What

Adds guarded() — a consumer-side, opt-in middleware guard wrapper — to @script-development/fs-http (0.4.1 → 0.5.0, additive/non-breaking). One generic wraps any of the three (arg) => void middleware bodies so a side-effect throw cannot corrupt the interceptor chain:

service.registerResponseMiddleware(guarded((response) => { /* ...may throw... */ }));

Why

fs-http invokes request/response/response-error middleware as synchronous, un-caught, un-awaited loops inside its axios interceptors. A throwing middleware body rejects a resolved 200 on the success path and masks the real API error on the error path. This is by design — the library stays sync-only + loud (the 2026-05-13 rejection of library-side try/catch holds). A 2026-07-02 fleet recon found every fs-http consumer (entreezuil ×6, emmie ×7, ublgenie ×2, BIO ×3) carries un-guarded middleware of exactly this shape; kendo already hand-guarded its own (WR-0078 / script-development/kendo#1538, n=2).

Rather than hand-roll try/catch across ~18 bodies fleet-wide, guarded() is the canonical primitive — the enforcement-ladder answer. It's opt-in at the registration site: loud library, defensive consumer. Default handler surfaces the swallowed throw via console.error (visible to error trackers); pass a GuardedMiddlewareErrorHandler to route it elsewhere. No re-throw.

Proven closed (end-to-end, against the real interceptor loop)

• Un-guarded throwing response body → rejects the resolved 200 (contrast test).
• Guarded throwing response body → 200 still resolves, throw routed to onError.
• Guarded throwing error body → still rejects with the ORIGINAL AxiosError, not the middleware's throw.

guarded.ts 100% coverage + 100% mutation (6/6). createHttpService and the interceptor loops are unchanged. Pre-1.0 peer-range cascade handled (loading 0.1.5 / adapter-store 0.3.1 / cached-adapter-store 0.2.4); lockfile synced, 0 nested registry copies.

Pairs with the fs-packages CLAUDE.md § Middleware Sync Contract doctrine block (#143) — that block will be cross-linked to guarded() once both land. Precedent: war-room deferred.md [adr] fs-packages-fs-http-async-aware-middleware-rejection-doctrine.

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