refactor: ConnectParams::prompter hands back an owned Arc

The accessor returned Option<&dyn Prompter>, a borrow that ends with the
connect call it arrived on. The prompter routinely outlives that call: an
interactive authentication flow gives it to the client library that will
present the URL, and a driver caching the resulting credential keeps it for
the life of the process.

A backend could not use what it was handed, only observe it, and would have
had to substitute an equivalent of its own -- the same object by luck rather
than by construction, and one that would silently stop being the same the day
core wraps what a driver declared.

Nothing outside core consumed this yet, so the type change costs no migration.

Author: maltesander

CHANGELOG.md

@@ -92,6 +92,11 @@ Everything a driver has to change for the catalog rework, in one place.
   does that in its own `connect`, which is already the call the application is
   blocked in.
 
+  `ConnectParams::prompter()` hands back an owned `Arc`, not a borrow, because
+  the prompter routinely outlives the `connect` it arrived on — an interactive
+  flow gives it to the client library that presents the URL, and a driver
+  caching the resulting credential keeps it for the process.
+
   Nothing existing changes: `Backend::prompter` is defaulted to `None`, so a
   driver that does not implement it behaves exactly as before, and
   `ConnectParams`' hand-written `Debug` and its `to_connection_string` are both

src/types/connect_params.rs

@@ -330,9 +330,17 @@ impl ConnectParams {
     /// `SQL_DRIVER_NOPROMPT`'s own clause in the spec says exactly that: "if the
     /// connection string contains enough information, the driver connects to
     /// the data source ... Otherwise, the driver returns SQL_ERROR."
+    ///
+    /// Owned rather than borrowed, because the prompter routinely outlives the
+    /// `connect` call it arrived on: an interactive flow hands it to the client
+    /// library that will present the URL, and a driver caching the resulting
+    /// credential keeps it for the process. A borrow ends with `connect` and
+    /// would force every such backend to substitute an equivalent of its own,
+    /// which is the same object by luck rather than by construction — and would
+    /// silently stop being the same the day core wraps what a driver declared.
     #[must_use]
-    pub fn prompter(&self) -> Option<&dyn Prompter> {
-        self.prompter.as_deref()
+    pub fn prompter(&self) -> Option<Arc<dyn Prompter>> {
+        self.prompter.clone()
     }
 
     /// Record the prompter this connect may use, just before