diff --git a/crates/mq-check/src/format.rs b/crates/mq-check/src/format.rs
index 79ca0d067..9f4c55392 100644
--- a/crates/mq-check/src/format.rs
+++ b/crates/mq-check/src/format.rs
@@ -58,7 +58,7 @@ pub(crate) fn syntax_diagnostics(hir: &Hir, source_id: SourceId) -> Vec<CheckDia
     let mut diagnostics: Vec<CheckDiagnostic> = hir
         .errors()
         .iter()
-        .filter(|error| hir_error_symbol(error).source.source_id == Some(source_id))
+        .filter(|error| error.symbol().source.source_id == Some(source_id))
         .map(|error| CheckDiagnostic {
             severity: Severity::Error,
             code: hir_error_code(error),
@@ -88,19 +88,12 @@ fn hir_error_code(error: &HirError) -> &'static str {
         HirError::UnresolvedSymbol { .. } => "hir::unresolved_symbol",
         HirError::ModuleNotFound { .. } => "hir::module_not_found",
         HirError::YieldOutsideFunction { .. } => "hir::yield_outside_function",
-    }
-}
-
-pub(crate) fn hir_error_symbol(error: &HirError) -> &Symbol {
-    match error {
-        HirError::UnresolvedSymbol { symbol, .. }
-        | HirError::ModuleNotFound { symbol, .. }
-        | HirError::YieldOutsideFunction { symbol } => symbol,
+        _ => "hir::unknown",
     }
 }
 
 pub(crate) fn hir_error_range(error: &HirError) -> mq_lang::Range {
-    hir_error_symbol(error).source.text_range.unwrap_or_default()
+    error.symbol().source.text_range.unwrap_or_default()
 }
 
 /// Returns a stable rule code for a [`HirWarning`] variant.
@@ -149,6 +142,7 @@ fn type_error_code(error: &TypeError) -> &'static str {
         TypeError::NullablePropagation { .. } => "typechecker::nullable_propagation",
         TypeError::UnreachableCode { .. } => "typechecker::unreachable_code",
         TypeError::NonExhaustiveMatch { .. } => "typechecker::non_exhaustive_patterns",
+        _ => "typechecker::unknown",
     }
 }
 
diff --git a/crates/mq-check/src/lib.rs b/crates/mq-check/src/lib.rs
index ba47b32b2..60710aa68 100644
--- a/crates/mq-check/src/lib.rs
+++ b/crates/mq-check/src/lib.rs
@@ -88,6 +88,7 @@ impl<'a> IntoIterator for &'a TypeEnv {
 /// Type checking errors
 #[derive(Debug, Error, Clone, Diagnostic)]
 #[allow(unused_assignments)]
+#[non_exhaustive]
 pub enum TypeError {
     #[error("Type mismatch: expected {expected}, found {found}")]
     #[diagnostic(code(typechecker::type_mismatch))]
@@ -263,6 +264,7 @@ pub(crate) fn walk_ancestors(
 
 /// Options for configuring the type checker behavior
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct TypeCheckerOptions {
     /// When true, arrays must contain elements of a single type.
     /// Heterogeneous arrays like `[1, "hello"]` will produce a type error.
@@ -274,6 +276,26 @@ pub struct TypeCheckerOptions {
     pub input_type: Option<types::Type>,
 }
 
+impl TypeCheckerOptions {
+    /// Sets `strict_array`.
+    pub fn with_strict_array(mut self, strict_array: bool) -> Self {
+        self.strict_array = strict_array;
+        self
+    }
+
+    /// Sets `no_exhaustive_patterns`.
+    pub fn with_no_exhaustive_patterns(mut self, no_exhaustive_patterns: bool) -> Self {
+        self.no_exhaustive_patterns = no_exhaustive_patterns;
+        self
+    }
+
+    /// Sets `input_type`.
+    pub fn with_input_type(mut self, input_type: Option<types::Type>) -> Self {
+        self.input_type = input_type;
+        self
+    }
+}
+
 /// Wall-clock time of each phase of [`TypeChecker::check_profiled`], in execution order.
 ///
 /// A phase that runs more than once appears once per run.
diff --git a/crates/mq-check/src/main.rs b/crates/mq-check/src/main.rs
index 1ea1edf2b..545f5a90a 100644
--- a/crates/mq-check/src/main.rs
+++ b/crates/mq-check/src/main.rs
@@ -48,11 +48,10 @@ struct Cli {
 
 impl Cli {
     fn type_checker_options(&self) -> TypeCheckerOptions {
-        TypeCheckerOptions {
-            strict_array: self.strict_array,
-            no_exhaustive_patterns: self.no_exhaustive_patterns,
-            input_type: self.input_type.clone(),
-        }
+        TypeCheckerOptions::default()
+            .with_strict_array(self.strict_array)
+            .with_no_exhaustive_patterns(self.no_exhaustive_patterns)
+            .with_input_type(self.input_type.clone())
     }
 }
 
@@ -252,7 +251,7 @@ fn check_syntax(w: &mut impl Write, hir: &mq_hir::Hir, source_id: mq_hir::Source
     let errors: Vec<(String, mq_lang::Range)> = hir
         .errors()
         .iter()
-        .filter(|error| format::hir_error_symbol(error).source.source_id == Some(source_id))
+        .filter(|error| error.symbol().source.source_id == Some(source_id))
         .map(|error| (error.to_string(), format::hir_error_range(error)))
         .collect();
     let warnings: Vec<(String, mq_lang::Range)> = hir
@@ -425,6 +424,7 @@ fn error_title(error: &TypeError) -> String {
         TypeError::NonExhaustiveMatch { missing, .. } => {
             format!("non-exhaustive patterns: missing case for {missing}")
         }
+        _ => error.to_string(),
     }
 }
 
@@ -560,10 +560,8 @@ mod tests {
 
     #[test]
     fn test_input_type_is_applied_to_the_checked_source() {
-        let options = TypeCheckerOptions {
-            input_type: Some(mq_check::type_expr::parse_type("code").unwrap()),
-            ..Default::default()
-        };
+        let options =
+            TypeCheckerOptions::default().with_input_type(Some(mq_check::type_expr::parse_type("code").unwrap()));
         let diagnostics = collect_check_diagnostics(".depth", None, false, &options);
         assert!(diagnostics.iter().any(|d| d.code == "typechecker::undefined_attribute"));
         let diagnostics = collect_check_diagnostics(".depth", None, false, &TypeCheckerOptions::default());
diff --git a/crates/mq-check/src/narrowing.rs b/crates/mq-check/src/narrowing.rs
index 1916808e9..92d095f8e 100644
--- a/crates/mq-check/src/narrowing.rs
+++ b/crates/mq-check/src/narrowing.rs
@@ -150,7 +150,8 @@ pub(crate) fn selector_kinds(selector: &mq_lang::Selector) -> Option<KindSet> {
         Selector::MdxTextExpression => one(NodeKind::MdxTextExpression),
         Selector::MdxJsEsm => one(NodeKind::MdxJsEsm),
         Selector::MdxJsxFlowElement => one(NodeKind::MdxJsxFlowElement),
-        Selector::Recursive | Selector::Attr(_) | Selector::Property(_) => return None,
+        // `Selector` is `#[non_exhaustive]`: unknown selectors narrow nothing.
+        _ => return None,
     })
 }
 
diff --git a/crates/mq-check/tests/node_types_test.rs b/crates/mq-check/tests/node_types_test.rs
index a04039043..63ed92a51 100644
--- a/crates/mq-check/tests/node_types_test.rs
+++ b/crates/mq-check/tests/node_types_test.rs
@@ -170,10 +170,10 @@ fn test_attribute_of_a_constructed_node_is_checked() {
 fn errors_with_input(code: &str, input_type: &str) -> Vec<mq_check::TypeError> {
     let mut hir = Hir::default();
     hir.add_code(None, code);
-    TypeChecker::with_options(mq_check::TypeCheckerOptions {
-        input_type: Some(mq_check::type_expr::parse_type(input_type).unwrap()),
-        ..Default::default()
-    })
+    TypeChecker::with_options(
+        mq_check::TypeCheckerOptions::default()
+            .with_input_type(Some(mq_check::type_expr::parse_type(input_type).unwrap())),
+    )
     .check(&hir)
 }
 
diff --git a/crates/mq-check/tests/type_errors_test.rs b/crates/mq-check/tests/type_errors_test.rs
index 46e0ef923..a13d3dcb0 100644
--- a/crates/mq-check/tests/type_errors_test.rs
+++ b/crates/mq-check/tests/type_errors_test.rs
@@ -419,20 +419,14 @@ fn test_narrowing_selector_various_structural() {
 /// Helper function to run type checker with strict array mode enabled
 fn check_types_strict_array(code: &str) -> Vec<TypeError> {
     let hir = create_hir(code);
-    let mut checker = TypeChecker::with_options(TypeCheckerOptions {
-        strict_array: true,
-        ..Default::default()
-    });
+    let mut checker = TypeChecker::with_options(TypeCheckerOptions::default().with_strict_array(true));
     checker.check(&hir)
 }
 
