diff --git a/docs/contract-additions/immutable-node-profiles.md b/docs/contract-additions/immutable-node-profiles.md
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+# Immutable Node Profile Contracts
+
+This contract addition defines the first SourceOS machine-readable surface for immutable Linux node and agent-runtime substrate profiles.
+
+## Why this exists
+
+The platform standards layer defines the general immutable host capability placement grammar. SourceOS needs a contract-native form that downstream implementation repos can validate, render, and emit evidence for.
+
+The key boundary is:
+
+- SourceOS immutable nodes are base substrate profiles.
+- Agent Machine and AgentPlane are the primary runtime/evidence consumers for node and agent-runtime substrate posture.
+- Desktop, shell, and workstation surfaces may display summarized posture and expose operator controls, but they do not own the node substrate.
+- Socios capability packs are optional automation commons and must not be required for a base SourceOS node.
+
+## Added schemas
+
+| Schema | Purpose | URN prefix |
+|---|---|---|
+| `ImmutableNodeProfile.json` | Top-level node/agent-runtime substrate profile tying together substrate posture, release refs, host placements, state schemas, validation commands, desktop consumer refs, and optional Socios pack refs. | `urn:srcos:immutable-node-profile:` |
+| `HostCapabilityPlacement.json` | Placement declaration for one node substrate capability, agent runtime workload, host extension, or state root. | `urn:srcos:host-capability-placement:` |
+| `NodeStateSchema.json` | Durable state root contract with rollback compatibility, mutability posture, and desktop visibility metadata. | `urn:srcos:node-state-schema:` |
+
+## Added examples
+
+| Example | Schema |
+|---|---|
+| `examples/immutablenodeprofile.json` | `schemas/ImmutableNodeProfile.json` |
+| `examples/hostcapabilityplacement.json` | `schemas/HostCapabilityPlacement.json` |
+| `examples/nodestateschema.json` | `schemas/NodeStateSchema.json` |
+
+## Validation
+
+The focused validator is:
+
+```bash
+python3 tools/validate_immutable_node_examples.py
+```
+
+A future hygiene pass should wire this into the repository `Makefile` and `schemas/README.md` once the contract slice is accepted.
+
+## Downstream implementation map
+
+| Downstream repo | Expected role |
+|---|---|
+| `SourceOS-Linux/sourceos-boot` | Consumes boot/release references and coordinates boot/recovery/install/rollback handoff. |
+| `SourceOS-Linux/agent-machine` | Renders and validates systemd, Quadlet, state roots, activation decisions, storage receipts, and runtime evidence. |
+| `SourceOS-Linux/sourceos-devtools` | Exposes `sourceosctl immutable-node plan|validate|inspect` operator flows. |
+| `SocioProphet/agentplane` | Consumes immutable-node activation/runtime evidence and replayable receipts. |
+| `SocioProphet/prophet-platform` | Consumes profiles as deployment/FogStack substrate evidence. |
+| `SocioProphet/sociosphere` | Registers topology and cross-repo governance edges. |
+| `SourceOS-Linux/sourceos-shell` | Desktop/shell consumer of summarized node posture only. |
+| `SociOS-Linux/socios` | Optional automation/personalization commons only after explicit enrollment. |
+
+## Non-goals
+
+This tranche does not:
+
+- implement boot execution;
+- mutate host state;
+- make Socios mandatory;
+- make desktop or shell surfaces the owner of node substrate contracts;
+- replace BootReleaseSet;
+- add a production node renderer;
+- add CI or Makefile wiring yet.
