Show managed plugin install progress and failures in Agent Host chat

[Anthony Kim (anthonykim1)]

Part of: https://github.com/microsoft/vscode-internalbacklog/issues/8906

TL;DR: Before a message starts, a Copilot session can install or update plugins required by the organization. It reports progress as session.info and failures as session.warning, both with type managed_plugins. Agent Host only logs these events, so chat sits on a generic "Working" and failures never reach the user. This PR shows the progress text in the waiting turn's status line and the failure as a warning in that turn. No SDK or protocol change.

Current flow

• The message waits while required plugins are prepared; chat shows "Working".
• On failure, the session continues without the plugin; VS Code only writes the warning to the log.

New flow

• Progress text ("Installing…", "Updating…", strict mode's "Initializing chat…") becomes the chat's activity while the turn is still pending. The status line reads chat activity, as it does for "Creating isolated worktree…", and the activity is mirrored onto the session summary that session lists show.
• The root user.message echo, root assistant.turn_start, a failure, or the end of the turn clears it.
• A failure becomes a warning-severity ManagedPluginPreparationFailure system notification in the waiting turn. Chat renders it as a warning that stays visible when the response collapses, with the message text escaped like the BYOK tool-limit notice.
• Progress outside a pending turn (for example, preparation started by custom agent selection) is only logged. A failure that arrives while no message is waiting, for example after a background policy refresh, is shown in the next sent turn unless a managed_plugins_complete info arrives first. Other AHP clients get plain activity text and a plain-text notification.

Screenshots (live in Code OSS with this PR, against a Copilot session that reports managed_plugins events, a test org policy that requires plugins, and a local plugin marketplace; click to expand)

Install: the waiting turn says why it is waiting

Here a chat's second message waits while a plugin that failed earlier installs. The Sessions list shows the same text as the chat's description:

That turn's answer lists the new plugin's skill (release-checklist-run):

Update: the same status line with the update text

Failure: a warning in the turn, and the answer continues

The warning text is the event's message as received.

Strict mode's "Initializing chat…" uses the same status line; it was not captured live.

Why the status line instead of the original spinner row (design mockup)

The spinner row needs a new protocol field so the client can tell this activity apart from others. The status line reuses existing activity plumbing; text and timing are the same.

Not in this PR

• A4 (persistent chat-input notice): dropped per feedback.
• C1 (repository-configured plugins): belongs with chat: Auto-install repository-configured plugins #338945; its action should read "Continue without waiting" rather than "Skip".
• Plugin-name chips (the events carry no plugin list), a "Show Log" link, and restoring the warning after reload (live only, like the BYOK notice).
• Intent, Fusion, and slash-command activity still go out as session activity, which the status line does not read (see the TODO on _emitAction). Only plugin preparation moves to chat activity here.

Risk to flag: Selecting a custom agent can also wait for plugin preparation, and setAgent gives rpc.agent.select a 30s control-plane timeout. A long install during agent selection can time out and mark the session for resync. Not changed here.

How to test

• ./scripts/test.sh --run src/vs/platform/agentHost/test/node/copilotAgentSession.test.ts --run src/vs/workbench/contrib/chat/test/browser/agentSessions/stateToProgressAdapter.test.ts: 1100 passing. The 8 new host tests fail against main's copilotAgentSession.ts.
• npm run typecheck-client: the same 385 errors as main in my environment (stale local node_modules); none new.
• npx eslint on the changed files: clean.
• Manual (done; screenshots above): with an org policy that requires a plugin, send a message. While the message waits, the status line shows "Installing plugins required by your organization admin…" and the Sessions list shows the same text; when the message waits for the install, the plugin's skill is available in that turn. After a new plugin version is published, a new chat shows "Updating plugins…" while its message waits. With an unreachable plugin source, a warning appears in the turn and the message is still answered. Once the plugin is installed, a follow-up message shows no plugin text.

---

Inspirations from:

• Progress is published as ChatActivityChanged, like the worktree creation progress in _resolveWorktreeBeforeSend. The state manager mirrors chat activity onto the session summary.
• The warning notification shape comes from reportByokToolsCapped.
• The warning mapping (keepVisibleWhenCollapsed) and host-text escaping come from the ByokToolLimitExceeded case and withConfigureToolsLink; the escaping is now the shared escapeHostText.
• "Waiting for admission" is turn.isPending, which ends at the root user.message echo in onUserMessage.
• The status line is the existing activity-to-progressMessage path in agentHostSessionHandler, which reads the chat state's activity.

[github-actions]

Screenshot Changes

Base: 95d4de1b Current: 501ad9bd

Changed (3)

sessions/chatCompositeBar/MixedStatuses/Light

Before	After

sessions/chatCompositeBar/OverflowingTabs/Light

Before	After

sessions/sessionChatInputToolbar/SessionChatPills_HorizontalOverflow/Light

Before	After