fix(ssr,dev): seed useNav() path at SSR + fix run({dev:true}) hot reload

[Aitthi]

Two framework-level fixes reported from the ketshopweb studio app.

Bug 1 — useNav() not active at SSR

A native layout renders a React island (SidebarNav) that derives its active link from useNav(). On SSR the active link was never highlighted; it only became active after a client-side navigation.

Root cause: nav.path is a globalThis singleton seeded client-side via __navInit, so the server always had path ''. And useNav passes getNavState as BOTH the client and server snapshot to useSyncExternalStore — so once the client seeded the path (before hydrateMarkersIn), React saw no mismatch and kept the inactive server className until the next navigation.

Fix: a per-request nav scope (runtime/navigation/server-context.ts) mirroring store/server-context.ts — a server-only AsyncLocalStorage that registers a resolver into the client-safe store.ts via __setServerNavResolver (so node:async_hooks never reaches the browser bundle). getNavState() consults the scope first (request path/search, phase: 'idle'), else the singleton. routes.ts opens the scope for every island/React SSR site: React full-doc + SPA-nav payload (via runInRequestContext's new trailing nav args) and the two native island-SSR Promise.all sites (which run outside the loader scope). renderFragment gains opt-in path/search. Client behavior unchanged (server renders the active markup; the client still __navInits from location.pathname before hydration, so both agree → no mismatch, active from first paint).

Bug 2 — run({ dev: true }) hot reload crash

Hot reload under the programmatic run({ dev: true }) path threw worker-registry: spawnAll called before registerInitialPool. serve()'s registerInitialPool gated on process.env.BRUST_DEV === '1' alone, while the dev coordinator/watcher gated on the broader dev = opts.dev || env flag — watcher live, pool never registered. run() now sets BRUST_DEV=1 when dev is enabled by either signal (what the brust dev CLI already does), unifying every BRUST_DEV-gated path.

Tests

• runtime/navigation/server-context.test.ts (7) — scoped path wins over singleton, ALS isolation, canonicalization, referential stability, survives awaits
• runtime/navigation/usenav-ssr.test.ts (3) — renderToString proves the active class appears under the scope, idle without it
• renderFragment path-seed (2)
• tests/dev-reload-option.test.ts — proven to fail without the bug-2 fix (gotReload=false)

Local baselines: biome ci 277 files clean · bun test runtime/ 850/0 · integration 100/0 · native-island-ssr 10/0 · dev-reload (CLI) 2/0. Pure TS — no Rust change.

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