fix(speckl): Rust generator — Date type, record structs, event enum (cycle 73)

Three defects found by deep-inspecting the Rust output against the
product spec (FederatedMeetupProduct.speckdl):

1. Date type undefined in Rust — emitted as 'Date' which doesn't exist.
   Fixed: Date maps to u64 (Unix timestamp) in both the primitive map
   and the ident fallback path.

2. Interface records (Money, Ticket, Order, etc.) not emitted as Rust
   structs — only events were emitted. The TS backend has the same gap.
   Fixed: record-kind interfaces now emit as Rust structs.

3. Decision log typed as Vec<FirstEventName> instead of an enum union.
   Fixed: emit a SpeckName_Event enum with one variant per event type,
   type the decision log as Vec<SpeckName_Event>.

57/57 tests pass. Both specs generate clean Rust output.

compiler/src/generators/rust.ts

@@ -198,6 +198,29 @@ function emitSpeck(speck: SpeckNode): string {
     return `#[derive(Debug, Clone)]\npub struct ${e.name} {\n${fields}\n}`;
   }).join('\n\n');
 
+  // Cycle 73: Event enum union for the decision log.
+  // Each variant wraps the corresponding event struct.
+  const eventEnum = events.length > 0
+    ? `#[derive(Debug, Clone)]\npub enum ${speck.name}Event {\n` +
+      events.map(e => `    ${e.name}(${e.name}),`).join('\n') +
+      `\n}`
+    : '';
+
+  // Cycle 73: Interface record structs (Money, Ticket, Order, etc.)
+  // Previously only events were emitted as structs. Interface records
+  // with fields (kind === 'record') are now emitted too.
+  const recordInterfaces = allInterfaces.filter(iface =>
+    iface?.kind === 'record' || (iface?.fields && iface.fields.length > 0)
+  );
+  const recordStructs = recordInterfaces.map(iface => {
+    const fields = iface.fields.map((f: any) => {
+      const name = snakeCase(cleanName(f.name));
+      const ty = rustType(f.type, speck.name, enumMap);
+      return `    pub ${name}: ${ty},`;
+    }).join('\n');
+    return `#[derive(Debug, Clone)]\npub struct ${iface.name} {\n${fields}\n}`;
+  }).join('\n\n');
+
   const structName = `${speck.name}Machine`;
 
   // State variables with original name + snake_case name mapping
@@ -276,8 +299,11 @@ function emitSpeck(speck: SpeckNode): string {
     `    }`
   ).join('\n\n');
 
-  // Decision log type
-  const logEventType = events.length > 0 ? `Vec<${events[0].name}>` : 'Vec<String>';
+  // Decision log type — cycle 73: use an enum union of all event types,
+  // not just the first one. If there are no events, fall back to String.
+  const logEventType = events.length > 0
+    ? `Vec<${speck.name}Event>`
+    : 'Vec<String>';
 
   // Struct definition
   const structDef = `/// Speck state machine: ${speck.name}\n` +
@@ -318,11 +344,13 @@ function emitSpeck(speck: SpeckNode): string {
     `// DO NOT EDIT MANUALLY — regenerate from .speckdl source\n\n` +
     `use std::collections::{HashMap, HashSet};\n\n` +
     `${stateEnum}\n\n` +
+    `${recordStructs ? recordStructs + '\n\n' : ''}` +
     `${eventStructs}\n\n` +
+    `${eventEnum ? eventEnum + '\n\n' : ''}` +
     `${structDef}\n\n` +
     `${constructor}\n\n` +
     `${actionImpl}\n` +
-    `${invariantImpl}\n` +
+    `${invariantImpl}` +
     `${verifyImpl}\n`;
 
   return file;
@@ -619,6 +647,8 @@ function rustType(t: any, speckName: string = '', enumMap?: Map<string, string[]
       Nat: 'u64', Int: 'i64', Real: 'f64',
       Bool: 'bool', String: 'String', Bytes: 'Vec<u8>',
       Number: 'f64',
+      // Cycle 73: Date → u64 Unix timestamp (avoids chrono dependency).
+      Date: 'u64',
     };
     return map[t.name] || t.name.toLowerCase();
   }
@@ -645,6 +675,7 @@ function rustType(t: any, speckName: string = '', enumMap?: Map<string, string[]
     if (rawName === 'Int') return 'i64';
     if (rawName === 'Bool') return 'bool';
     if (rawName === 'String') return 'String';
+    if (rawName === 'Date') return 'u64';
     // Handle Option<T> from SpeckDL's Option(Type) syntax
     const optionMatch = rawName.match(/^Option[_(]\s*(\w+)\s*\)?$/);
     if (optionMatch) {