surface

Development

How a downstream app consumes the shared @kolu/surface stack (@kolu/surface · surface-app · surface-nix-host · surface-mcp) — declaring a typed reactive surface, serving it, consuming it (SolidJS hooks or a CLI), and mirroring a remote surface over ssh. Grounded in the real consumers: kolu, pulam-web, drishti, odu, and the TUIs. Load when wiring a surface server/client/mirror, or reaching for getHostSession / a link / the `.use()` hooks. CHANGING the framework is gated separately — `.claude/rules/surface.md` (a paired, CI-green drishti PR pinned to final kolu HEAD).

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Using @kolu/surface (downstream consumer guide)

Declare a typed reactive surface once; the framework derives the oRPC contract, wires the server, and binds the Solid client hooks. This is the consumer guide — changing the framework needs a paired drishti PR (.claude/rules/surface.md).

Who uses it — match the closest consumer, don't hand-roll

Consumer	Shape	Notable
kolu (`client`+`server`)	one browser ⇄ one Node server, ONE ws	single-tier; two sibling surfaces; uses `surface`+`surface-app` only (not `-nix-host`)
pulam-web	browser ⇄ Node ⇄ ssh fleet mirror	one ws per host (`/rpc/ws?host=`); `connectSurface`; re-serves `terminalWorkspaceSurface`
drishti (`srid/drishti`)	browser ⇄ Node ⇄ ssh agent mirror	the canonical twin; 3 workspaces (common/agent/app)
odu (`juspay/odu`)	CI runner: stdio lanes → unix-socket fan-in → CLI/MCP	serve+consume+mirror over every transport at once; `surface-mcp` projection
pulam-tui / kaval-tui	one-shot CLI/TUI, no browser	transport-blind `{client,dispose}`; unix-socket local, ssh remote; no `.use()` hooks

The spine (real import paths)

Define — defineSurface({cells,collections,streams,events,procedures}) (@kolu/surface/define). Many surfaces over one transport: composeSurfaceContracts(map) + sibling clients, never merged.
Serve — implementSurface(surface, deps) / implementSurfaces(map, fwDeps, perKeyDeps) (@kolu/surface/server; inMemoryStore / inMemoryChannelByName back the cells/channels). Always flatten before serving: implement(surface.contract).router({ ...fragment.router }) — else oRPC double-prefixes /surface/surface/… and every call 404s.
Consume (SolidJS) — surfaceClient(surface, link) / surfaceClients(link, map) (@kolu/surface/solid) → client.cells.X.use({authority,initial,onError}), .collections.X.use({keys,onError}) then .byKey(id)?.() / .keys(), .streams.X.use(inputFn,{onError}) with .pending()/.error(), .events.X.use(inputFn,handler).
Consume (CLI/TUI) — no reactive hooks; raw awaited conn.client.surface.<verb>(…) + async-iterator iteration; a live board uses mirrorRemoteSurface(spec, client, {collections,streams}, {log}) (@kolu/surface/mirror) into plain callbacks.

Links (transport, swappable)

websocketLink(ws) (/links/websocket) · stdioLink (/links/stdio) · unixSocketLink({socketPath}) (/links/unix-socket) · directLink(router) (/links/direct, in-process identity, for tests). Serve side: serveOverStdio (/peer-server), serveOverUnixSocket (/unix-socket), oRPC RPCHandler (@orpc/server/ws, .upgrade(ws)) for browsers. CLIs keep ONE transport-blind Connection = {client, dispose} so every command is written once across local vs ssh.

Mirror a remote surface (drishti / pulam-web / odu)

Dial the host — getHostSession<contract>({host, binary, resolveDrvPath}) (@kolu/surface-nix-host): long-lived, nix copys the agent closure, runs <bin> --stdio over ssh, reconnects. buildHostRegistry fans out N hosts; one-shot CLIs use dialAgentOnce instead.
Mirror inward — pumpRemoteSurface({source, session, makeSink, …}) (-nix-host) folds the remote agent's frames into a local implementSurface re-serve via a SurfaceSink (makeSink, @kolu/surface/mirror). The parent implements the same surface; a remotely-unobservable cell (e.g. connection state) is parent-authoritative.
Re-serve — the local fragment served on /rpc/ws, accepted via acceptSurfaceSocket (@kolu/surface-app/server). Browsers connect with connectSurface (@kolu/surface-app/solid), which bundles socket + websocketLink + surfaceClient + a default-on liveness heartbeat.

Gotchas (hard-won, all real)

Procedures call off the FULL link, not the scoped client — surfaceClients per-key .rpc is typed unknown; reach the root link for raw procedures.
Raw streaming — unenrolledStreamCall(client.X, input, {signal, onRetry}) (@kolu/surface/client) carries the reconnect (STREAM_RETRY) context; a bare client.X(…) silently loses it. There is no stream namespace (.claude/rules/streaming.md is stale on that point).
Consume streams fine-grained — value-bearing → .streams.use() (replace-each-frame); delta-accumulate → mirrorRemoteSurface / createSubscription+reduce. Never coarse-read-and-copy: same-shape frames coalesce and the view freezes.
Snapshot-then-deltas + fail-fast — a cell always opens with a snapshot; firstFrameOrThrow (@kolu/surface/first-frame) treats an empty stream as a link failure, never a silent empty.
Liveness is on by construction — framework-reserved surface.system.live; connectSurface / HostSession / createServerLifecycle default their watchdog to it (probeSurfaceLive). Don't nominate your own probe unless you mean to (pulam-tui's version-cell probe is the rare, deliberate exception).
Version skew — gate on isContractVersionCompatible (major.minor), never a string ==.
Nix-baked deps — odu declares no @kolu/* in package.json; they're symlinked at Nix build (the bake-in-via-Nix convention). A bare pnpm install won't resolve them.

Reference

Runnable end-to-end: packages/surface/example/ (its mini-ci stdio example is odu's seed). Full API + rationale: each package's README.md. Match the closest consumer above; don't reinvent a primitive the table already shows how to use.

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