diff --git a/CHANGELOG.md b/CHANGELOG.md
index f747adeae..cd59f53fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ All notable changes to OriginWeave are documented in this file. The format follo
 - Refreshed the product-gap queue to 126 open pull requests (54 ready, 72 draft) after #190, #188, #185, #192, #182, #184, #115, #181, #116, #117, #118, #183, #114, #127, #112, #109, #186, #110, #108, #111, #174, and #113 were merged into their immediate stacked prerequisites. PRs #147, #146, #145, #144, #143, #142, #141, #139, #136, #132, #129, and #128 moved to ready after exact-head checks and thread review; these are queue-consolidation results, not protected-main shipment.
 
 ### Added
+- Added a fail-closed Chrome-permission separation boundary so reviewed Manifest V3 compatibility permissions, including `downloads` and `nativeMessaging`, can never mint any OriginWeave Agent action authority.
 - Corrected the 2026-08-26 product-gap snapshot with current #229 presentation-identity evidence, stacked-only #205 integration evidence, current base/head pairs, the 126-PR queue count, explicit root-versus-child merge ordering, and the active GitHub counted-approval gate.
 - Refreshed the product and technical gap baseline onto the 2026-08-26 live inventory: 126 open pull requests (54 ready, 72 draft), protected-main promotion of #168/#194/#196/#216/#151, a verified maintenance-loop record (supersession closure of #153, conflict reconciliations on #37/#149/#152/#173/#175, issue #212 option-(b) authorization on #43, Strix vuln-0001 homoglyph remediation on #124), provider-rerun outcome evidence, an organization review-pipeline congestion record, and refreshed merge-order queue guidance. Documentation evidence contracts were aligned to the same snapshot so the baseline, its dated markers, and the pinned exact-head rows cannot silently diverge.
 
diff --git a/crates/originweave-core/Cargo.toml b/crates/originweave-core/Cargo.toml
index dcda2a6c4..48a17e08e 100644
--- a/crates/originweave-core/Cargo.toml
+++ b/crates/originweave-core/Cargo.toml
@@ -11,7 +11,7 @@ homepage.workspace = true
 publish = false
 
 [lib]
-path = "src/root.rs"
+path = "src/crate_root.rs"
 
