HYTHE

A coordination bus + shared truth for your agent fleet. Self-hosted, two-component setup: a dockerized server plus a thin stdio bridge for your MCP clients.

HYTHE is an MCP server that lets multiple AI coding agents — Claude Code, Codex, Cursor, custom harnesses — share state, preserve context across sessions, and coordinate with each other. It is not another memory store. Its differentiators:

Supersession + current-state resolution: observations supersede each other (replace-current), and get_current_observation resolves the chain server-side — so readers get the newest non-superseded state. Conflict handling is implemented: checkpoint is branch-preserving CAS — concurrent writers branch rather than overwrite, and conflicts surface as heads, never silently resolved (contract-tested; see the evidence ledger).
Agent messaging with a tracked delivery lifecycle: direct and capability-based sends, message supersession, read-state as a shared signal, atomic ack+archive. (Described as tracked lifecycle, not guaranteed delivery — the states are honest about what the server knows.)
The Adaptive Coordination Protocol (ACP): the ETA-driven coordination discipline that co-evolved with the server — published as docs/SPEC.md with a real two-harness worked tutorial.

Documentation

Doc	What it covers
Quickstart	Clean machine → two coordinating agents in ~15 minutes
Concepts	One current truth, messaging lifecycle, resume/checkpoint, honest security model
Checkpoint / resume v3	Current-head pointer, reconciliation, record / patch, the v3 read model, and the one-time adoption step for scopes written before v3
ACP SPEC	The coordination protocol, versioned (1.0.0)
Tutorial	Annotated transcript of a real Claude Code ↔ Codex review loop from the original Engram deployment
Tool compatibility map	The 20-tool v1 surface; every retired tool and its exact replacement
Backup & restore	Tested SQLite backup/restore/compaction runbook
Agent credential operator	Offline issuance, attestation, promotion, rotation, and revocation
Private-residue adjudication	Hash-bound, owner-approved disposition of ambiguous historical rows
SQLite physical sanitation	Verified offline VACUUM and no-clobber promotion after logical cleanup
Pavilion production	Pinned deployment, readiness, shutdown, canary, and rollback contract

Status

Version 0.2.0. This source tree and package define the reviewed 0.2.0 release. Version 0.2.0 preserves 0.1.7's dual-proof agent authorization, exact-mailbox/private-payload containment, bounded related-context discovery, latency-SLO recovery and the offline adjudicator, and adds checkpoint / resume resultVersion: 3: an explicit current-head pointer per scope, a reconcile operation that folds live heads into one survivor and resolves divergent values causally, append-only verified fact/loop versions, a read model that only promotes values proven on the accepted lineage, and record / patch operations on the pointed head. Every v1 / v2 request and result shape is frozen; v3 is opt-in per call, so a 0.1.7 client keeps working against a 0.2.0 server. The dependency tree moved to Express 5, clearing two moderate qs advisories. This release runs on the reference production host since 2026-09-05. All 0.2.0 rollout configurations pin @hythe/mcp@0.2.0; verify that the registry returns that exact version before production use. The predecessor @tomcat65/engram-mcp and io.github.tomcat65/engram remain available as compatibility history and are never unpublished. See CHANGELOG.md and the v3 guide.

House rule: every claim in these docs must trace to a test or a measurement (see the evidence ledger below). Claims that don't are bugs.

