docs: add decision for cache server stub

Co-authored-by: me <me@kentcdodds.com>

Author: cursoragent

docs/decisions/047-mock-cache-server-in-tests.md

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+# Mock Cache Server in Tests
+
+Date: 2026-02-01
+
+Status: accepted
+
+## Context
+
+Our Vitest suite runs in a Vite-powered environment that attempts to bundle
+imports for jsdom tests. The app cache implementation imports `node:sqlite`,
+which Vite cannot bundle for client-like environments. This caused CI failures
+when Vitest upgraded and began resolving the cache module for jsdom suites.
+Additionally, the cache module requires `CACHE_DATABASE_PATH`, which is not
+needed for unit tests and creates friction for running tests locally.
+
+## Decision
+
+We will provide a test-only cache server stub and instruct Vite/Vitest to
+resolve `cache.server.ts` to this stub when running Vitest. The stub provides
+in-memory cache behavior and a minimal `cachified` implementation sufficient
+for the tests. Production and development builds continue to use the real
+SQLite-backed cache implementation.
+
+## Consequences
+
+- **Stable CI tests**: Vitest no longer tries to bundle `node:sqlite`, and the
+  cache module no longer requires `CACHE_DATABASE_PATH` in unit tests.
+- **Scoped behavior**: Cache behavior in unit tests is simplified to in-memory
+  semantics, so SQLite-specific behavior is not exercised in those tests.
+- **No runtime impact**: Only Vitest uses the stub; production and development
+  environments remain unchanged.