diff --git a/Makefile b/Makefile
index 1c91fa6..f764cbf 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: validate-no-merge-duplication validate validate-json validate-yaml validate-quadlet validate-render validate-evidence validate-governance validate-policy-fabric validate-agent-registry validate-superconscious-runtime-plan validate-activation validate-supply-chain validate-release-bundle validate-sourceos-projections validate-package validate-cli validate-formula validate-runtime-install-receipts doctor probe validate-artifact-digest-honesty validate-consent-before-staging
+.PHONY: validate-no-merge-duplication validate validate-json validate-yaml validate-quadlet validate-render validate-evidence validate-governance validate-policy-fabric validate-agent-registry validate-superconscious-runtime-plan validate-activation validate-attestation validate-supply-chain validate-release-bundle validate-sourceos-projections validate-package validate-cli validate-formula validate-runtime-install-receipts doctor probe validate-artifact-digest-honesty validate-consent-before-staging
 
 PYTHON ?= python3
 RUBY ?= ruby
@@ -22,7 +22,7 @@ DECIDED_AT := 2026-05-04T12:51:00Z
 PYCLI := PYTHONPATH=src $(PYTHON) -m agent_machine.cli
 PYMOD := PYTHONPATH=src $(PYTHON) -m
 
-validate: validate-no-merge-duplication validate-json validate-yaml validate-quadlet validate-render validate-evidence validate-governance validate-policy-fabric validate-agent-registry validate-superconscious-runtime-plan validate-activation validate-supply-chain validate-release-bundle validate-sourceos-projections validate-package validate-cli validate-formula validate-runtime-install-receipts validate-artifact-digest-honesty validate-consent-before-staging
+validate: validate-no-merge-duplication validate-json validate-yaml validate-quadlet validate-render validate-evidence validate-governance validate-policy-fabric validate-agent-registry validate-superconscious-runtime-plan validate-activation validate-attestation validate-supply-chain validate-release-bundle validate-sourceos-projections validate-package validate-cli validate-formula validate-runtime-install-receipts validate-artifact-digest-honesty validate-consent-before-staging
 
 validate-no-merge-duplication:
 	$(PYTHON) scripts/validate-no-merge-duplication.py
@@ -88,6 +88,9 @@ validate-activation:
 	$(PYCLI) activate evaluate $(LOCAL_AGENTPOD) --policy-dir $(POLICY_DIR) --expected-status allowed --grant-dir $(GRANT_DIR) --grant-id urn:srcos:agent-machine:agent-registry-grant:active-loopback-activation --session-ref urn:srcos:session:local-bootstrap --deployment-receipt-id $(DEPLOYMENT_RECEIPT_ID) --agent-machine-id urn:srcos:agent-machine:m2-asahi-local --provider-id urn:srcos:agent-machine:inference-provider:asahi-llama-cpp --storage-receipt-dir $(RECEIPT_DIR) --decided-at $(DECIDED_AT) --decision-id urn:srcos:agent-machine:activation-decision:local-llama-cpp-allowed --pretty >/tmp/agent-machine-pycli-resolved-policy-grant-activation-allowed.json
 	$(BOOTSTRAP_CLI) activate evaluate $(LOCAL_AGENTPOD) $(READY_POLICY) $(READY_GRANT) --deployment-receipt-id $(DEPLOYMENT_RECEIPT_ID) --storage-receipt-dir $(RECEIPT_DIR) --decided-at $(DECIDED_AT) --decision-id urn:srcos:agent-machine:activation-decision:local-llama-cpp-allowed --pretty >/tmp/agent-machine-bootstrap-evaluate-activation-allowed.json
 
+validate-attestation:
+	$(PYTHON) scripts/validate-attestation.py
+
 validate-supply-chain:
 	$(PYTHON) scripts/validate-supply-chain.py
 	$(PYMOD) agent_machine.supply_chain $(PINNED_AGENTPOD) --strict
diff --git a/contracts/attestation-decision.schema.json b/contracts/attestation-decision.schema.json
