fix(lint): clear Rust 1.96 clippy debt (14 lints) + criterion black_box deprecation (#308)

CI's toolchain rolled to Rust 1.96; `cargo clippy --all-targets -- -D
warnings` now fails on 14 pre-existing lints in `corpus/`,
`exchange/smtlib.rs` and `verification/pareto_arbiter.rs`, plus
deprecated `criterion::black_box` in both bench targets. These were
invisible while the fmt red (#305) short-circuited the rust-ci job, and
they block every PR's rust-ci (first seen on #306, whose own module is
clippy-clean).

All fixes are mechanical with no behaviour change. `cargo clippy
--all-targets` clean locally; 1174 lib tests green; `cargo fmt --check`
clean.

Unblocks rust-ci for #306 and keeps the main-green clock (L3→L1 gate)
alive.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

benches/proof_benchmarks.rs

@@ -6,7 +6,8 @@
 //! Run with: cargo bench
 //! Generates HTML reports in target/criterion/
 
-use criterion::{black_box, criterion_group, criterion_main, BenchmarkId, Criterion};
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
+use std::hint::black_box;
 
 use echidna::core::{Context, Goal, Hypothesis, ProofState, Term};
 use echidna::provers::{ProverConfig, ProverFactory, ProverKind};

benches/routing_benchmarks.rs

@@ -14,7 +14,8 @@
 //! Run with: `cargo bench --bench routing_benchmarks`
 //! Generates HTML reports in `target/criterion/`
 
-use criterion::{black_box, criterion_group, criterion_main, BenchmarkId, Criterion};
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
+use std::hint::black_box;
 
 use echidna::agent::AgentConfig;
 use echidna::dispatch::DispatchConfig;

src/rust/corpus/acl2_books.rs

@@ -361,8 +361,10 @@ fn classify_form(form: &str, line: usize, pf: &mut ParsedFile) {
             if name.is_empty() {
                 return;
             }
-            let mut hz = AxiomUsage::default();
-            hz.postulate = true;
+            let mut hz = AxiomUsage {
+                postulate: true,
+                ..Default::default()
+            };
             hz.other.push("defaxiom".to_string());
             flag_hazards(rest_body, &mut hz);
             pf.decls.push(DraftDecl {
@@ -379,8 +381,10 @@ fn classify_form(form: &str, line: usize, pf: &mut ParsedFile) {
             if name.is_empty() {
                 return;
             }
-            let mut hz = AxiomUsage::default();
-            hz.postulate = true;
+            let mut hz = AxiomUsage {
+                postulate: true,
+                ..Default::default()
+            };
             hz.other.push("defstub".to_string());
             pf.decls.push(DraftDecl {
                 name,

src/rust/corpus/isabelle.rs

@@ -546,10 +546,8 @@ fn parse_theorem_like(
             }
             // `using … by …` and `unfolding … by …` patterns also
             // terminate on the trailing `by`.
-            if t.contains(" by ") || t.ends_with(" by") {
-                if !t.starts_with("proof") {
-                    terminated = true;
-                }
+            if (t.contains(" by ") || t.ends_with(" by")) && !t.starts_with("proof") {
+                terminated = true;
             }
         }
         j += 1;

src/rust/corpus/metamath.rs

@@ -314,8 +314,10 @@ fn extract_module_name(src: &str) -> Option<String> {
 }
 
 fn parse_mm_file(raw: &str) -> ParsedFile {
-    let mut pf = ParsedFile::default();
-    pf.module_name = extract_module_name(raw);
+    let mut pf = ParsedFile {
+        module_name: extract_module_name(raw),
+        ..Default::default()
+    };
 
     let toks = lex(raw);
     let mut scope_stack: Vec<String> = Vec::new();

src/rust/corpus/minif2f.rs

@@ -160,7 +160,7 @@ fn terminators(ext: &str) -> &'static [&'static str] {
 
 /// Identify the start-of-statement on a line and return
 /// `(opening_token_index, name)` if found.
-fn match_opening<'a>(line: &'a str, ext: &str) -> Option<(usize, String)> {
+fn match_opening(line: &str, ext: &str) -> Option<(usize, String)> {
     let trim = line.trim_start();
     for kw in opening_tokens(ext) {
         if let Some(rest) = trim.strip_prefix(*kw) {

src/rust/corpus/tptp.rs

@@ -372,9 +372,9 @@ fn parse_annotated_formula(stmt: &str, line: usize) -> Option<DraftDecl> {
     for k in &kinds {
         if let Some(r) = stmt.strip_prefix(k) {
             let r2 = r.trim_start();
-            if r2.starts_with('(') {
+            if let Some(stripped) = r2.strip_prefix('(') {
                 head = Some(k);
-                rest = Some(&r2[1..]);
+                rest = Some(stripped);
                 break;
             }
         }

src/rust/corpus/why3.rs

@@ -329,8 +329,8 @@ fn parse_envelope(
     }
 
     // Imports / clones inside the envelope.
-    for k in (start + 1)..body_end {
-        let t = lines[k].trim_start();
+    for line in lines.iter().take(body_end).skip(start + 1) {
+        let t = line.trim_start();
         let import_rest = t
             .strip_prefix("use import ")
             .or_else(|| t.strip_prefix("use export "))

src/rust/exchange/smtlib.rs

@@ -144,10 +144,10 @@ impl SmtLibExchange {
             }
         }
 
-        infos.sort_by(|a, b| key_of(a).cmp(&key_of(b)));
-        options.sort_by(|a, b| key_of(a).cmp(&key_of(b)));
-        sorts.sort_by(|a, b| key_of(a).cmp(&key_of(b)));
-        funs.sort_by(|a, b| key_of(a).cmp(&key_of(b)));
+        infos.sort_by_key(key_of);
+        options.sort_by_key(key_of);
+        sorts.sort_by_key(key_of);
+        funs.sort_by_key(key_of);
         // defs preserve original order: dependencies between defines are
         // significant and we don't track them here.
 

src/rust/verification/pareto_arbiter.rs

@@ -35,20 +35,15 @@ pub struct AttemptOutcome {
 
 /// How to pick a recommendation when multiple frontier points
 /// remain after Pareto filtering.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, Serialize, Deserialize)]
 pub enum Tiebreak {
+    #[default]
     MinAxiom,
     MinLatency,
     MaxConfidence,
     MinCertificate,
 }
 
-impl Default for Tiebreak {
-    fn default() -> Self {
-        Tiebreak::MinAxiom
-    }
-}
-
 /// Arbitration decision: the frontier, a recommendation, and how
 /// many of the inputs were dominated.
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -153,6 +148,7 @@ impl Default for ParetoArbiter {
 /// - a.axiom_cost              <= b.axiom_cost
 /// - a.certificate_size_bytes  <= b.certificate_size_bytes
 /// - a.confidence              >= b.confidence
+///
 /// AND at least one of these is strict.
 fn dominates(a: &AttemptOutcome, b: &AttemptOutcome) -> bool {
     let no_worse = a.latency_ms <= b.latency_ms
@@ -162,11 +158,10 @@ fn dominates(a: &AttemptOutcome, b: &AttemptOutcome) -> bool {
     if !no_worse {
         return false;
     }
-    let strictly_better = a.latency_ms < b.latency_ms
+    a.latency_ms < b.latency_ms
         || a.axiom_cost < b.axiom_cost
         || a.certificate_size_bytes < b.certificate_size_bytes
-        || a.confidence > b.confidence;
-    strictly_better
+        || a.confidence > b.confidence
 }
 
 #[cfg(test)]