diff --git a/docs/adr/ADR-003-runtime-platform-plugin-responsibilities.md b/docs/adr/ADR-003-runtime-platform-plugin-responsibilities.md
new file mode 100644
index 00000000..7f0ffd1a
--- /dev/null
+++ b/docs/adr/ADR-003-runtime-platform-plugin-responsibilities.md
@@ -0,0 +1,66 @@
+# ADR-003: Runtime adapts to the platform; the plugin adapts to each runtime
+
+**Status:** Accepted — committed architecture
+**Date:** 2026-06-25
+**Supersedes context:** RFC `rfc-platform-mcp-as-plugin` §2b/§3.4 (platform-MCP-as-plugin, de-bake)
+**Related incident:** 2026-06-25 fleet-wide concierge `degraded` (half-wired `loaded_mcp_tools` producer)
+
+## Context
+
+Molecule runs one agent codebase across many runtimes (claude-code, codex,
+hermes, openclaw, gemini-cli) and exposes the same capabilities (management MCP,
+A2A, memory) on all of them. Which component adapts to which was, until now,
+tribal knowledge: the *plugin → runtime* half was documented, but the
+*runtime → platform* status contract lived only in source docstrings, the named
+contract doc (`api-protocol/registry-and-heartbeat.md`) was stale, and the
+de-bake rationale lived only in an RFC. There was no single canonical statement
+and no ADR.
+
+That gap had teeth. On 2026-06-25 every de-baked concierge was marked
+`degraded` because the runtime reported `mcp_server_present=true` but never
+produced `loaded_mcp_tools` — the producer was a scaffold with **zero callers**,
+`omitempty` masked it, the unit tests bypassed the production gate with
+`force=True`, and the only end-to-end check was a non-deterministic LLM
+self-enumeration that was also `continue-on-error` and didn't run on PRs. A
+half-wired producer crossing the runtime↔platform seam shipped silently.
+
+## Decision
+
+Adopt as **committed architecture** the two-layer, opposite-direction
+responsibility split, and **enforce it with guardrails** so it cannot regress to
+tribal knowledge:
+
+1. **The runtime adapts the agent to the platform.** It owns the register/
+   heartbeat **status contract** (`mcp_server_present` *and* `loaded_mcp_tools`),
+   reported runtime-agnostically in one place. Every gate-consumed field must
+   have a wired producer + a liveness test. The required tool id should be pinned
+   in a shared contract and **derived** on both sides rather than hardcoded per
+   layer — *target state*; today core holds it as a literal const guarded by a
+   drift test and the runtime enumerates it live (contract-pin in progress).
+
+2. **The plugin adapts its abilities to each runtime.** One runtime-agnostic
+   descriptor (the plugin = SSOT); per-runtime renderers write it into native
+   config. Renderer + reader + present-probe move in lockstep; an unmapped
+   runtime fails **closed**.
+
+3. **Platform-ness is a composition, not an image.** A concierge is an ordinary
+   runtime image + the org-admin key + the management MCP plugin. "Is this a
+   concierge?" is detected via `mcp_server_present()`, not the baked-image marker
+   (runtime#181). The baked `molecule-platform-agent` image is being removed and
+   guarded against return — *in progress* (artifact deletion + absence guard,
+   #78); until then the CP still carries vestigial `resolvePlatformAgentImage`
+   references.
+
+The full statement, the field tables, and the guardrail matrix live in
+[`architecture/runtime-platform-plugin-responsibilities.md`](/architecture/runtime-platform-plugin-responsibilities).
+
+## Consequences
+
+- New runtimes and new plugins have a single doc to conform to; reviewers have a
+  named contract to check against.
+- A set of red-on-regression guardrails becomes required (producer-liveness boot
+  test, contract-drift blocking with `loaded_mcp_tools` pinned, renderer/reader
+  lockstep, deterministic online+`create_workspace` e2e, de-bake absence guard).
+  Until each is green it is tracked under the guardrail/SSOT workstream.
+- The stale `api-protocol/registry-and-heartbeat.md` "five fields" status model
+  is corrected to include the MCP status fields.
diff --git a/docs/api-protocol/registry-and-heartbeat.md b/docs/api-protocol/registry-and-heartbeat.md
index f35bb6c5..882ce581 100644
--- a/docs/api-protocol/registry-and-heartbeat.md
+++ b/docs/api-protocol/registry-and-heartbeat.md
@@ -38,7 +38,33 @@ await platform.post("/registry/heartbeat", json={
 })
 ```
 
-Five fields. Memory usage, CPU, queue depth — those are infrastructure metrics for Prometheus/Grafana or CloudWatch. The platform registry is a service discovery layer, not a metrics store.