Evidence ledger

Claim	Evidence	Source	Date
Tree green, full gates	Source and clean installed-package gates cover 49 Vitest files (530 passed, 2 skipped, 6 explicit todos), 107 migration checks, 43 release-tree checks, 31 agent-kit checks, zero production npm audit findings, registry validation, and an isolated Docker start/readiness/MCP/WebSocket/graceful-shutdown canary.	`.github/workflows/ci.yml`, `tests/`, `src/migrations/`, `clients/agent-kit/tests/test-setup.sh`, `scripts/verify-hythe-release-tree.test.mjs`, `scripts/verify-packed-consumer.mjs`	2026-08-14
Compaction identity fails closed	Startup and post-compaction hooks reject missing, conflicting, or invalid identity; the bridge binds acting tools and message-resource recipients to the configured exact lane before any HTTP request.	`clients/agent-kit/tests/test-setup.sh`, `tests/contract-bridge-identity.test.ts`	2026-08-13
Exact mailboxes stay isolated	Houston/Hythe, case variants, display metadata, legacy identity history, cross-tenant poisoning, suffix handles, lifecycle changes, supersession, HTTP, and ENG-4 authorship have negative isolation coverage.	`tests/contract-message-identity-isolation.test.ts`, `tests/contract-eng4-p0.test.ts`	2026-08-13
Private message bodies stay out of shared graph surfaces	Historical, oversized, malformed, alias-linked, relation-linked, imported, exported, searched, graphed, logged, and restored payload paths are covered; hidden children do not leak through counts.	`tests/contract-message-payload-isolation.test.ts`, `tests/contract-data-payload-isolation.test.ts`, `tests/contract-log-confidentiality.test.ts`	2026-08-13
Cleanup is offline and fail-closed	Migration 007, owner-approved adjudication, and physical sanitation are dry-run/plan-first, bind execution to reviewed database and decision evidence, require verified no-clobber artifacts, refuse unresolved custody, and preserve rollback state.	`src/migrations/007-private-message-residue.mjs`, `src/migrations/private-message-residue-adjudication.mjs`, `src/migrations/vacuum-sanitized-database.mjs`, `docs/`	2026-08-14
Per-agent authority is server-derived	The base key proves deployment/tenant access; a separate protected-file `hya1` credential proves the exact agent. Required mode rejects stripped proof, mismatched identity, insufficient scope, revoked credentials, and stale WebSocket sessions.	`src/agent-auth/`, `tests/contract-agent-auth-foundation.test.ts`, `tests/contract-agent-auth-server.test.ts`, `tests/contract-agent-key-client.test.ts`	2026-08-14
Install and discovery surfaces agree	CLI and registry surfaces require an exact lane identity and expose only a protected per-agent key-file path plus an explicit authorization mode; tools and resource templates served through HTTP match the stdio bridge path.	`tests/contract-cli.test.ts`, `tests/contract-agent-key-client.test.ts`, `tests/contract-mcp-resources-http.test.ts`, `scripts/verify-hythe-release-tree.test.mjs`	2026-08-14
Current head is explicit, never guessed	The pointer advances only from the pointed head; stale parents branch without becoming current; a pointer at a non-live snapshot fails closed; snapshot rows are immutable by trigger. 33 contract tests.	`tests/contract-eng4-h1-head-pointer.test.ts`	2026-09-03
Versions and coverage are exact and verified	Every ledger tuple gets exactly one disposition; the startup backfill is all-or-nothing and idempotent; a bidirectional parity verifier fails closed on any missing, extra or mismatched row. 32 contract tests.	`tests/contract-eng4-h2-version-foundation.test.ts`	2026-09-03
Reconciliation is CAS-bound and causal	Exact live-head set and pointer are compare-and-set; every non-survivor head is retired (never deleted); divergent values resolve only by bound accept, reject or lineage reject; the record is payload-bound and re-verified on replay and read. 34 contract tests.	`tests/contract-eng4-h3-reconcile.test.ts`	2026-09-04
The v3 read model promotes only proven values	`currentFacts` / `openLoops` come only from verified versions on the accepted lineage with provenance; everything else is accounted as divergent or legacy with closed coverage. 29 contract tests.	`tests/contract-eng4-h4-read-model.test.ts`	2026-09-04
record / patch cannot promote stale state	Only the pointed head is admitted (conflict otherwise); state is materialized from the hash-verified payload; each payload is read once per call; snapshot resources serve exactly the verified bytes. 21 contract tests, four review rounds.	`tests/contract-eng4-h5-record-patch.test.ts`	2026-09-04
Express 5 keeps the HTTP contract	A bodiless or wrong-content-type request is handled like an empty JSON body on every parsed route, never a framework 500; production audit reports zero findings.	`tests/contract-express5-body-contract.test.ts`, `.github/workflows/ci.yml` run 33878587010	2026-09-04
Production migration verified on a copy first	The v3 schema and backfill were exercised against a copy of the production database on the production host before cutover; the live cutover took 17 s with row counts identical to the verified cold backup.	`docs/PAVILION-PRODUCTION.md`; operator log `engram-prod/releases/hythe-74a324c-cutover-20260905T005551Z.log` on the host	2026-09-05

v1 surface (short)

Install (two-component setup): server via docker compose up, then the @hythe/mcp stdio bridge per MCP client; first-run wizard stores the API key in a protected .env and prints secret-free file-referencing config for Claude Code / Codex / Cursor / Claude Desktop; optional namespaced (demo-*) demo seed on an otherwise empty DB.
Knowledge graph: entities, observations, relations, supersession, current-state resolution, conflict surfacing.
Related-context discovery: exact scope anchoring plus automatic bounded vector retrieval and graph-path reranking, with currentness/evidence/provenance explanations and no implicit writes.
Agent messaging: direct, capability-based, superseding; tracked delivery lifecycle.
resume / checkpoint: budgeted one-call session rehydration with closed coverage accounting, and CAS-protected, branch-preserving structured state capture. With resultVersion: 3: an explicit current-head pointer, reconcile to fold heads and resolve divergent values, verified fact/loop versions with provenance, and record / patch on the pointed head — see the v3 guide.
ACP: the coordination protocol as a versioned spec + real worked example.

Embedding runtime contract

The published npm package does not install a transformer engine by default. Without one, HYTHE still provides deterministic 384-dimension token-hash vectors plus lexical ranking; it does not download a model or create a model cache. @xenova/transformers@2.17.2 is an optional peer for operators who deliberately provide it from their own audited dependency root.

The Docker image keeps semantic behavior stable through a separate, locked /opt/hythe-transformers runtime. Its startup preflight loads the configured Xenova/all-MiniLM-L6-v2 q8 model and requires one finite 384-dimension embedding before the server starts. When SQLITE_VEC_ALLOW_REMOTE_MODELS=false, the configured SQLITE_VEC_CACHE_DIR must already contain that model. Do not switch between transformer and hash embeddings on a populated vector index: retain the same provider/model/dimensions or rebuild the vector index first.

License

Apache-2.0