feat: add Slack Agent messaging experience (agent_view) support

[damianborowy-nexos]

Summary

Add support for Slack's Agent messaging experience (agent_view), the 2026 replacement for assistant_view.

• Core:
  • new onAppContextChanged event carrying the active-view context as a normalized AppContextEntity[] (channel / canvas / list / message / unknown) describing what the user is currently viewing
  • AppHomeOpenedEvent now carries the same folded active-view context as optional entities
• Slack adapter:
  • agentView config flag (now under agent_view the app_home_opened is a signal that DM was opened, regardless of tab, and the active-view context is folded onto DM messages)
  • app_context_changed routing
  • getAppContext(message) helper to read the folded context off a DM message
  • under agentView, DM messages are threaded per Slack's new model - each user message is a thread root
• Bumped @slack/web-api to ^7.18.0

Slack references

• Agent messaging experience: https://docs.slack.dev/changelog/2026/06/30/agent-messages-tab/
• Active-view context: https://docs.slack.dev/changelog/2026/07/02/app-context/

Test plan

• Ran pnpm validate
• Covered with unit tests and an integration replay test through the full webhook flow
• Tested it on a live app that uses chat, confirmed that new agent view is fully operational, bot responses are properly sent as thread replies, new events are properly captured (and everything works just like it previously did when agentView flag is not active), active-view context is properly passed to onAppContextChanged, AppHomeOpenedEvent, and to agent view DMs

Checklist

• All commits are signed and verified
• All commits are signed off for the DCO (git commit -s)
• pnpm validate passes
• Changeset added
• Documentation updated

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	npm/​@​slack/​web-api@​7.18.0

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