feat(roster): atomos as the 5th MCP — ECM compose/verify executor

Add atomos v0.1.0 to the MCP catalogue + its run template.

- roster/mcps.yaml: atomos entry (oci-image, wiring_mode: transport, closed
  3-tool set mcp__atomos__{compose_handoff,verify_envelope,verify_pins}),
  pinned to the v0.1.0 multi-arch INDEX digest sha256:ff2449e9…
  (github-attested, commit 5c10193).
- cli/templates/mcp/atomos.mcp.json.tmpl: workspace-mounting executor template
  (mirrors tonberry; :/workspace:z SELinux default + --cap-drop ALL + no-new-privileges).

atomos is the tonberry-analog for the ECM context lifecycle — an alternate
surface to the canonical `eidolons context` bash kernel (byte-parity, CI
drift-guarded). Orchestrator/host-facing (transport); the kernel verbs remain
what Eidolons use.

Verified: 5 MCPs; `eidolons mcp list` shows atomos@0.1.0; jsonschema atomos
entry 0 strict errors; make schema + crystalium skew guard OK; digest =
release-manifest manifest_sha256; template jq-valid + fenced.

ESL: lite, maker=vivi != checker=kupo, archived at
.spectra/changes/archive/2026-07-07-roster-atomos-mcp/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Rynaro

.spectra/changes/archive/2026-07-07-roster-atomos-mcp/change.json

@@ -0,0 +1,30 @@
+{
+  "esl_version": "1.1",
+  "change_id": "roster-atomos-mcp",
+  "status": "archived",
+  "tier": "lite",
+  "maker": "vivi",
+  "checker": "kupo",
+  "has_code": true,
+  "acceptance_checks": [
+    {
+      "id": "AC-1",
+      "verify_method": "yq: roster/mcps.yaml lists 5 MCPs incl. atomos; `eidolons mcp list` shows atomos @ stable 0.1.0"
+    },
+    {
+      "id": "AC-2",
+      "verify_method": "jsonschema (Draft7): the atomos entry (mcps[4]) is strictly schema-clean — 0 errors; `make schema` passes; crystalium skew guard unaffected (OK)"
+    },
+    {
+      "id": "AC-3",
+      "verify_method": "digest sha256:ff2449e9… is the v0.1.0 multi-arch INDEX from Rynaro/atomos release-manifest.json (commit 5c10193, github_attestation:true)"
+    },
+    {
+      "id": "AC-4",
+      "verify_method": "jq: cli/templates/mcp/atomos.mcp.json.tmpl is valid JSON; mounts __PROJECT_ROOT__:/workspace:z (SELinux default) with --cap-drop ALL + no-new-privileges (capability starvation matches the atomos fence)"
+    }
+  ],
+  "spec_ref": "spec.md",
+  "drift_checked": true,
+  "archive_path": "archive/2026-07-07-roster-atomos-mcp"
+}

.spectra/changes/archive/2026-07-07-roster-atomos-mcp/promotion.envelope.json

@@ -0,0 +1,18 @@
+{
+  "envelope_version": "1.0",
+  "from": {
+    "eidolon": "idg"
+  },
+  "to": {
+    "eidolon": "orchestrator"
+  },
+  "performative": "INFORM",
+  "objective": "INFORM(promotion): archived change \"roster-atomos-mcp\" ready for CRYSTALIUM Semantic promotion.",
+  "context_delta": {
+    "archive_path": "archive/2026-07-07-roster-atomos-mcp",
+    "change_id": "roster-atomos-mcp",
+    "intent": "promotion",
+    "spec_ref": "spec.md",
+    "summary": "atomos rostered as the 5th MCP (catalogue entry + template) pinned to the v0.1.0 INDEX digest. Route to mcp__crystalium__ingest (Semantic layer)."
+  }
+}

