@@ -262,6 +262,26 @@ If you're already authenticated via `gcloud`, omit `credentials_path`:
 | Field | Required | Description |
 |-------|----------|-------------|
 | `path` | No | Database file path. Omit or use `":memory:"` for in-memory |
+| `create` | No | Create the database file if it is missing (default: `false`) |
+
+!!! warning "The store must already exist"
+    Connecting never creates the database. If the file is missing, the connection
+    fails with an error naming the path it looked for — an empty database would
+    otherwise answer every query with no rows and no error, which reads as a
+    successful query against an empty warehouse. Set `"create": true` only when
+    you intend this store to be created.
+
+!!! note "How a relative `path` is resolved"
+    A relative `path` is resolved once, when the config is loaded, against the
+    directory that declares it:
+
+    - `~/.altimate-code/connections.json` → resolved against `~/.altimate-code`
+    - `<project>/.altimate-code/connections.json` → resolved against `<project>`
+    - `ALTIMATE_CODE_CONN_*` environment variables → resolved against the project root
+
+    It is never resolved against the current working directory, so `--dir` cannot
+    re-point an existing connection at a different file. Absolute paths are always
+    safest.
 
 !!! note "Concurrent access"
     DuckDB does not support concurrent write access to the same file. If another process holds a write lock, Altimate Code automatically retries the connection in **read-only** mode so you can still query the data. A clear error message is shown if read-only access also fails.
@@ -443,10 +463,16 @@ If you're already authenticated via `gcloud`, omit `credentials_path`:
 |-------|----------|-------------|
 | `path` | No | Database file path. Omit or use `":memory:"` for in-memory |
 | `readonly` | No | Open in read-only mode (default: `false`) |
+| `create` | No | Create the database file if it is missing (default: `false`) |
 
 !!! note
     SQLite uses Bun's built-in `bun:sqlite` driver. WAL journal mode is enabled automatically for writable databases.
 