+Five fields for an ordinary workspace. Memory usage, CPU, queue depth — those are infrastructure metrics for Prometheus/Grafana or CloudWatch. The platform registry is a service discovery layer, not a metrics store.
+
+### Platform-agent (concierge) status fields
+
+A `kind=platform` concierge reports **two additional fields** that the
+online/degraded gate reads (built by `platform_agent_identity.identity_gate_payload`):
+
+```python
+    # platform concierge only — read by the online/degraded gate
+    "mcp_server_present": True,                       # management molecule-platform MCP is DECLARED/wired (RCA#2970)
+    "loaded_mcp_tools": ["mcp__molecule-platform__create_workspace", ...],  # tools ACTUALLY loaded (core#3082)
+```
+
+`mcp_server_present` (declared) is **necessary but not sufficient** — a
+declared-but-dead MCP is the false-green core#3082 catches, so the concierge also
+reports `loaded_mcp_tools`, the namespaced ids that actually loaded into the
+model. The runtime produces `loaded_mcp_tools` by enumerating the connected MCP
+servers over the wire (retrying in the background until the management MCP is
+connectable), so the concierge reaches `online` without waiting for a user turn.
+Tri-state: the field is **omitted** until something is observed (grace window
+applies), `[]` when a server connected with zero tools, or the id list. The
+required tool id is `mcp__molecule-platform__create_workspace`; *current state*
+core holds it as a literal const (`conciergePlatformMCPCreateWorkspaceTool`)
+guarded by a contract **drift test**, and the contract pins the management server
+name + status-field shape only — pinning the full id in the contract and deriving
+both sides is a *target* (in progress). See
+[Runtime ↔ Platform ↔ Plugin Responsibilities](/architecture/runtime-platform-plugin-responsibilities).
 
 `active_tasks` is included because the canvas uses it for a busy indicator on the node, and it sets up backpressure for Phase 2 without a schema change.
 
@@ -83,6 +109,14 @@ The workspace self-reports its health via the heartbeat payload. The platform de
 | `error_rate >= 0.5` and status is `online` | `online` -> `degraded` | `WORKSPACE_DEGRADED` |
 | `error_rate < 0.1` and status is `degraded` | `degraded` -> `online` | `WORKSPACE_ONLINE` |
 
+For a `kind=platform` concierge, two **MCP-presence** transitions also apply
+(fail-closed; `registry.go`):
+
+| Condition | Transition | Rationale |
+|-----------|-----------|-----------|
+| `mcp_server_present=false` on register/heartbeat | refuse `online` | RCA#2970 — no management MCP, refuse to serve a crippled concierge |
+| `mcp_server_present=true` but `loaded_mcp_tools` absent / lacks `mcp__molecule-platform__create_workspace` past the grace window | `online` -> `degraded` | core#3082 — MCP declared but its tools never loaded (false-green) |
+
 **What counts as an error:** Only things that indicate the workspace itself is broken — 5xx responses, timeouts, connection errors. Client errors (400, 403) are the caller's fault and are not counted.
 
 The workspace tracks errors locally using a rolling 60-second window and includes the stats in every heartbeat. The platform doesn't sit in the A2A message path, so it can't monitor response codes directly — self-reporting via heartbeat is the mechanism.
diff --git a/docs/architecture/runtime-platform-plugin-responsibilities.md b/docs/architecture/runtime-platform-plugin-responsibilities.md
new file mode 100644
index 00000000..e6a9ce4d
--- /dev/null
+++ b/docs/architecture/runtime-platform-plugin-responsibilities.md
@@ -0,0 +1,133 @@
+# Runtime ↔ Platform ↔ Plugin: division of responsibilities
+
+> **Status:** Committed architecture (see [ADR-003](/adr/ADR-003-runtime-platform-plugin-responsibilities)).
+> This page is the single canonical statement of *who adapts to whom*. If you are
+> wiring a new runtime, a new plugin, or anything the online/degraded gate reads,
+> start here.