new file mode 100644
index 0000000..d793a18
--- /dev/null
+++ b/contracts/attestation-decision.schema.json
@@ -0,0 +1,36 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "urn:srcos:agent-machine:schema:attestation-decision:v0.1.0",
+  "title": "AttestationDecision",
+  "description": "Host attestation decision for whether an Agent Machine host may be activated. activation_permitted is true only if ALL blocking checks pass; a single blocking failure denies activation. Advisory checks (TELEMETRY_BOUNDARY/SEAM-013, DISPLAY_UUID_STABILITY/SEAM-008) warn only and never block. Field names are snake_case per Tranche Work Order T2-1.",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["specVersion","kind","attestation_id","host_id","attested_at","attested_by","activation_permitted","overall_status","check_results"],
+  "properties": {
+    "specVersion": { "type": "string", "const": "0.1.0" },
+    "kind": { "type": "string", "const": "AttestationDecision" },
+    "attestation_id": { "type": "string", "pattern": "^urn:srcos:agent-machine:attestation-decision:[a-z0-9][a-z0-9-]*$" },
+    "host_id": { "type": "string", "minLength": 1 },
+    "attested_at": { "type": "string", "format": "date-time" },
+    "attested_by": { "type": "string", "minLength": 1 },
+    "activation_permitted": { "type": "boolean" },
+    "overall_status": { "type": "string", "enum": ["pass","fail","partial"] },
+    "check_results": {
+      "type": "array",
+      "minItems": 1,
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["check_id","check_name","status","expected","actual","blocking"],
+        "properties": {
+          "check_id": { "type": "string", "minLength": 1 },
+          "check_name": { "type": "string" },
+          "status": { "type": "string", "enum": ["pass","fail","warn","skip"] },
+          "expected": { "type": "string" },
+          "actual": { "type": "string" },
+          "blocking": { "type": "boolean" }
+        }
+      }
+    }
+  }
+}
diff --git a/docs/architecture/attestation-model.md b/docs/architecture/attestation-model.md
new file mode 100644
index 0000000..0fed6b2
--- /dev/null
+++ b/docs/architecture/attestation-model.md
@@ -0,0 +1,46 @@
+# Attestation Model (v0.1)
+
+## Attestation vs activation
+**Attestation** measures host trust (SIP, NVRAM, MDM, SEP, security-DB schema,
+DNS, TLS, EFI) and emits an `AttestationDecision`. **Activation** (existing
+`ActivationDecision`) decides whether an AgentPod may run. Attestation is a
+*prerequisite input* to activation: `activation_permitted: false` from
+attestation blocks activation regardless of policy/grant state.
+
+## Check taxonomy
+- **Blocking** (a single failure denies activation): `SIP_STATUS`,
+  `NVRAM_INTEGRITY`, `MDM_PROFILE_AUDIT`, `SEP_PARTICIPATION`,
+  `SECURITY_DB_SCHEMA`, `DNS_INTEGRITY`, `TLS_CIPHER_AUDIT`, `EFI_SIGNATURE`.
+- **Advisory** (warn only): `TELEMETRY_BOUNDARY` (SEAM-013),
+  `DISPLAY_UUID_STABILITY` (SEAM-008).
+
+`activation_permitted` is true **iff every blocking check passes** — enforced by
+`scripts/validate-attestation.py`.
+
+## Failure-mode basis (SEAM references)
+Each check maps to an observed diagnostic failure mode:
+- `SIP_STATUS` — SIP disabled via NVRAM (csr-active-config=0x67) — SEAM-001.
+- `NVRAM_INTEGRITY` — world-writable nvram.plist — SEAM-001.
+- `MDM_PROFILE_AUDIT` — unauthorized MDM enrollment (IBM MaaS360) — SEAM-002.
+- `SEP_PARTICIPATION` — SEP non-participation in keybag (ANOMALY-007) — SEAM-003.
+- `SECURITY_DB_SCHEMA` — iCloud Keychain schema mismatch (v24.6 vs v25+;
+  missing ZSEQUENCENUMBER in ZPEER; broken escrow chain).
