test(database): require one SQL statement per exec during initialization

The performance capture counts one exec call as one statement, because
SQL cannot be split reliably in the counter (trigger bodies contain
semicolons). The historical-upgrade driver now wraps exec on every
connection initDatabase opens and fails on a batch, so that counting
assumption holds for the fresh profile and all historical schemas.
Documents the definition in the counter and the architecture docs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/performance-journeys.md

@@ -124,7 +124,9 @@ ordered against the worker's responses, not against wall-clock: statements
 whose count is still in flight when `ready-to-show` is dispatched are not.
 One call of `run`, `get`, `all`, `iterate` or `exec` that returns normally is
 one statement; on the launch workloads this matches the number of SQL trace
-lines exactly.
+lines exactly. An `exec` with several statements would count as one, so the
+shared connection passes one statement per call, and its historical-upgrade
+test fails on a batch.
 
 `main.sqlStatementsBeforeReadyToShow` is not yet deterministic. The main
 thread runs the shared connection's schema creation and migrations (about 90

docs/architecture/sqlite-db-worker.md

@@ -455,7 +455,9 @@ execution methods of better-sqlite3's `Statement` prototype and the
 connection's `exec`, not through the `verbose` callback: a callback makes
 better-sqlite3 expand every statement's SQL, which made bulk inserts two to
 four times slower. A call that throws is not counted, which matches the SQL
-trace for statements that fail before execution. The main process counts its
+trace for statements that fail before execution. One `exec` call counts as
+one statement, so initialization passes one statement per call; the
+historical-upgrade test enforces it. The main process counts its
 own shared connection the same way (`services/main-sql-statement-count.ts`,
 through the shared library's connection observer). Without the flag both
 connections are opened unchanged. See