diff --git a/examples/hostcapabilityplacement.json b/examples/hostcapabilityplacement.json
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+++ b/examples/hostcapabilityplacement.json
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+{
+  "id": "urn:srcos:host-capability-placement:sourceos-supervisor",
+  "type": "HostCapabilityPlacement",
+  "specVersion": "2.2.0",
+  "name": "SourceOS host supervisor",
+  "placementClass": "image-baked-host-capability",
+  "authority": "sourceos-base",
+  "primaryPlane": "node-substrate",
+  "mandatoryForBaseNode": true,
+  "requiresEnrollment": false,
+  "lifecycleCoupling": "host-release",
+  "pathHints": [
+    "/usr/libexec/sourceos/supervisor",
+    "/usr/lib/systemd/system/sourceos-supervisor.service"
+  ],
+  "evidenceRefs": [
+    "urn:srcos:release-receipt:sourceos-supervisor-bootstrap"
+  ],
+  "policyRef": "urn:srcos:policy:immutable-node-host-supervisor",
+  "notes": "Base SourceOS node substrate capability. This is not a desktop-owned feature and not a Socios enrollment dependency."
+}
diff --git a/examples/immutablenodeprofile.json b/examples/immutablenodeprofile.json
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+++ b/examples/immutablenodeprofile.json
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+{
+  "id": "urn:srcos:immutable-node-profile:m2-asahi-agent-node-dev",
+  "type": "ImmutableNodeProfile",
+  "specVersion": "2.2.0",
+  "name": "M2 Asahi SourceOS agent node dev profile",
+  "channel": "m2-asahi-dev",
+  "primaryPlane": "agent-runtime-substrate",
+  "substrate": {
+    "strategy": "bootc-first",
+    "hostMutationPosture": "staged-updates-only",
+    "sociosRequired": false
+  },
+  "bootReleaseSetRef": "urn:srcos:boot-release-set:m2-asahi-dev",
+  "releaseSetRef": "urn:srcos:release-set:m2-asahi-dev",
+  "agentMachineProfileRef": "urn:srcos:agent-machine-profile:m2-asahi-dev",
+  "agentPlaneRuntimeRef": "urn:srcos:agentplane-runtime:m2-asahi-dev",
+  "workstationProfileRef": "urn:srcos:workstation-profile:workstation-v0",
+  "desktopConsumerRefs": [
+    "urn:srcos:desktop-consumer:sourceos-settings-node-status",
+    "urn:srcos:desktop-consumer:sourceos-shell-node-posture"
+  ],
+  "hostCapabilityPlacementRefs": [
+    "urn:srcos:host-capability-placement:sourceos-supervisor"
+  ],
+  "nodeStateSchemaRefs": [
+    "urn:srcos:node-state-schema:sourceos-evidence-root"
+  ],
+  "optionalSociosCapabilityPackRefs": [
+    "urn:socios:capability-pack:automation-commons-opt-in"
+  ],
+  "validation": {
+    "planCommand": "sourceosctl immutable-node plan --profile m2-asahi-agent-node-dev --dry-run",
+    "validateCommand": "sourceosctl immutable-node validate --profile m2-asahi-agent-node-dev",
+    "inspectCommand": "sourceosctl immutable-node inspect --profile m2-asahi-agent-node-dev",
+    "evidenceCommand": "agent-machine release evidence inspect --profile m2-asahi-agent-node-dev"
+  },
+  "policyRefs": [
+    "urn:srcos:policy:immutable-node-base",
+    "urn:srcos:policy:socios-opt-in-required"
+  ],
+  "evidenceRefs": [
+    "urn:srcos:release-receipt:m2-asahi-dev"
+  ],
+  "notes": "Node/agent-runtime substrate profile. Workstation and shell references are consumers only. Optional Socios pack reference does not imply enrollment."
+}
diff --git a/examples/nodestateschema.json b/examples/nodestateschema.json
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+++ b/examples/nodestateschema.json
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+{
+  "id": "urn:srcos:node-state-schema:sourceos-evidence-root",
+  "type": "NodeStateSchema",
+  "specVersion": "2.2.0",
+  "name": "SourceOS evidence root",
+  "rootPath": "/var/lib/sourceos/evidence",
+  "stateClass": "append-only-evidence",
+  "primaryPlane": "execution-evidence",
+  "schemaRef": "urn:srcos:release-receipt:sourceos-evidence",
+  "rollbackCompatibility": "required-n-and-n-minus-1",
+  "mutability": "append-only",
+  "owner": "agent-machine",
+  "evidenceRequired": true,
+  "desktopVisible": true,
+  "notes": "Durable evidence root survives host rollback. Desktop surfaces may display summarized posture, but Agent Machine and evidence consumers own the state contract."
