diff --git a/src/collaboration/CollaborativeCwlEditor.fieldBoundary.test.tsx b/src/collaboration/CollaborativeCwlEditor.fieldBoundary.test.tsx
new file mode 100644
index 00000000..c25b27de
--- /dev/null
+++ b/src/collaboration/CollaborativeCwlEditor.fieldBoundary.test.tsx
@@ -0,0 +1,58 @@
+import { cleanup, render, screen } from '@testing-library/react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import * as Y from 'yjs';
+import { CollaborativeCwlEditor } from './CollaborativeCwlEditor.js';
+import type { CollaborativeCwlEditorProps } from './types.js';
+
+const COLLABORATION_FIELD_MAX_CODE_UNITS = 1_024;
+const INVALID_COLLABORATION_FIELD_MESSAGE =
+  'Collaboration field must be a string within the supported length.';
+
+afterEach(cleanup);
+
+function captureRenderFailure(field: unknown): unknown {
+  const consoleError = vi
+    .spyOn(console, 'error')
+    .mockImplementation(() => undefined);
+  let failure: unknown;
+  try {
+    render(
+      <CollaborativeCwlEditor
+        document={new Y.Doc()}
+        field={field as CollaborativeCwlEditorProps['field']}
+      />,
+    );
+  } catch (error) {
+    failure = error;
+  } finally {
+    consoleError.mockRestore();
+  }
+  return failure;
+}
+
+describe('CollaborativeCwlEditor field resource boundary', () => {
+  it('rejects non-string runtime field metadata through a stable redacted error', () => {
+    expect(captureRenderFailure(42)).toEqual(
+      new RangeError(INVALID_COLLABORATION_FIELD_MESSAGE),
+    );
+  });
+
+  it('rejects oversized field metadata before normalization without reflecting it', () => {
+    const privateMarker = 'private-room-marker';
+    const field = `${privateMarker}${'x'.repeat(COLLABORATION_FIELD_MAX_CODE_UNITS)}`;
+    const failure = captureRenderFailure(field);
+
+    expect(failure).toEqual(new RangeError(INVALID_COLLABORATION_FIELD_MESSAGE));
+    expect(String(failure)).not.toContain(privateMarker);
+  });
+
+  it('accepts an in-bound custom field at the local ceiling', () => {
+    const field = 'x'.repeat(COLLABORATION_FIELD_MAX_CODE_UNITS);
+
+    render(<CollaborativeCwlEditor document={new Y.Doc()} field={field} />);
+
+    expect(screen.getByRole('status')).toHaveTextContent(
+      'Collaboration ready · 0 remote collaborators',
+    );
+  });
+});
diff --git a/src/collaboration/CollaborativeCwlEditor.providerAwarenessFailure.test.tsx b/src/collaboration/CollaborativeCwlEditor.providerAwarenessFailure.test.tsx
new file mode 100644
index 00000000..90720322
--- /dev/null
+++ b/src/collaboration/CollaborativeCwlEditor.providerAwarenessFailure.test.tsx
@@ -0,0 +1,51 @@
+// @vitest-environment node
+
+import { renderToString } from 'react-dom/server';
+import { describe, expect, it } from 'vitest';
+import * as Y from 'yjs';
+import { CollaborativeCwlEditor } from './CollaborativeCwlEditor.js';
+import type {
+  CollaborationAwareness,
+  CollaborationProviderLike,
+} from './types.js';
+
+function validAwareness(): CollaborationAwareness {
+  const states = new Map<number, Record<string, unknown>>();
+  return {
+    clientID: 17,
+    states,
+    getLocalState: () => null,
+    getStates: () => states,
+    setLocalStateField: () => undefined,
+    on: () => undefined,
+    off: () => undefined,
+  };
+}
+
+describe('collaborative editor provider awareness access', () => {
+  it('contains a private awareness getter failure after configuration validation', () => {
+    const privateFailure = new Error('sensitive-provider-awareness-internal');
+    const awareness = validAwareness();
+    let reads = 0;
+    const provider = Object.defineProperty({}, 'awareness', {
+      enumerable: true,
+      get() {
+        reads += 1;
+        if (reads === 1) return awareness;
+        throw privateFailure;
+      },
+    }) as CollaborationProviderLike;
+
+    let observed: unknown;
+    try {
+      renderToString(
+        <CollaborativeCwlEditor document={new Y.Doc()} provider={provider} />,
+      );
+    } catch (error) {
+      observed = error;
+    }
+
+    expect(observed).toBeUndefined();
+    expect(reads).toBe(2);
+  });
+});
diff --git a/src/collaboration/CollaborativeCwlEditor.providerListenerFailure.test.tsx b/src/collaboration/CollaborativeCwlEditor.providerListenerFailure.test.tsx
new file mode 100644
index 00000000..42861b59
--- /dev/null
+++ b/src/collaboration/CollaborativeCwlEditor.providerListenerFailure.test.tsx
@@ -0,0 +1,87 @@
+import { cleanup, render } from '@testing-library/react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import * as Y from 'yjs';
+import { CollaborativeCwlEditor } from './CollaborativeCwlEditor.js';