 /// Helper function to run type checker with tuple mode enabled
 fn check_types_tuple(code: &str) -> Vec<TypeError> {
     let hir = create_hir(code);
-    let mut checker = TypeChecker::with_options(TypeCheckerOptions {
-        strict_array: false,
-        ..Default::default()
-    });
+    let mut checker = TypeChecker::with_options(TypeCheckerOptions::default().with_strict_array(false));
     checker.check(&hir)
 }
 
diff --git a/crates/mq-crawler/src/http_client.rs b/crates/mq-crawler/src/http_client.rs
index e1f106072..779f56938 100644
--- a/crates/mq-crawler/src/http_client.rs
+++ b/crates/mq-crawler/src/http_client.rs
@@ -15,6 +15,7 @@ use url::Url;
 ///
 /// Retries on network errors, `429`, and `5xx`; other client errors (e.g. `404`) are not retried.
 #[derive(Debug, Clone, PartialEq)]
+#[non_exhaustive]
 pub struct RetryConfig {
     /// Retry attempts after the initial request fails.
     pub max_retries: u32,
@@ -26,6 +27,32 @@ pub struct RetryConfig {
     pub backoff_multiplier: f64,
 }
 
+impl RetryConfig {
+    /// Sets `max_retries`.
+    pub fn with_max_retries(mut self, max_retries: u32) -> Self {
+        self.max_retries = max_retries;
+        self
+    }
+
+    /// Sets `initial_backoff`.
+    pub fn with_initial_backoff(mut self, initial_backoff: Duration) -> Self {
+        self.initial_backoff = initial_backoff;
+        self
+    }
+
+    /// Sets `max_backoff`.
+    pub fn with_max_backoff(mut self, max_backoff: Duration) -> Self {
+        self.max_backoff = max_backoff;
+        self
+    }
+
+    /// Sets `backoff_multiplier`.
+    pub fn with_backoff_multiplier(mut self, backoff_multiplier: f64) -> Self {
+        self.backoff_multiplier = backoff_multiplier;
+        self
+    }
+}
+
 impl Default for RetryConfig {
     fn default() -> Self {
         Self {
@@ -54,6 +81,7 @@ impl RetryConfig {
 
 /// Default `Authorization` header credentials for a `reqwest`-based [`HttpClient`].
 #[derive(Debug, Clone)]
+#[non_exhaustive]
 pub enum AuthConfig {
     /// `Authorization: Basic <base64(user:pass)>`.
     Basic { username: String, password: Option<String> },
@@ -81,6 +109,7 @@ impl FetchError {
 /// Multiple strategies can be combined; they are executed in order:
 /// network-idle / selector wait first, then the fixed delay.
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct ChromiumWaitConfig {
     /// Optional fixed delay applied after all other strategies complete.
     pub fixed_delay: Duration,
@@ -95,6 +124,32 @@ pub struct ChromiumWaitConfig {
     pub strategy_timeout: Duration,
 }
 
+impl ChromiumWaitConfig {
+    /// Sets `fixed_delay`.
+    pub fn with_fixed_delay(mut self, fixed_delay: Duration) -> Self {
+        self.fixed_delay = fixed_delay;
+        self
+    }
+
+    /// Sets `wait_for_selector`.
+    pub fn with_wait_for_selector(mut self, wait_for_selector: Option<String>) -> Self {
+        self.wait_for_selector = wait_for_selector;
+        self
+    }
+
+    /// Sets `network_idle`.
+    pub fn with_network_idle(mut self, network_idle: bool) -> Self {
+        self.network_idle = network_idle;
+        self
+    }
+
+    /// Sets `strategy_timeout`.
+    pub fn with_strategy_timeout(mut self, strategy_timeout: Duration) -> Self {
+        self.strategy_timeout = strategy_timeout;
+        self
+    }
+}
+
 /// Enum for different HTTP client implementations
 #[derive(Debug, Clone)]
 pub enum HttpClient {
diff --git a/crates/mq-crawler/src/main.rs b/crates/mq-crawler/src/main.rs
index 16a42907a..dda671cac 100644
--- a/crates/mq-crawler/src/main.rs
+++ b/crates/mq-crawler/src/main.rs
@@ -226,12 +226,11 @@ async fn main() {
         v
     });
 
-    let retry_config = mq_crawler::http_client::RetryConfig {
-        max_retries: args.max_retries,
-        initial_backoff: std::time::Duration::from_secs_f64(args.retry_initial_backoff.max(0.0)),
-        max_backoff: std::time::Duration::from_secs_f64(args.retry_max_backoff.max(0.0)),
-        backoff_multiplier: args.retry_backoff_multiplier,
-    };
+    let retry_config = mq_crawler::http_client::RetryConfig::default()
+        .with_max_retries(args.max_retries)
+        .with_initial_backoff(std::time::Duration::from_secs_f64(args.retry_initial_backoff.max(0.0)))
+        .with_max_backoff(std::time::Duration::from_secs_f64(args.retry_max_backoff.max(0.0)))
+        .with_backoff_multiplier(args.retry_backoff_multiplier);
 
     let header_map = match build_header_map(&args.headers, &args.cookie) {
         Ok(header_map) => header_map,
@@ -309,12 +308,11 @@ async fn main() {
             std::time::Duration::from_secs_f64(headless_wait_secs)
         };
 
-        let wait_config = mq_crawler::http_client::ChromiumWaitConfig {
-            fixed_delay,
-            wait_for_selector: args.headless_wait_for_selector.clone(),
-            network_idle: args.headless_network_idle,
-            strategy_timeout,
-        };
+        let wait_config = mq_crawler::http_client::ChromiumWaitConfig::default()
+            .with_fixed_delay(fixed_delay)
+            .with_wait_for_selector(args.headless_wait_for_selector.clone())
+            .with_network_idle(args.headless_network_idle)
+            .with_strategy_timeout(strategy_timeout);
 
         mq_crawler::http_client::HttpClient::new_chromium(args.chrome_path, wait_config, retry_config.clone())
             .await
@@ -381,12 +379,10 @@ async fn main() {
         args.output,
         args.concurrency,
         format,
-        mq_markdown::ConversionOptions {
-            extract_scripts_as_code_blocks: args.conversion.extract_scripts_as_code_blocks,
-            generate_front_matter: args.conversion.generate_front_matter,
-            use_title_as_h1: args.conversion.use_title_as_h1,
-            base_url: None,
-        },
+        mq_markdown::ConversionOptions::default()
+            .with_extract_scripts_as_code_blocks(args.conversion.extract_scripts_as_code_blocks)
+            .with_generate_front_matter(args.conversion.generate_front_matter)
+            .with_use_title_as_h1(args.conversion.use_title_as_h1),
         args.depth,
         effective_allowed,
         sitemap_seed_urls,
diff --git a/crates/mq-dap/src/error.rs b/crates/mq-dap/src/error.rs
index 6fd5954a5..9046b7825 100644
--- a/crates/mq-dap/src/error.rs
+++ b/crates/mq-dap/src/error.rs
@@ -4,6 +4,7 @@ use dap::prelude::Command;
 use thiserror::Error;
 