+- `DNS_INTEGRITY` — resolution returning 102.165.31.x (adversary IPs) — SEAM-004.
+- `TLS_CIPHER_AUDIT` — cipher downgrade (RC4_128_MD5) — SEAM-005.
+- `EFI_SIGNATURE` — unsigned/tampered EFI — SEAM-001.
+
+## Telemetry boundary (SEAM-013)
+`TELEMETRY_BOUNDARY` is **advisory, not blocking**: Claude Desktop
+`sessionSampleRate:100` means sensitive output must not route through a
+100%-sampled surface. Recorded as a warn signal in the decision, not a hard
+gate.
+
+## Out-of-band ledger
+The `attest` runtime CLI (T2-3, follow-up) must append each decision to
+`$LEDGER_PATH` as NDJSON and never silently drop; `$LEDGER_PATH` must never be
+local-only for a ledger-writing artifact.
+
+## References
+`AttestationDecision` (T2-1, `contracts/attestation-decision.schema.json`);
+`ActivationDecision` (existing). Runtime `attest` subcommand: T2-3 (deferred to a
+macOS attestation environment — the schema/contract here is what T4-4 depends on).
diff --git a/examples/attestation-decision.failed-mdm.json b/examples/attestation-decision.failed-mdm.json
new file mode 100644
index 0000000..3f84ea3
--- /dev/null
+++ b/examples/attestation-decision.failed-mdm.json
@@ -0,0 +1,92 @@
+{
+  "specVersion": "0.1.0",
+  "kind": "AttestationDecision",
+  "attestation_id": "urn:srcos:agent-machine:attestation-decision:failed-mdm",
+  "host_id": "host-alpha-001",
+  "attested_at": "2026-07-31T04:00:00Z",
+  "attested_by": "urn:srcos:agent-machine:attest",
+  "activation_permitted": false,
+  "overall_status": "fail",
+  "check_results": [
+    {
+      "check_id": "SIP_STATUS",
+      "check_name": "System Integrity Protection",
+      "status": "pass",
+      "expected": "csr-active-config=0x00 (enabled)",
+      "actual": "0x00 (enabled)",
+      "blocking": true
+    },
+    {
+      "check_id": "NVRAM_INTEGRITY",
+      "check_name": "NVRAM plist permissions",
+      "status": "pass",
+      "expected": "0644 root-owned",
+      "actual": "0644 root-owned",
+      "blocking": true
+    },
+    {
+      "check_id": "MDM_PROFILE_AUDIT",
+      "check_name": "MDM configuration profile audit",
+      "status": "fail",
+      "expected": "no unrecognized profiles",
+      "actual": "IBM MaaS360 (unauthorized)",
+      "blocking": true
+    },
+    {
+      "check_id": "SEP_PARTICIPATION",
+      "check_name": "Secure Enclave participation",
+      "status": "pass",
+      "expected": "SEP participates in keybag",
+      "actual": "SEP participates in keybag",
+      "blocking": true
+    },
+    {
+      "check_id": "SECURITY_DB_SCHEMA",
+      "check_name": "iCloud Keychain schema",
+      "status": "pass",
+      "expected": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "actual": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "blocking": true
+    },
+    {
+      "check_id": "DNS_INTEGRITY",
+      "check_name": "DNS resolution integrity",
+      "status": "pass",
+      "expected": "platform endpoints resolve normally",
+      "actual": "platform endpoints resolve normally",
+      "blocking": true
+    },
+    {
+      "check_id": "TLS_CIPHER_AUDIT",
+      "check_name": "TLS cipher suite audit",
+      "status": "pass",
+      "expected": "TLS1.2+; no RC4/MD5/SHA1",
+      "actual": "TLS1.2+; no RC4/MD5/SHA1",
+      "blocking": true
+    },
+    {
+      "check_id": "EFI_SIGNATURE",
+      "check_name": "EFI firmware signature",
+      "status": "pass",
+      "expected": "signed vendor firmware",
+      "actual": "signed vendor firmware",
+      "blocking": true
+    },
+    {
+      "check_id": "TELEMETRY_BOUNDARY",
+      "check_name": "Claude Desktop telemetry boundary (SEAM-013)",
+      "status": "warn",
+      "expected": "sensitive output not routed through 100%-sampled surface",
