result {
             Ok(result) => Self::Result {
diff --git a/src/tool_call.rs b/src/tool_call.rs
index d8c808b9..5b5ae590 100644
--- a/src/tool_call.rs
+++ b/src/tool_call.rs
@@ -56,6 +56,7 @@ pub struct ToolCall {
 }
 
 impl ToolCall {
+    #[must_use]
     pub fn new(tool_call_id: impl Into<ToolCallId>, title: impl Into<String>) -> Self {
         Self {
             tool_call_id: tool_call_id.into(),
@@ -361,6 +362,7 @@ impl From<ToolCall> for ToolCallUpdate {
 pub struct ToolCallId(pub Arc<str>);
 
 impl ToolCallId {
+    #[must_use]
     pub fn new(id: impl Into<Arc<str>>) -> Self {
         Self(id.into())
     }
@@ -487,6 +489,7 @@ pub struct Content {
 }
 
 impl Content {
+    #[must_use]
     pub fn new(content: impl Into<ContentBlock>) -> Self {
         Self {
             content: content.into(),
@@ -571,6 +574,7 @@ pub struct Diff {
 }
 
 impl Diff {
+    #[must_use]
     pub fn new(path: impl Into<PathBuf>, new_text: impl Into<String>) -> Self {
         Self {
             path: path.into(),
@@ -624,6 +628,7 @@ pub struct ToolCallLocation {
 }
 
 impl ToolCallLocation {
+    #[must_use]
     pub fn new(path: impl Into<PathBuf>) -> Self {
         Self {
             path: path.into(),