feat(dsh): adapt to DSH 0.1.5-alpha.1

Move the plugin onto the DSH 0.1.5-alpha.1 baseline (peer floor
^0.1.5-alpha.1, CI pinned to the alpha dist-tag) and fix the two host
contract changes that alpha line introduced.

Baseline:
- all @deepseek-ai/dsh-* peer/dev deps -> 0.1.5-alpha.1; optional peer
  @deepseek-ai/dsh-client-ui-sidebar-right (declared, unused until the
  native-surface phase); devDep @deepseek-ai/dsh-agent-loop (inbox fold)
- dsh.plugin.json engines >=0.1.5-alpha.1; version 0.19.0-alpha.0;
  SIDEBAR_SERVICE_VERSION follows

Live assistant stream (assistant/chunk is gone):
- 0.1.5 publishes in-flight model deltas as process-local
  agent/assistant-stream frames instead of durable assistant/chunk events
  and embeds the settled stream in assistant/message / assistant/attempt.
  src/assistant-live.ts folds the frames into a bounded per-session buffer;
  sidechat.events serves the current attempt as `live` rows (replaced every
  poll, never a delta) and the transcript renders them; the inherited
  in-progress snapshot reads message content / attempt stream / live frames.

Cold session reads (persistence.inspect is gone):
- 0.1.5 reads a stored session through an explicit read handle
  (open(id,'read') -> handle.read() -> close()). src/session-store.ts owns
  that protocol; every cold read (sidechat transcript, cold-resume preset,
  session.cwd, changes replay) goes through it.

Dead code and docs:
- drop the remote.session.openWorkspacePath interception: 0.1.5's chat opens
  files through ctx.sidebarRight.openResource instead, so the wrapper had no
  caller and would hijack the host's "open in app" gesture; the
  interceptOpenPath pref, its settings row and its locale keys go with it
- AGENTS.md §3 + external-plugin-guide.md describe the new baseline
- vitest setup bridges Node's localStorage accessor to jsdom's store (the
  pre-existing 26 failures on Node >= 22)
- desktop-layout e2e seeds through host RPC and types into the Lexical
  composer (0.1.5 replaced the textarea) instead of driving the directory
  picker

Verified: pnpm typecheck / lint / build / test (124 files, 1327 tests) /
check:consumer-types, plus pnpm test:mount against a real
@deepseek-ai/dsh@0.1.5-alpha.1 host (18/18).

src/client/intercept.tsx

@@ -11,7 +11,6 @@ import type { Context } from '../context-types.ts'
 import { firstLeaf, revealPaths, togglePanel, type SidebarStore } from './state.ts'
 import { t } from './locales.ts'
 import { resolveSidebarPath, selectProducedFiles } from './produced-files.ts'
-import { wrapOpenWorkspacePath, type OpenWorkspacePathService } from './openpath-intercept.ts'
 import css from './sidebar.module.css'
 
 /** Open a file in the sidebar's editor (used by the intercepted row and the explorer). */
@@ -25,13 +24,6 @@ export function openSidebarFile(ctx: Context, store: SidebarStore, sessionId: st
   ctx.get('betterSidebar')?.openTab({ type: 'editor', title, path: absolute, id: `editor:${absolute}` })
 }
 
-/**
- * The produced files the turn-tail selector last matched for the visible
- * session. The "Show in folder" gesture carries no file path of its own
- * (`'.'`), so the reveal highlights exactly these rows when available.
- */
-let lastProduced: readonly string[] = []
-
 /**
  * Reveal the produced files in the sidebar explorer: expand their parent
  * directories, highlight the rows, and focus the explorer tab (expanding the
@@ -137,9 +129,7 @@ export function registerTurnTailInterception(ctx: Context, store: SidebarStore):
     select: (owner) => {
       if (store.getSuspended()) return null
       if (store.getPrefs().tabsEnabled['editor'] === false) return null
-      const matched = selectProducedFiles(owner)
-      if (matched !== null) lastProduced = matched
-      return matched
+      return selectProducedFiles(owner)
     },
     priority: -1,
     registrant: 'dsh-better-sidebar',
@@ -149,38 +139,3 @@ export function registerTurnTailInterception(ctx: Context, store: SidebarStore):
     }),
   }, SidebarProducedFiles))
 }
-
-/**
- * Register the chat file-open interception: shadows
- * `remote.session.openWorkspacePath` — the single funnel every chat-side
- * file open goes through on alpha hosts (tool-row path links, the
- * produced-files row, prose mentions, inline-code paths) — so opens land in
- * the sidebar editor instead of the Host OS. The folder-reveal gesture
- * ("Show in folder" passes `'.'`) is the one exception: it is routed to the
- * explorer. Gated by BOTH the `interceptOpenPath` pref and the editor tab's
- * enable switch; declined opens fall through to the original remote call.
- *
- * The `remote.session` namespace service mounts asynchronously (the gateway
- * client creates it when the session-controller contribution arrives) and
- * is recreated on contribution remounts, so the wrapper installs through
- * `ctx.inject`: the callback runs once the service exists and re-runs after
- * every remount, re-applying the shadow on the fresh instance. Returns the
- * disposer (disposes the inject fiber, which restores the original method
- * descriptor — HMR-safe).
- */
-export function registerOpenPathInterception(ctx: Context, store: SidebarStore): () => void {
-  const fiber = ctx.inject(['remote.session'], (fctx) => {
-    fctx.effect(() => {
-      const service = fctx.get('remote.session') as OpenWorkspacePathService
-      return wrapOpenWorkspacePath(service, {
-        takeoverEnabled: () => !store.getSuspended()
-          && store.getPrefs().interceptOpenPath !== false
-          && store.getPrefs().tabsEnabled['editor'] !== false,
-        currentSessionId: () => ctx.sessions.list.getSnapshot().current,
-        openInSidebar: (path, sessionId) => { openSidebarFile(ctx, store, sessionId, path) },
-        revealInExplorer: (_path, sessionId) => { revealInExplorer(ctx, store, sessionId, lastProduced) },
-      })
-    }, 'dsh-better-sidebar: open-path interception wrap')
-  })
-  return () => { void fiber.dispose() }
-}