Bump MSRV to 1.96.0

.github/actions/install-rust/action.yml

@@ -32,7 +32,7 @@ runs:
         elif [ "${{ inputs.toolchain }}" = "msrv" ]; then
           echo "version=1.$msrv.0" >> "$GITHUB_OUTPUT"
         elif [ "${{ inputs.toolchain }}" = "wasmtime-ci-pinned-nightly" ]; then
-          echo "version=nightly-2026-08-12" >> "$GITHUB_OUTPUT"
+          echo "version=nightly-2026-08-20" >> "$GITHUB_OUTPUT"
         elif [ "${{ inputs.toolchain }}" = "wasmtime-ci-oss-fuzz-pin" ]; then
           # Do not change this number unless OSS-Fuzz has updated. If you update
           # this version and do not update OSS-Fuzz then you will break our

Cargo.toml

@@ -225,7 +225,7 @@ authors = ["The Wasmtime Project Developers"]
 edition = "2024"
 # Wasmtime's current policy is that this number can be no larger than the
 # current stable release of Rust minus 2.
-rust-version = "1.95.0"
+rust-version = "1.96.0"
 
 [workspace.lints.rust]
 # Turn on some lints which are otherwise allow-by-default in rustc.

crates/fiber/src/windows.rs

@@ -178,7 +178,19 @@ impl Fiber {
 impl Drop for Fiber {
     fn drop(&mut self) {
         unsafe {
+            let is_fiber = IsThreadAFiber() != 0;
+            if !is_fiber {
+                // DeleteFiber runs FLS destructors. Make those destructors
+                // observe a fiber so Rust does not run thread-local cleanup
+                // for the live thread.
+                let fiber = ConvertThreadToFiber(ptr::null_mut());
+                assert!(!fiber.is_null(), "failed to make current thread a fiber");
+            }
             DeleteFiber(self.fiber);
+            if !is_fiber {
+                let res = ConvertFiberToThread();
+                assert!(res != 0, "failed to convert main thread back");
+            }
         }
     }
 }