diff --git a/TASKS.md b/TASKS.md
index 28a9681..1cb82c4 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -144,5 +144,6 @@ Progress:
 - done:
   - Phase 0 / task `0.1`: создан `crank-core::ext` module skeleton
   - Phase 0 / task `0.2`: `MachineCredentialVerifier` и связанные типы вынесены из `apps/mcp-server` в public seam `crank_core::ext::auth`
+  - Phase 0 / task `0.5`: введены `PolicyEngine`, `SessionActor`, `PolicyAction`, `PolicyScope`, `PolicyDecision` и default `OwnerOnlyPolicyEngine` в public seam `crank_core::ext::access`
   - Phase 0 / task `0.7`: введены `CapabilityProfile` и `CommunityCapabilityProfile`, а `admin-api` capability payload теперь собирается через public seam вместо локального literal
   - backward-compatible alias `CommunityMachineCredentialVerifier` сохранен, поведение Community не изменено
diff --git a/crates/crank-core/src/ext/access.rs b/crates/crank-core/src/ext/access.rs
index 8b13789..259093f 100644
--- a/crates/crank-core/src/ext/access.rs
+++ b/crates/crank-core/src/ext/access.rs
@@ -1 +1,142 @@
+use crate::{MembershipRole, UserId, WorkspaceId};
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct SessionActor {
+    pub user_id: UserId,
+    pub workspace_id: WorkspaceId,
+    pub role: MembershipRole,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[allow(clippy::enum_variant_names)]
+pub enum PolicyAction {
+    ReadWorkspace,
+    WriteWorkspace,
+    ReadWorkspaceAccess,
+    WriteWorkspaceAccess,
+    ReadOperation,
+    WriteOperation,
+    ReadAgent,
+    WriteAgent,
+    ReadPlatformApiKey,
+    WritePlatformApiKey,
+    ReadSecret,
+    WriteSecret,
+    ReadAuthProfile,
+    WriteAuthProfile,
+    ReadObservability,
+    ReadCapability,
+}
+
+impl PolicyAction {
+    pub fn is_read(self) -> bool {
+        matches!(
+            self,
+            Self::ReadWorkspace
+                | Self::ReadWorkspaceAccess
+                | Self::ReadOperation
+                | Self::ReadAgent
+                | Self::ReadPlatformApiKey
+                | Self::ReadSecret
+                | Self::ReadAuthProfile
+                | Self::ReadObservability
+                | Self::ReadCapability
+        )
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum PolicyScope {
+    Workspace(WorkspaceId),
+    Global,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum PolicyDecision {
+    Allow,
+    Deny { reason: &'static str },
+}
+
+pub trait PolicyEngine: Send + Sync {
+    fn check(
+        &self,
+        actor: &SessionActor,
+        action: PolicyAction,
+        scope: PolicyScope,
+    ) -> PolicyDecision;
+}
+
+#[derive(Clone, Copy, Debug, Default)]
+pub struct OwnerOnlyPolicyEngine;
+
+impl PolicyEngine for OwnerOnlyPolicyEngine {
+    fn check(
+        &self,
+        actor: &SessionActor,
+        action: PolicyAction,
+        _scope: PolicyScope,
+    ) -> PolicyDecision {
+        if matches!(actor.role, MembershipRole::Owner) || action.is_read() {
+            PolicyDecision::Allow
+        } else {
+            PolicyDecision::Deny {
+                reason: "write actions require owner role in community",
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{
+        OwnerOnlyPolicyEngine, PolicyAction, PolicyDecision, PolicyEngine, PolicyScope,
+        SessionActor,
+    };
+    use crate::{MembershipRole, UserId, WorkspaceId};
+
+    fn actor(role: MembershipRole) -> SessionActor {
+        SessionActor {
+            user_id: UserId::new("user_01"),
+            workspace_id: WorkspaceId::new("ws_01"),
+            role,
+        }
+    }
+
+    #[test]
+    fn owner_is_allowed_for_write_actions() {
+        let decision = OwnerOnlyPolicyEngine.check(
+            &actor(MembershipRole::Owner),
+            PolicyAction::WriteWorkspace,
+            PolicyScope::Workspace(WorkspaceId::new("ws_01")),
+        );
+
+        assert_eq!(decision, PolicyDecision::Allow);
+    }
+
+    #[test]
+    fn non_owner_is_allowed_for_read_actions() {
+        let decision = OwnerOnlyPolicyEngine.check(
+            &actor(MembershipRole::Viewer),
+            PolicyAction::ReadWorkspace,
+            PolicyScope::Workspace(WorkspaceId::new("ws_01")),
+        );
+
+        assert_eq!(decision, PolicyDecision::Allow);
+    }
+
+    #[test]
+    fn non_owner_is_denied_for_write_actions() {
+        let decision = OwnerOnlyPolicyEngine.check(
+            &actor(MembershipRole::Admin),
+            PolicyAction::WriteWorkspace,
+            PolicyScope::Workspace(WorkspaceId::new("ws_01")),
+        );
+
+        assert_eq!(
+            decision,
+            PolicyDecision::Deny {
+                reason: "write actions require owner role in community",
+            }
+        );
+    }
+}
diff --git a/crates/crank-core/src/lib.rs b/crates/crank-core/src/lib.rs
index 39f27fd..a38af30 100644
--- a/crates/crank-core/src/lib.rs
+++ b/crates/crank-core/src/lib.rs
@@ -32,6 +32,9 @@ pub use cache::{
 pub use edition::{
     EditionCapabilities, EditionLimits, MachineAccessMode, OperationSecurityLevel, ProductEdition,
 };
+pub use ext::access::{
+    OwnerOnlyPolicyEngine, PolicyAction, PolicyDecision, PolicyEngine, PolicyScope, SessionActor,
+};
 pub use ext::auth::{
     MachineCredentialVerifier, MachineCredentialVerifierError, SharedMachineCredentialVerifier,
     VerifiedMachineCredential,