fix(web): keep host-plane services out of the preset, and pin the lane's skill roots

Moving the agent plane behind per-session presets took five rows with it that
the host still owns, and the Web surface stopped booting: `host-apiproxy`
injects `subagents`, so with the registry disabled here the entry never
activated and `dsh web` died at plugin-tree load.

The criterion is injection, not subject matter. A host row that injects a
service resolves it before any session exists, so there is no agent to key by:
`bash-env` (which `apps/cli/src/web.ts` injects to publish `DSH_WEB_URL`), the
`subagents` registry and its spawn/fork backends (a process singleton whose
cross-session queries the api-proxy serves, and whose provider names are
globally unique), and `tool-subagent-report` (a continuable setup on that
singleton, registered once per live session by a list that is not scope-aware)
all stay host-plane. What a preset chooses is which delegation TOOLS it sees.

The browser lane needs the second half: skill roots now resolve inside a preset,
a subtree the lane's include patches cannot reach, so the row's documented
environment fallback is pinned for the whole scaffold lifetime — presets mount
when a session is created, not at boot. Without it a developer's real
~/.dsh/skills enters replay requests and goldens while CI sees none.

apps/web/tests/scaffold.ts

@@ -240,6 +240,31 @@ export async function launchWebScaffold(options: LaunchOptions = {}): Promise<We
   // paths at load, and an in-process boot must NEVER touch the developer's
   // real ~/.dsh document or credential file.
   const harnessHome = join(workspaceCwd, '.dsh-home')
+  // Skill discovery is model-visible input, and its roots now resolve inside a
+  // PRESET — a subtree this lane's include patches cannot reach, because the
+  // roster mounts it directly per session rather than as a row of the booted
+  // tree. The row's documented fallback is the environment, so pin that: the
+  // whole scaffold lifetime, not just the boot, since presets mount when a
+  // session is created. Without this a developer's real ~/.dsh/skills silently
+  // enters replay requests and goldens while CI sees none.
+  const skillRootEnvironment = {
+    DSH_HOME: join(workspaceCwd, '.dsh-home'),
+    DSH_AGENTS_HOME: join(workspaceCwd, '.agents-home'),
+    DSH_BUNDLED_SKILL_DIR: join(workspaceCwd, '.bundled-skills'),
+  }
+  const originalSkillRootEnvironment = Object.fromEntries(
+    Object.keys(skillRootEnvironment).map(key => [key, process.env[key]]),
+  )
+  let skillRootEnvironmentRestored = false
+  const restoreSkillRootEnvironment = (): void => {
+    if (skillRootEnvironmentRestored) return
+    skillRootEnvironmentRestored = true
+    for (const [key, value] of Object.entries(originalSkillRootEnvironment)) {
+      if (value === undefined) Reflect.deleteProperty(process.env, key)
+      else process.env[key] = value
+    }
+  }
+  Object.assign(process.env, skillRootEnvironment)
   let persistenceRoot: string
   try {
     persistenceRoot = await mkdtemp(join(tmpdir(), 'dsh-web-e2e-sessions-'))
@@ -415,6 +440,7 @@ export async function launchWebScaffold(options: LaunchOptions = {}): Promise<We
     if (process.cwd() !== originalCwd) process.chdir(originalCwd)
     const cleanupFailures = await cleanupScaffoldWorld(ctx, workspaceCwd, persistenceRoot)
     restoreCredentialEnvironment()
+    restoreSkillRootEnvironment()
     if (cleanupFailures.length > 0) {
       throw new AggregateError([error, ...cleanupFailures], 'web scaffold setup failed and cleanup was incomplete')
     }
@@ -462,6 +488,7 @@ export async function launchWebScaffold(options: LaunchOptions = {}): Promise<We
         failures.push(...await cleanupScaffoldWorld(ctx, workspaceCwd, persistenceRoot))
       } finally {
         restoreCredentialEnvironment()
+        restoreSkillRootEnvironment()
       }
       if (failures.length > 0) throw new AggregateError(failures, 'web scaffold teardown failed')
     },