 #[derive(Error, Debug)]
+#[non_exhaustive]
 pub enum MqAdapterError {
     #[error("Unhandled command: {0:?}")]
     UnhandledCommand(Box<Command>),
diff --git a/crates/mq-ffi/src/lib.rs b/crates/mq-ffi/src/lib.rs
index 77939ac65..9f7526c1f 100644
--- a/crates/mq-ffi/src/lib.rs
+++ b/crates/mq-ffi/src/lib.rs
@@ -109,12 +109,11 @@ impl From<MqConversionOptions> for ConversionOptions {
                 .filter(|s| !s.is_empty())
                 .map(|s| s.to_string())
         };
-        ConversionOptions {
-            extract_scripts_as_code_blocks: options.extract_scripts_as_code_blocks,
-            generate_front_matter: options.generate_front_matter,
-            use_title_as_h1: options.use_title_as_h1,
-            base_url,
-        }
+        ConversionOptions::default()
+            .with_extract_scripts_as_code_blocks(options.extract_scripts_as_code_blocks)
+            .with_generate_front_matter(options.generate_front_matter)
+            .with_use_title_as_h1(options.use_title_as_h1)
+            .with_base_url(base_url)
     }
 }
 
diff --git a/crates/mq-formatter/benches/benchmark.rs b/crates/mq-formatter/benches/benchmark.rs
index 4296e1c8b..12780d860 100644
--- a/crates/mq-formatter/benches/benchmark.rs
+++ b/crates/mq-formatter/benches/benchmark.rs
@@ -46,13 +46,10 @@ def y(): test;
 | let a = 2
 | import "a.mq"
 def b(): test;"#;
-    let config = FormatterConfig {
-        indent_width: 2,
-        sort_imports: true,
-        sort_functions: true,
-        sort_fields: true,
-        max_width: None,
-    };
+    let config = FormatterConfig::default()
+        .with_sort_imports(true)
+        .with_sort_functions(true)
+        .with_sort_fields(true);
     let mut formatter = Formatter::new(Some(config));
     formatter.format(code).unwrap();
 }
diff --git a/crates/mq-formatter/src/formatter.rs b/crates/mq-formatter/src/formatter.rs
index dbf4a43fb..bb21da1bb 100644
--- a/crates/mq-formatter/src/formatter.rs
+++ b/crates/mq-formatter/src/formatter.rs
@@ -59,6 +59,7 @@ enum SortPriority {
 }
 
 #[derive(Clone, Debug)]
+#[non_exhaustive]
 pub struct FormatterConfig {
     pub indent_width: usize,
     pub sort_imports: bool,
@@ -67,6 +68,38 @@ pub struct FormatterConfig {
     pub max_width: Option<usize>,
 }
 
+impl FormatterConfig {
+    /// Sets `indent_width`.
+    pub fn with_indent_width(mut self, indent_width: usize) -> Self {
+        self.indent_width = indent_width;
+        self
+    }
+
+    /// Sets `sort_imports`.
+    pub fn with_sort_imports(mut self, sort_imports: bool) -> Self {
+        self.sort_imports = sort_imports;
+        self
+    }
+
+    /// Sets `sort_functions`.
+    pub fn with_sort_functions(mut self, sort_functions: bool) -> Self {
+        self.sort_functions = sort_functions;
+        self
+    }
+
+    /// Sets `sort_fields`.
+    pub fn with_sort_fields(mut self, sort_fields: bool) -> Self {
+        self.sort_fields = sort_fields;
+        self
+    }
+
+    /// Sets `max_width`.
+    pub fn with_max_width(mut self, max_width: Option<usize>) -> Self {
+        self.max_width = max_width;
+        self
+    }
+}
+
 impl Default for FormatterConfig {
     fn default() -> Self {
         Self {
diff --git a/crates/mq-formatter/src/main.rs b/crates/mq-formatter/src/main.rs
index 4a3838d8e..6fec58e88 100644
--- a/crates/mq-formatter/src/main.rs
+++ b/crates/mq-formatter/src/main.rs
@@ -52,13 +52,14 @@ struct Cli {
 fn main() -> miette::Result<()> {
     let cli = Cli::parse();
 
-    let mut formatter = mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig {
-        indent_width: cli.indent_width,
-        sort_imports: cli.sort_imports,
-        sort_fields: cli.sort_fields,
-        sort_functions: cli.sort_functions,
-        max_width: cli.max_width,
-    }));
+    let mut formatter = mq_formatter::Formatter::new(Some(
+        mq_formatter::FormatterConfig::default()
+            .with_indent_width(cli.indent_width)
+            .with_sort_imports(cli.sort_imports)
+            .with_sort_fields(cli.sort_fields)
+            .with_sort_functions(cli.sort_functions)
+            .with_max_width(cli.max_width),
+    ));
 
     if let Some(files) = &cli.files
         && files.len() == 1
diff --git a/crates/mq-formatter/tests/integration_tests.rs b/crates/mq-formatter/tests/integration_tests.rs
index 8f4ce1e4d..b4ddbc9b3 100644
--- a/crates/mq-formatter/tests/integration_tests.rs
+++ b/crates/mq-formatter/tests/integration_tests.rs
@@ -52,10 +52,7 @@ fn test_bundled_mq_files_format_idempotently() {
     assert!(paths.len() > 2, "no bundled .mq files found under {root}");
 
     for max_width in [None, Some(60)] {
-        let config = mq_formatter::FormatterConfig {
-            max_width,
-            ..Default::default()
-        };
+        let config = mq_formatter::FormatterConfig::default().with_max_width(max_width);
         for path in &paths {
             let code = std::fs::read_to_string(path).unwrap();
             let formatted = mq_formatter::Formatter::new(Some(config.clone()))
diff --git a/crates/mq-hir/src/error.rs b/crates/mq-hir/src/error.rs
index 2108d81de..ff2adcbb8 100644
--- a/crates/mq-hir/src/error.rs
+++ b/crates/mq-hir/src/error.rs
@@ -4,6 +4,7 @@ use thiserror::Error;
 use crate::{Hir, ScopeId, ScopeKind, Symbol, SymbolKind};
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum HirError {
     #[error(
         "Unresolved symbol: {}",
@@ -22,6 +23,17 @@ pub enum HirError {
     YieldOutsideFunction { symbol: Symbol },
 }
 
+impl HirError {
+    /// The symbol the error is reported on.
+    pub fn symbol(&self) -> &Symbol {
+        match self {
+            HirError::UnresolvedSymbol { symbol, .. }
+            | HirError::ModuleNotFound { symbol, .. }
+            | HirError::YieldOutsideFunction { symbol } => symbol,
+        }
+    }
+}
+
 #[derive(Debug, Error)]
 pub enum HirWarning {
     #[error("Unreachable code after halt() function call")]
diff --git a/crates/mq-lang/src/ast/node.rs b/crates/mq-lang/src/ast/node.rs
index ba0135624..a46e5264c 100644
--- a/crates/mq-lang/src/ast/node.rs
+++ b/crates/mq-lang/src/ast/node.rs
@@ -14,6 +14,7 @@ use std::{
 /// Represents a function parameter with an optional default value
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub struct Param {
     pub ident: IdentWithToken,
     pub default: Option<Shared<Node>>,
@@ -210,6 +211,7 @@ impl Node {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, Debug, Eq, Clone)]
+#[non_exhaustive]
 pub struct IdentWithToken {
     pub name: Ident,
     #[cfg_attr(feature = "ast-json", serde(skip_serializing, skip_deserializing, default))]
@@ -264,6 +266,7 @@ pub enum StringSegment {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub enum Pattern {
     Literal(Literal),
     Ident(IdentWithToken),
@@ -277,6 +280,7 @@ pub enum Pattern {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub struct MatchArm {
     pub pattern: Pattern,
     pub guard: Option<Shared<Node>>,
@@ -285,6 +289,7 @@ pub struct MatchArm {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub enum Literal {
     String(String),
     Bytes(Vec<u8>),
@@ -302,6 +307,7 @@ impl From<&str> for Literal {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub enum AccessTarget {
     Call(IdentWithToken, Box<Args>),
     Ident(IdentWithToken),
@@ -334,6 +340,7 @@ impl Display for Literal {
 /// Compiles directly to a VM opcode; see `Expr::BinaryOp`.
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone, Copy)]
+#[non_exhaustive]
 pub enum BinaryOp {
     Add,
     Sub,
@@ -375,6 +382,7 @@ impl Display for BinaryOp {
 /// A prefix operator (`!` or `-`). Compiles directly to a VM opcode; see `Expr::UnaryOp`.
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone, Copy)]
+#[non_exhaustive]
 pub enum UnaryOp {
     Not,
     Neg,
@@ -397,6 +405,7 @@ impl Display for UnaryOp {
 
