feat(ipc): async server handlers + server-side per-fork ordering

[charlielye]

What

Moves request ordering from the client into the database. Previously each TS client serialized its own reads/writes per fork (WorldStateOpsQueue); a second async client could corrupt state by skipping that contract. This makes the wsdb server own per-fork ordering, built on an async server-handler codegen pattern adopted symmetrically across all four languages.

Stacked on #24198 (concurrent reactor).

Codegen — async server handlers (C++, Rust, Zig; TS already async)

The generated server dispatch hands each handler the decoded command plus a respond callback, instead of returning a value. A handler may run inline or defer to a thread pool and call respond when ready. The wire protocol is unchanged, so the cross-language interop matrix and golden fixtures are untouched.

• C++: void handle_x(Ctx&, Cmd&&, Responder<Resp>); make_*_handler returns void(span, RawRespond); serve() drives it via run_reactor.
• Rust: Handler trait methods take Responder<Resp>; handle_request collects synchronously so the runtime/echo glue is unchanged.
• Zig: dispatch hands handlers a Responder (ok/err); handleRequest unchanged.
• TS: already Promise-returning — no change.

Each language's echo server updated to the new shape (~6 handlers each).

wsdb — server-side per-fork ordering

Each of the 40 handlers declares its own ordering by calling schedule_read (reads run concurrently; committed reads bypass ordering) or schedule_write (exclusive on its fork), extracting its fork from the typed command. WsdbScheduler implements the read-batch / write-barrier model per fork, with an inline fast path when idle and a dispatch pool distinct from WorldState's intra-op pool. The hand-rolled request classifier is gone — read/write + fork come from the typed handler.

Testing

• Cross-language echo matrix (build + interop + goldens 22/22) green across C++/Rust/Zig/TS.
• aztec-wsdb builds; ipc-runtime reactor/echo gtests green.
• native_world_state.test.ts (50 tests incl. Concurrent requests, which asserts read-your-writes ordering) green against the async server.
• parallel_read.bench SHM: ~3.7x read scaling (8.1k → 30.4k reads/s, c=1 → c=16).
• Full root bootstrap: wsdb + yarn-project + bb build clean.

Client queue removed

With the server owning per-fork ordering, the TS client's per-fork WorldStateOpsQueue is now redundant and has been deleted: IpcWorldState sends every op immediately and the server serializes writes / parallelizes reads. With the client queue gone, native_world_state.test.ts's Concurrent requests test now genuinely exercises server-side read/write ordering (and passes), and the TS-consumer no longer pays the queue's per-op overhead.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XfznXp9wzGWLU6LC8EHtpi

[charlielye]

Superseded by the restack. The reactor (#24198) and ordering work have been combined into a single machinery commit on #24198, which now targets next and sits below the wsdb cutover (#23036). The WorldStateOpsQueue removal moved into the cutover PR. Closing as the commits here are now redistributed across #24198 and #23036.