cairntir

Multi-Host Continuity

Decision: accepted 2026-07-27 Priority: foundation / ship blocker Hosts: Codex, Cursor, Claude Code, Qwen Code

Invariant

A memory written through any supported host is the same memory seen through every other host. “Same” means:

• one canonical database path;
• one embedding-space identity and index generation;
• one wing identity for the same project;
• one MCP tool contract;
• verbatim drawer content and stable IDs;
• host/model provenance that does not change retrieval meaning.

There is no Codex memory, Cursor memory, Claude memory, or Qwen memory. There is Cairntir memory, reached through four adapters.

Boundary

The core owns:

• drawers, taxonomy, retrieval, integrity, provenance, and durable workflows;
• MCP tools/resources/prompts;
• canonical policy text for session start, recall, and remember;
• adapter diagnostics and compatibility fixtures.

Host adapters own:

• registering the Cairntir MCP server;
• installing or referencing startup instructions;
• reporting host/client identity when available;
• translating host-specific configuration failures into doctor findings.
• reading a bounded host-owned transcript tail only after explicit recovery opt-in, with host-specific completion markers isolated from the core.

Adapters must not select a different embedder, database, schema, or memory policy.

Current official surfaces

These are volatile integration details and must remain isolated:

• Codex: AGENTS.md for project instructions and codex mcp / config.toml for MCP launchers.
• Cursor: .cursor/rules/*.mdc for project rules and .cursor/mcp.json or ~/.cursor/mcp.json for MCP servers. Cursor CLI also reads root AGENTS.md and CLAUDE.md.
• Claude Code: CLAUDE.md for instructions and claude mcp for MCP registration.
• Qwen Code: QWEN.md, .qwen/settings.json, and project-scoped JSONL under ~/.qwen/projects/<sanitized-cwd>/chats.

Primary references:

• https://github.com/openai/codex/blob/main/docs/agents_md.md
• https://github.com/openai/codex/blob/main/codex-rs/README.md
• https://github.com/openai/codex/blob/main/codex-rs/rollout/src/recorder.rs
• https://docs.cursor.com/context/rules
• https://docs.cursor.com/context/model-context-protocol
• https://docs.cursor.com/en/agent/chat/history
• https://docs.anthropic.com/en/docs/claude-code/cli-usage
• https://github.com/QwenLM/qwen-code/blob/main/docs/users/features/headless.md

Implemented foundation

cairntir init --host claude|codex|cursor|qwen|all [--user] now installs host-specific MCP wiring while keeping one host-neutral policy body:

• Claude: project .mcp.json or authoritative user registration through the claude CLI; CLAUDE.md policy;
• Codex: project .codex/config.toml or authoritative user registration through the codex CLI; AGENTS.md policy;
• Cursor: project or global mcp.json; project .cursor/rules/cairntir.mdc.
• Qwen Code: project or user .qwen/settings.json; QWEN.md policy.

Existing JSON/TOML/instruction content is preserved. Cairntir only updates blocks carrying its own markers and fails closed on ambiguous conflicts. cairntir doctor inspects both project and user wiring without changing it.

Cursor’s global User Rules are managed through Cursor Settings and have no documented file-backed API. User-scope setup therefore installs the global MCP entry and reports the one manual rule step instead of claiming false success.

Transcript recovery follows the same honesty rule. Qwen Code, Claude Code, and Codex have verified JSONL adapters. Cursor documents local SQLite chat history but no stable transcript schema, so recovery returns an unsupported receipt and never probes private tables. The host-specific reader produces a host-neutral untrusted evidence record; no adapter writes a drawer.

Host/model/session provenance fields are now immutable on every write, and the automated four-adapter continuity fixture proves that all four hosts can write and recall through one store without changing drawer identity. Runtime model is explicitly unknown when a host does not disclose its selected model to the MCP subprocess; Cairntir records that limitation instead of inventing a name.

Acceptance test

For a temporary project and temporary Cairntir home:

1. each adapter reports installed and resolves the same MCP command;
2. Codex writes a uniquely identified drawer;
3. Cursor retrieves the complete verbatim drawer;
4. Claude Code supersedes it;
5. Codex sees the full supersession chain;
6. doctor reports one database path, embedding-space ID, and generation for all four;
7. the provenance records which host performed each action without changing the wing or drawer identity.

The test may use adapter simulators in CI. A release candidate also requires a human-operated smoke test against current host versions because configuration surfaces change faster than the Cairntir core.

Live acceptance result

The release-candidate smoke completed on 2026-07-29 against the live canonical store:

1. Codex wrote #125 with immutable host=codex.
2. Cursor recalled #125 and wrote #126 with immutable host=cursor.
3. Claude Code recalled the chain and wrote passing retry #130 with immutable host=claude, source drawer #126, and complete verbatim content.
4. Codex recalled #130 and exact-fetched its complete content and provenance.
5. Doctor reported 130 drawers / 130 vectors, matching embedding space and generation, SQLite integrity ok, zero foreign-key errors, and no stranded workflows.

The append-only evidence also records three important integration lessons:

• Claude Desktop and Claude Code are distinct surfaces. A Desktop write through a generic registration produced #127 with host=unknown and was rejected as acceptance evidence.
• A launcher connection is not enough; acceptance reads the immutable drawer receipt after every write.
• Windows harnesses must send protocol-shaped prompts through standard input or otherwise quote pipe characters safely. Two truncated harness attempts (#128 and #129) were preserved, diagnosed, and superseded by #130.

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