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
+#[non_exhaustive]
 pub enum Expr {
     As(IdentWithToken, Shared<Node>),
     Block(Program),
diff --git a/crates/mq-lang/src/cst/error.rs b/crates/mq-lang/src/cst/error.rs
index 598438e87..48ea4569d 100644
--- a/crates/mq-lang/src/cst/error.rs
+++ b/crates/mq-lang/src/cst/error.rs
@@ -3,6 +3,7 @@ use thiserror::Error;
 use crate::{Shared, Token, TokenKind, selector};
 
 #[derive(Error, Debug, PartialEq, Clone, PartialOrd, Eq, Ord)]
+#[non_exhaustive]
 pub enum ParseError {
     #[error("Unexpected token `{0}`")]
     UnexpectedToken(Shared<Token>),
diff --git a/crates/mq-lang/src/engine.rs b/crates/mq-lang/src/engine.rs
index eaaf719f0..78a489db8 100644
--- a/crates/mq-lang/src/engine.rs
+++ b/crates/mq-lang/src/engine.rs
@@ -30,6 +30,7 @@ use crate::{
 
 /// An error returned when a value cannot be added to an [`Engine`] environment.
 #[derive(Debug, thiserror::Error, PartialEq, Eq)]
+#[non_exhaustive]
 pub enum DefineValueError {
     /// The value contains execution state that belongs to a particular VM.
     #[error("cannot define a VM-bound {0}")]
diff --git a/crates/mq-lang/src/error.rs b/crates/mq-lang/src/error.rs
index 3462563cc..dcbd75ad9 100644
--- a/crates/mq-lang/src/error.rs
+++ b/crates/mq-lang/src/error.rs
@@ -13,6 +13,7 @@ use crate::{
 
 #[allow(clippy::useless_conversion)]
 #[derive(Debug, thiserror::Error, PartialEq)]
+#[non_exhaustive]
 pub enum InnerError {
     #[error(transparent)]
     Runtime(#[from] RuntimeError),
@@ -54,6 +55,7 @@ impl InnerError {
 /// Represents a high-level error with diagnostic information for the user.
 #[derive(PartialEq, Debug, thiserror::Error)]
 #[error("{cause}")]
+#[non_exhaustive]
 pub struct Error {
     /// The underlying cause of the error.
     pub cause: InnerError,
diff --git a/crates/mq-lang/src/error/runtime.rs b/crates/mq-lang/src/error/runtime.rs
index 111f81658..4bdc52773 100644
--- a/crates/mq-lang/src/error/runtime.rs
+++ b/crates/mq-lang/src/error/runtime.rs
@@ -12,6 +12,7 @@ type ArgType = Vec<SmolStr>;
 type ErrorToken = Token;
 
 #[derive(Error, Debug, PartialEq)]
+#[non_exhaustive]
 pub enum RuntimeError {
     /// An uncaught runtime error annotated with the VM frames active at the failure point.
     #[error("{source}\n{trace}")]
diff --git a/crates/mq-lang/src/error/syntax.rs b/crates/mq-lang/src/error/syntax.rs
index 668ab8574..e3a853b72 100644
--- a/crates/mq-lang/src/error/syntax.rs
+++ b/crates/mq-lang/src/error/syntax.rs
@@ -5,6 +5,7 @@ use crate::{Token, module::ModuleId, selector};
 
 /// Errors that occur during parsing of mq source code.
 #[derive(Error, Debug, PartialEq)]
+#[non_exhaustive]
 pub enum SyntaxError {
     /// An environment variable was not found.
     #[error("Undefined environment variable `{1}`")]
diff --git a/crates/mq-lang/src/io/error.rs b/crates/mq-lang/src/io/error.rs
index 61a4ec65e..66f0af542 100644
--- a/crates/mq-lang/src/io/error.rs
+++ b/crates/mq-lang/src/io/error.rs
@@ -6,6 +6,7 @@ use thiserror::Error;
 /// already use (e.g. `ModuleError` for module resolution, the builtin
 /// evaluator's own error type) rather than surface it to `miette` directly.
 #[derive(Debug, Clone, PartialEq, Error)]
+#[non_exhaustive]
 pub enum IoError {
     #[error("{0} not found")]
     NotFound(Cow<'static, str>),
diff --git a/crates/mq-lang/src/lexer.rs b/crates/mq-lang/src/lexer.rs
index 8a8797de7..2dbcd011d 100644
--- a/crates/mq-lang/src/lexer.rs
+++ b/crates/mq-lang/src/lexer.rs
@@ -9,6 +9,7 @@ use crate::number::Number;
 use crate::range::{Position, Range};
 
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct Options {
     pub ignore_errors: bool,
     pub include_spaces: bool,
diff --git a/crates/mq-lang/src/lib.rs b/crates/mq-lang/src/lib.rs
index f2c89d382..27348b5ee 100644
--- a/crates/mq-lang/src/lib.rs
+++ b/crates/mq-lang/src/lib.rs
@@ -478,12 +478,10 @@ mod tests {
     </html>"#;
         let result = parse_html_input_with_options(
             input,
-            mq_markdown::ConversionOptions {
-                extract_scripts_as_code_blocks: true,
-                generate_front_matter: true,
-                use_title_as_h1: true,
-                base_url: None,
-            },
+            mq_markdown::ConversionOptions::default()
+                .with_extract_scripts_as_code_blocks(true)
+                .with_generate_front_matter(true)
+                .with_use_title_as_h1(true),
         );
         assert!(result.is_ok());
         assert_eq!(
diff --git a/crates/mq-lang/src/module/error.rs b/crates/mq-lang/src/module/error.rs
index d551f5af2..e2559a2c3 100644
--- a/crates/mq-lang/src/module/error.rs
+++ b/crates/mq-lang/src/module/error.rs
@@ -6,6 +6,7 @@ use std::borrow::Cow;
 
 /// Errors that can occur while loading or resolving mq modules.
 #[derive(Debug, PartialEq, Error)]
+#[non_exhaustive]
 pub enum ModuleError {
     #[error("Module `{0}` is already loaded")]
     AlreadyLoaded(Cow<'static, str>),
diff --git a/crates/mq-lang/src/mqc.rs b/crates/mq-lang/src/mqc.rs
index 8caabb82f..cf5404e21 100644
--- a/crates/mq-lang/src/mqc.rs
+++ b/crates/mq-lang/src/mqc.rs
@@ -56,6 +56,7 @@ const RECOMPILE_HELP: &str = "Recompile the program from its source with this ve
 
