command: Operand carries a source span

Each WHERE-expression Operand now records the byte span of the
terminal it was built from — the precise per-literal highlight
target for an expression WARNING (finishing ADR-0027 §2's
highlight/hint wiring). parse_operand captures MatchedItem::span;
the RowFilter::eq convenience constructor uses Operand::NO_SPAN.

PartialEq is hand-written to ignore the span — it is editor
metadata, so Command equality stays whitespace- and
position-independent, which the Expr test corpus relies on.
No behaviour change; 1100 tests still pass, clippy clean.

src/dsl/command.rs

@@ -257,9 +257,15 @@ impl RowFilter {
     #[must_use]
     pub fn eq(column: impl Into<String>, value: Value) -> Self {
         Self::Where(Expr::Predicate(Predicate::Compare {
-            left: Operand::Column(column.into()),
+            left: Operand::Column {
+                name: column.into(),
+                span: Operand::NO_SPAN,
+            },
             op: CompareOp::Eq,
-            right: Operand::Literal(value),
+            right: Operand::Literal {
+                value,
+                span: Operand::NO_SPAN,
+            },
         }))
     }
 }
@@ -322,10 +328,48 @@ pub enum Predicate {
 
 /// A comparison operand — a column reference or a literal
 /// (ADR-0026 §1: operands are never nested expressions).
-#[derive(Debug, Clone, PartialEq, Eq)]
+///
+/// Each operand carries the byte `span` it occupied in the
+/// source. The span feeds the precise per-literal WARNING
+/// highlight (ADR-0027) and is otherwise editor metadata —
+/// `PartialEq` is hand-written to **ignore** it, so two
+/// operands are equal when their column / value match
+/// regardless of where they were typed. This keeps `Command`
+/// equality whitespace- and position-independent (the bulk of
+/// the `Expr` test corpus relies on it).
+#[derive(Debug, Clone, Eq)]
 pub enum Operand {
-    Column(String),
-    Literal(Value),
+    Column { name: String, span: (usize, usize) },
+    Literal { value: Value, span: (usize, usize) },
+}
+
+impl Operand {
+    /// Span used for operands built without a source position
+    /// (the [`RowFilter::eq`] convenience constructor).
+    pub const NO_SPAN: (usize, usize) = (0, 0);
+
+    /// The byte range this operand occupied in the source —
+    /// [`Operand::NO_SPAN`] for programmatically-built operands.
+    #[must_use]
+    pub const fn span(&self) -> (usize, usize) {
+        match self {
+            Self::Column { span, .. } | Self::Literal { span, .. } => *span,
+        }
+    }
+}
+
+impl PartialEq for Operand {
+    /// Compares column name / literal value only — the source
+    /// `span` is deliberately excluded (see the type docs).
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Self::Column { name: a, .. }, Self::Column { name: b, .. }) => a == b,
+            (Self::Literal { value: a, .. }, Self::Literal { value: b, .. }) => {
+                a == b
+            }
+            _ => false,
+        }
+    }
 }
 
 /// The six comparison operators. `<>` and `!=` both parse to

src/dsl/grammar/expr.rs

@@ -520,22 +520,28 @@ impl<'a> ExprParser<'a> {
     }
 
     /// `operand := literal | column_ref`.
+    ///
+    /// Every operand records the byte `span` of the terminal it
+    /// was built from — the precise highlight target for an
+    /// expression WARNING (ADR-0027).
     fn parse_operand(&mut self) -> Result<Operand, ValidationError> {
         let item = self
             .advance()
             .ok_or_else(|| drift_error("expected an operand"))?;
+        let span = item.span;
+        let literal = |value: Value| Operand::Literal { value, span };
         match &item.kind {
             MatchedKind::Ident { role: "expr_column", .. } => {
-                Ok(Operand::Column(item.text.clone()))
+                Ok(Operand::Column { name: item.text.clone(), span })
             }
-            MatchedKind::Word("null") => Ok(Operand::Literal(Value::Null)),
-            MatchedKind::Word("true") => Ok(Operand::Literal(Value::Bool(true))),
-            MatchedKind::Word("false") => Ok(Operand::Literal(Value::Bool(false))),
+            MatchedKind::Word("null") => Ok(literal(Value::Null)),
+            MatchedKind::Word("true") => Ok(literal(Value::Bool(true))),
+            MatchedKind::Word("false") => Ok(literal(Value::Bool(false))),
             MatchedKind::NumberLit => {
-                Ok(Operand::Literal(Value::Number(item.text.clone())))
+                Ok(literal(Value::Number(item.text.clone())))
             }
             MatchedKind::StringLit => {
-                Ok(Operand::Literal(Value::Text(item.text.clone())))
+                Ok(literal(Value::Text(item.text.clone())))
             }
             _ => Err(drift_error("expected a column or literal operand")),
         }
@@ -598,11 +604,24 @@ mod tests {
     }
 
     fn col(name: &str) -> Operand {
-        Operand::Column(name.to_string())
+        Operand::Column {
+            name: name.to_string(),
+            span: Operand::NO_SPAN,
+        }
+    }
+
+    /// A literal operand with no source span — the span is
+    /// ignored by `Operand`'s `PartialEq`, so test trees built
+    /// with this compare equal to walked ones.
+    fn lit(value: Value) -> Operand {
+        Operand::Literal {
+            value,
+            span: Operand::NO_SPAN,
+        }
     }
 
     fn num(n: &str) -> Operand {
-        Operand::Literal(Value::Number(n.to_string()))
+        lit(Value::Number(n.to_string()))
     }
 
     fn compare(left: Operand, op: CompareOp, right: Operand) -> Expr {
@@ -644,16 +663,12 @@ mod tests {
             compare(
                 col("Name"),
                 CompareOp::Eq,
-                Operand::Literal(Value::Text("Ada".to_string())),
+                lit(Value::Text("Ada".to_string())),
             ),
         );
         assert_eq!(
             parse_expr("Active = true"),
-            compare(
-                col("Active"),
-                CompareOp::Eq,
-                Operand::Literal(Value::Bool(true)),
-            ),
+            compare(col("Active"), CompareOp::Eq, lit(Value::Bool(true))),
         );
         assert_eq!(
             parse_expr("a = -7"),
@@ -708,7 +723,7 @@ mod tests {
             parse_expr("Name like 'A%'"),
             Expr::Predicate(Predicate::Like {
                 target: col("Name"),
-                pattern: Operand::Literal(Value::Text("A%".to_string())),
+                pattern: lit(Value::Text("A%".to_string())),
                 negated: false,
             }),
         );

src/dsl/walker/mod.rs

@@ -542,7 +542,13 @@ fn predicate_warnings(
 }
 
 const fn is_null_literal(operand: &Operand) -> bool {
-    matches!(operand, Operand::Literal(crate::dsl::value::Value::Null))
+    matches!(
+        operand,
+        Operand::Literal {
+            value: crate::dsl::value::Value::Null,
+            ..
+        }
+    )
 }
 
 /// If one operand is a known column and the other a non-null
@@ -556,8 +562,10 @@ fn pair_type_mismatch(
     columns: &[crate::completion::TableColumn],
 ) -> Option<String> {
     let (column, literal) = match (a, b) {
-        (Operand::Column(c), Operand::Literal(v))
-        | (Operand::Literal(v), Operand::Column(c)) => (c, v),
+        (Operand::Column { name: c, .. }, Operand::Literal { value: v, .. })
+        | (Operand::Literal { value: v, .. }, Operand::Column { name: c, .. }) => {
+            (c, v)
+        }
         _ => return None,
     };
     // `null` fits any column; `= NULL` is flagged separately.