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+# Listing 1: Trace format selection and writer/reader interfaces
+
+This listing examines the public API surface that lets clients choose a trace format, create reader or writer instances, and record events. It covers `TraceEventsFileFormat` and related constants, factory functions, the `TraceReader` trait, `NonStreamingTraceWriter` structure, and the comprehensive `TraceWriter` trait.
+
+**Start the enumeration of supported trace file formats.**
+```rust
+#[derive(Debug, Clone, Copy)]
+pub enum TraceEventsFileFormat {
+```
+
+**List JSON and two binary formats.**
+```rust
+    Json,
+    BinaryV0,
+    Binary,
+}
+```
+
+**Provide constants for representing missing values and the top-level function.**
+```rust
+pub const NONE_TYPE_ID: TypeId = TypeId(0);
+pub const NONE_VALUE: ValueRecord = ValueRecord::None { type_id: NONE_TYPE_ID };
+pub const TOP_LEVEL_FUNCTION_ID: FunctionId = FunctionId(0);
+```
+
+**Construct a trace reader for a given format.**
+```rust
+pub fn create_trace_reader(format: TraceEventsFileFormat) -> Box<dyn TraceReader> {
+```
+
+**Match on the format to instantiate the proper reader.**
+```rust
+    match format {
+        TraceEventsFileFormat::Json => Box::new(JsonTraceReader {}),
+        TraceEventsFileFormat::BinaryV0 | TraceEventsFileFormat::Binary => Box::new(BinaryTraceReader {}),
+    }
+}
+```
+
+**Construct a trace writer for a program, arguments, and format.**
+```rust
+pub fn create_trace_writer(program: &str, args: &[String], format: TraceEventsFileFormat) -> Box<dyn TraceWriter> {
+```
+
+**Begin matching on the requested format.**
+```rust
+    match format {
+```
+
+**Use the in-memory writer for JSON and legacy binary formats.**
+```rust
+        TraceEventsFileFormat::Json | TraceEventsFileFormat::BinaryV0 => {
+            let mut result = Box::new(NonStreamingTraceWriter::new(program, args));
+            result.set_format(format);
+            result
+        }
+```
+
+**Produce a streaming CBOR writer for the current binary format and return.**
+```rust
+        TraceEventsFileFormat::Binary => Box::new(crate::cbor_zstd_writer::CborZstdTraceWriter::new(program, args)),
+    }
+}
+```
+
+**Define the trait for loading stored traces.**
+```rust
+pub trait TraceReader {
+    fn load_trace_events(&mut self, path: &Path) -> Result<Vec<TraceLowLevelEvent>, Box<dyn Error>>;
+}
+```
+
+**Begin declaration of a writer that accumulates events in memory.**
+```rust
+pub struct NonStreamingTraceWriter {
+```
+
+**Fields track metadata, collected events, format, and output path.**
+```rust
+    base: AbstractTraceWriterData,
+    pub events: Vec<TraceLowLevelEvent>,
+    format: TraceEventsFileFormat,
+    trace_events_path: Option<PathBuf>,
+}
+```
+
+**Implement constructor initializing storage and format.**
+```rust
+impl NonStreamingTraceWriter {
+    pub fn new(program: &str, args: &[String]) -> Self {
+        NonStreamingTraceWriter {
+            base: AbstractTraceWriterData::new(program, args),
+```
+
+**Set up empty event list, default binary format, and unset path.**
+```rust
+            events: vec![],
+            format: TraceEventsFileFormat::Binary,
+            trace_events_path: None,
+        }
+    }
+```
+
+**Allow callers to override output format.**
+```rust
+    pub fn set_format(&mut self, format: TraceEventsFileFormat) {
+        self.format = format;
+    }
+}
+```
+
+**Declare the `TraceWriter` trait which extends `AbstractTraceWriter`.**
+```rust
+pub trait TraceWriter: AbstractTraceWriter {
+```
+
+**Provide default metadata handling and leave event writing abstract.**
+```rust
+    fn begin_writing_trace_metadata(&mut self, path: &Path) -> Result<(), Box<dyn Error>> {
