Add AgentConfigurationService for root config read/write/persist to
agent-host-config.json. Wire root action dispatch and side effects so
that host plugin changes are persisted and republished as session
customizations. Implement PluginController in copilotAgent.ts to merge
host-owned and client-synced plugins, resolve them into IParsedPlugin
snapshots, and feed them into the SDK via _buildSessionConfig().

Co-authored-by: Copilot <[email protected]>

Add RemoteAgentPluginController for add/remove plugin commands and
RemoteAgentCustomizationItemProvider that surfaces host-owned and
session-synced plugins. Expand each plugin directory via IFileService
to discover individual skills, agents, instructions, and prompts for
per-type sections. Extend pluginListWidget with remote item rendering,
toolbar actions, group headers, and live refresh on itemProvider
changes.

Co-authored-by: Copilot <[email protected]>

Add tests for host config dispatch, side effect republishing, scope
filtering, and the remote harness item provider (distinct item keys
for scope-distinct plugins, client-synced vs host-owned separation).

Co-authored-by: Copilot <[email protected]>

Add ICustomizationDisableProvider interface (opt-out model) alongside the
existing ICustomizationSyncProvider. Add AgentCustomizationDisableProvider
implementation and LocalAgentHostCustomizationItemProvider with shared
enumerateLocalCustomizationsForHarness() and resolveCustomizationRefs()
helpers.

Co-authored-by: Copilot <[email protected]>

Replace ICustomizationSyncProvider usage with ICustomizationDisableProvider
across all consumers. Simplify ProviderCustomizationItemSource to a single
required itemProvider (no more dual local/remote path). Update harness
descriptors to use disableProvider. Listen to both disable provider and
prompts service change events for auto-sync. Add throttling for bundler
re-resolves.

Co-authored-by: Copilot <[email protected]>

Delete AgentCustomizationSyncProvider and its tests. The opt-out
ICustomizationDisableProvider is now the only sync model.

Co-authored-by: Copilot <[email protected]>

- Fix synthetic bundle URI scheme: synced-customization:// URIs must not
  be wrapped as agent-host:// since the server lacks that scheme; expansion
  now reads the client in-memory FS directly
- Suppress client-synced plugin entries from the Plugins list (they are
  already shown under 'Enabled Locally'); their contents still expand into
  per-type tabs (Skills, Agents, etc.)
- Propagate childGroupKey through expansion so host-originated items land
  in the 'Remote' group and client-synced items land in 'Client' group
- Rename groups to 'Remote' / 'Client' in both the Plugins view and the
  per-type tabs
- Remove redundant 'Remote Host' badge from host-configured plugin items
- Add dotfile filter (.DS_Store etc.) in _collectFromTypeDir
- Include PromptsStorage.extension in SYNCABLE_STORAGE_SOURCES so built-in
  extension skills reach the agent host SDK
- Remove checkbox column from Agent Customizations list widget
- Enhance debug report with installed harnesses and plugins (Stages 5-6)
- Fix test: add IPromptsService stub to agentHostChatContribution test

Co-authored-by: Copilot <[email protected]>

Reverts the broad StateAction widening on the dispatchAction/dispatch
interface boundary. Instead of accepting any StateAction (which includes
server-only emissions like SessionReady, SessionDelta, etc.), the API
now accepts the precise ClientAction union:

  ClientAction = ClientRootAction | ClientSessionAction | ClientTerminalAction

This restores compile-time safety: passing a server-only action to
dispatch() is now a type error. The new type is exported from
sessionActions.ts alongside the existing SessionAction/TerminalAction
aliases.

Internal server-side state management (reducers, subscriptions,
dispatchServerAction, dispatchClientAction) continues to use the
broad StateAction type as appropriate.

The one root action clients legitimately dispatch (RootConfigChanged,
used to push plugin configuration changes) is included in
ClientRootAction, so the remote harness's dispatchCustomizations()
call compiles correctly.

Co-authored-by: Copilot <[email protected]>

The provideChatSessionCustomizations method was skipping client-synced
items from the top-level items map with the comment that the local
'Enabled Locally' section already shows them. This is wrong for the
remote harness  there is no local section, and client-syncedcontext
plugins should appear as distinct 'Client' group entries alongside
host-owned 'Remote' group entries.

Fixes the failing test:
  RemoteAgentHostCustomizationHarness
    provider keeps client-synced entries distinct from host-owned entries

Co-authored-by: Copilot <[email protected]>

Covers:
- Client-synced vs host-owned group assignment (remote-client/remote-host)
- Synthetic bundle hidden from top-level but expanded for children
- Synced-customization scheme URI preserved (not wrapped as agent-host://)
- Status/statusMessage propagation from session customizations
- Change event firing on SessionCustomizationsChanged action
- Remove action only on host items, not client-synced items
- Multi-entry remove dispatch
- Multiple client-synced entries with distinct keys
- SKILL.md collision prevention with subdirectory layout
- Mixed SKILL.md and non-SKILL.md skill coexistence
- Nonce includes subdirectory path for SKILL.md files
- Rebundle clears previous tree
- Bundle description includes file count

Co-authored-by: Copilot <[email protected]>

Dynamic groups (e.g. remote-host, remote-client) were appended after
the built-in group, causing built-in to appear above them. Insert
dynamic groups before the built-in entry so it always stays last.

Co-authored-by: Copilot <[email protected]>

Remove the 'Add Workspace Plugin' button and its backing methods
(addPluginForWorkspace, getWorkspaceScope). Plugins are now always
added at the host scope. Simplifies addConfiguredPlugin accordingly.

Co-authored-by: Copilot <[email protected]>

The 'Client' group header already communicates that entries are synced
from the client. The full-width 'Synced' badge was redundant and
visually inconsistent with inline badges elsewhere.

Co-authored-by: Copilot <[email protected]>