+      "actual": "sessionSampleRate:100",
+      "blocking": false
+    },
+    {
+      "check_id": "DISPLAY_UUID_STABILITY",
+      "check_name": "Display UUID stability (SEAM-008)",
+      "status": "warn",
+      "expected": "stable displayUUID",
+      "actual": "stable displayUUID",
+      "blocking": false
+    }
+  ]
+}
diff --git a/examples/attestation-decision.failed-sip.json b/examples/attestation-decision.failed-sip.json
new file mode 100644
index 0000000..e7cb0b1
--- /dev/null
+++ b/examples/attestation-decision.failed-sip.json
@@ -0,0 +1,92 @@
+{
+  "specVersion": "0.1.0",
+  "kind": "AttestationDecision",
+  "attestation_id": "urn:srcos:agent-machine:attestation-decision:failed-sip",
+  "host_id": "host-alpha-001",
+  "attested_at": "2026-07-31T04:00:00Z",
+  "attested_by": "urn:srcos:agent-machine:attest",
+  "activation_permitted": false,
+  "overall_status": "fail",
+  "check_results": [
+    {
+      "check_id": "SIP_STATUS",
+      "check_name": "System Integrity Protection",
+      "status": "fail",
+      "expected": "csr-active-config=0x00 (enabled)",
+      "actual": "0x67 (SIP disabled via NVRAM)",
+      "blocking": true
+    },
+    {
+      "check_id": "NVRAM_INTEGRITY",
+      "check_name": "NVRAM plist permissions",
+      "status": "pass",
+      "expected": "0644 root-owned",
+      "actual": "0644 root-owned",
+      "blocking": true
+    },
+    {
+      "check_id": "MDM_PROFILE_AUDIT",
+      "check_name": "MDM configuration profile audit",
+      "status": "pass",
+      "expected": "no unrecognized profiles",
+      "actual": "no unrecognized profiles",
+      "blocking": true
+    },
+    {
+      "check_id": "SEP_PARTICIPATION",
+      "check_name": "Secure Enclave participation",
+      "status": "pass",
+      "expected": "SEP participates in keybag",
+      "actual": "SEP participates in keybag",
+      "blocking": true
+    },
+    {
+      "check_id": "SECURITY_DB_SCHEMA",
+      "check_name": "iCloud Keychain schema",
+      "status": "pass",
+      "expected": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "actual": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "blocking": true
+    },
+    {
+      "check_id": "DNS_INTEGRITY",
+      "check_name": "DNS resolution integrity",
+      "status": "pass",
+      "expected": "platform endpoints resolve normally",
+      "actual": "platform endpoints resolve normally",
+      "blocking": true
+    },
+    {
+      "check_id": "TLS_CIPHER_AUDIT",
+      "check_name": "TLS cipher suite audit",
+      "status": "pass",
+      "expected": "TLS1.2+; no RC4/MD5/SHA1",
+      "actual": "TLS1.2+; no RC4/MD5/SHA1",
+      "blocking": true
+    },
+    {
+      "check_id": "EFI_SIGNATURE",
+      "check_name": "EFI firmware signature",
+      "status": "pass",
+      "expected": "signed vendor firmware",
+      "actual": "signed vendor firmware",
+      "blocking": true
+    },
+    {
+      "check_id": "TELEMETRY_BOUNDARY",
+      "check_name": "Claude Desktop telemetry boundary (SEAM-013)",
+      "status": "warn",
+      "expected": "sensitive output not routed through 100%-sampled surface",
+      "actual": "sessionSampleRate:100",
+      "blocking": false
+    },
+    {
+      "check_id": "DISPLAY_UUID_STABILITY",
+      "check_name": "Display UUID stability (SEAM-008)",
+      "status": "warn",
+      "expected": "stable displayUUID",
+      "actual": "stable displayUUID",
+      "blocking": false
+    }
+  ]
+}
diff --git a/examples/attestation-decision.passed.json b/examples/attestation-decision.passed.json
new file mode 100644
index 0000000..f469cb9
--- /dev/null
+++ b/examples/attestation-decision.passed.json
@@ -0,0 +1,92 @@