+}
diff --git a/schemas/HostCapabilityPlacement.json b/schemas/HostCapabilityPlacement.json
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+++ b/schemas/HostCapabilityPlacement.json
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+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://schemas.srcos.ai/v2/HostCapabilityPlacement.json",
+  "title": "HostCapabilityPlacement",
+  "description": "A SourceOS immutable-node placement declaration for one node substrate capability, agent runtime workload, host extension, or durable state root.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["id", "type", "specVersion", "name", "placementClass", "authority"],
+  "properties": {
+    "id": { "type": "string", "pattern": "^urn:srcos:host-capability-placement:", "description": "Stable URN identifier. Pattern: urn:srcos:host-capability-placement:<local-id>." },
+    "type": { "const": "HostCapabilityPlacement", "description": "Discriminator constant — always HostCapabilityPlacement." },
+    "specVersion": { "type": "string", "description": "Spec version of this document, e.g. 2.2.0." },
+    "name": { "type": "string", "minLength": 1, "description": "Human-readable capability name." },
+    "placementClass": {
+      "type": "string",
+      "enum": ["image-baked-host-capability", "sysext-host-capability", "confext-policy-config-capability", "quadlet-bound-service-workload", "quadlet-floating-service-workload", "var-state-object"],
+      "description": "Canonical immutable-node placement class."
+    },
+    "authority": {
+      "type": "string",
+      "enum": ["sourceos-base", "sourceos-boot", "agent-machine", "sourceos-devtools", "agentplane", "prophet-platform", "sourceos-desktop-consumer", "socios-optional-pack"],
+      "description": "Repo or plane class that owns the implementation boundary for this capability."
+    },
+    "primaryPlane": {
+      "type": "string",
+      "enum": ["node-substrate", "agent-runtime-substrate", "boot-recovery", "operator-tooling", "execution-evidence", "platform-runtime", "desktop-consumer", "optional-commons"],
+      "description": "Primary architectural plane for this capability. Desktop should normally be consumer, not owner."
+    },
+    "mandatoryForBaseNode": { "type": "boolean", "default": false, "description": "Whether the capability is required for a base SourceOS immutable node without Socios enrollment." },
+    "requiresEnrollment": { "type": "boolean", "default": false, "description": "Whether activation requires opt-in enrollment, Proof-of-Life, or signed intent." },
+    "lifecycleCoupling": { "type": "string", "enum": ["host-release", "extension-release", "service-release", "state-schema", "operator-local"], "description": "Primary lifecycle to which this capability is coupled." },
+    "pathHints": { "type": "array", "items": { "type": "string" }, "description": "Expected implementation paths such as /usr/libexec/sourceos, /usr/share/containers/systemd, /var/lib/sourceos, or /var/lib/socios." },
+    "evidenceRefs": { "type": "array", "items": { "type": "string" }, "description": "Optional references to evidence records emitted by the capability." },
+    "policyRef": { "type": ["string", "null"], "description": "Optional policy identifier or URN governing activation or mutation." },
+    "notes": { "type": ["string", "null"], "description": "Human-readable review notes." }
+  }
+}
diff --git a/schemas/ImmutableNodeProfile.json b/schemas/ImmutableNodeProfile.json
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index 0000000..84f3dba
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+++ b/schemas/ImmutableNodeProfile.json
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+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://schemas.srcos.ai/v2/ImmutableNodeProfile.json",
+  "title": "ImmutableNodeProfile",