 /// An error from compiling to or loading a `.mqc` file.
 #[derive(Debug, thiserror::Error, miette::Diagnostic)]
+#[non_exhaustive]
 pub enum MqcError {
     #[error("not an mq bytecode file")]
     #[diagnostic(code(mq::mqc::not_mqc))]
diff --git a/crates/mq-lang/src/runtime/runtime_value.rs b/crates/mq-lang/src/runtime/runtime_value.rs
index 44e579eb9..9406ed4ff 100644
--- a/crates/mq-lang/src/runtime/runtime_value.rs
+++ b/crates/mq-lang/src/runtime/runtime_value.rs
@@ -60,6 +60,7 @@ pub enum ResumeBuiltin {
 /// program execution, including numbers, strings, markdown nodes, functions,
 /// and more complex data structures.
 #[derive(Clone, Default)]
+#[non_exhaustive]
 pub enum RuntimeValue {
     /// A numeric value.
     Number(Number),
diff --git a/crates/mq-lang/src/selector.rs b/crates/mq-lang/src/selector.rs
index 1ab971401..548caa48c 100644
--- a/crates/mq-lang/src/selector.rs
+++ b/crates/mq-lang/src/selector.rs
@@ -91,6 +91,7 @@ fn escape_property_key(key: &str) -> String {
 /// for HTML. Each variant matches a specific type of markdown element.
 #[cfg_attr(feature = "ast-json", derive(Serialize, Deserialize))]
 #[derive(PartialEq, PartialOrd, Debug, Eq, Clone)]
+#[non_exhaustive]
 pub enum Selector {
     /// Matches blockquote elements (e.g., `> quoted text`).
     Blockquote,
diff --git a/crates/mq-lint/src/config.rs b/crates/mq-lint/src/config.rs
index e39e07302..1a2a7d697 100644
--- a/crates/mq-lint/src/config.rs
+++ b/crates/mq-lint/src/config.rs
@@ -6,6 +6,7 @@ use crate::RuleId;
 
 /// Per-rule enable/disable flag.
 #[derive(Debug, Clone)]
+#[non_exhaustive]
 pub struct RuleConfig {
     pub enabled: bool,
 }
@@ -45,6 +46,7 @@ impl Default for ComplexityThresholds {
 
 /// Top-level linter configuration.
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct LintConfig {
     /// Per-rule overrides. Rules not listed here use their default enabled state.
     pub rules: HashMap<RuleId, RuleConfig>,
diff --git a/crates/mq-lsp/src/error.rs b/crates/mq-lsp/src/error.rs
index c6e52c02a..e76d9da11 100644
--- a/crates/mq-lsp/src/error.rs
+++ b/crates/mq-lsp/src/error.rs
@@ -2,6 +2,7 @@ use tower_lsp_server::ls_types;
 use tower_lsp_server::ls_types::NumberOrString;
 
 #[derive(Debug, Clone)]
+#[non_exhaustive]
 pub enum LspError {
     SyntaxError(mq_lang::Diagnostic),
     TypeError(mq_check::TypeError),
diff --git a/crates/mq-lsp/src/main.rs b/crates/mq-lsp/src/main.rs
index 179f8212f..6f02cf830 100644
--- a/crates/mq-lsp/src/main.rs
+++ b/crates/mq-lsp/src/main.rs
@@ -78,11 +78,9 @@ fn parse_input_type(src: &str) -> Result<mq_check::types::Type, String> {
 #[tokio::main]
 async fn main() {
     let cli = Cli::parse();
-    let type_check_config = mq_check::TypeCheckerOptions {
-        strict_array: cli.type_check.strict_array,
-        input_type: cli.type_check.input_type.clone(),
-        ..Default::default()
-    };
+    let type_check_config = mq_check::TypeCheckerOptions::default()
+        .with_strict_array(cli.type_check.strict_array)
+        .with_input_type(cli.type_check.input_type.clone());
 
     let mut lint_config = mq_lint::LintConfig::default();
     for rule_id in &cli.lint.disable_lint_rule {
diff --git a/crates/mq-lsp/src/refactor.rs b/crates/mq-lsp/src/refactor.rs
index 4082ec53f..50d72194f 100644
--- a/crates/mq-lsp/src/refactor.rs
+++ b/crates/mq-lsp/src/refactor.rs
@@ -214,12 +214,9 @@ fn deletion_range(container: &[Shared<CstNode>], idx: usize) -> MqRange {
 }
 
 fn format_snippet(code: &str) -> String {
-    mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig {
-        indent_width: 2,
-        ..Default::default()
-    }))
-    .format(code)
-    .unwrap_or_else(|_| code.to_string())
+    mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig::default().with_indent_width(2)))
+        .format(code)
+        .unwrap_or_else(|_| code.to_string())
 }
 
 fn single_edit_action(
diff --git a/crates/mq-lsp/src/server.rs b/crates/mq-lsp/src/server.rs
index 62b6db0a8..242aaa3f5 100644
--- a/crates/mq-lsp/src/server.rs
+++ b/crates/mq-lsp/src/server.rs
@@ -361,10 +361,8 @@ impl LanguageServer for Backend {
         // Replace the whole original text, not the formatted length.
         let end = document_end_position(&text);
         let formatted_text = tokio::task::spawn_blocking(move || {
-            let mut formatter = mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig {
-                indent_width: 2,
-                ..Default::default()
-            }));
+            let mut formatter =
+                mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig::default().with_indent_width(2)));
             match nodes {
                 Some(nodes) => formatter.format_with_cst(&mut Vec::clone(&nodes)),
                 None => formatter.format(&text),
@@ -454,11 +452,8 @@ impl LanguageServer for Backend {
         }
 
         let formatted_range = tokio::task::spawn_blocking(move || {
-            mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig {
-                indent_width: 2,
-                ..Default::default()
-            }))
-            .format(&selected)
+            mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig::default().with_indent_width(2)))
+                .format(&selected)
         })
         .await
         .map_err(|_| jsonrpc::Error::new(jsonrpc::ErrorCode::InternalError))?
@@ -632,6 +627,7 @@ impl Backend {
 }
 
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct LspConfig {
     module_paths: Vec<PathBuf>,
     enable_type_checking: bool,
@@ -813,12 +809,10 @@ mod tests {
             .await
             .unwrap()
             .unwrap();
-        let expected = mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig {
-            indent_width: 2,
-            ..Default::default()
-        }))
-        .format(text)
-        .unwrap();
+        let expected =
+            mq_formatter::Formatter::new(Some(mq_formatter::FormatterConfig::default().with_indent_width(2)))
+                .format(text)
+                .unwrap();
         assert_eq!(edits[0].new_text, expected);
         assert_eq!(edits[0].range.end, document_end_position(text));
 
@@ -2494,10 +2488,7 @@ mod tests {
         let config = LspConfig::new(
             vec![],
             true,
-            mq_check::TypeCheckerOptions {
-                strict_array: true,
-                ..Default::default()
-            },
+            mq_check::TypeCheckerOptions::default().with_strict_array(true),
             true,
             lint_config,
         );
@@ -2513,10 +2504,7 @@ mod tests {
         let config = LspConfig::new(
             vec![],
             true,
-            mq_check::TypeCheckerOptions {
-                input_type: Some(input_type.clone()),
-                ..Default::default()
-            },
+            mq_check::TypeCheckerOptions::default().with_input_type(Some(input_type.clone())),
             false,
             mq_lint::LintConfig::default(),
         );
@@ -2733,10 +2721,7 @@ mod tests {
             config: LspConfig::new(
                 vec![],
                 true,
-                mq_check::TypeCheckerOptions {
-                    strict_array: true,
-                    ..Default::default()
-                },
+                mq_check::TypeCheckerOptions::default().with_strict_array(true),
                 false,
                 mq_lint::LintConfig::default(),
             ),
@@ -2784,10 +2769,7 @@ mod tests {
             config: LspConfig::new(
                 vec![],
                 true,
-                mq_check::TypeCheckerOptions {
-                    strict_array: false,
-                    ..Default::default()
-                },
+                mq_check::TypeCheckerOptions::default().with_strict_array(false),
                 false,
                 mq_lint::LintConfig::default(),
             ),
diff --git a/crates/mq-markdown/examples/html_convert.rs b/crates/mq-markdown/examples/html_convert.rs
index 98e465c79..15ee1db4b 100644
--- a/crates/mq-markdown/examples/html_convert.rs
+++ b/crates/mq-markdown/examples/html_convert.rs
@@ -15,12 +15,7 @@ fn main() {
         std::process::exit(1);
     });
 
