build(rust): pin toolchain to 1.96.0 + fix the two 1.96-only clippy lints

Root-causes the recurring Build-Check skew. CI installs floating `stable`
(now 1.96) via dtolnay/rust-toolchain@stable, but local dev had drifted to an
older stable (1.94) whose clippy could not see two `collapsible_match` lints
1.96 flags -- so #85's clippy pass (run on 1.94) still left main Build-Check red.

- rust-toolchain.toml pins channel = "1.96.0" (+ clippy, rustfmt) so `cargo`
  uses the SAME toolchain locally and in CI, removing the silent skew.
- Fix the two 1.96 `collapsible_match` lints (clippy --fix -> match guards),
  behaviour-preserving:
    * src/lsp/handlers/definition.rs (TypeDef goto-definition arm)
    * src/vm/optimizer.rs (JumpIfFalse/JumpIfTrue nop-removal arm)

Verified with the pinned 1.96.0: `cargo clippy -- -D warnings` exit 0,
`cargo fmt --check` clean, `cargo test --lib` 173/173 passing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013wg3Mtq2QFhYi4XVw1Z6z7

Author: claude

rust-toolchain.toml

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: MPL-2.0
+# Pin the Rust toolchain so local builds and CI use the SAME compiler + clippy.
+#
+# Why this exists: CI installs `stable` (dtolnay/rust-toolchain@stable in
+# .github/workflows/security.yml + e2e.yml). When a developer's local `stable`
+# lagged CI's, clippy versions diverged (1.94 local vs 1.96 CI) and the
+# `Build Check` gate (`cargo clippy -- -D warnings`) failed on `main` with
+# `collapsible_match` lints that local clippy could not see. Pinning a single
+# version makes `cargo clippy` / `cargo fmt` deterministic across local and CI.
+#
+# Bump this deliberately (and re-run `cargo clippy` + `cargo fmt` locally)
+# rather than letting `stable` drift underneath the lint gate.
+[toolchain]
+channel = "1.96.0"
+components = ["clippy", "rustfmt"]

src/lsp/handlers/definition.rs

@@ -63,14 +63,12 @@ pub async fn goto_definition(
                     })));
                 }
             }
-            TopLevelItem::TypeDef(type_def) => {
-                if type_def.name == word {
-                    let range = span_to_range(&type_def.span, &doc.source);
-                    return Ok(Some(GotoDefinitionResponse::Scalar(Location {
-                        uri: uri.clone(),
-                        range,
-                    })));
-                }
+            TopLevelItem::TypeDef(type_def) if type_def.name == word => {
+                let range = span_to_range(&type_def.span, &doc.source);
+                return Ok(Some(GotoDefinitionResponse::Scalar(Location {
+                    uri: uri.clone(),
+                    range,
+                })));
             }
             _ => {}
         }

src/vm/optimizer.rs

@@ -282,10 +282,10 @@ impl Optimizer {
                         *target = new_indices[*target];
                     }
                 }
-                OpCode::JumpIfFalse(ref mut target) | OpCode::JumpIfTrue(ref mut target) => {
-                    if *target < new_indices.len() {
-                        *target = new_indices[*target];
-                    }
+                OpCode::JumpIfFalse(ref mut target) | OpCode::JumpIfTrue(ref mut target)
+                    if *target < new_indices.len() =>
+                {
+                    *target = new_indices[*target];
                 }
                 _ => {}
             }