M2.9: budget lambda work and bound wildcard substring search

Sweep findings from the ac8da7d4 security scan (storytold-gridcraft-agent-
findings.json), remaining on main at 72c1d57d:

- finding 14 (crates/calc/src/eval.rs:988): every lambda invocation now
  spends one charge against a per-cell work budget (16M — one per cell of
  the largest array a reference may expand to), so a hostile, deeply
  nested LAMBDA/LET formula stops at the bound a legitimately wide one
  could reach instead of growing exponentially with nesting. Exhaustion
  is #CALC!, like the existing depth cap. Metered at `call_lambda_values`
  so every path into a body is counted (direct application, MAP/REDUCE/
  SCAN/BYROW/BYCOL/MAKEARRAY, D-function criteria); the criteria
  sub-evaluator hands its spend back to the parent.
- finding 16 (crates/functions/src/criteria.rs:313): `match_from` takes a
  step budget (1<<26: an honest match against Excel's 32,767-char cell
  ceiling costs a few hundred thousand steps), and `wildcard_find` drops
  the leading star run (a no-op for a prefix match) so the first literal
  anchor skips straight to its occurrences; all suffix attempts share one
  budget. Star churn degrades to no-match instead of quadratic work.

Unit tests: mock-host exhaustion/under-budget for lambda applications
(eval::fuel_tests), nested REDUCE under budget in full recalc, wildcard
behaviour unchanged.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

crates/calc/src/eval.rs

@@ -22,6 +22,11 @@ const FULL_SIZE_CELLS: u64 = 16_384;
 /// range, so that formulas over them stay fast.
 const FULL_SIZE_BOUNDED_CELLS: u64 = 1_048_576;
 const MAX_DEPTH: usize = 400;
+/// Lambda invocations one cell may make. A semantically bounded formula in Excel can invoke
+/// its lambda at most once per cell of an array (capped here by `MAX_CELLS`), so this covers
+/// every legitimate call; hostile work that grows past one dimension (a LAMBDA that recurses
+/// or nest `MAP` into `MAP`) then stops at the same bound instead of squaring.
+const LAMBDA_FUEL: u64 = MAX_CELLS;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct Area {
@@ -88,6 +93,11 @@ pub struct Evaluator<'h> {
     pub at: CellRef,
     env: Vec<(String, Ev)>,
     depth: usize,
+    /// Lambda invocations this cell still has left. Every call spends one charge, so a
+    /// compact hostile formula (a LAMBDA that calls itself, nested `MAP`s over big arrays)
+    /// runs out of work after the same number of calls that a legitimately wide one could
+    /// make, instead of an amount of work that squares with array nesting (#2382).
+    fuel: u64,
 }
 
 struct FnCtx<'a, 'h> {
@@ -127,8 +137,11 @@ impl Ctx for FnCtx<'_, '_> {
                 _ => None,
             })
             .collect();
-        let mut ev = Evaluator { host: &mut *self.ev.host, sheet: area.sheet, at, env, depth: self.ev.depth };
-        Some(matches!(ev.value(&shifted).scalar().to_bool(), Ok(true)))
+        let mut ev = Evaluator { host: &mut *self.ev.host, sheet: area.sheet, at, env, depth: self.ev.depth, fuel: self.ev.fuel };
+        let v = matches!(ev.value(&shifted).scalar().to_bool(), Ok(true));
+        // The child's spend counts against this cell's budget.
+        self.ev.fuel = ev.fuel;
+        Some(v)
     }
     fn has_lambda(&self) -> bool {
         self.lambda.is_some()
@@ -147,7 +160,7 @@ impl Ctx for FnCtx<'_, '_> {
 
 impl<'h> Evaluator<'h> {
     pub fn new(host: &'h mut dyn Host, sheet: usize, at: CellRef) -> Self {
-        Evaluator { host, sheet, at, env: Vec::new(), depth: 0 }
+        Evaluator { host, sheet, at, env: Vec::new(), depth: 0, fuel: LAMBDA_FUEL }
     }
 
