put the browsed folder in the url on /files

the file browser's currentPath was useState, so back and forward did nothing and a
folder could not be linked to. it is `?path=` now on /files, and the breadcrumbs are
real links.

opt-in, keyed on the parsed workspace identity rather than the base path: a dashboard
can hold two file browsers and one shared param would move both, while an unscoped
panel (cwd `~`) sits on dashboards too, so `basePath === '/'` would have caught the
wrong ones.

two things the audit line did not know. `?view=` is ephemeral — useFileViewerPanels
wipes it on mount — so `path` is this screen's first durable param. and four
setSearchParams({...}) calls replaced the whole query string, which would have made
opening any file silently reset the folder to home; they go through a setViewerParams
helper now that carries `path` across.

folder rows stay buttons. cmd/ctrl/shift-click is already multi-select in FileItem and
open is double-click, so anchor semantics collide with a gesture that exists. that is a
product decision, not a defect — written up for the owner rather than guessed at.

docs/navigation-audit.md

@@ -42,9 +42,9 @@ was in this list; the Projects feature was removed end to end on 2026-07-30, so
 and navigate-site 22 below still name it — they are the record of work that happened, not of code that exists.)
 **Section routes** (a param that names a view rather than an entity): `/settings/:page/:section`,
 `/soulseek/:section`, `/headscale/:section`, `/wallet/:section`, `/system-monitor/:scope`.
-**Query-param screens:** `/music?path=`.
-**Genuinely flat, still:** `/` `/files` `/plans` `/terminal` `/desktop` `/code-editor` `/qr-transfer`.
-`/files` and `/code-editor` are M4 and M5 — the last two that ought not to be.
+**Query-param screens:** `/music?path=`, `/files?path=`.
+**Genuinely flat, still:** `/` `/plans` `/terminal` `/desktop` `/code-editor` `/qr-transfer`.
+`/code-editor` is M5 — the last one that ought not to be.
 The five settings pages are route **pairs** now, not flat screens — `/settings/{profile,ai,system,integrations,user-management}`
 plus a `:section` each (M6). There has never been a `/settings/apps`; that entry was wrong when this list
 was written.
@@ -80,7 +80,7 @@ are good building blocks. The **Workspace/Panel framework** contains **zero** ro
 | ~~M1~~ | ~~`Screens/Dashboard/CapabilityPage.tsx:431`~~ | task / skill / process | `/tasks/:dirName`, `/skills/:dirName`, `/processes/:dirName` | **Done.** One component backed three screens, so one change covered all of them. The auto-select-`items[0]` effect is gone — the bare route is now the list with an empty detail pane. `editing`/`isNew` moved to `?edit=1` / `?new=1` because a `<Link>` row cannot imperatively reset them. |
 | ~~M2~~ | ~~`Screens/Dashboard/TaskLogs/index.tsx:104`~~ | a task-log run | `/task-logs/:id` | **Done.** As predicted — the detail fetch already keyed off the id, so only its source changed. `showDetail` is gone; the mobile swap and both back arrows derive from the param. |
 | ~~M3~~ | ~~`Screens/Dashboard/Activity/ActivityScreen.tsx:63,73`~~ | background task / detached job | `/activity/:id` | **Done.** One param for both row kinds; the screen looks the id up in the polled registry and derives `task=`/`path=` from the row. The SSE effect now depends on that derived *string*, so the 3s poll no longer risks re-opening the stream. An id that has left the registry says so instead of hanging on "waiting for output". |
-| M4 | `FileBrowser/.../useFileBrowserApp.ts:269`, `FileItem.tsx:516`, `Breadcrumb.tsx:16`, search-hit `:249` | a folder | `/files?path=<dir>` | **files** already open via `?view=`; **folders** are pure `currentPath` state — no URL, no back/forward. Folder rows + crumbs → `<Link>` on a `?path=` param. |
+| ~~M4~~ | ~~`FileBrowser/.../useFileBrowserApp.ts:269`~~, `FileItem.tsx:516`, ~~`Breadcrumb.tsx:16`~~ | a folder | `/files?path=<dir>` | **Partly done — the rest is an owner decision, not a defect.** `currentPath` is `?path=` on `/files`, so back/forward and linking a folder work, and the crumbs are `<Link>`s. Two things the audit line did not know: `?view=` is *ephemeral* (wiped on mount by `useFileViewerPanels`), so `path` is the screen's first durable param, and four `setSearchParams({…})` calls replaced the whole query string — opening any file would have silently reset the folder. They go through a `setViewerParams` helper now that keeps `path`. Opt-in via the parsed `WorkspaceIdentity` (`screens/files`), because a dashboard can hold two browsers and one shared param would move both. **Folder *items* stay buttons:** ⌘/Ctrl/Shift-click is already bound to multi-select in `FileItem.tsx` and open is double-click, so anchor semantics collide with an existing gesture. |
 | M5 | `CodeEditor/FileTree.tsx:59`, `EditorTabs.tsx:33` | open source file / active tab | `/code-editor?file=<path>` (+ `open=` for tabs) | tree file rows → `<Link>`; active file in a param. |
 | ~~M6~~ | `Settings/SettingsPanel.tsx` | a settings sub-section | `/settings/:page/:section` | **Done.** `<NavLink>` + `useParams`, five `*_SELECTED` globals gone, one `SettingsRoute` guard per page. The "one change covers all settings pages" claim was *almost* right: Integrations builds its own sidebar and did not go through `createSettingsPanelComponents`, and it also held the Enterprise/Personal tab in a second global — derived from the section key now, which is what fixes deep-linking a Personal section. |
 | M7 | `workspaces/components/Combobox.tsx:53` | caller-supplied route | (existing) | shared widget: `href`-bearing options do `navigate(option.href)`; render them as `<Link>`. Every caller inherits the opaque click. |
@@ -217,7 +217,7 @@ publishers means changing the chat panel, which is another agent's, so it is wri
 - [x] **M1** Capabilities → `/tasks|skills|processes/:dirName`, rows → `<Link>`; `CapabilityPage` takes an explicit `basePath` (not reused from `endpoint`, which only happens to match). Selection is `useParams`, the mobile pane swap and back arrow are derived from it, delete navigates to the bare route, and the two per-item modes are `?edit=1` / `?new=1`. No `<Navigate>` guard: an unknown `dirName` gets the empty detail pane. **Needs runtime test.**
 - [x] **M2** TaskLogs → `/task-logs/:id`; rows are `<Link>`s, `showDetail` deleted. **Needs runtime test.**
 - [x] **M3** Activity → `/activity/:id`; the `{label, query}` selection object is gone — the id is the URL and the stream query is derived from the registry row. `/activity` also had no `usePageTitle` rule (it read "Officer"); added. **Needs runtime test.**
-- [ ] **M4** FileBrowser folders → `/files?path=`; folder rows + breadcrumbs → `<Link>` (`useFileBrowserApp.ts:269`, `FileItem.tsx`, `Breadcrumb.tsx`).
+- [x] **M4** FileBrowser folders → `/files?path=`; breadcrumbs are `<Link>`s. Folder *rows* deliberately still buttons — ⌘-click is multi-select, open is double-click; converting them needs an owner call on the gesture.
 - [ ] **M5** CodeEditor active file → `/code-editor?file=` (`FileTree.tsx:59`, `EditorTabs.tsx:33`).
 - [ ] **M7** Combobox: render `href` options as `<Link>` (`Combobox.tsx:53`).