-    let options = ConversionOptions {
-        extract_scripts_as_code_blocks: false,
-        generate_front_matter: false,
-        use_title_as_h1: false,
-        base_url: None,
-    };
+    let options = ConversionOptions::default();
 
     match convert_html_to_markdown(&html, options) {
         Ok(md) => print!("{}", md),
diff --git a/crates/mq-markdown/src/html_to_markdown/options.rs b/crates/mq-markdown/src/html_to_markdown/options.rs
index a293cdd6c..5ec20d9bb 100644
--- a/crates/mq-markdown/src/html_to_markdown/options.rs
+++ b/crates/mq-markdown/src/html_to_markdown/options.rs
@@ -1,4 +1,5 @@
 #[derive(Debug, Clone, Default)]
+#[non_exhaustive]
 pub struct ConversionOptions {
     pub extract_scripts_as_code_blocks: bool,
     pub generate_front_matter: bool,
@@ -6,3 +7,29 @@ pub struct ConversionOptions {
     /// Base URL for resolving relative `href`/`src` values; falls back to `<base href>`.
     pub base_url: Option<String>,
 }
+
+impl ConversionOptions {
+    /// Sets `extract_scripts_as_code_blocks`.
+    pub fn with_extract_scripts_as_code_blocks(mut self, extract_scripts_as_code_blocks: bool) -> Self {
+        self.extract_scripts_as_code_blocks = extract_scripts_as_code_blocks;
+        self
+    }
+
+    /// Sets `generate_front_matter`.
+    pub fn with_generate_front_matter(mut self, generate_front_matter: bool) -> Self {
+        self.generate_front_matter = generate_front_matter;
+        self
+    }
+
+    /// Sets `use_title_as_h1`.
+    pub fn with_use_title_as_h1(mut self, use_title_as_h1: bool) -> Self {
+        self.use_title_as_h1 = use_title_as_h1;
+        self
+    }
+
+    /// Sets `base_url`.
+    pub fn with_base_url(mut self, base_url: Option<String>) -> Self {
+        self.base_url = base_url;
+        self
+    }
+}
diff --git a/crates/mq-markdown/src/lib.rs b/crates/mq-markdown/src/lib.rs
index cf2963cfe..2aada2b3d 100644
--- a/crates/mq-markdown/src/lib.rs
+++ b/crates/mq-markdown/src/lib.rs
@@ -43,10 +43,7 @@
 //! use mq_markdown::{Markdown, RenderOptions, ListStyle};
 //!
 //! let mut doc = "- Item 1\n- Item 2".parse::<Markdown>().unwrap();
-//! doc.set_options(RenderOptions {
-//!     list_style: ListStyle::Plus,
-//!     ..Default::default()
-//! });
+//! doc.set_options(RenderOptions::default().with_list_style(ListStyle::Plus));
 //!
 //! // Now renders with "+" instead of "-"
 //! println!("{}", doc);
diff --git a/crates/mq-markdown/src/node.rs b/crates/mq-markdown/src/node.rs
index 48871b594..375f62a20 100644
--- a/crates/mq-markdown/src/node.rs
+++ b/crates/mq-markdown/src/node.rs
@@ -153,12 +153,33 @@ pub const EMPTY_NODE: Node = Node::Text(Text {
 });
 
 #[derive(Debug, Clone, Default, PartialEq)]
+#[non_exhaustive]
 pub struct RenderOptions {
     pub list_style: ListStyle,
     pub link_url_style: UrlSurroundStyle,
     pub link_title_style: TitleSurroundStyle,
 }
 
+impl RenderOptions {
+    /// Sets `list_style`.
+    pub fn with_list_style(mut self, list_style: ListStyle) -> Self {
+        self.list_style = list_style;
+        self
+    }
+
+    /// Sets `link_url_style`.
+    pub fn with_link_url_style(mut self, link_url_style: UrlSurroundStyle) -> Self {
+        self.link_url_style = link_url_style;
+        self
+    }
+
+    /// Sets `link_title_style`.
+    pub fn with_link_title_style(mut self, link_title_style: TitleSurroundStyle) -> Self {
+        self.link_title_style = link_title_style;
+        self
+    }
+}
+
 #[derive(Debug, Clone, Default, PartialEq)]
 pub enum ListStyle {
     #[default]
@@ -785,12 +806,17 @@ pub struct HorizontalRule {
     pub position: Option<Position>,
 }
 
