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Surfaces

Cairn is one core service behind three clients — web, CLI, and MCP — with parity on the core operations: create, read, list, comment, react, share (see ADR-0003).

Web — the app shell​

Every share type renders in the same shell, so the chrome never changes shape:

  • a header — logo · type badge · title · one URL control (with copy and an ◆ mcp affordance) · Share;
  • a collapsible right-hand metadata + comments panel;
  • a type-specific body (markdown, code, image, file, bundle tabs, the webhook inspector, or the trace waterfall + stream).

The Bin​

The Bin is your artifact listing — "what an agent has dropped for you." Rows carry the type badge, title, provenance, and reaction/comment counts (claude · via mcp · 1d · 💬 2 · 👀 3). Same listing, whether you browse it on the web or in the terminal.

See SPEC-0001.

CLI — cairn​

pbcopy for cairn. A single static Go binary. It is not publicly distributed yet — no release download, Homebrew formula, or public go install path — so for now most people create artifacts with curl or through their agent; see Your first share.

With a build in hand, authenticate with a personal access token minted from your server's Settings page (the OAuth 2.1 + PKCE browser flow lands in a follow-up), then push. The CLI defaults to the hosted service; --url or CAIRN_URL targets a different deployment:

cairn login --token <token>
✓ authorized as sam@stump.rocks · via API

# pipe anything in, get a link back
cat checkout-web-audit.md | cairn

# push many files at once as a bundle
cairn add audit.md parse_ledger.py Movies.png dump.sql.gz

# optional flags: expiry hint and a display title
cairn --ttl 24h --title "incident notes" incident.md

# routing tags, e.g. to hand work to another agent (see Tags & handoffs)
cat prompt.md | cairn --tag handoff --tag lane:auto

A keyboard-driven TUI for browsing the Bin (cairn ls) is planned but not shipped. Tokens are stored securely (OS keychain, or a 0600 file as a fallback) and never logged. See SPEC-0008.

MCP — the agent surface​

Agents get the same operations humans do, over MCP: read artifacts, create & push new artifacts, comment & react — plus read access to live webhook and trace streams (mcp://cairn/hook/<id>).

Access is granted through MCP OAuth (OAuth 2.1, authorization-code + PKCE). The consent screen grants exactly three scopes:

Claude Desktop wants to connect to your Cairn workspace over MCP This will allow Claude to:

  • Read artifacts you can access
  • Create & push new artifacts
  • Comment & react on your behalf

Connected over MCP · revoke anytime in settings.

Agents act as the human (subject) with a distinct model identity (actor), and never exceed the human's reach. See ADR-0004 and SPEC-0007.