docs(03): capture phase context

.planning/phases/03-test-infrastructure/03-CONTEXT.md

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+# Phase 3: Test Infrastructure - Context
+
+**Gathered:** 2026-03-02
+**Status:** Ready for planning
+
+<domain>
+## Phase Boundary
+
+Create `database.NewTestDB(t)` — an in-memory SQLite test helper that mirrors production setup (migrations + PRAGMAs) — and apply production SQLite PRAGMAs (`synchronous=NORMAL`, `cache_size=-8000`, `mmap_size=67108864`) to the real `NewDB()`. This phase delivers the test foundation; actual test writing happens in Phases 4-5.
+
+</domain>
+
+<decisions>
+## Implementation Decisions
+
+### Test Helper API Shape
+- `NewTestDB(t *testing.T)` returns `*DB` only — no cleanup function, no error return
+- Cleanup registered internally via `t.Cleanup()` — callers just use the DB and forget
+- No functional options — every test DB gets the full production-mirror setup (PRAGMAs + all migrations)
+- Does NOT expose raw `*sql.DB` — tests use `DB.ExecContext()` / `DB.Queries` like production code
+- Lives in `database/testhelper.go` (exported, importable by other packages)
+
+### PRAGMA Behavior
+- All PRAGMAs applied identically in tests and production — even `mmap_size` on `:memory:` (verifies code path, true mirror)
+- Shared `applyPRAGMAs(*sql.DB)` internal function called by both `NewDB()` and `NewTestDB()` — single source of truth
+- Test DBs use the same connection string params as production (`?_busy_timeout=5000&_journal_mode=WAL`)
+- PRAGMAs applied before schema creation — tuning first, then DDL/DML
+
+### Test Helper Scope
+- No test data seeding helpers in Phase 3 — Phases 4-5 create fixtures as needed
+- Future test phases should use `sqlcgen.Queries` (not raw SQL) for inserting test data — same path as production
+- Skip the orphan cleanup query in `NewTestDB` — test DBs start empty, no orphans to clean
+- No health check (SELECT 1) — trust that successful Open + PRAGMAs + migrations means the DB is usable
+
+### Claude's Discretion
+- Internal helper function naming (`applyPRAGMAs` vs `configurePRAGMAs` vs similar)
+- Whether `NewTestDB` calls `t.Fatal()` or `t.Helper()` + `t.Fatal()` on setup failure
+- Exact error wrapping style in the shared PRAGMA function
+
+</decisions>
+
+<specifics>
+## Specific Ideas
+
+- The shared `applyPRAGMAs` function is the key architectural piece — it prevents production and test PRAGMA sets from drifting apart
+- `NewTestDB` should mirror the `NewDB` code path as closely as possible, minus the file-path resolution and orphan cleanup
+- Connection string for test: `":memory:?_busy_timeout=5000&_journal_mode=WAL"` (same params, in-memory URI)
+
+</specifics>
+
+<deferred>
+## Deferred Ideas
+
+None — discussion stayed within phase scope
+
+</deferred>
+
+---
+
+*Phase: 03-test-infrastructure*
+*Context gathered: 2026-03-02*