+/// A Markdown node.
+///
+/// Some variants exist only when their feature (`callout`, `embed`, `wikilink`) is enabled,
+/// and more may be added. Match with a wildcard arm.
 #[derive(Debug, Clone, Default)]
 #[cfg_attr(
     feature = "json",
     derive(serde::Serialize, serde::Deserialize),
     serde(rename_all = "camelCase", untagged)
 )]
+#[non_exhaustive]
 pub enum Node {
     Blockquote(Blockquote),
     Break(Break),
diff --git a/crates/mq-markdown/tests/html_to_markdown_property_tests.rs b/crates/mq-markdown/tests/html_to_markdown_property_tests.rs
index 790feff4e..99c5b8b99 100644
--- a/crates/mq-markdown/tests/html_to_markdown_property_tests.rs
+++ b/crates/mq-markdown/tests/html_to_markdown_property_tests.rs
@@ -82,10 +82,7 @@ proptest! {
         let html = format!(
             r#"<html><head><meta name="description" content="{desc}"></head><body><p>Body</p></body></html>"#
         );
-        let options = ConversionOptions {
-            generate_front_matter: true,
-            ..Default::default()
-        };
+        let options = ConversionOptions::default().with_generate_front_matter(true);
         let md = convert_html_to_markdown(&html, options).unwrap();
         prop_assert!(md.contains(&desc), "description missing from front matter:\n{md}");
     }
diff --git a/crates/mq-markdown/tests/html_to_markdown_tests.rs b/crates/mq-markdown/tests/html_to_markdown_tests.rs
index 2817c84c1..f148cf12c 100644
--- a/crates/mq-markdown/tests/html_to_markdown_tests.rs
+++ b/crates/mq-markdown/tests/html_to_markdown_tests.rs
@@ -37,82 +37,52 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
 )]
 #[case::script_tag_inline_javascript_default_type(
     "<script>alert('Hello');</script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```\nalert('Hello');\n```",
 )]
 #[case::script_tag_inline_javascript_text_javascript(
     "<script type=\"text/javascript\">console.log(1);</script>",
-    ConversionOptions{
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```javascript\nconsole.log(1);\n```"
 )]
 #[case::script_tag_inline_javascript_application_javascript(
     "<script type=\"application/javascript\">let a = 1;</script>",
-    ConversionOptions{
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```javascript\nlet a = 1;\n```"
 )]
 #[case::script_tag_inline_javascript_module(
     "<script type=\"module\">import { B } from './mod.js';</script>",
-    ConversionOptions{
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```javascript\nimport { B } from './mod.js';\n```"
 )]
 #[case::script_tag_inline_json_ld(
     "<script type=\"application/ld+json\">{\"@context\":\"schema.org\"}</script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```json\n{\"@context\":\"schema.org\"}\n```"
 )]
 #[case::script_tag_inline_json(
     "<script type=\"application/json\">{\"key\":\"value\"}</script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```json\n{\"key\":\"value\"}\n```"
 )]
 #[case::script_tag_unknown_type(
     "<script type=\"text/custom\">content</script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```\ncontent\n```"
 )]
 #[case::script_tag_empty_content(
     "<script></script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```\n\n```"
 )]
 #[case::script_tag_external_src_ignored_when_option_true(
     "<script src=\"app.js\"></script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     ""
 )]
 #[case::script_tag_with_html_comments_and_cdata(
     "<script><!-- alert(1); // --><![CDATA[\nalert(2);\n//]]></script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     &format!("```\n{}\n```", "<!-- alert(1); // --><![CDATA[\nalert(2);\n//]]>")
 )]
 #[case::front_matter_disabled(
@@ -122,171 +92,107 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
 )]
 #[case::front_matter_title_only(
     "<html><head><title>My Title</title></head><body><p>Body</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\ntitle: My Title\n---\n\nBody",
 )]
 #[case::front_matter_description(
     "<html><head><meta name=\"description\" content=\"Page description.\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\ndescription: Page description.\n---\n\nB",
 )]
 #[case::front_matter_keywords_single(
     "<html><head><meta name=\"keywords\" content=\"rust\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nkeywords:\n  - rust\n---\n\nB",
 )]
 #[case::front_matter_keywords_multiple_comma_separated(
     "<html><head><meta name=\"keywords\" content=\"rust, web, html\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nkeywords:\n  - rust\n  - web\n  - html\n---\n\nB",
 )]
 #[case::front_matter_keywords_comma_space_separated(
     "<html><head><meta name=\"keywords\" content=\"rust, web,  html \"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nkeywords:\n  - rust\n  - web\n  - html\n---\n\nB",
 )]
 #[case::front_matter_author(
     "<html><head><meta name=\"author\" content=\"Jules Verne\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: Jules Verne\n---\n\nB",
 )]
 #[case::front_matter_all_present(
     "<html><head><title>Full Test</title><meta name=\"description\" content=\"Desc here\"><meta name=\"keywords\" content=\"key1,key2\"><meta name=\"author\" content=\"Author Name\"></head><body><p>Content</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: Author Name\ndescription: Desc here\nkeywords:\n  - key1\n  - key2\ntitle: Full Test\n---\n\nContent",
 )]
 #[case::front_matter_no_head_tag(
     "<html><body><p>Only body</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "Only body",
 )]
 #[case::front_matter_empty_head(
     "<html><head></head><body><p>Body</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "Body",
 )]
 #[case::front_matter_no_relevant_tags_in_head(
     "<html><head><meta name=\"viewport\" content=\"width=device-width\"></head><body><p>Body</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "Body", // No relevant tags for front matter
 )]
 #[case::front_matter_with_script_extraction_option(
     "<html><head><title>Script Page</title></head><body><script>let x=1;</script><p>Text</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true).with_extract_scripts_as_code_blocks(true),
     "---\ntitle: Script Page\n---\n\n```\nlet x=1;\n```\n\nText",
 )]
 #[case::front_matter_html_fragment_no_head(
     "<p>Just a paragraph</p><meta name=\"description\" content=\"Hidden\">",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "Just a paragraph", // Meta tag not in <head> context
 )]
 #[case::front_matter_og_description_fallback(
     "<html><head><meta property=\"og:description\" content=\"OGP desc\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\ndescription: OGP desc\n---\n\nB",
 )]
 #[case::front_matter_name_description_wins_over_og(
     "<html><head><meta name=\"description\" content=\"Named desc\"><meta property=\"og:description\" content=\"OGP desc\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\ndescription: Named desc\n---\n\nB",
 )]
 #[case::front_matter_schema_author_wins_over_twitter_handle(
     r#"<html><head><meta name="twitter:creator" content="@jverne"><script type="application/ld+json">{"@type":"Article","author":{"name":"Jules Verne"}}</script></head><body><p>B</p></body></html>"#,
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: Jules Verne\n---\n\nB",
 )]
 #[case::front_matter_twitter_creator_fallback(
     "<html><head><meta name=\"twitter:creator\" content=\"@jverne\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: \"@jverne\"\n---\n\nB",
 )]
 #[case::front_matter_article_published_time(
     "<html><head><meta property=\"article:published_time\" content=\"2024-01-02T00:00:00Z\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\npublished: \"2024-01-02T00:00:00Z\"\n---\n\nB",
 )]
 #[case::front_matter_og_image_and_site_name(
     "<html><head><meta property=\"og:image\" content=\"https://example.com/a.png\"><meta property=\"og:site_name\" content=\"Example Site\"></head><body><p>B</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nimage: \"https://example.com/a.png\"\nsite: Example Site\n---\n\nB",
 )]
 #[case::front_matter_multibyte_description_and_author(
     "<html><head><meta name=\"description\" content=\"日本語の説明文です\"><meta name=\"author\" content=\"山田太郎\"></head><body><p>本文</p></body></html>",
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: 山田太郎\ndescription: 日本語の説明文です\n---\n\n本文",
 )]
 #[case::front_matter_json_ld_article(
     r#"<html><head><script type="application/ld+json">{"@type":"Article","headline":"JSON-LD Title","author":{"name":"Ada Lovelace"},"datePublished":"2023-05-01"}</script></head><body><p>B</p></body></html>"#,
-    ConversionOptions {
-        generate_front_matter: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_generate_front_matter(true),
     "---\nauthor: Ada Lovelace\npublished: 2023-05-01\n---\n\nB",
 )]
 #[case::script_tag_leading_newline_stripping(
     "<script>\n  var x = 1;\n</script>",
-    ConversionOptions {
-        extract_scripts_as_code_blocks: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_extract_scripts_as_code_blocks(true),
     "```\n  var x = 1;\n```",
 )]
 #[case::table_with_align_attribute(
@@ -1218,34 +1124,22 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
 #[case::h1_not_closed("<h1>Hello World", ConversionOptions::default(), "# Hello World")]
 #[case::use_title_as_h1_true(
     "<html><head><title>My Document</title></head><body><p>Body text</p></body></html>",
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "# My Document\n\nBody text"
 )]
 #[case::use_title_as_h1_true_with_no_body(
     "<html><head><title>Only Title</title></head><body></body></html>",
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "# Only Title"
 )]
 #[case::use_title_as_h1_true_with_no_title(
     "<html><head></head><body><p>Body only</p></body></html>",
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "Body only"
 )]
 #[case::use_title_as_h1_false(
     "<html><head><title>My Document</title></head><body><p>Body text</p></body></html>",
-    ConversionOptions {
-        use_title_as_h1: false,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(false),
     "Body text"
 )]
 #[case::use_title_as_h1_true_with_main(
@@ -1253,10 +1147,7 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
         "<html><head><title>Page Title</title></head>",
         "<body><nav>Nav</nav><main><p>Main content</p></main></body></html>"
     ),
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "# Page Title\n\nMain content"
 )]
 #[case::use_title_as_h1_true_with_article(
@@ -1264,10 +1155,7 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
         "<html><head><title>Article Title</title></head>",
         "<body><aside>Sidebar</aside><article><p>Article content</p></article></body></html>"
     ),
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "# Article Title\n\nArticle content"
 )]
 #[case::use_title_as_h1_true_with_role_main(
@@ -1275,10 +1163,7 @@ fn assert_conversion_with_options(html: &str, expected_markdown: &str, options:
         "<html><head><title>Role Main Title</title></head>",
         "<body><div role=\"main\"><p>Role main content</p></div></body></html>"
     ),
-    ConversionOptions {
-        use_title_as_h1: true,
-        ..ConversionOptions::default()
-    },
+    ConversionOptions::default().with_use_title_as_h1(true),
     "# Role Main Title\n\nRole main content"
 )]
 #[case::pre_with_code_and_text(
@@ -1902,10 +1787,7 @@ fn test_html_comment_stripped() {
 fn test_base_url_resolves_relative_links_and_images() {
     let html = r#"<p><a href="/absolute-path">a</a> and <a href="../sibling">b</a> and
         <img src="pic.png" alt="x"> and <a href="https://other.com/x">already-absolute</a></p>"#;
-    let options = ConversionOptions {
-        base_url: Some("https://example.com/blog/post/".to_string()),
-        ..Default::default()
-    };
+    let options = ConversionOptions::default().with_base_url(Some("https://example.com/blog/post/".to_string()));
     let md = convert_html_to_markdown(html, options).unwrap();
     assert!(md.contains("[a](https://example.com/absolute-path)"));
     assert!(md.contains("[b](https://example.com/blog/sibling)"));
@@ -1925,10 +1807,7 @@ fn test_base_href_tag_resolves_relative_links_when_no_explicit_base_url() {
 fn test_explicit_base_url_takes_priority_over_base_href_tag() {
     let html = r#"<html><head><base href="https://ignored.example.com/"></head>
         <body><p><a href="rel">link</a></p></body></html>"#;
-    let options = ConversionOptions {
-        base_url: Some("https://example.com/blog/".to_string()),
-        ..Default::default()
-    };
+    let options = ConversionOptions::default().with_base_url(Some("https://example.com/blog/".to_string()));
     let md = convert_html_to_markdown(html, options).unwrap();
     assert!(md.contains("[link](https://example.com/blog/rel)"));
 }
diff --git a/crates/mq-run/src/cli.rs b/crates/mq-run/src/cli.rs
index 605614fd9..ede83cd93 100644
--- a/crates/mq-run/src/cli.rs
+++ b/crates/mq-run/src/cli.rs
@@ -3047,22 +3047,23 @@ impl Cli {
     fn build_markdown(&self, runtime_values: &[mq_lang::RuntimeValue]) -> mq_markdown::Markdown {
         let mut markdown =
             mq_markdown::Markdown::new(runtime_values.iter().flat_map(Self::runtime_value_to_nodes).collect());
-        markdown.set_options(mq_markdown::RenderOptions {
-            list_style: match self.output.list_style.clone() {
-                ListStyle::Dash => mq_markdown::ListStyle::Dash,
-                ListStyle::Plus => mq_markdown::ListStyle::Plus,
-                ListStyle::Star => mq_markdown::ListStyle::Star,
-            },
-            link_title_style: match self.output.link_title_style.clone() {
-                LinkTitleStyle::Double => mq_markdown::TitleSurroundStyle::Double,
-                LinkTitleStyle::Single => mq_markdown::TitleSurroundStyle::Single,
-                LinkTitleStyle::Paren => mq_markdown::TitleSurroundStyle::Paren,
-            },
-            link_url_style: match self.output.link_url_style.clone() {
-                LinkUrlStyle::None => mq_markdown::UrlSurroundStyle::None,
-                LinkUrlStyle::Angle => mq_markdown::UrlSurroundStyle::Angle,
-            },
-        });
+        markdown.set_options(
+            mq_markdown::RenderOptions::default()
+                .with_list_style(match self.output.list_style.clone() {
+                    ListStyle::Dash => mq_markdown::ListStyle::Dash,
+                    ListStyle::Plus => mq_markdown::ListStyle::Plus,
+                    ListStyle::Star => mq_markdown::ListStyle::Star,
+                })
+                .with_link_title_style(match self.output.link_title_style.clone() {
+                    LinkTitleStyle::Double => mq_markdown::TitleSurroundStyle::Double,
+                    LinkTitleStyle::Single => mq_markdown::TitleSurroundStyle::Single,
+                    LinkTitleStyle::Paren => mq_markdown::TitleSurroundStyle::Paren,
+                })
+                .with_link_url_style(match self.output.link_url_style.clone() {
+                    LinkUrlStyle::None => mq_markdown::UrlSurroundStyle::None,
+                    LinkUrlStyle::Angle => mq_markdown::UrlSurroundStyle::Angle,
+                }),
+        );
         markdown
     }
 