+
+Molecule runs the **same agent code across many runtimes** (claude-code, codex,
+hermes, openclaw, gemini-cli, …) and exposes the **same capabilities** (the
+management MCP, A2A, memory) regardless of which runtime an org picks. Two
+adapter layers make that work, and they have **opposite directions**:
+
+| Layer | Adapts… | …to… | Lives in |
+|-------|---------|------|----------|
+| **Runtime** | the agent | **the platform** | `molecule-ai-workspace-runtime` (shared pip pkg) |
+| **Plugin**  | its abilities | **each runtime** | the plugin (descriptor) + per-runtime renderers |
+
+Stated as one sentence each:
+
+- **The runtime's job is to adapt the agent to the platform.** It registers,
+  heartbeats, and reports the status the platform's online/degraded gate reads —
+  **runtime-agnostically, in one place**. The platform never asks "which runtime
+  is this?"; it reads a fixed status contract.
+- **The plugin's job is to adapt its abilities to each runtime.** It ships one
+  runtime-agnostic descriptor; a per-runtime renderer writes that descriptor into
+  the runtime's *native* MCP config. The same plugin works on every runtime, and
+  the agent stays runtime-switchable.
+
+## 1. Runtime → Platform: the status contract
+
+The runtime reports to the platform on **register + every heartbeat** via one
+payload builder (`platform_agent_identity.identity_gate_payload`). The platform's
+fail-closed online/degraded gate (`workspace-server/internal/handlers/registry.go`)
+consumes it. The load-bearing fields:
+
+| Field | Meaning | Consumed by |
+|-------|---------|-------------|
+| `mcp_server_present` | the management `molecule-platform` MCP is **declared/wired** in the active runtime's native config | RCA#2970 online gate |
+| `loaded_mcp_tools` | the management MCP's tools **actually loaded** into the model (the `mcp__<server>__<tool>` ids) | core#3082 degrade gate |
+
+**Both halves are required.** "Declared" (`mcp_server_present`) is necessary but
+not sufficient — a declared-but-dead server is the exact false-green core#3082
+catches, so the runtime must also report what *loaded* (`loaded_mcp_tools`). The
+runtime produces `loaded_mcp_tools` **at init** (it enumerates the connected MCP
+servers itself — `loaded_mcp_tools_probe.py`), so the gate can flip
+`degraded → online` **without waiting for a user turn**. This enumeration is
+runtime-agnostic: it speaks the MCP wire protocol directly, not any one SDK's
+tool-list message.
+
+**Rule:** any field the gate reads MUST have a runtime-side **producer** that is
+actually wired (not just a scaffold) and a **liveness test**. A producer that is
+unreferenced serializes (`omitempty`) identically to a correctly-warming-up one —
+that is how a half-wired producer silently degrades every concierge (the
+2026-06-25 incident).
+
+> **Current state vs target.** Today the required tool id is a Go **literal
+> constant** (`conciergePlatformMCPCreateWorkspaceTool`) guarded by a contract
+> **drift test**, and `contracts/mcp-plugin-delivery.contract.json` pins the
+> management **server name** + the **status-field** shape — it does **not** yet
+> pin the full tool id, and the runtime does not derive it (it enumerates the
+> live MCP). **Target** (guardrail/SSOT workstream, in progress): pin the full
+> id `mcp__molecule-platform__create_workspace` in the contract and have core's
+> gate **derive** it, so a rename on either side fails the (blocking) drift
+> check rather than agreeing by convention.
+
+## 2. Plugin → Runtime: per-runtime rendering
+
+The plugin declaration is the **single source of truth** for its MCP descriptor
+(server name, command, args, env). A per-runtime **shape adapter** renders that
+one descriptor into the runtime's native config:
+
+| Runtime | Native MCP config |
+|---------|-------------------|
+| claude-code | `.claude/settings.json` (`mcpServers`) |
+| codex | `~/.codex/config.toml` |
+| gemini-cli | `settings.json` |
+| openclaw | `~/.openclaw/openclaw.json` |
+
+Renderers + their inverse readers + the present-probe live in
+`molecule-ai-workspace-runtime/molecule_runtime/mcp_render.py`
+(`_RUNTIME_SPECS` / `render_for_runtime` / `read_mcp_servers_for` /
+`management_mcp_present_for`), dispatched **by runtime name** — never by a baked
+image. See [agentskills-compat](/plugins/agentskills-compat) and
+[cli-runtime](/agent-runtime/cli-runtime) for the plugin author's view.
+
+**Rule:** adding a runtime means adding its renderer **and** reader **and**
+present-probe together (kept in lockstep by a test). An unmapped runtime must
+fail **closed**, never silently fall back to `.claude/settings.json` (the #3159
+mis-attribution class).
