Internal organization

The solution separates a pure, dependency-free protocol core from the runtime, transports, and host that carry it.

Project	Language	Contents
src/Undertow.Protocol	F#	The pure tier: ordered JSON AST, spillway (sequencing, validation, nacks, signals), signet (JWT), silt (git objects + Historian shapes), initial-summary planning, document-channel decisions, origin policy. Zero project references.
src/Undertow.Abstractions	C#	IDocumentStore / IGitObjectStore, the etag’d CommitSequencedAsync seam
src/Undertow.Runtime	C#	Document sessions (per-document SemaphoreSlim), registries, channel dispatch, broadcaster, sweepers, limits
src/Undertow.Transports	C#	The two wire transports plus the fragmentation reader
src/Undertow.Storage.Memory / .Sqlite	C#	Storage backends — SQLite (WAL) is the persistent default
src/Undertow.Server	C#	ASP.NET host: env config, RestLess middleware, auth, REST router
tools/Undertow.WireDiff	C#	Wire recorder + shadow differ against transcript directories

Naming

The water-infrastructure names are load-bearing vocabulary shared with the Floodgate/Levee family:

• spillway — sequencing and validation: what flows through, in what order, and what gets nacked.
• signet — JWT encoding and decoding.
• silt — git objects and Historian storage shapes: what settles and is kept.

Concurrency shape

Sequencing is per-document: each document session owns its ordering (a per-document SemaphoreSlim in the runtime tier). This mirrors the reference’s one-actor-per-document design — the same shape, in .NET terms.

Storage

ets and shelf map to the SQLite backend (WAL mode); memory keeps everything in-process. Op history is capped and idle documents are evicted on a configurable window (UNDERTOW_DOC_IDLE_MS), matching the reference’s behavior.