+  "description": "A SourceOS immutable-node profile for node and agent-runtime substrate contracts. Desktop and workstation surfaces may consume this profile, but they do not own the node substrate.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["id", "type", "specVersion", "name", "channel", "substrate"],
+  "properties": {
+    "id": { "type": "string", "pattern": "^urn:srcos:immutable-node-profile:", "description": "Stable URN identifier. Pattern: urn:srcos:immutable-node-profile:<local-id>." },
+    "type": { "const": "ImmutableNodeProfile", "description": "Discriminator constant — always ImmutableNodeProfile." },
+    "specVersion": { "type": "string", "description": "Spec version of this document, e.g. 2.2.0." },
+    "name": { "type": "string", "minLength": 1, "description": "Human-readable immutable node profile name." },
+    "channel": { "type": "string", "minLength": 1, "description": "Realization channel such as linux-dev, linux-stable, m2-asahi-dev, or fog-node." },
+    "primaryPlane": { "type": "string", "enum": ["node-substrate", "agent-runtime-substrate"], "description": "Primary plane for this profile. ImmutableNodeProfile is not a desktop-owned contract." },
+    "substrate": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["strategy", "hostMutationPosture", "sociosRequired"],
+      "properties": {
+        "strategy": { "type": "string", "enum": ["bootc-first", "ostree-compatible", "rpm-ostree", "coreos-assembler", "nixos-adapter", "other"], "description": "Primary immutable-host realization strategy." },
+        "hostMutationPosture": { "type": "string", "enum": ["immutable-runtime", "staged-updates-only", "lab-live-mutation-allowed", "unknown"], "description": "Allowed host mutation posture for this profile." },
+        "sociosRequired": { "const": false, "description": "Base SourceOS immutable nodes must not require Socios enrollment. Optional Socios packs are modeled separately." }
+      }
+    },
+    "bootReleaseSetRef": { "type": ["string", "null"], "description": "Optional BootReleaseSet or boot/recovery handoff reference." },
+    "releaseSetRef": { "type": ["string", "null"], "description": "Optional ReleaseSet assignment reference." },
+    "agentMachineProfileRef": { "type": ["string", "null"], "description": "Optional Agent Machine or AgentPod profile reference for local runtime realization." },
+    "agentPlaneRuntimeRef": { "type": ["string", "null"], "description": "Optional AgentPlane runtime/evidence contract reference that consumes node activation or runtime receipts." },
+    "workstationProfileRef": { "type": ["string", "null"], "description": "Optional WorkstationProfile reference for desktop/workstation consumption. This must not make the desktop the owner of the node substrate." },
+    "desktopConsumerRefs": { "type": "array", "items": { "type": "string" }, "description": "Optional desktop, shell, settings, or workstation surfaces that may display summarized node posture." },
+    "hostCapabilityPlacementRefs": { "type": "array", "items": { "type": "string", "pattern": "^urn:srcos:host-capability-placement:" }, "description": "References to HostCapabilityPlacement objects used by this profile." },
+    "nodeStateSchemaRefs": { "type": "array", "items": { "type": "string", "pattern": "^urn:srcos:node-state-schema:" }, "description": "References to NodeStateSchema objects used by this profile." },
+    "optionalSociosCapabilityPackRefs": { "type": "array", "items": { "type": "string" }, "description": "Optional Socios capability pack references. Presence does not imply base node dependency or enrollment." },
+    "validation": {
+      "type": "object",
+      "additionalProperties": false,
+      "properties": {
+        "planCommand": { "type": ["string", "null"] },
+        "validateCommand": { "type": ["string", "null"] },
+        "inspectCommand": { "type": ["string", "null"] },
+        "evidenceCommand": { "type": ["string", "null"] }
+      },
+      "description": "Operator-facing dry-run, validation, inspection, and evidence entrypoints. These are usually implemented by sourceosctl and Agent Machine, not desktop code."