+{
+  "specVersion": "0.1.0",
+  "kind": "AttestationDecision",
+  "attestation_id": "urn:srcos:agent-machine:attestation-decision:passed",
+  "host_id": "host-alpha-001",
+  "attested_at": "2026-07-31T04:00:00Z",
+  "attested_by": "urn:srcos:agent-machine:attest",
+  "activation_permitted": true,
+  "overall_status": "pass",
+  "check_results": [
+    {
+      "check_id": "SIP_STATUS",
+      "check_name": "System Integrity Protection",
+      "status": "pass",
+      "expected": "csr-active-config=0x00 (enabled)",
+      "actual": "0x00 (enabled)",
+      "blocking": true
+    },
+    {
+      "check_id": "NVRAM_INTEGRITY",
+      "check_name": "NVRAM plist permissions",
+      "status": "pass",
+      "expected": "0644 root-owned",
+      "actual": "0644 root-owned",
+      "blocking": true
+    },
+    {
+      "check_id": "MDM_PROFILE_AUDIT",
+      "check_name": "MDM configuration profile audit",
+      "status": "pass",
+      "expected": "no unrecognized profiles",
+      "actual": "no unrecognized profiles",
+      "blocking": true
+    },
+    {
+      "check_id": "SEP_PARTICIPATION",
+      "check_name": "Secure Enclave participation",
+      "status": "pass",
+      "expected": "SEP participates in keybag",
+      "actual": "SEP participates in keybag",
+      "blocking": true
+    },
+    {
+      "check_id": "SECURITY_DB_SCHEMA",
+      "check_name": "iCloud Keychain schema",
+      "status": "pass",
+      "expected": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "actual": "v25+ with ZSEQUENCENUMBER in ZPEER",
+      "blocking": true
+    },
+    {
+      "check_id": "DNS_INTEGRITY",
+      "check_name": "DNS resolution integrity",
+      "status": "pass",
+      "expected": "platform endpoints resolve normally",
+      "actual": "platform endpoints resolve normally",
+      "blocking": true
+    },
+    {
+      "check_id": "TLS_CIPHER_AUDIT",
+      "check_name": "TLS cipher suite audit",
+      "status": "pass",
+      "expected": "TLS1.2+; no RC4/MD5/SHA1",
+      "actual": "TLS1.2+; no RC4/MD5/SHA1",
+      "blocking": true
+    },
+    {
+      "check_id": "EFI_SIGNATURE",
+      "check_name": "EFI firmware signature",
+      "status": "pass",
+      "expected": "signed vendor firmware",
+      "actual": "signed vendor firmware",
+      "blocking": true
+    },
+    {
+      "check_id": "TELEMETRY_BOUNDARY",
+      "check_name": "Claude Desktop telemetry boundary (SEAM-013)",
+      "status": "pass",
+      "expected": "sensitive output not routed through 100%-sampled surface",
+      "actual": "sensitive output not routed through sampled surface",
+      "blocking": false
+    },
+    {
+      "check_id": "DISPLAY_UUID_STABILITY",
+      "check_name": "Display UUID stability (SEAM-008)",
+      "status": "pass",
+      "expected": "stable displayUUID",
+      "actual": "stable displayUUID",
+      "blocking": false
+    }
+  ]
+}
diff --git a/scripts/validate-attestation.py b/scripts/validate-attestation.py
new file mode 100644
index 0000000..2ce2b9d
--- /dev/null
+++ b/scripts/validate-attestation.py
@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+"""Validate AttestationDecision contract + examples (T2-1, T2-4/5).
+
+Asserts the fail-closed activation rule by construction:
+  * every example validates against contracts/attestation-decision.schema.json;
+  * all eight required BLOCKING checks are present;
+  * activation_permitted is true IFF every blocking check passed — a single
+    blocking failure must deny activation;
+  * overall_status is consistent (pass = all checks pass; fail = a blocking
+    check failed; partial otherwise);
+  * the passed/failed-sip/failed-mdm fixtures carry the expected verdicts.