+        AbstractTraceWriter::begin_writing_trace_metadata(self, path)
+    }
+    fn begin_writing_trace_events(&mut self, path: &Path) -> Result<(), Box<dyn Error>>;
+```
+
+**Delegate path file initialization to the underlying writer.**
+```rust
+    fn begin_writing_trace_paths(&mut self, path: &Path) -> Result<(), Box<dyn Error>> {
+        AbstractTraceWriter::begin_writing_trace_paths(self, path)
+    }
+```
+
+**Start tracing and request identifiers for paths.**
+```rust
+    fn start(&mut self, path: &Path, line: Line) {
+        AbstractTraceWriter::start(self, path, line)
+    }
+    fn ensure_path_id(&mut self, path: &Path) -> PathId {
+        AbstractTraceWriter::ensure_path_id(self, path)
+    }
+```
+
+**Allocate a unique identifier for a function.**
+```rust
+    fn ensure_function_id(&mut self, function_name: &str, path: &Path, line: Line) -> FunctionId {
+        AbstractTraceWriter::ensure_function_id(self, function_name, path, line)
+    }
+```
+
+**Allocate type identifiers, either by components or explicit record.**
+```rust
+    fn ensure_type_id(&mut self, kind: TypeKind, lang_type: &str) -> TypeId {
+        AbstractTraceWriter::ensure_type_id(self, kind, lang_type)
+    }
+    fn ensure_raw_type_id(&mut self, typ: TypeRecord) -> TypeId {
+        AbstractTraceWriter::ensure_raw_type_id(self, typ)
+    }
+```
+
+**Intern variable names for later reference.**
+```rust
+    fn ensure_variable_id(&mut self, variable_name: &str) -> VariableId {
+        AbstractTraceWriter::ensure_variable_id(self, variable_name)
+    }
+```
+
+**Register source file paths and function declarations.**
+```rust
+    fn register_path(&mut self, path: &Path) {
+        AbstractTraceWriter::register_path(self, path)
+    }
+    fn register_function(&mut self, name: &str, path: &Path, line: Line) {
+        AbstractTraceWriter::register_function(self, name, path, line)
+    }
+```
+
+**Capture line execution and function invocation with arguments.**
+```rust
+    fn register_step(&mut self, path: &Path, line: Line) {
+        AbstractTraceWriter::register_step(self, path, line)
+    }
+    fn register_call(&mut self, function_id: FunctionId, args: Vec<FullValueRecord>) {
+        AbstractTraceWriter::register_call(self, function_id, args)
+    }
+```
+
+**Helper to build an argument record and note function returns.**
+```rust
+    fn arg(&mut self, name: &str, value: ValueRecord) -> FullValueRecord {
+        AbstractTraceWriter::arg(self, name, value)
+    }
+    fn register_return(&mut self, return_value: ValueRecord) {
+        AbstractTraceWriter::register_return(self, return_value)
+    }
+```
+
+**Record ad-hoc events within the trace.**
+```rust
+    // TODO: add metadata arg
+    fn register_special_event(&mut self, kind: EventLogKind, content: &str) {
+        AbstractTraceWriter::register_special_event(self, kind, content)
+    }
+```
+
+**Convert type descriptions into records and register them.**
+```rust
+    fn to_raw_type(&self, kind: TypeKind, lang_type: &str) -> TypeRecord {
+        AbstractTraceWriter::to_raw_type(self, kind, lang_type)
+    }
+    fn register_type(&mut self, kind: TypeKind, lang_type: &str) {
+        AbstractTraceWriter::register_type(self, kind, lang_type)
+    }
+```
+
+**Support registering arbitrary type records and assembly snippets.**
+```rust
+    fn register_raw_type(&mut self, typ: TypeRecord) {
+        AbstractTraceWriter::register_raw_type(self, typ)
+    }
+    fn register_asm(&mut self, instructions: &[String]) {
+        AbstractTraceWriter::register_asm(self, instructions)
+    }
+```
+
+**Store a variable and its value in one step.**
+```rust
+    fn register_variable_with_full_value(&mut self, name: &str, value: ValueRecord) {