 [dependencies]
 unicode-normalization = "=0.1.25"
diff --git a/crates/originweave-core/src/chrome_permission_authority.rs b/crates/originweave-core/src/chrome_permission_authority.rs
new file mode 100644
index 000000000..264c45f1f
--- /dev/null
+++ b/crates/originweave-core/src/chrome_permission_authority.rs
@@ -0,0 +1,73 @@
+//! Separation between Chrome extension compatibility permissions and Agent authority.
+
+use crate::ActionKind;
+use std::fmt;
+
+/// Why a Chrome extension permission cannot authorize an OriginWeave Agent action.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ChromePermissionAuthorityError {
+    /// The permission names a reviewed Chrome compatibility surface, not Agent authority.
+    CompatibilitySurfaceOnly,
+    /// The permission is not a reviewed Chrome surface and still grants no Agent capability.
+    UnrecognizedPermission,
+}
+
+impl fmt::Display for ChromePermissionAuthorityError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let message = match self {
+            Self::CompatibilitySurfaceOnly => {
+                "Chrome compatibility permission cannot authorize an OriginWeave Agent action"
+            }
+            Self::UnrecognizedPermission => {
+                "Chrome permission is not a reviewed compatibility surface and cannot authorize an OriginWeave Agent action"
+            }
+        };
+        formatter.write_str(message)
+    }
+}
+
+impl std::error::Error for ChromePermissionAuthorityError {}
+
+const REVIEWED_CHROME_COMPATIBILITY_PERMISSIONS: &[&str] = &[
+    "bookmarks",
+    "commands",
+    "declarativeNetRequest",
+    "declarativeNetRequestWithHostAccess",
+    "downloads",
+    "history",
+    "nativeMessaging",
+    "scripting",
+    "sidePanel",
+    "storage",
+    "tabs",
+    "windows",
+];
+
+/// Refuse to treat a Chrome extension permission as OriginWeave Agent authority.
+///
+/// A successful Chrome compatibility proof never becomes an OriginWeave Agent
+/// capability. Adapters must keep browser compatibility evidence and explicit
+/// OriginWeave grants separate and call this boundary before exposing a typed
+/// action to policy. The action is accepted only to make that separation
+/// explicit at the adapter boundary; no action kind can make this function
+/// return success.
+pub fn chrome_permission_authorizes_agent_action(
+    permission: &str,
+    _action: ActionKind,
+) -> Result<(), ChromePermissionAuthorityError> {
+    if !is_exact_chrome_permission_token(permission) {
+        return Err(ChromePermissionAuthorityError::UnrecognizedPermission);
+    }
+    if REVIEWED_CHROME_COMPATIBILITY_PERMISSIONS.contains(&permission) {
+        return Err(ChromePermissionAuthorityError::CompatibilitySurfaceOnly);
+    }
+    Err(ChromePermissionAuthorityError::UnrecognizedPermission)
+}
+
+fn is_exact_chrome_permission_token(permission: &str) -> bool {
+    let mut characters = permission.chars();
+    let Some(first) = characters.next() else {
+        return false;
+    };
+    first.is_ascii_lowercase() && characters.all(|character| character.is_ascii_alphabetic())
+}
diff --git a/crates/originweave-core/src/crate_root.rs b/crates/originweave-core/src/crate_root.rs
new file mode 100644
index 000000000..f2419c7de
--- /dev/null
+++ b/crates/originweave-core/src/crate_root.rs
@@ -0,0 +1,22 @@
+//! OriginWeave core contracts plus narrowly scoped adapter authority boundaries.
+//!
+//! The existing deterministic core remains implemented in `lib.rs`; this crate
+//! root re-exports that protected-main API and adds the independently reviewed
+//! Chrome-permission separation boundary without weakening existing authority.
+
+#![forbid(unsafe_code)]
+#![deny(missing_docs)]
+
+#[path = "lib.rs"]
+mod base;
+pub use base::*;
+
+mod chrome_permission_authority;
+pub use chrome_permission_authority::{
+    ChromePermissionAuthorityError, chrome_permission_authorizes_agent_action,
+};
+
+/// Stateless MCP routing validation that maps only explicit tools to typed actions.
+pub mod mcp;
+/// Deterministic fail-closed release benchmark acceptance aggregation.
+pub mod release_acceptance;
diff --git a/crates/originweave-core/src/root.rs b/crates/originweave-core/src/root.rs
deleted file mode 100644
index c47a136d4..000000000
--- a/crates/originweave-core/src/root.rs
+++ /dev/null
@@ -1,17 +0,0 @@
-//! Shared security and governance contracts for OriginWeave.
-//!
-//! The historical core contracts remain source-compatible while adapter-specific
-//! boundaries can live in focused modules without changing their authority model.
-
-#![forbid(unsafe_code)]
-#![deny(missing_docs)]
-
-#[path = "lib.rs"]
-mod contracts;
-
-pub use contracts::*;
-
-/// Stateless MCP routing validation that maps only explicit tools to typed actions.
-pub mod mcp;
-/// Deterministic fail-closed release benchmark acceptance aggregation.
-pub mod release_acceptance;
diff --git a/crates/originweave-core/tests/chrome_permission_authority.rs b/crates/originweave-core/tests/chrome_permission_authority.rs
new file mode 100644
index 000000000..c78bf7331
--- /dev/null
+++ b/crates/originweave-core/tests/chrome_permission_authority.rs
@@ -0,0 +1,61 @@
+use originweave_core::{
+    ActionKind, ChromePermissionAuthorityError, chrome_permission_authorizes_agent_action,
+};
+
+#[test]
+fn chrome_compatibility_permissions_never_mint_agent_authority() {
+    for permission in [
+        "downloads",
+        "bookmarks",
+        "history",
+        "storage",
+        "tabs",
+        "windows",
+        "scripting",
+        "commands",
+        "sidePanel",
+        "declarativeNetRequest",
+        "declarativeNetRequestWithHostAccess",
+        "nativeMessaging",
+    ] {
+        assert_eq!(
+            chrome_permission_authorizes_agent_action(permission, ActionKind::Download),
+            Err(ChromePermissionAuthorityError::CompatibilitySurfaceOnly)
+        );
+    }
+}
+
+#[test]
+fn malformed_or_unreviewed_chrome_permissions_remain_unrecognized() {
+    for permission in [
+        "",
+        "DOWNLOADS",
+        "downloads\nhttps://example.invalid",
+        "cookies",
+        "downloads ",
+    ] {
+        assert_eq!(
+            chrome_permission_authorizes_agent_action(permission, ActionKind::Download),
+            Err(ChromePermissionAuthorityError::UnrecognizedPermission)
+        );
+    }
+}
+
+#[test]
+fn chrome_permission_authority_errors_are_standard_credential_safe_errors() {
+    let cases = [
+        (
+            ChromePermissionAuthorityError::CompatibilitySurfaceOnly,
+            "Chrome compatibility permission cannot authorize an OriginWeave Agent action",
+        ),
+        (
+            ChromePermissionAuthorityError::UnrecognizedPermission,
+            "Chrome permission is not a reviewed compatibility surface and cannot authorize an OriginWeave Agent action",
+        ),
+    ];
+
+    for (error, expected_message) in cases {
+        assert_eq!(error.to_string(), expected_message);
+        assert!(std::error::Error::source(&error).is_none());
+    }
+}