     /// Evaluates to a value (references are dereferenced; multi-cell → array).
@@ -983,6 +996,13 @@ impl<'h> Evaluator<'h> {
     }
 
     fn call_lambda_values(&mut self, l: &Lambda, bound: Vec<(String, Ev)>) -> Ev {
+        // #2382: one charge per invocation, so a cell's total work stays bounded however the
+        // lambdas nest. Foregrounding the charge here means every path into a body (direct
+        // `(2,3)` application, `MAP`/`REDUCE`/`BYROW` helpers, D-function criteria) meters.
+        self.fuel = match self.fuel.checked_sub(1) {
+            Some(f) => f,
+            None => return err(CellError::Calc),
+        };
         let saved = std::mem::replace(&mut self.env, l.env.clone());
         self.env.extend(bound);
         let r = self.eval(&l.body);
@@ -1984,3 +2004,54 @@ pub fn is_known_function(n: &str) -> bool {
 
 #[allow(dead_code)]
 fn unused(_: RefKind) {}
+
+#[cfg(test)]
+mod fuel_tests {
+    use super::*;
+    use gridcraft_model::Workbook;
+
+    struct Empty {
+        wb: Workbook,
+    }
+    impl Host for Empty {
+        fn workbook(&self) -> &Workbook {
+            &self.wb
+        }
+        fn cell_value(&mut self, _sheet: usize, _c: CellRef) -> Value {
+            Value::Empty
+        }
+        fn now_serial(&self) -> f64 {
+            0.0
+        }
+        fn random(&mut self) -> f64 {
+            0.0
+        }
+    }
+
+    fn eval_with(fuel: u64, src: &str) -> Value {
+        let mut host = Empty { wb: Workbook::default() };
+        let mut ev = Evaluator::new(&mut host, 0, CellRef::new(0, 0));
+        ev.fuel = fuel;
+        ev.value(&gridcraft_formula::parser::parse(src).unwrap_or_else(|e| panic!("{e}")))
+    }
+
+    #[test]
+    fn lambda_calls_spend_fuel_and_run_out_quietly() {
+        // Three applications, one charge each: 3 inside the budget. (A nested MAP wouldn't do
+        // here: an inner MAP result is an array, and MAP of array elements is #CALC! on shape,
+        // which happens well before the budget does.)
+        let r = eval_with(3, "=LAMBDA(x,LAMBDA(y,LAMBDA(z,z+1)(3))(2))(1)");
+        assert_eq!(r, Value::number(4.0), "{r:?}");
+        // One charge short: the nest bottoms out in #CALC! instead of running unbounded.
+        let r = eval_with(2, "=LAMBDA(x,LAMBDA(y,LAMBDA(z,z+1)(3))(2))(1)");
+        assert!(matches!(r, Value::Error(CellError::Calc)), "{r:?}");
+        // One charge short of a single application: #CALC! with a zero budget.
+        let r = eval_with(0, "=LAMBDA(x,x+1)(2)");
+        assert!(matches!(r, Value::Error(CellError::Calc)), "{r:?}");
+        let r = eval_with(1, "=LAMBDA(x,x+1)(2)");
+        assert_eq!(r, Value::number(3.0));
+        // A flat helper map keeps working (3 of 3 invokes inside the budget).
+        let r = eval_with(3, "=MAP({1,2,3},LAMBDA(x,x*2))");
+        assert!(matches!(r, Value::Array(_)) && !matches!(&r, Value::Array(a) if a.data.iter().any(|v| matches!(v, Value::Error(_)))), "{r:?}");
+    }
+}

crates/calc/src/tests.rs

@@ -570,6 +570,24 @@ fn lambda_helpers_check_shapes_and_parameters() {
     assert_eq!(t.num("B7"), 2.0);
 }
 
+#[test]
+fn lambda_calls_spend_one_work_budget_per_cell() {
+    // #2382: lambda nesting multiplies invocations, and the budget meters every one of them.
+    // Exhaustion itself is tested on a mock host in `eval::fuel_tests` (burning the real 16M
+    // budget in a full recalc needs tens of millions of calls, far too slow for a unit test);
+    // here the same nested shape runs inside it: 6 × 9 ≈ 59k scalar REDUCE invocations.
+    let mut t = T::new();
+    t.set(
+        "A1",
+        "=LET(s,SEQUENCE(9),REDUCE(0,s,LAMBDA(a,v,REDUCE(0,s,LAMBDA(a,v,REDUCE(0,s,LAMBDA(a,v,REDUCE(0,s,LAMBDA(a,v,REDUCE(0,s,LAMBDA(a,v,a+v)))))))))))",
+    );
+    // The bodies are the same inner reduce, so every level sums to 45 while the invocation
+    // count multiplies by 9 per level (9, 81, 729, 6561, 59049 calls).
+    assert_eq!(t.num("A1"), 45.0);
+    t.set("A2", "=REDUCE(0,SEQUENCE(4000),LAMBDA(a,v,a+v))");
+    assert_eq!(t.num("A2"), 4000.0 * 4001.0 / 2.0);
+}
+
 #[test]
 fn accounting_negative_text_coerces() {
     let mut t = T::new();

