feat(startup): add startup_account, the account the dropdown opens on

Answers "start me in work - Inbox rather than All accounts - Inbox". The key
names an account by its [account.<key>] suffix and the dropdown is set to it
before the startup query runs; because a built-in filter composes with the
dropdown, that is the whole mechanism and the key never reaches a query
builder. Validated on load: a name matching no account is reported and cleared,
since the dropdown has no entry for it and would sit on All accounts without
saying why.

Which side applies the scope depends on what the startup entry is, and getting
it wrong is silent in both directions. A generated filter comes back from
resolvedQuery() already scoped, so letting runQuery() apply the dropdown again
gives path:"work/**" and (path:"work/**" and (tag:inbox)). A saved query does
not, because resolvedQuery() ignores the account key for one, so claiming it
was already scoped leaves it unscoped with the dropdown pointing at Work.

The first of those shipped in this session's working tree and passed its test,
because the assertion used contains() and the double-scoped string contains the
scope too. It asserts the exact query now. The second was found by writing the
test for the case rather than by reading, and is covered by
aStartupAccountAlsoScopesASavedStartupQuery.

The README's startup_query documentation was wrong on two counts after the
previous commit: the fallback is the Unread filter rather than the first query
in the file, and the name can now match a built-in filter.

1 files changed, 12 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 942fe41..10d9ecb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,18 @@ point at which they are stable.
 
 ## [Unreleased]
 
+### Added
+
+- **`startup_account` under `[general]`**, naming the account the dropdown
+  starts on by its `[account.<key>]` suffix. With a `startup_query` naming a
+  built-in filter, the application opens on that account's view of it:
+  `startup_account = work` with `startup_query = Inbox` starts in
+  "work - Inbox" rather than "All accounts - Inbox".
+
+  It sets the starting scope, not a sticky one. Clicking a saved query that
+  names no account still clears the selection, as it always has. A key naming
+  no configured account is reported at startup and ignored.
+
 ### Changed
 
 - The built-in filters carry icons, like the Save button at the other end of