+    },
+    "policyRefs": { "type": "array", "items": { "type": "string" }, "description": "Policy references that govern activation, mutation, enrollment, or rollback." },
+    "evidenceRefs": { "type": "array", "items": { "type": "string" }, "description": "Evidence or receipt references expected from this node profile." },
+    "notes": { "type": ["string", "null"], "description": "Human-readable review notes." }
+  }
+}
diff --git a/schemas/NodeStateSchema.json b/schemas/NodeStateSchema.json
new file mode 100644
index 0000000..2315a57
--- /dev/null
+++ b/schemas/NodeStateSchema.json
@@ -0,0 +1,25 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://schemas.srcos.ai/v2/NodeStateSchema.json",
+  "title": "NodeStateSchema",
+  "description": "A SourceOS immutable-node durable state schema declaration for rollback-aware node substrate and agent runtime state roots.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["id", "type", "specVersion", "name", "rootPath", "stateClass", "rollbackCompatibility"],
+  "properties": {
+    "id": { "type": "string", "pattern": "^urn:srcos:node-state-schema:", "description": "Stable URN identifier. Pattern: urn:srcos:node-state-schema:<local-id>." },
+    "type": { "const": "NodeStateSchema", "description": "Discriminator constant — always NodeStateSchema." },
+    "specVersion": { "type": "string", "description": "Spec version of this document, e.g. 2.2.0." },
+    "name": { "type": "string", "minLength": 1, "description": "Human-readable state root name." },
+    "rootPath": { "type": "string", "pattern": "^/var/(lib|cache)/", "description": "Durable or rebuildable state root. Authoritative mutable truth must not live under /usr or /etc." },
+    "stateClass": { "type": "string", "enum": ["durable-truth", "append-only-evidence", "replay-checkpoint", "model-cache", "rebuildable-cache", "operator-local"], "description": "Semantic class of the state root." },
+    "primaryPlane": { "type": "string", "enum": ["node-substrate", "agent-runtime-substrate", "execution-evidence", "platform-runtime", "desktop-consumer", "optional-commons"], "description": "Primary architectural plane for the state root. Desktop surfaces should usually consume state summaries, not own durable node state." },
+    "schemaRef": { "type": ["string", "null"], "description": "Optional schema, contract, or URN reference for records stored in this root." },
+    "rollbackCompatibility": { "type": "string", "enum": ["required-n-and-n-minus-1", "best-effort", "not-required-rebuildable", "operator-managed"], "description": "Rollback compatibility expectation for readers and writers of this state root." },
+    "mutability": { "type": "string", "enum": ["append-only", "controlled-write", "rebuildable", "ephemeral-cache"], "description": "Expected write posture for this root." },
+    "owner": { "type": ["string", "null"], "description": "Owning plane or repository class for this state root." },
+    "evidenceRequired": { "type": "boolean", "default": false, "description": "Whether writes to this state root require evidence emission." },
+    "desktopVisible": { "type": "boolean", "default": false, "description": "Whether desktop/workstation surfaces may display this state root's summarized posture." },
+    "notes": { "type": ["string", "null"], "description": "Human-readable review notes." }
+  }
+}
diff --git a/tools/validate_immutable_node_examples.py b/tools/validate_immutable_node_examples.py
new file mode 100644
index 0000000..ea37d87
--- /dev/null
+++ b/tools/validate_immutable_node_examples.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""Validate immutable-node contract examples against their schemas."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import jsonschema
+
+ROOT = Path(__file__).resolve().parents[1]
+
+PAIRS = [
+    ("schemas/HostCapabilityPlacement.json", "examples/hostcapabilityplacement.json"),
+    ("schemas/NodeStateSchema.json", "examples/nodestateschema.json"),
+    ("schemas/ImmutableNodeProfile.json", "examples/immutablenodeprofile.json"),
+]
+
+
+def load_json(path: str) -> object:
+    with (ROOT / path).open("r", encoding="utf-8") as fh:
+        return json.load(fh)
+
+
+def main() -> None:
+    for schema_path, example_path in PAIRS:
+        schema = load_json(schema_path)
+        example = load_json(example_path)
+        jsonschema.Draft202012Validator.check_schema(schema)
+        jsonschema.validate(instance=example, schema=schema)
+        print(f"OK: {example_path} validates against {schema_path}")
+
+
+if __name__ == "__main__":
+    main()