feat: adapt to DSH 0.1.7-alpha.1 and yield the read-only previews

DSH 0.1.7-alpha.1 is 1299 commits past 0.1.6-alpha.2 and rewrites four
contracts this plugin was built on. The peer floor moves to
^0.1.7-alpha.1 (semver's prerelease rule means ^0.1.6-alpha.2 can never
match a 0.1.7 prerelease); 0.1.6-alpha.2 and earlier stay on v0.19.1.
Released as 0.21.0-alpha.1 (dist-tag alpha).

Hard breaks:
- dsh-settings was rewritten: register(ns, schema) is gone, a form is
  addressed by the plugin row's Loader entry id and read from the
  module's exported Config. The preferences are merged into Config and
  marked volatile — which requires DSH's own schemastery, because only
  that build wraps a volatile field in the cosmokit reference the
  loader's volatile commit walks. With the public package a settings
  write reports success and revision 1 while the effective value never
  changes.
- ui-primitives renamed its whole icon family (IconXxx14/16 ->
  IconXxxRegular/Medium): 26 imported symbols, 17 files. The failing
  mode is render-time, not load-time. Five call sites that relied on the
  old 14px default now pass size={14} explicitly.
- Session format v4 rejects source.kind === 'plugin'; the side-chat
  boundary injection now writes plugin:dsh-better-sidebar, the same kind
  DSH's own v3->v4 migration produces, so historical threads survive.
  Tool results moved to role 'tool' with top-level content/isError; all
  four parsers accept both shapes.
- The client session snapshot dropped subagentsByParent/jobsBySession
  and the on-demand subagent-catalog observation API. The Tasks page
  reads projectionsBySession and a new jobs.list route.

Yields and convergence:
- The read-only previews go to DSH's documentpreview (Office->PDF, a
  spreadsheet worker, zoom, per-directory refresh); editor.canOpen
  refuses those 26 extensions. Markdown, HTML (with its sandbox
  switches) and the editable code buffer stay.
- The host browser kind is desktop-profile-only now, so the web e2e
  lanes expect no browser entry and assert its absence.
- Link takeover claims only urlTarget links and passes the rest to the
  host, fixing a regression from the 0.1.6 round: the fallback pointed
  at a 'browser' type the plugin no longer registers, so http links in
  its own markdown did nothing.

Also fixed, found along the way:
- The file tree refreshes live (new directory watch over the plugin's
  own socket), since the plugin owns the `files` kind.
- ctx.sessions.list has no `current` field at either tag; the three
  readers were dead. They now use ctx.sidebarRight.mounted.
- package.json.files was missing lib/client-locale.js.
- Two genuinely dead call sites: sessions.openSubagent/open/
  refreshSubagents do not exist on the current baseline, so the
  topology click, the jump-back and the retry were all no-ops.
- The test harness window shim lacked addEventListener, which the 0.1.7
  primitives call at module-evaluation time; and the e2e token exchange
  needs Playwright's request stack, not Node's fetch.

tests/e2e/host.ts

@@ -60,6 +60,41 @@ export async function exchangeLaunchCookie(
 /** The `name=value` pair of the auth cookie, once per process. */
 let cookieHeader: string | undefined
 
+/**
+ * Exchange the launch token through Playwright's own request stack.
+ *
+ * {@link exchangeLaunchCookie} takes any `fetch`, but the Node global one
+ * cannot stand in for a browser here: the host's static fallback answers a
+ * plain Node GET of the token URL with an empty `405` and no `Set-Cookie`
+ * (reproduced on both `0.1.5-rc.2` and `0.1.7-alpha.1`, so it is a harness
+ * quirk rather than a host regression), which left every later `/api` call
+ * unauthenticated and the lane's session seeding dead. Playwright's request
+ * context speaks enough of a browser shape to complete the exchange, and
+ * `maxRedirects: 0` keeps the `303` from being followed — following it drops
+ * the `Set-Cookie` this exists to capture.
+ * @param launchUrl - the token URL as printed by the host.
+ * @returns the `name=value` cookie pair.
+ */
+export async function exchangeLaunchCookieViaPlaywright(launchUrl: string): Promise<string> {
+  const context = await request.newContext()
+  try {
+    await context.get(launchUrl, { maxRedirects: 0 })
+    const [cookie] = (await context.storageState()).cookies
+    if (cookie === undefined) {
+      throw new Error('token exchange produced no cookie — cannot authenticate /api seeding')
+    }
+    return `${cookie.name}=${cookie.value}`
+  } finally {
+    await context.dispose()
+  }
+}
+
+/** The exchanged cookie pair, memoised for the process. */
+async function authCookie(): Promise<string> {
+  cookieHeader ??= await exchangeLaunchCookieViaPlaywright(RAW_URL)
+  return cookieHeader
+}
+
 /** page.goto through the host auth. A plain navigation goes to PAGE_URL (the
  *  token URL performs the browser's exchange), but a STAMPED navigation
  *  cannot: the exchange answers `303 → /` and silently DROPS every sibling
@@ -69,11 +104,11 @@ let cookieHeader: string | undefined
  *  context, so the seeding is per-call and idempotent. */
 export async function gotoPage(page: Page, extra: Record<string, string> = {}): Promise<void> {
   if (Object.keys(extra).length > 0) {
-    if (cookieHeader === undefined) cookieHeader = await exchangeLaunchCookie(RAW_URL)
-    const eq = cookieHeader.indexOf('=')
+    const header = await authCookie()
+    const eq = header.indexOf('=')
     await page.context().addCookies([{
-      name: cookieHeader.slice(0, eq),
-      value: cookieHeader.slice(eq + 1),
+      name: header.slice(0, eq),
+      value: header.slice(eq + 1),
       url: ORIGIN,
     }])
     await page.goto(pageUrlWith(ORIGIN, extra), { waitUntil: 'domcontentloaded' })
@@ -84,12 +119,9 @@ export async function gotoPage(page: Page, extra: Record<string, string> = {}):
 
 /** Authenticated request context for host RPC seeding (cookie attached). */
 export async function createHostApi(): Promise<APIRequestContext> {
-  if (cookieHeader === undefined) {
-    cookieHeader = await exchangeLaunchCookie(RAW_URL)
-  }
   return request.newContext({
     baseURL: ORIGIN,
-    extraHTTPHeaders: { cookie: cookieHeader },
+    extraHTTPHeaders: { cookie: await authCookie() },
   })
 }