fix(directory-picker-browse): keep the typed level in the last pane

Skipping the draft-following scan whenever ANY pane happened to list the
directory was the cheaper rule and the wrong one: erasing a segment left the
level being typed on the LEFT, with its own child pane still standing to its
right, so the two panes stopped reading as "where I am, and where I came
from".

The pane arity is now the invariant the editor maintains — the last pane lists
the level the path names, its parent sits beside it, and only a display root
lists alone. Only that last pane's own tail costs no scan; every other
directory part re-lands.

packages/host/directory-picker-browse/README.md

@@ -6,7 +6,7 @@ The **in-app browsing backend** of the [directory-picker seam](../directory-pick
 
 Behavior facts: listings return **directories only**, name-sorted, with symlinks-to-directories followed (broken/cyclic links skipped — the probe `stat` failing means "not enterable") and a host-owned `hidden` flag (POSIX dot convention) left for the client to act on; `crumbs` is the root-to-target ancestor chain, the root crumb labeled by its full path (`/`, `C:\`); an absent `list` path means the host account's home directory. `createDirectory` is non-recursive (a missing parent is a real failure, not a level to invent) and validates the name as a single non-blank segment even when called directly, mirroring the wire schema's fence. Both primitives reject an explicit path that is not fully qualified — relative forms, and on Windows the rooted drive-less forms (`\foo`, `/foo`) and incomplete UNC prefixes (`\\`, `\\server`) that `isAbsolute` accepts — with `directory-unreadable`/`directory-create-failed`, instead of letting `resolve` rebase it under the host process cwd or current drive. One `list` call returns at most `maxEntries` rows (config, default 1000 — the bound GitHub's web UI applies to directory listings), and the level streams through a bounded window so memory stays O(maxEntries) no matter how many children the directory holds: a cut level keeps the name-sorted head, counts hidden rows against the bound, probes only windowed candidates, and reports `truncated: true` so the client can say the level is incomplete (a windowed broken symlink is not backfilled from beyond the window — the eviction already marks the level truncated); window insertion is binary with an O(1) full-window tail rejection, and `list` threads the caller's `AbortSignal` so a disconnect or timeout stops the scan instead of letting it outlive the caller. Failures throw the seam's typed `DirectoryPickerError`. Policy rationale: [the directory-picker capability seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md).
 
-**Dual-face package**: the browser half (`./client`) fills [ui-workspace's](../../client/ui-workspace/README.md) two directory-flow holes with the in-app **Select Workspace Directory** dialog (figma `Harness` 813-23126 family — Miller two-column view whose navigations land selection-anchored and quiet: the previous view keeps rendering while a crumb jump or a submitted path is scanned (a "Loading…" pill floats over it only once the scan outlives a 300ms silence window, never shifting the columns), then target and parent legs land as one two-pane frame with the target re-selected as its actual parent-level entry — so stepping back never collapses and no intermediate frame flashes (a parent leg outliving its 200ms wait bound lands the target alone and upgrades in place; a failed or truncated parent leg keeps the single-pane landing; the display root keeps the single wide level); breadcrumb with a click-to-edit path zone, advertised by the pencil glyph at the bar's right edge and lit on hover in the editor's own footprint, whose editor seeds a trailing separator and then keeps the panes under the draft: the final segment prefix-filters the level its directory part names (case-insensitively, over the listed — possibly truncated — rows only; a tail nobody matches releases the filter instead of emptying the pane), while a directory part no pane lists is scanned after a 250ms rest and lands like any other navigation — selection-anchored, two-pane away from the display root — so typing deeper descends and erasing segments walks back up, moving the Miller view without leaving the editor (a level a pane already shows needs no scan at all: the filter alone answers the draft) — a speculative scan is silent when it fails, and Enter still navigates by the exact text, owning the view until it lands; the editor cancels on Escape or when focus leaves the dialog card (window/tab switches and in-card focus moves keep the draft), and panes the draft walked to stay where the walk ended — the crumbs name that level and Open's fallback target follows them, so cancelling closes the editor rather than rewinding the walk; a fixed-label show-hidden footer toggle over the host's `hidden` flags, with a dot-led typed prefix revealing its matches and the current selection exempt from every filter; nested New-folder dialog), driving `host.listDirectory`/`host.createDirectory` and registering its own locale namespace (`directory-browser`, zh default / en). One cordis.yml row therefore composes both sides of the browse interaction; the client carries no capability-kind branching, and mounting a second flow package fails at load (the holes are `single` kind).
+**Dual-face package**: the browser half (`./client`) fills [ui-workspace's](../../client/ui-workspace/README.md) two directory-flow holes with the in-app **Select Workspace Directory** dialog (figma `Harness` 813-23126 family — Miller two-column view whose navigations land selection-anchored and quiet: the previous view keeps rendering while a crumb jump or a submitted path is scanned (a "Loading…" pill floats over it only once the scan outlives a 300ms silence window, never shifting the columns), then target and parent legs land as one two-pane frame with the target re-selected as its actual parent-level entry — so stepping back never collapses and no intermediate frame flashes (a parent leg outliving its 200ms wait bound lands the target alone and upgrades in place; a failed or truncated parent leg keeps the single-pane landing; the display root keeps the single wide level); breadcrumb with a click-to-edit path zone, advertised by the pencil glyph at the bar's right edge and lit on hover in the editor's own footprint, whose editor seeds a trailing separator and then keeps the panes under the draft: the final segment prefix-filters the level its directory part names (case-insensitively, over the listed — possibly truncated — rows only; a tail nobody matches releases the filter instead of emptying the pane), while any other directory part is scanned after a 250ms rest and lands like any other navigation — selection-anchored, two-pane away from the display root — so typing deeper descends and erasing segments walks back up, moving the Miller view without leaving the editor; the pane arity is the invariant, the last pane always listing the level the path names with its parent beside it (only that level's own tail costs no scan, and only a display root lists alone) — a speculative scan is silent when it fails, and Enter still navigates by the exact text, owning the view until it lands; the editor cancels on Escape or when focus leaves the dialog card (window/tab switches and in-card focus moves keep the draft), and panes the draft walked to stay where the walk ended — the crumbs name that level and Open's fallback target follows them, so cancelling closes the editor rather than rewinding the walk; a fixed-label show-hidden footer toggle over the host's `hidden` flags, with a dot-led typed prefix revealing its matches and the current selection exempt from every filter; nested New-folder dialog), driving `host.listDirectory`/`host.createDirectory` and registering its own locale namespace (`directory-browser`, zh default / en). One cordis.yml row therefore composes both sides of the browse interaction; the client carries no capability-kind branching, and mounting a second flow package fails at load (the holes are `single` kind).
 
 ## Model Experience