perf: fast digests for user-signed actions, leaner ws/http per-request paths - #86

…t paths

User-signed actions (approveAgent, usdSend, and the other 15) no longer pay
viem's generic hashTypedData. The EIP-712 domain is fixed and every shipped
types object is a module constant, so typehash plans compile once per types
identity (WeakMap) and domain separators once per chainId, following the
_fastDigest pattern used for Agent/SendMultiSig. Signing routes through the
raw-digest capability (WASM when present); remote and ledger wallets fall
back to signTypedData unchanged. Digests are byte-identical to viem's
hashTypedData across all 17 types x 5 chain IDs (userSignedDigest.test.ts).
Measured: 2.5 us vs 56 us per digest; multisig_user_signed_3_signers -22%.
Multi-sig computes the shared digest once per call and only after a
capability check, so stub/remote signers never pay for a digest they
cannot use.

Websocket transport:

- The dispatcher schedules request timeouts on the shared abort.TimeoutWheel
  (as HttpTransport already did) instead of a native setTimeout per request:
  ws_request_round_trip -10%.
- Routing stops allocating per frame: .toLowerCase() is gated behind an
  uppercase check (the server sends lowercase hex), and routed event-type
  strings are interned per channel+key instead of re-concatenated:
  webData3_frame_dispatch_e2e -38%, l2book_dispatch_50_coins -28%.
- WebSocketTransport.request drops a pointless async/return await.

Subscriptions and utils:

- fastAssetCtxs decodes the node:zlib Buffer via Buffer.toString("utf8")
  instead of a shared TextDecoder on the hottest decode path; the
  DecompressionStream fallback fuses its two .then hops into one.
- floatToWire renders the double once (toFixed(9)) and derives the 8-decimal
  wire string by digit-9 rounding with carry: -20%, fuzz-verified
  byte-identical over 1.8M values.

Http transport:

- Error paths skip the redaction walk for signature-free payloads (all info
  requests), gated on a wire-string check.
- No AbortController or TimeoutWheel entry is allocated when timeout is null
  and no signal exists; the wheel hands out a shared frozen null-handle.
- Explorer requests skip the pre-send JSON.parse (flat weight needs no
  parsed form); billing snapshots materialize lazily for surcharge/error
  paths only. Info/exchange billing still parses the wire form — a pinned
  test contract requires billing to derive from the serialized payload.

Exchange shell:

- Signing moves outside the per-wallet nonce lock; wire order is preserved
  by a per-(wallet x network) dispatch chain instead, so concurrent callers
  on one wallet (where signing is a network round trip for any remote
  wallet) sign in parallel while the server still sees strictly increasing
  nonces. Covered by the new _dispatchOrder tests.
- extractNonceFieldName and static signatureChainId validation are memoized
  per types/config identity; the multi-sig inner hash no longer round-trips
  through hex; msgpack uint64 writes integers without BigInt boxing.

Perf harness:

- subscribe_user_trio stabilised (from the abandoned
  perf/stabilize-subscribe-user-trio branch): 20 iterations per sample
  instead of 1, and MockWebSocket keeps only the latest instance instead of
  retaining every socket. Run-to-run spread falls from 33% to ~3%, stopping
  the scenario flipping the gate on unrelated PRs.
- New scenarios: eip712_user_signed_digest (+viem oracle pair),
  approve_agent_e2e_no_ecdsa. Baseline re-recorded (the committed one was
  stale since 0.1.4 and failed the local gate closed).

Full suite vs old baseline: 11 faster, 0 regressed. perf:gate PASS.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>