crates/functions/src/criteria.rs

@@ -264,15 +264,27 @@ pub(crate) fn has_wildcards(pattern: &str) -> bool {
 pub(crate) fn wildcard_match(pattern: &str, text: &str) -> bool {
     let p = tokenize(pattern);
     let t = lower_chars(text);
-    match_from(&p, &t, true).is_some()
+    let mut budget = MAX_STEPS;
+    match_from(&p, &t, true, &mut budget).is_some()
 }
 
+/// Steps one `match_from` call may take. An honest match against Excel's 32,767-character
+/// cell ceiling costs a few hundred thousand; a hostile one (star churn) is capped instead
+/// of quadratic — a call that spends more gives up and reports no match, quiet degradation
+/// like the other work caps on far-past-realistic input.
+const MAX_STEPS: u64 = 1 << 26;
+
 /// Greedy-free matcher: returns the matched length of `t` when `p` matches a prefix of `t`
-/// (or all of `t` when `whole`). Iterative with backtracking on the last star (linear-ish).
-fn match_from(p: &[Tok], t: &[char], whole: bool) -> Option<usize> {
+/// (or all of `t` when `whole`). Iterative with backtracking on the last star (linear-ish,
+/// quadratic at worst). `(budget, whole)`: the budget is spent one per loop step; a call that
+/// would spend more than it has gives up and reports no match — quiet degradation, as with the
+/// other work caps on far-past-realistic input (an honest match against Excel's 32,767-char
+/// cell ceiling costs a few hundred thousand steps).
+fn match_from(p: &[Tok], t: &[char], whole: bool, budget: &mut u64) -> Option<usize> {
     let (mut pi, mut ti) = (0usize, 0usize);
     let mut star: Option<(usize, usize)> = None;
     loop {
+        *budget = budget.checked_sub(1)?;
         if pi == p.len() && (!whole || ti == t.len()) {
             return Some(ti);
         }
@@ -307,10 +319,32 @@ fn match_from(p: &[Tok], t: &[char], whole: bool) -> Option<usize> {
 pub(crate) fn wildcard_find(pattern: &str, text: &str, start: usize) -> Option<usize> {
     let p = tokenize(pattern);
     let t = lower_chars(text);
+    // A leading run of stars never matters for a prefix match (it consumes nothing), so
+    // dropping it lets the anchor below skip linearly through the text (#2382).
+    let skip = p.iter().take_while(|tk| matches!(tk, Tok::Star)).count();
+    let p = &p[skip.min(p.len())..];
     if p.is_empty() {
         return if start <= t.len() { Some(start) } else { None };
     }
-    (start..t.len()).find(|&i| t.get(i..).is_some_and(|rest| match_from(&p, rest, false).is_some()))
+    // The first token that consumes a character anchors the scan: a literal skips straight
+    // to its occurrences, and after leading `?`s each attempt only pays for the `?` run and
+    // one suffix try. Every attempt shares one budget, so the total work stays flat.
+    let anys = p.iter().take_while(|tk| matches!(tk, Tok::Any)).count();
+    let anchor = p.get(anys);
+    let mut budget = MAX_STEPS;
+    let mut i = start;
+    while i < t.len() {
+        let hit = match (anchor, t.get(i + anys)) {
+            (Some(Tok::Char(c)), Some(rest)) => *rest == *c && match_from(p, &t[i..], false, &mut budget).is_some(),
+            (Some(Tok::Char(_)), None) => break, // the anchor char no longer exists ahead
+            _ => match_from(p, &t[i..], false, &mut budget).is_some(),
+        };
+        if hit {
+            return Some(i);
+        }
+        i += 1;
+    }
+    None
 }
 
 /// Exact-or-wildcard equality used by MATCH/VLOOKUP/XLOOKUP exact modes: text with wildcards