fix(wasm): keep synchronous pathfinding off browser pthread pool

src/floyd_warshall_optimized.zig

@@ -9,6 +9,7 @@
 //! source-destination queries.
 
 const std = @import("std");
+const builtin = @import("builtin");
 
 const INF: u32 = std.math.maxInt(u32);
 
@@ -223,7 +224,12 @@ pub fn FloydWarshallOptimized(comptime config: Config) type {
 
         /// Run the Floyd-Warshall algorithm to compute all shortest paths
         pub fn generate(self: *Self) void {
-            if (config.parallel and self.size > 64) {
+            // Browser pthread pools are shared with persistent engine workers.
+            // This synchronous spawn/join algorithm cannot reserve a worker
+            // budget there; CPU discovery also uses unsupported sysctlbyname
+            // in Zig 0.16's Emscripten libc implementation. Keep web on SIMD
+            // until pathfinding can use an asynchronous, budgeted job API.
+            if (config.parallel and !builtin.single_threaded and builtin.os.tag != .emscripten and self.size > 64) {
                 self.generateParallel();
             } else if (config.simd) {
                 self.generateSimd();

src/nav/floyd_warshall.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const builtin = @import("builtin");
 const types = @import("types.zig");
 const graph_mod = @import("graph.zig");
 const zig_utils = @import("zig_utils");
@@ -15,7 +16,9 @@ const U32_INF: u32 = std.math.maxInt(u32);
 
 /// Optimized FW backend: SIMD + multi-threading via zig-utils.
 const FWOptimized = zig_utils.FloydWarshallOptimized(.{
-    .parallel = true,
+    // The synchronous zig-utils implementation cannot reserve workers from
+    // the browser's shared pthread pool. Use SIMD on threaded web too.
+    .parallel = !builtin.single_threaded and builtin.os.tag != .emscripten,
     .simd = true,
 });