Track session-reference attachment support across chat session types

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#323,969 0 comments 0 reactions 1 assignee View on GitHub

@anthonykim1 is already working on this.

Since Jul 2, 2026.

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Description

agent-host

Related: https://github.com/microsoft/vscode/issues/315193
Related PR: https://github.com/microsoft/vscode/pull/323773

Context

PR #323773 is intentionally scoped to Agent Host session references that can resolve to a Copilot CLI events.jsonl file. That gives Agent Host Copilot a concrete model-readable attachment source without introducing a new AHP attachment kind or attempting broader session migration.

This issue tracks the broader attachment matrix for session references across chat/session providers.

Current scoped behavior in #323773

  • Agent Host-backed chats only show attachable Copilot CLI sessions in the Sessions... picker.
  • Supported session references are converted into:
    • a visible session chip (Simple attachment) for UI/replay metadata
    • a hidden Resource attachment pointing at the host-local events.jsonl
  • Unsupported session references are not converted as model-readable attachments by Agent Host.

Session attachment matrix

Referenced session type Example URI Readable history source Supported by #323773? Follow-up path
EH Copilot CLI copilotcli:/<id> Local ~/.copilot/session-state/<id>/events.jsonl Yes Keep using events.jsonl as attachment source
Local Agent Host Copilot CLI agent-host-copilotcli:/<id> Local ~/.copilot/session-state/<id>/events.jsonl Yes Keep using events.jsonl as attachment source
Remote Agent Host Copilot CLI remote-<authority>-copilotcli:/<id> Remote host ~/.copilot/session-state/<id>/events.jsonl, when connection/home resolves Yes, when resolvable Keep using host-local events.jsonl path
Other Agent Host/AHP sessions provider-specific Agent Host session URI No shared events.jsonl contract No Need first-class AHP session-reference support or an IChatModel/session-content path
Claude Code sessions provider-specific session URI Not Copilot CLI events.jsonl No Need provider-specific or common session model access
Local/workbench chat sessions workbench chat session URI IChatModel/chat session model, not Copilot CLI events.jsonl No Need IChatModel/session-content attachment path
Other extension-host chat sessions extension/provider-specific URI Provider-specific, no shared events.jsonl contract No Need provider-specific or first-class session-reference contract

Open questions

  • Should session references become a first-class AHP attachment concept instead of being represented through Simple + Resource?
  • Should non-Copilot-CLI sessions expose model-readable attachment content through IChatModel, IChatSessionsService, or provider-specific session content APIs?
  • What UI affordance should distinguish a visible session chip from hidden model-readable context resources?

Non-goal

This issue is about attaching a referenced session as context. Full session migration/porting for continue in should be tracked separately.

/cc @connor4312 @roblourens

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