libsql client-ts upstream issue #288 makes PRAGMA busy_timeout ineffective
for async transactions, so concurrent db.transaction() calls reliably surface
SQLITE_BUSY. Introduce DbService.withWriteTx as a serialized write helper:
- Process-wide FIFO mutex (async-mutex) serializes write transactions.
- libsql client's default BEGIN IMMEDIATE protects against read-then-write
tx upgrade failures (no override needed at the drizzle layer).
- Single 50ms BUSY retry guards against transient external locks.
Reads do NOT need this — WAL gives readers snapshot isolation that is never
blocked by writers.
Includes unit tests (FIFO ordering, finally release on throw, single BUSY
retry, persistent BUSY rethrow, non-BUSY passthrough) plus a real-libsql
integration test. Updates the DbService test mock with a passthrough
withWriteTx so dependent services do not throw "is not a function" in
tests. Documents the API in database-patterns.md and points
CLAUDE.md / data-api-overview.md at the new pattern.
Replace ad-hoc vi.mock('@main/core/application') calls across test files
with a centralized mockApplicationFactory(overrides?) utility that provides
all registered services by default and supports per-service overrides.
- Add tests/__mocks__/main/DbService.ts (standalone DbService mock)
- Add tests/__mocks__/main/application.ts (unified factory)
- Simplify tests/main.setup.ts global mock
- Migrate 4 test files to use mockApplicationFactory
- Document unified mock system in CLAUDE.md and README.md
Signed-off-by: fullex <0xfullex@gmail.com>