+
+## 3. Corollaries
+
+- **No logic in the wrong layer.** The platform-facing gate has zero
+  `if runtime == …` branches; runtime selection happens once via `ADAPTER_MODULE`
+  → `get_adapter`, and per-runtime shape happens via the `mcp_render` dispatch.
+  No platform logic is baked into a plugin.
+- **Tool ids should be SSOT.** Re-spelling `mcp__molecule-platform__create_workspace`
+  per layer is how the codex#142 `mcp__platform__` vs `mcp__molecule-platform__`
+  drift happened. *Current state:* core holds it as a literal const guarded by a
+  drift test; the runtime enumerates it from the live MCP (no literal). *Target:*
+  pin the full id in the contract and derive core's gate from it (in progress).
+- **Platform-ness is a composition, not an image.** A platform concierge is an
+  **ordinary runtime image** plus (a) the org-admin key and (b) the management
+  MCP plugin — *not* a special baked `molecule-platform-agent` image. The baked
+  image structurally binds the concierge to claude-code; for any non-claude-code
+  concierge it is not just redundant but **wrong**
+  ([rfc-platform-mcp-as-plugin](/design/rfc-platform-mcp-as-plugin) §3.4). Detect
+  "is this a concierge?" via the **composition** (`mcp_server_present()`), never
+  the baked-image marker (`MOLECULE_PLATFORM_AGENT_IMAGE_BAKED`), which is absent
+  on a de-baked concierge.
+
+## 4. How this is enforced (guardrails)
+
+Each rule should be a red-on-regression test so the principle can't drift back
+into tribal knowledge. **Status is honest** — ✅ enforced in CI today,
+◻ target/in-progress (guardrail/SSOT workstream, post the 2026-06-25 audit):
+
+| Rule | Guardrail | Status |
+|------|-----------|--------|
+| Plugin renders per-runtime native config | `test_mcp_plugin_delivery_contract` (codex writes `config.toml`, not claude settings) | ✅ |
+| No runtime branching in the gate | gate has zero `if runtime==`; `…RoutesThroughPort` | ✅ |
+| Unmapped runtime fails closed | G6 `test_mcp_render_completeness_g6` | ✅ |
+| Prompt SSOT (filename / channel) | G0 `test_prompt_filename_ssot_g0`, G1 `test_prompt_channel_ssot_g1`, `test_mcp_ssot` | ✅ |
+| `loaded_mcp_tools` producer fires through the real gate | `test_debaked_concierge_runs_via_mcp_server_present` (runtime#181) | ✅ (partial) |
+| Renderer/reader/present-probe lockstep | `test_mcp_render_lockstep` (`set(_RUNTIME_SPECS)==set(_RUNTIME_READERS)`) | ◻ target |
+| Full tool id derived from a shared contract | pin `mcp__molecule-platform__create_workspace` in the contract + derive core's gate | ◻ target |
+| `loaded_mcp_tools` / required tool pinned both sides + blocking drift | `mcp-plugin-delivery-contract-drift` made fail-closed, runtime copy in the compare set | ◻ target |
+| Producer-liveness via the full `main.py` boot path | boot test (real gate, no `force`) | ◻ target |
+| Concierge reaches online + has `create_workspace` | **current**: e2e LLM self-enumeration; **target**: deterministic `status=online` + heartbeat `loaded_mcp_tools` ∋ `create_workspace` | ◻ target (pending the deterministic e2e PR) |
+| Baked image cannot return | de-bake absence guard (fails if `Dockerfile.platform-agent` / `resolvePlatformAgentImage` / baked publish job reappear) | ◻ target (#78) |
+
+See the guardrail audit (2026-06-25) for the full enforced/gap analysis; the ◻
+items are tracked under the guardrail/SSOT workstream.
diff --git a/docs/index.md b/docs/index.md
index 2bbe5037..bd12b13d 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -63,6 +63,7 @@ features:
 - [Product Overview](/product/overview)
 - [Product Narrative](/product/molecule-product-doc)
 - [System Architecture](/architecture/architecture)
+- [Runtime ↔ Platform ↔ Plugin Responsibilities](/architecture/runtime-platform-plugin-responsibilities)
 - [Comprehensive Technical Documentation](/architecture/molecule-technical-doc)
 - [Memory Architecture](/architecture/memory)
 - [Workspace Runtime](/agent-runtime/workspace-runtime)