diff --git a/crates/mq-wasm/src/script.rs b/crates/mq-wasm/src/script.rs
index b91e8532c..a61034f2e 100644
--- a/crates/mq-wasm/src/script.rs
+++ b/crates/mq-wasm/src/script.rs
@@ -228,12 +228,11 @@ pub struct ConversionOptions {
 
 impl From<ConversionOptions> for mq_markdown::ConversionOptions {
     fn from(options: ConversionOptions) -> Self {
-        Self {
-            extract_scripts_as_code_blocks: options.extract_scripts_as_code_blocks,
-            generate_front_matter: options.generate_front_matter,
-            use_title_as_h1: options.use_title_as_h1,
-            base_url: Some(options.base_url).filter(|s| !s.is_empty()),
-        }
+        mq_markdown::ConversionOptions::default()
+            .with_extract_scripts_as_code_blocks(options.extract_scripts_as_code_blocks)
+            .with_generate_front_matter(options.generate_front_matter)
+            .with_use_title_as_h1(options.use_title_as_h1)
+            .with_base_url(Some(options.base_url).filter(|s| !s.is_empty()))
     }
 }
 
@@ -687,31 +686,38 @@ pub async fn run(code: &str, content: &str, options: JsValue) -> Result<String,
                     })
                     .collect(),
             );
-            markdown.set_options(mq_markdown::RenderOptions {
-                list_style: options
-                    .list_style
-                    .map(|style| match style {
-                        ListStyle::Dash => mq_markdown::ListStyle::Dash,
-                        ListStyle::Plus => mq_markdown::ListStyle::Plus,
-                        ListStyle::Star => mq_markdown::ListStyle::Star,
-                    })
-                    .unwrap_or_default(),
-                link_title_style: options
-                    .link_title_style
-                    .map(|style| match style {
-                        TitleSurroundStyle::Double => mq_markdown::TitleSurroundStyle::Double,
-                        TitleSurroundStyle::Single => mq_markdown::TitleSurroundStyle::Single,
-                        TitleSurroundStyle::Paren => mq_markdown::TitleSurroundStyle::Paren,
-                    })
-                    .unwrap_or_default(),
-                link_url_style: options
-                    .link_url_style
-                    .map(|style| match style {
-                        UrlSurroundStyle::Angle => mq_markdown::UrlSurroundStyle::Angle,
-                        UrlSurroundStyle::None => mq_markdown::UrlSurroundStyle::None,
-                    })
-                    .unwrap_or_default(),
-            });
+            markdown.set_options(
+                mq_markdown::RenderOptions::default()
+                    .with_list_style(
+                        options
+                            .list_style
+                            .map(|style| match style {
+                                ListStyle::Dash => mq_markdown::ListStyle::Dash,
+                                ListStyle::Plus => mq_markdown::ListStyle::Plus,
+                                ListStyle::Star => mq_markdown::ListStyle::Star,
+                            })
+                            .unwrap_or_default(),
+                    )
+                    .with_link_title_style(
+                        options
+                            .link_title_style
+                            .map(|style| match style {
+                                TitleSurroundStyle::Double => mq_markdown::TitleSurroundStyle::Double,
+                                TitleSurroundStyle::Single => mq_markdown::TitleSurroundStyle::Single,
+                                TitleSurroundStyle::Paren => mq_markdown::TitleSurroundStyle::Paren,
+                            })
+                            .unwrap_or_default(),
+                    )
+                    .with_link_url_style(
+                        options
+                            .link_url_style
+                            .map(|style| match style {
+                                UrlSurroundStyle::Angle => mq_markdown::UrlSurroundStyle::Angle,
+                                UrlSurroundStyle::None => mq_markdown::UrlSurroundStyle::None,
+                            })
+                            .unwrap_or_default(),
+                    ),
+            );
             markdown.to_string()
         })
 }
diff --git a/crates/mq-web-api/src/api.rs b/crates/mq-web-api/src/api.rs
index 4708c3bc4..8d6fc9d69 100644
--- a/crates/mq-web-api/src/api.rs
+++ b/crates/mq-web-api/src/api.rs
@@ -352,13 +352,12 @@ pub fn check(request: CheckApiRequest) -> CheckApiResponse {
 
 /// Formats mq query code using the given formatting options.
 pub fn format_query(request: FormatApiRequest) -> miette::Result<FormatApiResponse> {
-    let config = FormatterConfig {
-        indent_width: request.indent_width.unwrap_or(2),
-        sort_imports: request.sort_imports.unwrap_or(false),
-        sort_functions: request.sort_functions.unwrap_or(false),
-        sort_fields: request.sort_fields.unwrap_or(false),
-        max_width: request.max_width,
-    };
+    let config = FormatterConfig::default()
+        .with_indent_width(request.indent_width.unwrap_or(2))
+        .with_sort_imports(request.sort_imports.unwrap_or(false))
+        .with_sort_functions(request.sort_functions.unwrap_or(false))
+        .with_sort_fields(request.sort_fields.unwrap_or(false))
+        .with_max_width(request.max_width);
     let formatted = Formatter::new(Some(config))
         .format(&request.query)
         .map_err(|e| miette!("Format error: {}", e))?;
@@ -487,6 +486,7 @@ fn type_error_kind(e: &mq_check::TypeError) -> String {
         mq_check::TypeError::NullablePropagation { .. } => "nullable_propagation",
         mq_check::TypeError::UnreachableCode { .. } => "unreachable_code",
         mq_check::TypeError::NonExhaustiveMatch { .. } => "non_exhaustive_match",
+        _ => "unknown",
     }
     .to_string()
 }