+!!! warning "The store must already exist"
+    As with DuckDB, connecting never creates the database, and a relative `path`
+    resolves against the directory of the config that declares it — not the current
+    working directory. See the DuckDB section above for the full rules.
+
 ## SQL Server
 
 ```json
 
@@ -191,6 +191,11 @@ MongoDB supports server versions 3.6 through 8.0. Queries use MQL (MongoDB Query
 |--------|--------------|
 | File | `path: "./my-database.sqlite"` |
 
+For both file-backed drivers, the database must already exist — connecting never
+creates it. Pass `create: true` to create it deliberately. A relative `path`
+resolves against the directory of the config that declares it, not the current
+working directory. See [Warehouses](configure/warehouses.md#duckdb) for the full rules.
+
 ## SSH Tunneling
 
 Connect through a bastion host by adding SSH config to any connection:
 
@@ -2,6 +2,7 @@
  * DuckDB driver using the `duckdb` package.
  */
 
+import { assertStoreExists } from "./file-store"
 import type { ConnectionConfig, Connector, ConnectorResult, ExecuteOptions, SchemaColumn } from "./types"
 import { loadOptionalDriver } from "./resolve"
 
@@ -118,6 +119,9 @@ export async function connect(config: ConnectionConfig): Promise<Connector> {
 
   return {
     async connect() {
+      // altimate_change start — never conjure an empty store on open
+      assertStoreExists(config, dbPath, "DuckDB")
+      // altimate_change end
       // altimate_change start — retry with read-only on lock errors
       const tryConnect = (accessMode?: string): Promise<any> =>
         new Promise<any>((resolve, reject) => {
 
@@ -0,0 +1,71 @@
+/**
+ * Shared guards for file-backed drivers (DuckDB, SQLite).
+ *
+ * Both engines create an empty database when asked to open a file that does
+ * not exist. For a warehouse connection that is never what the caller wants:
+ * a mistyped or mis-resolved path then yields a working connector over an
+ * empty database, so every query succeeds and returns nothing. An agent handed
+ * that result reports "no tables" instead of an error.
+ *
+ * Opening a store is therefore read-or-fail by default. Creation is opt-in via
+ * `create: true`, which the tools that deliberately materialize a local store
+ * (local test scratch databases, schema sync targets) pass explicitly.
+ */
+
+import * as fs from "fs"
+import type { ConnectionConfig } from "./types"
+
+/**
+ * Whether `dbPath` names a file on the local filesystem, and so can be
+ * existence-checked before the driver opens it.
+ *
+ * Only the exact string `:memory:` is an in-memory database. Both engines
+ * treat `:memory:named` — and any other colon-prefixed name — as an ordinary
+ * (if oddly named) file: DuckDB really does write a file called
+ * `:memory:named`, so those must stay inside the guard. An empty path is
+ * DuckDB's in-memory database and SQLite's anonymous temporary one; neither
+ * touches disk.
+ *
+ * A scheme-qualified target is not a local file: MotherDuck (`md:`), object
+ * storage (`s3://`), DuckLake, and any other scheme a DuckDB extension
+ * provides. Those are left to the driver, which reports an unknown scheme as a
+ * missing-extension error rather than silently creating anything. The pattern
+ * requires two or more characters before the colon so a Windows drive letter
+ * (`C:\data\wh.duckdb`) stays a path.
+ */
+export function isLocalFilePath(dbPath: string): boolean {
+  if (dbPath === "" || dbPath === ":memory:") return false
+  if (/^[a-zA-Z][a-zA-Z0-9+.-]+:/.test(dbPath)) return false
+  return true
+}
+
+/** Whether the caller explicitly opted in to creating the store. */
+export function allowsCreate(config: ConnectionConfig): boolean {
+  return config.create === true
+}
+
+/**
+ * Throw unless the store is safe to open: it already exists, the caller opted
+ * in to creating it, or the path is not a local file at all.
+ *
+ * @param engine Human-readable engine name used in the error message.
+ * @param allowCreate Whether this open will actually create the store. Defaults
+ *   to the config's `create` flag; a driver passes it explicitly when its own
+ *   options can veto creation — SQLite never creates a read-only connection.
+ */
+export function assertStoreExists(
+  config: ConnectionConfig,
+  dbPath: string,
+  engine: string,
+  allowCreate: boolean = allowsCreate(config),
+): void {
+  if (allowCreate) return
+  if (!isLocalFilePath(dbPath)) return
+  if (fs.existsSync(dbPath)) return
+  throw new Error(
+    `${engine} database file not found: "${dbPath}". ` +
+      `Opening a warehouse connection never creates the database — an empty store would answer every query with no rows. ` +
+      `Check the "path" in your connection config (relative paths resolve against the config file's directory, not the current directory), ` +
+      `or pass "create": true if this store is meant to be created.`,
+  )
+}
@@ -4,6 +4,9 @@ export type { Connector, ConnectorResult, SchemaColumn, ConnectionConfig } from
 // Re-export config normalization
 export { normalizeConfig, sanitizeConnectionString } from "./normalize"
 
+// Re-export file-backed store guards
+export { allowsCreate, assertStoreExists, isLocalFilePath } from "./file-store"
+
 // Re-export driver connect functions
 export { connect as connectPostgres } from "./postgres"
 export { connect as connectSnowflake } from "./snowflake"
 
@@ -4,6 +4,7 @@
  */
 
 import { Database } from "bun:sqlite"
+import { allowsCreate, assertStoreExists } from "./file-store"
 import type { ConnectionConfig, Connector, ConnectorResult, ExecuteOptions, SchemaColumn } from "./types"
 
 export async function connect(config: ConnectionConfig): Promise<Connector> {
@@ -13,10 +14,20 @@ export async function connect(config: ConnectionConfig): Promise<Connector> {
   return {
     async connect() {
       const isReadonly = config.readonly === true
+      // altimate_change start — never conjure an empty store on open.
+      // A read-only connection never creates, so `create: true` cannot excuse a
+      // missing file there; the guard is told the effective decision.
+      const willCreate = !isReadonly && allowsCreate(config)
+      assertStoreExists(config, dbPath, "SQLite", willCreate)
       db = new Database(dbPath, {
         readonly: isReadonly,
-        create: !isReadonly,
+        // `create` alone is no longer implied by "not readonly", so the
+        // read-write flag has to be explicit — bun:sqlite rejects an options
+        // object that sets no open flag at all.
+        readwrite: !isReadonly,
+        create: willCreate,
       })
+      // altimate_change end
       if (!isReadonly) {
         db.exec("PRAGMA journal_mode = WAL")
       }
 
@@ -178,7 +178,7 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb" })
+      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb", create: true })
       await connector.connect()
       expect(connectAttempts).toBe(2) // First failed, second succeeded in READ_ONLY
       // The retry must specifically request READ_ONLY — two attempts alone don't
@@ -219,7 +219,11 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb" })
+      // altimate_change start — bypass the store-existence guard for this mock:
+      // it never touches the real filesystem, and the test targets lock-error
+      // classification, not the existence check.
+      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb", create: true })
+      // altimate_change end
 
       try {
         await connector.connect()
@@ -267,7 +271,10 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb" })
+      // altimate_change start — bypass the store-existence guard for this mock;
+      // see the identical note above.
+      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb", create: true })
+      // altimate_change end
       await connector.connect()
 
       expect(attempts).toBe(2)
@@ -306,7 +313,11 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb", readonly: true })
+      // altimate_change start — bypass the store-existence guard for this mock;
+      // see the identical note above. `create` and `readonly` are independent
+      // flags: `create` only controls the existence check, not access mode.
+      const connector = await connect({ type: "duckdb", path: "/tmp/test.duckdb", readonly: true, create: true })
+      // altimate_change end
 
       try {
         await connector.connect()
@@ -405,7 +416,7 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/sync-lock.duckdb" })
+      const connector = await connect({ type: "duckdb", path: "/tmp/sync-lock.duckdb", create: true })
       await connector.connect()
       expect(connectAttempts).toBe(2)
       expect(await connector.execute("SELECT 1")).toMatchObject({ columns: ["ok"], rows: [[1]], row_count: 1 })
@@ -430,7 +441,7 @@ describe("DuckDB driver", () => {
       }))
 
       const { connect } = await import("../src/duckdb")
-      const connector = await connect({ type: "duckdb", path: "/tmp/corrupt.duckdb" })
+      const connector = await connect({ type: "duckdb", path: "/tmp/corrupt.duckdb", create: true })
       await expect(connector.connect()).rejects.toThrow("catalog is corrupt")
     })
   })