+        AbstractTraceWriter::register_variable_with_full_value(self, name, value)
+    }
+```
+
+**Separate registration of variable names and associated values.**
+```rust
+    fn register_variable_name(&mut self, variable_name: &str) {
+        AbstractTraceWriter::register_variable_name(self, variable_name)
+    }
+    fn register_full_value(&mut self, variable_id: VariableId, value: ValueRecord) {
+        AbstractTraceWriter::register_full_value(self, variable_id, value)
+    }
+```
+
+**Emit compound values and individual cells.**
+```rust
+    fn register_compound_value(&mut self, place: Place, value: ValueRecord) {
+        AbstractTraceWriter::register_compound_value(self, place, value)
+    }
+    fn register_cell_value(&mut self, place: Place, value: ValueRecord) {
+        AbstractTraceWriter::register_cell_value(self, place, value)
+    }
+```
+
+**Describe updates to compound items or cell contents.**
+```rust
+    fn assign_compound_item(&mut self, place: Place, index: usize, item_place: Place) {
+        AbstractTraceWriter::assign_compound_item(self, place, index, item_place)
+    }
+    fn assign_cell(&mut self, place: Place, new_value: ValueRecord) {
+        AbstractTraceWriter::assign_cell(self, place, new_value)
+    }
+```
+
+**Track variables pointing to places and their removal.**
+```rust
+    fn register_variable(&mut self, variable_name: &str, place: Place) {
+        AbstractTraceWriter::register_variable(self, variable_name, place)
+    }
+    fn drop_variable(&mut self, variable_name: &str) {
+        AbstractTraceWriter::drop_variable(self, variable_name)
+    }
+```
+
+**Record an assignment with explicit pass-by semantics.**
+```rust
+    fn assign(&mut self, variable_name: &str, rvalue: RValue, pass_by: PassBy) {
+        AbstractTraceWriter::assign(self, variable_name, rvalue, pass_by)
+    }
+```
+
+**Bind variables to storage locations or drop multiple at once.**
+```rust
+    fn bind_variable(&mut self, variable_name: &str, place: Place) {
+        AbstractTraceWriter::bind_variable(self, variable_name, place)
+    }
+    fn drop_variables(&mut self, variable_names: &[String]) {
+        AbstractTraceWriter::drop_variables(self, variable_names)
+    }
+```
+
+**Build an rvalue from a single variable.**
+```rust
+    fn simple_rvalue(&mut self, variable_name: &str) -> RValue {
+        AbstractTraceWriter::simple_rvalue(self, variable_name)
+    }
+```
+
+**Build an rvalue from multiple variable dependencies.**
+```rust
+    fn compound_rvalue(&mut self, variable_dependencies: &[String]) -> RValue {
+        AbstractTraceWriter::compound_rvalue(self, variable_dependencies)
+    }
+```
+
+**Remove the last step event when necessary.**
+```rust
+    fn drop_last_step(&mut self) {
+        AbstractTraceWriter::drop_last_step(self)
+    }
+```
+
+**Insert an event directly into the stream.**
+```rust
+    fn add_event(&mut self, event: TraceLowLevelEvent) {
+        AbstractTraceWriter::add_event(self, event)
+    }
+```
+
+**Append multiple events in one call.**
+```rust
+    fn append_events(&mut self, events: &mut Vec<TraceLowLevelEvent>) {
+        AbstractTraceWriter::append_events(self, events)
+    }
+```
+
+**Finish writing metadata before finalizing events and paths.**
+```rust
+    fn finish_writing_trace_metadata(&mut self) -> Result<(), Box<dyn Error>> {
+        AbstractTraceWriter::finish_writing_trace_metadata(self)
+    }
+```
+
+**Leave event completion abstract and provide default path finalization.**
+```rust
+    fn finish_writing_trace_events(&mut self) -> Result<(), Box<dyn Error>>;
+    fn finish_writing_trace_paths(&mut self) -> Result<(), Box<dyn Error>> {
+        AbstractTraceWriter::finish_writing_trace_paths(self)
+    }
+}
+```