.spectra/changes/archive/2026-07-07-roster-atomos-mcp/spec.md

@@ -0,0 +1,73 @@
+---
+Title: Roster atomos as the 5th MCP
+Version: 1.0.0
+Date: 2026-07-07
+Author: orchestrator (roster addition; scribed — tonberry container writes SELinux-blocked this session)
+tier: lite
+Target: roster/mcps.yaml, cli/templates/mcp/atomos.mcp.json.tmpl
+---
+
+# Roster atomos as the 5th MCP (LITE spec)
+
+## Framing
+
+`Rynaro/atomos` v0.1.0 shipped (the ECM compose/verify executor MCP — a Go stdio
+server, the tonberry-analog for the context lifecycle). This change adds it to the
+nexus MCP catalogue so `eidolons mcp install atomos` can wire it, making it the
+**5th sibling MCP** (atlas-aci · junction · crystalium · tonberry · **atomos**).
+
+Atomos is an **alternate surface** to the canonical `eidolons context` bash kernel:
+same inputs ⇒ same bytes (T1 brief + T2 envelope byte-parity, CI drift-guarded).
+The kernel verbs remain what Eidolons use; atomos is orchestrator/host-facing, so it
+is rostered `wiring_mode: transport` (registered in `.mcp.json`, never injected into
+an Eidolon's `tools:` allowlist — the same posture as junction).
+
+## Scope / non-goals
+
+- IN: the `atomos` catalogue entry in `roster/mcps.yaml` (source ghcr, versions with
+  the v0.1.0 INDEX digest, `exposes_tools` = the closed 3-tool set, `install.template`)
+  and the run template `cli/templates/mcp/atomos.mcp.json.tmpl`.
+- OUT: `roster/index.yaml` (MCPs live in `mcps.yaml` only; crystalium is the special
+  dual-tracked case — the skew guard is crystalium-specific and unaffected here);
+  local install into THIS project (a separate `eidolons mcp install atomos`); any
+  change to atomos itself (its own repo); nexus kernel edits.
+
+## Design notes
+
+- **Digest**: `sha256:ff2449e92cae030e8cb25796c2b9e06ad4814e59ac6db8fc19beffc5606d8a73`
+  — the multi-arch INDEX digest captured by the atomos release workflow into
+  `release-manifest.json` (v0.1.0, commit 5c10193, `github_attestation: true`).
+- **Template**: mirrors `tonberry.mcp.json.tmpl` (both are workspace-mounting stateless
+  executors). Mounts `__PROJECT_ROOT__:/workspace:z` — atomos writes the handoff
+  sidecar pair under `.eidolons/.context/`; the `:z` SELinux relabel is carried over
+  from the tonberry template fix (inert on non-SELinux hosts). `--cap-drop ALL` +
+  `--security-opt no-new-privileges` matches atomos's capability-starvation fence
+  (no network, no crystalium mount).
+- **Tools**: `mcp__atomos__{compose_handoff,verify_envelope,verify_pins}` — the closed
+  set enforced in atomos by a registry-exact + source deny-list fence.
+
+## Acceptance checks
+
+**AC-1 — atomos is in the catalogue.** `yq '.mcps[].name' roster/mcps.yaml` lists
+five, ending in `atomos`; `eidolons mcp list` shows `atomos` at stable `0.1.0`.
+- verify_method: observed 2026-07-07 (5 MCPs; `atomos … 0.1.0 install missing`).
+
+**AC-2 — schema + guards clean.** The atomos entry is strictly schema-conformant and
+the existing gates are unaffected.
+- verify_method: `jsonschema` Draft7 → atomos (mcps[4]) 0 errors; `make schema` passes;
+  `check_roster_mcp_skew` OK (crystalium 1.8.0 match).
+
+**AC-3 — digest is the real, attested INDEX.** The pinned digest matches the v0.1.0
+release-manifest.
+- verify_method: `release-manifest.json` `manifest_sha256` == the rostered digest.
+
+**AC-4 — template is valid + fenced.** `jq empty` the template; it mounts `:z` and
+drops all capabilities.
+- verify_method: `jq empty cli/templates/mcp/atomos.mcp.json.tmpl`; grep `:/workspace:z`
+  + `--cap-drop ALL`.
+
+## Notes for the executor
+
+- Pure roster/data + one template; no CLI code path changes. `eidolons mcp install
+  atomos` (generic driver) wires it — no per-MCP install code needed (unlike the
+  bespoke `mcp_atlas_aci*` path, atomos is a plain oci-image executor like tonberry).

.spectra/changes/archive/2026-07-07-roster-atomos-mcp/verify.envelope.json

@@ -0,0 +1,17 @@
+{
+  "envelope_version": "1.0",
+  "from": {
+    "eidolon": "kupo"
+  },
+  "to": {
+    "eidolon": "orchestrator"
+  },
+  "performative": "INFORM",
+  "objective": "INFORM(verify): change \"roster-atomos-mcp\" PASS — maker(vivi)!=checker(kupo); atomos entry strictly schema-clean (0 errors), 5 MCPs, make schema + skew OK, digest attested, template :z-fenced.",
+  "context_delta": {
+    "maker": "vivi",
+    "checker": "kupo",
+    "verdict": "pass",
+    "evidence": "yq 5 MCPs incl atomos; eidolons mcp list atomos@0.1.0; jsonschema mcps[4] 0 errors; make schema pass; check_roster_mcp_skew OK; digest=release-manifest manifest_sha256 (attested); template jq-valid + :/workspace:z + --cap-drop ALL"
+  }
+}