+import type {
+  CollaborationAwareness,
+  CollaborationAwarenessEvent,
+  CollaborationProviderLike,
+} from './types.js';
+
+afterEach(cleanup);
+
+function awarenessWith(
+  on: CollaborationAwareness['on'],
+  off: CollaborationAwareness['off'],
+): CollaborationAwareness {
+  const states = new Map<number, Record<string, unknown>>();
+  return {
+    clientID: 23,
+    states,
+    getLocalState: () => null,
+    getStates: () => states,
+    setLocalStateField: () => undefined,
+    on,
+    off,
+  };
+}
+
+describe('collaborative editor provider listener failure containment', () => {
+  it('does not leak a private change-listener registration failure', () => {
+    const privateFailure = new Error('sensitive-provider-on-internal');
+    const awareness = awarenessWith(
+      (_event: CollaborationAwarenessEvent) => {
+        throw privateFailure;
+      },
+      () => undefined,
+    );
+    const provider: CollaborationProviderLike = { awareness };
+    const consoleError = vi
+      .spyOn(console, 'error')
+      .mockImplementation(() => undefined);
+
+    let observed: unknown;
+    try {
+      render(
+        <CollaborativeCwlEditor document={new Y.Doc()} provider={provider} />,
+      );
+    } catch (error) {
+      observed = error;
+    } finally {
+      consoleError.mockRestore();
+    }
+
+    expect(observed).toBeUndefined();
+  });
+
+  it('does not leak a private change-listener cleanup failure', () => {
+    const privateFailure = new Error('sensitive-provider-off-internal');
+    let offCalls = 0;
+    const awareness = awarenessWith(
+      () => undefined,
+      () => {
+        offCalls += 1;
+        throw privateFailure;
+      },
+    );
+    const provider: CollaborationProviderLike = { awareness };
+    const mounted = render(
+      <CollaborativeCwlEditor document={new Y.Doc()} provider={provider} />,
+    );
+    const consoleError = vi
+      .spyOn(console, 'error')
+      .mockImplementation(() => undefined);
+
+    let observed: unknown;
+    try {
+      mounted.unmount();
+    } catch (error) {
+      observed = error;
+    } finally {
+      consoleError.mockRestore();
+    }
+
+    expect(observed).toBeUndefined();
+    expect(offCalls).toBeGreaterThan(0);
+  });
+});
diff --git a/src/collaboration/CollaborativeCwlEditor.runtimeState.test.tsx b/src/collaboration/CollaborativeCwlEditor.runtimeState.test.tsx
new file mode 100644
index 00000000..72607f78
--- /dev/null
+++ b/src/collaboration/CollaborativeCwlEditor.runtimeState.test.tsx
@@ -0,0 +1,60 @@
+// @vitest-environment node
+
+import { renderToString } from 'react-dom/server';
+import { describe, expect, it } from 'vitest';
+import * as Y from 'yjs';
+import { CollaborativeCwlEditor } from './CollaborativeCwlEditor.js';
+
+describe('collaborative editor runtime state contracts', () => {
+  it('rejects a non-boolean editable state instead of coercing it into edit authority', () => {
+    expect(() =>
+      renderToString(
+        <CollaborativeCwlEditor
+          document={new Y.Doc()}
+          editable={'false' as unknown as boolean}
+        />,
+      ),
+    ).toThrowError(
+      new RangeError('editor editable state must be a boolean when provided'),
+    );
+  });
+
+  it('rejects a non-boolean toolbar visibility state instead of coercing it', () => {
+    expect(() =>
+      renderToString(
+        <CollaborativeCwlEditor
+          document={new Y.Doc()}
+          hideToolbar={'false' as unknown as boolean}
+        />,
+      ),
+    ).toThrowError(
+      new RangeError(
+        'editor toolbar visibility state must be a boolean when provided',
+      ),
+    );
+  });
+
+  it('preserves omitted and explicit boolean states', () => {
+    expect(() =>
+      renderToString(<CollaborativeCwlEditor document={new Y.Doc()} />),
+    ).not.toThrow();
+    expect(() =>
+      renderToString(
+        <CollaborativeCwlEditor
+          document={new Y.Doc()}
+          editable
+          hideToolbar={false}
+        />,
+      ),
+    ).not.toThrow();
+    expect(() =>
+      renderToString(
+        <CollaborativeCwlEditor
+          document={new Y.Doc()}
+          editable={false}
+          hideToolbar
+        />,
+      ),
+    ).not.toThrow();
+  });
+});
diff --git a/src/collaboration/CollaborativeCwlEditor.tsx b/src/collaboration/CollaborativeCwlEditor.tsx
index eea89b6c..a0f1166e 100644
--- a/src/collaboration/CollaborativeCwlEditor.tsx
+++ b/src/collaboration/CollaborativeCwlEditor.tsx
@@ -33,6 +33,21 @@ import {
 } from './awareness.js';
 import type { CollaborativeCwlEditorProps } from './types.js';
 
