Speeds up calls from JS into .NET through the DotNetBridge (classic and Node-API engines), and fixes several marshaling bugs found while benchmarking.

Performance

Bridge-only cost per call (BenchmarkDotNet, through the real InvokeBinary entry point, new AbiBenchmarks):

End to end on classic V8 (each op in its own process, medians of 3; this machine is noisy, ±20%): static calls 1.4x, overloaded calls 2.6x, constructing/returning objects 2.0–2.2x, property get/set 1.3x, member resolution 4.5x. The Node-API engine under Node shows the same pattern.

What changed:

• Lazy COM pointers. Box created a COM wrapper (CCW) for every returned object, about two thirds of the cost of a construct. Only C#/WinRT objects and JS subclass instances get one eagerly now. Other objects get one when first passed to a WinRT API: both runtimes already fall back to GetNativePtrForHandle when __native_ptr is missing, and the JS proxy fetches it on first read of __native_ptr.
• No allocation per response. Responses go to a reusable per-thread buffer, and Free leaves it alone. This is safe because the runtime consumes each response before making another call on the thread (including nested calls from JS callbacks).
• No string.Intern. Every decoded string was interned, argument values included: a global lock per call, and every distinct string passed to .NET stayed alive for the life of the process. Names now come from a per-thread decode cache, and argument strings aren't interned.
• Less reflection. Box, ResolveType and property lookups now cache per type instead of reflecting or allocating on every call.
• JS proxies. Members are looked up in per-type maps instead of scanned with indexOf. Method functions and resolved assemblies are reused, and calls avoid the request object and spread.
• Rust. Responses are parsed in place (no copy), and names go through stack buffers.

Fixes

• Overload resolution took the first same-arity overload the arguments converted to: Math.Abs(-0.5) returned 0, Math.Max(3.5, 2) returned 4, Math.Abs(-128) could overflow through Abs(sbyte), and new StringBuilder('q') threw. Methods and constructors now pick the best fit by argument type (exact > widening > narrowing that fits > object), with the old try-each loop kept as the fallback.
• Collections other than arrays came back as JS array copies, so new ArrayList().Add(1) was impossible and native code never saw the same instance. They now stay .NET objects and act like arrays: length, list[i] (get and set), for...of, spread, map/filter/…, JSON.stringify. Arrays are still copied into JS arrays.
• DateTime / DateTimeOffset / TimeSpan came back as ToString() strings, so TimeSpan.FromSeconds(2).TotalMilliseconds was undefined. They are now objects with their members, and String(value) still gives the .NET string. A JS Date converts to DateTime/DateTimeOffset parameters, and strings parse for those types and for Guid.
• params arrays and array arguments: String.Join(',', 'a', 'b') failed, and a JS array argument was sent as the string "a,b". Arrays now marshal (wire tag 0x07) to array, IEnumerable<T>, IList<T> and List<T>-style parameters, and trailing arguments fill a params array.
• Callbacks: a JS function passed straight as a delegate got raw {__handle, __type} objects (m.Value was undefined in a Regex.Replace evaluator). It now gets the same proxies a method result would.
• Plain JS fields set on .NET objects or namespaces were silently dropped (sb.tag = 3 then sb.tag gave a function); they are kept now. '' + obj threw "Method 'valueOf' not found"; it now falls through to toString.
• get_Item(key) with an argument now calls the indexer instead of throwing, and indexers are no longer listed as readable properties.

Compatibility

• The runtime and bridge ship together, but in mixed versions: an older runtime with this bridge reads obj.__native_ptr as undefined for plain .NET objects (passing them to WinRT still works through the __handle fallback). A newer runtime with an older bridge can't send array arguments (tag 0x07 is new).
• JS code that relied on non-array collections being real JS arrays (Array.isArray) or on date/time results being strings will see objects now. Array methods, iteration, length, indexing and String(value) keep working.
• template/framework/dotnet-bridge was already behind dotnet-bridge/ before this change; build.ps1 regenerates it.

Testing

• dotnet-bridge-tests: 120 passed (new OverloadSelectionTests, MarshalingTests).
• integration-tests: all suites pass, including 6 new end-to-end .NET tests in new_features.rs (real classic engine + published bridge).
• windows-napi npm test: 406 passed.
• A 41-check behavior script and a script for every fix give identical output on classic and on Node-API (Node addon against the real bridge). Mixed runtime/bridge versions were also run.