Slice 1: surface system + WS transport + composition root

Pure-core feature libraries assembled at the composition root:
- core/protocol: pure reducer over surface catalog/spec/error messages
- features/surface-host: generic field-kind interpreter (toggle/progress/
  selector/stat/button) + pure plan logic; no surface-id special-casing
- adapters/ws: injected WebSocket client (effects at the edge)
- app: composition root store (Svelte 5 runes over the pure reducer),
  host-relative surface WS URL resolution (resolveWsUrl), root App.svelte

Verified green: svelte-check 0/0, vitest 84 passed, biome clean, vite build ok.

1 files changed, 74 insertions, 0 deletions

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+# Dispatch Web — Constitution (root AGENTS.md)
+
+> Loaded every session. Non-obvious, project-specific rules only. If a fresh
+> frontier model could infer it from the code, it is NOT here (P6).
+> Full design + rationale: `../arch-rewrite/notes/frontend-design.md` (and the
+> backend's `notes/restructure-plan.md` §1 for P1–P8).
+
+## What this is
+The **web frontend** for Dispatch — a SEPARATE repo from the backend
+(`../arch-rewrite`). It is a **thin shell + pure feature libraries + a surface
+host**, NOT a default-SvelteKit ball of mud. It consumes the backend's typed
+contracts (`@dispatch/ui-contract` + the wire types) over HTTP + a WebSocket.
+There is **no mandatory "chat is the root"**: the app is a COMPOSITION of feature
+modules + surfaces, assembled at the composition root; legitimate frontends may
+compose without chat at all.
+
+## Stack
+Bun + Vite + Svelte 5 (runes) + TypeScript (strict). Biome for lint/format
+(tabs, double quotes, semicolons, width 100) — **biome covers `.ts`/`.js` ONLY;
+`.svelte` correctness is `svelte-check`'s job** (biome can't read Svelte template
+semantics — it flags template-used vars as unused). Vitest + `@testing-library/
+svelte` for tests.
+
+## The non-negotiable rules
+- **Pure core / injected shell.** Decision logic (reducers, view-models,
+  formatters, parsers) is pure `input → output`: zero DOM, zero `fetch`/WebSocket,
+  zero Svelte import. Effects (WebSocket, fetch, IndexedDB, history, clipboard)
+  are INJECTED at the edges. State is a pure reducer; Svelte runes are a THIN
+  reactive wrapper over it, never the home of logic.
+- **No ambient state.** State is owned per-unit and passed explicitly. No
+  module-global mutable store reached from everywhere — that is the old FE's
+  "tools leak across tabs" / "model resets on tab switch" bug class.
+- **Components are thin.** A `.svelte` file wires props/events to pure logic and
+  renders; it holds no business logic.
+- **One owner per unit.** Each feature module / file has exactly ONE editing
+  agent. To change another unit you report the need up — you do not edit it.
+- **Contracts are the only cross-unit surface.** You see other units' public
+  exports (`index.ts`) and the imported `@dispatch/ui-contract` / wire types —
+  never their internals. Needing internals ⇒ the contract is incomplete; report it.
+- **The surface interpreter is GENERIC.** It switches on field KINDS
+  (toggle/progress/...), NEVER on a surface id. No `if (surface.id === "...")` —
+  that imports a feature's identity and breaks isolation.
+- **Typed coupling.** Cross-feature links are typed imports/callbacks; no
+  stringly-typed event bus. Discovery-by-id (surface catalog, subscribe) is
+  sanctioned DATA flow, not a code reference.
+
+## Backend seam (cross-repo)
+The backend is `../arch-rewrite` (separate repo; `lsp references` does NOT span
+the boundary). You consume `@dispatch/ui-contract` (surfaces) + the wire types as
+a pinned dependency. Need a backend contract change? REPORT IT UP — the
+orchestrator carries it across (couriered via the user). Never reach into the
+backend repo.
+
+## Surfaces (the modular UI mechanism)
+A **surface** is backend-declared, frontend-agnostic data (fields + values +
+actions), rendered generically. See `frontend-design.md` §4. You render surfaces;
+you never special-case a specific one.
+
+## Commands
+- `bun run typecheck` — svelte-check
+- `bun run test` — vitest
+- `bun run check` — biome (`.ts`/`.js`)
+- `bun run build` — vite build
+
+## Reports
+Finish a task → write `reports/<your-unit>.md` (gitignored): what you built, the
+public surface, test/typecheck/build output, and any contract gaps / change-
+requests (incl. backend-contract CRs for the orchestrator to courier).
+
+## Vocabulary
+Use `GLOSSARY.md`. Shared backend terms are canonical (conversation, turn, step,
+chunk, AgentEvent, model name, …). FE terms: surface, region, field kind,
+action / action ref, surface catalog. **"view" is RESERVED** (old-Dispatch sidebar
+UX, future). Never invent a synonym.