CHANGELOG.md

@@ -8,6 +8,10 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). Version
 
 ## [Unreleased]
 
+### Added
+
+- **atomos rostered as the 5th MCP** (`roster/mcps.yaml` + new `cli/templates/mcp/atomos.mcp.json.tmpl`). atomos v0.1.0 (`ghcr.io/rynaro/atomos@sha256:ff2449e92cae030e8cb25796c2b9e06ad4814e59ac6db8fc19beffc5606d8a73`, multi-arch INDEX, github-attested; commit `5c10193`) is the **ECM compose/verify executor MCP** — the tonberry-analog for the context lifecycle. It exposes the closed 3-tool set `mcp__atomos__{compose_handoff,verify_envelope,verify_pins}` at **byte-parity with the `eidolons context` kernel** (an alternate surface, never the sole path; T1 brief + T2 envelope byte-exact, CI drift-guarded against the kernel oracle). Rostered `wiring_mode: transport` (orchestrator/host-facing, like junction — the kernel verbs remain what Eidolons use). The template mirrors tonberry's workspace-mounting executor shape (`:/workspace:z` SELinux default, `--cap-drop ALL`, `--security-opt no-new-privileges` — matching atomos's capability-starvation fence); `eidolons mcp install atomos` wires it via the generic oci-image driver. Build spec + repo: [`Rynaro/atomos`](https://github.com/Rynaro/atomos); GO decision: `docs/specs/ecm/decisions/atomos-go-no-go.md`.
+
 ## [2.2.0] — 2026-07-07 — ECM P1: the context economy ships
 
 ### Changed

cli/templates/mcp/atomos.mcp.json.tmpl

@@ -0,0 +1,26 @@
+{
+  "mcpServers": {
+    "atomos": {
+      "command": "docker",
+      "args": [
+        "run",
+        "--rm",
+        "-i",
+        "--name",
+        "atomos-__PROJECT_SLUG__",
+        "--label",
+        "eidolons.project=__PROJECT_SLUG__",
+        "-v",
+        "__PROJECT_ROOT__:/workspace:z",
+        "-w",
+        "/workspace",
+        "--cap-drop",
+        "ALL",
+        "--security-opt",
+        "no-new-privileges",
+        "ghcr.io/rynaro/atomos@__IMAGE_DIGEST__",
+        "serve"
+      ]
+    }
+  }
+}

roster/mcps.yaml

@@ -277,3 +277,52 @@ mcps:
         - docker_daemon
         - image_local
         - registry_reachable
+
+  - name: atomos
+    display_name: "atomos"
+    scope: system
+    kind: oci-image
+    description: "ECM (Eidolons Context Management) compose/verify executor — composes the session-handoff brief + ECL envelope and verifies envelope integrity / pin survival, byte-identical to the canonical `eidolons context` bash kernel. An alternate surface, never the sole path."
+    use_cases:
+      - "Compose a session-handoff brief + ECL INFORM / ecm/handoff-brief envelope at byte/SHA parity with the kernel."
+      - "Verify ECL envelope integrity (the full SHA-256 verdict matrix) at a receiver gate."
+      - "Probe pin-set survival after a lossy context operation."
+    related_eidolons: []
+    grants_to_eidolons: []
+    wiring_mode: transport
+    exposes_tools:
+      # Orchestrator/host-facing (transport) — the kernel verbs (`eidolons context`)
+      # remain what Eidolons use; atomos is the MCP-surface alternate for hosts that
+      # prefer a tool call. Tool namespace derives from the .mcp.json key "atomos".
+      glob: "mcp__atomos__*"
+      list:
+        - mcp__atomos__compose_handoff
+        - mcp__atomos__verify_envelope
+        - mcp__atomos__verify_pins
+    source:
+      type: ghcr
+      image: "ghcr.io/rynaro/atomos"
+    versions:
+      latest: "0.1.0"
+      pins:
+        stable: "0.1.0"
+      releases:
+        "0.1.0":
+          # MVP: 3 compose/verify tools at byte-parity with the eidolons kernel
+          # (T1 brief + T2 envelope byte-exact); closed-registry + source deny-list
+          # fence; distroless multi-arch INDEX digest. ATOMOS_VERSION 0.1.0; commit 5c10193.
+          digest: "sha256:ff2449e92cae030e8cb25796c2b9e06ad4814e59ac6db8fc19beffc5606d8a73"
+          released_at: "2026-07-07T00:00:00Z"
+    install:
+      hosts_wired:
+        - ".mcp.json"
+        - ".cursor/mcp.json"
+        - ".github/agents/*"
+        - ".codex/config.toml"
+      template: "cli/templates/mcp/atomos.mcp.json.tmpl"
+    health:
+      probes:
+        - docker_cli
+        - docker_daemon
+        - image_local
+        - registry_reachable