+const COLLABORATION_FIELD_MAX_CODE_UNITS = 1_024;
+const INVALID_COLLABORATION_FIELD_MESSAGE =
+  'Collaboration field must be a string within the supported length.';
+
+/** Read host-owned awareness for presentation without leaking getter failures. */
+function readProviderAwareness(
+  provider: CollaborativeCwlEditorProps['provider'],
+) {
+  try {
+    return provider?.awareness;
+  } catch {
+    return undefined;
+  }
+}
+
 /**
  * Provider-neutral collaborative Inkspan surface backed exclusively by a
  * host-owned Yjs document. Inkspan owns neither network nor persistence
@@ -97,8 +112,23 @@ export const CollaborativeCwlEditor = forwardRef<
     ariaRequired,
   } = props;
 
+  if (typeof editable !== 'boolean') {
+    throw new RangeError('editor editable state must be a boolean when provided');
+  }
+  if (typeof hideToolbar !== 'boolean') {
+    throw new RangeError(
+      'editor toolbar visibility state must be a boolean when provided',
+    );
+  }
   assertCollaborationConfiguration(provider, user);
-  if (field.trim() === '') {
+  if (
+    typeof field !== 'string' ||
+    field.length > COLLABORATION_FIELD_MAX_CODE_UNITS
+  ) {
+    throw new RangeError(INVALID_COLLABORATION_FIELD_MESSAGE);
+  }
+  const normalizedField = field.trim();
+  if (normalizedField === '') {
     throw new Error('collaboration field must not be empty');
   }
   if (
@@ -108,7 +138,6 @@ export const CollaborativeCwlEditor = forwardRef<
     throw new Error('collaboration document must be a Y.Doc instance');
   }
 
-  const normalizedField = field.trim();
   const normalizedPlaceholder = useMemo(
     () => normalizeEditorPlaceholder(placeholder),
     [placeholder],
@@ -289,17 +318,27 @@ export const CollaborativeCwlEditor = forwardRef<
   ]);
 
   const [remoteCollaborators, setRemoteCollaborators] = useState(() =>
-    countRemoteCollaborators(provider?.awareness),
+    countRemoteCollaborators(readProviderAwareness(provider)),
   );
   useEffect(() => {
-    const awareness = provider?.awareness;
+    const awareness = readProviderAwareness(provider);
     const updateCount = () => {
       setRemoteCollaborators(countRemoteCollaborators(awareness));
     };
     updateCount();
     if (!awareness) return;
-    awareness.on('change', updateCount);
-    return () => awareness.off('change', updateCount);
+    try {
+      awareness.on('change', updateCount);
+    } catch {
+      return;
+    }
+    return () => {
+      try {
+        awareness.off('change', updateCount);
+      } catch {
+        // Host-owned listener cleanup failure is contained at unmount.
+      }
+    };
   }, [provider]);
 
   const collaboratorLabel =