+"""
+
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+
+try:
+    import jsonschema
+except ImportError:  # pragma: no cover
+    print("ERR: jsonschema not installed", file=sys.stderr)
+    sys.exit(2)
+
+ROOT = Path(__file__).resolve().parents[1]
+SCHEMA = ROOT / "contracts" / "attestation-decision.schema.json"
+EXAMPLES = {
+    "passed": True,
+    "failed-sip": False,
+    "failed-mdm": False,
+}
+REQUIRED_BLOCKING = {
+    "SIP_STATUS", "NVRAM_INTEGRITY", "MDM_PROFILE_AUDIT", "SEP_PARTICIPATION",
+    "SECURITY_DB_SCHEMA", "DNS_INTEGRITY", "TLS_CIPHER_AUDIT", "EFI_SIGNATURE",
+}
+
+
+def load(p: Path) -> dict:
+    return json.loads(p.read_text(encoding="utf-8"))
+
+
+def fail(msg: str) -> None:
+    print(f"FAIL: {msg}", file=sys.stderr)
+    sys.exit(1)
+
+
+def main() -> int:
+    schema = load(SCHEMA)
+    jsonschema.Draft202012Validator.check_schema(schema)
+    validator = jsonschema.Draft202012Validator(schema)
+
+    for name, expect_permitted in EXAMPLES.items():
+        path = ROOT / "examples" / f"attestation-decision.{name}.json"
+        doc = load(path)
+        errs = sorted(validator.iter_errors(doc), key=lambda e: list(e.path))
+        if errs:
+            fail(f"{path.name} schema-invalid: {errs[0].message}")
+
+        checks = doc["check_results"]
+        blocking = [c for c in checks if c["blocking"]]
+        blocking_ids = {c["check_id"] for c in blocking}
+        missing = REQUIRED_BLOCKING - blocking_ids
+        if missing:
+            fail(f"{path.name}: missing required blocking checks: {sorted(missing)}")
+
+        all_blocking_pass = all(c["status"] == "pass" for c in blocking)
+        any_blocking_fail = any(c["status"] == "fail" for c in blocking)
+        all_pass = all(c["status"] == "pass" for c in checks)
+
+        # activation_permitted IFF all blocking checks pass.
+        if doc["activation_permitted"] != all_blocking_pass:
+            fail(
+                f"{path.name}: activation_permitted={doc['activation_permitted']} but "
+                f"all_blocking_pass={all_blocking_pass} (fail-closed rule violated)"
+            )
+        # overall_status consistency.
+        expected_overall = "fail" if any_blocking_fail else ("pass" if all_pass else "partial")
+        if doc["overall_status"] != expected_overall:
+            fail(f"{path.name}: overall_status={doc['overall_status']} but expected {expected_overall}")
+        # fixture-level expectation.
+        if doc["activation_permitted"] != expect_permitted:
+            fail(f"{path.name}: expected activation_permitted={expect_permitted}")
+
+    print(
+        f"OK: AttestationDecision schema + {len(EXAMPLES)} examples valid; "
+        f"fail-closed activation rule and 8 blocking checks enforced"
+    )
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/src/agent_machine/contracts.py b/src/agent_machine/contracts.py
index 5b12bd3..fd41498 100644
--- a/src/agent_machine/contracts.py
+++ b/src/agent_machine/contracts.py
@@ -47,6 +47,7 @@ def schema_by_kind(root: Path | None = None) -> dict[str, Path]:
     return {
         "A2AStateMachine": base / "a2a-state-machine.schema.json",
         "ActivationDecision": base / "activation-decision.schema.json",
+        "AttestationDecision": base / "attestation-decision.schema.json",
         "ArtifactConsentRecord": base / "artifact-consent-record.schema.json",
         "AgentMachine": base / "agent-machine.schema.json",
         "AgentPlaneRuntimeEvidence": base / "agentplane-runtime-evidence.schema.json",