[FEATURE] Session continuity between Cowork and the Microsoft 365 add-ins

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Cowork sessions and the Claude add-ins in Microsoft 365 are separate contexts that cannot see each other, so every crossing between them costs a full re-brief.

When a Cowork session produces a .docx or .pptx and I open it in Word or PowerPoint to keep working, the add-in knows nothing about the session that made it — the source data, the constraints, and the decisions already settled are all gone. In the other direction, when I am working in a document and hit something that needs real multi-step work, I have to leave, start a Cowork session, re-upload the file, and retype the context I just gave the add-in.

For any document that goes through more than one round this repeats, and the two sides drift: the add-in makes edits that contradict what the Cowork session established, because it never saw it.

Proposed Solution

A session context that both Cowork and the M365 add-ins can attach to, so a piece of work moves in either direction without a re-brief.

• From a Cowork session: a "Continue in Word / Excel / PowerPoint" action on a generated file. When that file is opened in the Office app, the add-in offers to attach to the originating session and comes up with its history already loaded.
• From an add-in: a "Continue in Cowork" action that hands the current document plus the add-in conversation to a Cowork session, so the heavier multi-step work picks up where the add-in left off.
• The link persists on the file, so a document can round-trip several times and both ends stay current.
• Scoped to a single signed-in Claude account — no cross-account sharing.

Alternative Solutions

Today's workaround is manual: export from Cowork, download, open in Office, then paste a hand-written summary of the session into the add-in — and in reverse, re-upload the file to a fresh Cowork session and retype everything. Both are lossy, and neither survives more than a round or two.

A lighter version that would still help: have Cowork write a context sidecar alongside the document that the add-in can read, rather than a live session link.

Priority

High - Significant impact on productivity

Feature Category

Other

Use Case Example

1. In Cowork I build a summary deck from a financial model in Excel. The session establishes which scenario is base case, which figures are still provisional, and the naming conventions for the slides.
2. I open the generated .pptx in PowerPoint to adjust the layout by hand.
3. The add-in attaches to that session, so when I ask it to "add a slide for the downside case" it already knows what the downside case is and matches the formatting the session established.
4. Later I return to Cowork. The session sees the slides I added in PowerPoint and updates the summary to stay consistent.

Additional Context

Filing this as a Cowork-side capability: the add-in is the far end of the handoff, but the session and its context live in Cowork.

Related open issues, none of which cover this:

• #71630 (portable conversation context across Claude Code, claude.ai and Cowork) — continuity between Claude surfaces, but not the Office add-ins.
• #81317 (allow individual plans to enable M365 write tools) — access scope, not continuity.
• #81764 (bridge local stdio MCP servers into cloud Cowork sessions) — transport, not continuity.