Merge branch 'main' into claude/m3-implementation-57f9d7

Three files conflicted, and two of the resolutions are more than a choice of
side.

QuickConnectTests had both branches fixing the same build break — main's M2
merge left the shell's constructor with an ISftpSessionFactory nobody passed.
Main's version wins because it carries a comment saying why the palette never
needs a session.

VaultSession's conflict is adjacent edits: main added the remembered sign-in
members and this branch changed SyncAsync's summary from "the active vault" to
"one vault". Both kept.

VaultViewModel is the one that matters. Main taught the background pass to
report a sync that had to start over, on the grounds that a machine which
silently re-read a whole vault has had something happen to it; this branch
turned a pass into one report per readable vault. Taking either side alone
would have lost the other, so ResyncedFromStart is now one of the conditions
IsWorthReporting checks, per vault.

Merging also broke something neither branch could have caught alone, and the
build would not have said a word. SyncOnceAsync cleared LastSyncFailed
unconditionally, which was right while a pass was one vault and a failure was
an exception that never reached that line. A failure is now a report — one
unreachable team vault must not stop the others syncing — so the flag was being
cleared over a vault that had just failed, lighting the titlebar SYNCED. It is
computed from the report instead, in the one place both callers go through, so
the manual command gets it as well as the loop. The background pass still
swallows the message and keeps the fact, which is what
AnAutomaticPassThatFails_LeavesTheStatusAlone is there to hold it to.

Two comments the auto-merge left describing a world with one vault in it: the
SCOPES rail's, which said team vaults are refused by the access service, and
the host sidebar's "One heading, for one vault".

docs/design-import-gaps.md

@@ -193,8 +193,14 @@ What the row did not anticipate is that the interesting half is not the endpoint
 
 ## Preferences
 
-The screen ships with what is real — this machine's device key, locking, and syncing — and lists the rest
-as absent rather than omitting it silently.
+The screen ships with what is real — this machine's device key, locking, syncing, and signing out — and
+lists the rest as absent rather than omitting it silently.
+
+> **Signing out is not on the design and is here anyway.** The design has no way to leave a machine, and
+> without one there is no way to hand a laptop on, to enrol a second account, or to get past a forgotten
+> passphrase — which is unrecoverable by construction, so the unlock screen would otherwise be a dead end.
+> It empties the local cache and withdraws the device key from the account; it cannot end the session at the
+> identity provider, and says so.
 
 | Design element | Layer | What it would take |
 | --- | --- | --- |