diff --git a/src/lib/stores/resilient-local-storage.ts b/src/lib/stores/resilient-local-storage.ts
new file mode 100644
index 000000000..40ab1330d
--- /dev/null
+++ b/src/lib/stores/resilient-local-storage.ts
@@ -0,0 +1,82 @@
+import { createJSONStorage, type StateStorage } from 'zustand/middleware';
+
+/** Lists the server hydrates again. Drafts and the result on screen stay. */
+const BULKY_LISTS = [
+  'sourceLibrary',
+  'sourceFolders',
+  'savedCases',
+  'savedAttacks',
+  'savedBrainstorms',
+  'savedFactoids',
+  'savedChats',
+  'savedFlowcharts',
+  'savedCrossfires',
+];
+
+function isQuotaError(error: unknown): boolean {
+  if (!(error instanceof DOMException)) return false;
+  return error.name === 'QuotaExceededError' || error.name === 'NS_ERROR_DOM_QUOTA_REACHED' || error.code === 22;
+}
+
+function readState(serialized: string): { envelope: { state?: Record<string, unknown> }; state: Record<string, unknown> } | null {
+  try {
+    const envelope = JSON.parse(serialized) as { state?: Record<string, unknown> };
+    if (!envelope.state || typeof envelope.state !== 'object') return null;
+    return { envelope, state: envelope.state };
+  } catch {
+    return null;
+  }
+}
+
+/** Drop source text first. Titles and ids stay, so the library does not flash empty. */
+export function withoutSourceText(serialized: string): string | null {
+  const parsed = readState(serialized);
+  if (!parsed || !Array.isArray(parsed.state.sourceLibrary)) return null;
+  parsed.state.sourceLibrary = parsed.state.sourceLibrary.map((item) => {
+    if (!item || typeof item !== 'object') return item;
+    return { ...(item as Record<string, unknown>), content: '' };
+  });
+  return JSON.stringify(parsed.envelope);
+}
+
+/** Last try: forget the bulky copies and keep the open draft. */
+export function withoutBulkyLists(serialized: string): string | null {
+  const parsed = readState(serialized);
+  if (!parsed) return null;
+  for (const key of BULKY_LISTS) delete parsed.state[key];
+  return JSON.stringify(parsed.envelope);
+}
+
+/**
+ * Zustand persist lets a full localStorage throw out of a tool page. On a quota
+ * error, retry without source text, then without the bulky lists, then keep
+ * going in memory.
+ */
+export function resilientSetItem(storage: Pick<Storage, 'setItem'>, key: string, value: string): void {
+  const attempts = [value, withoutSourceText(value), withoutBulkyLists(value)]
+    .filter((attempt): attempt is string => typeof attempt === 'string');
+  const seen = new Set<string>();
+  let lastQuota: unknown;
+  for (const attempt of attempts) {
+    if (seen.has(attempt)) continue;
+    seen.add(attempt);
+    try {
+      storage.setItem(key, attempt);
+      return;
+    } catch (error) {
+      if (!isQuotaError(error)) throw error;
+      lastQuota = error;
+    }
+  }
+  console.warn('[SessionStore] Local storage is full; this change stays in memory.', lastQuota);
+}
+
+const resilientStorage: StateStorage = {
+  getItem: (name) => localStorage.getItem(name),
+  setItem: (name, value) => resilientSetItem(localStorage, name, value),
+  removeItem: (name) => localStorage.removeItem(name),
+};
+
+export function resilientLocalStorage() {
+  return createJSONStorage(() => resilientStorage);
+}
diff --git a/src/lib/stores/session-store.ts b/src/lib/stores/session-store.ts
index dcdea8e78..5ec10fcf4 100644
--- a/src/lib/stores/session-store.ts
+++ b/src/lib/stores/session-store.ts
@@ -1,5 +1,6 @@
 import { create } from 'zustand';
-import { persist, createJSONStorage } from 'zustand/middleware';
+import { persist } from 'zustand/middleware';
+import { resilientLocalStorage } from '@/lib/stores/resilient-local-storage';
 import type { Node, Edge } from 'reactflow';
 import type { GenerateOutput, GenerateInput } from '../ai/schemas/generate';
 import type { AttackOutput, AttackInput } from '../ai/schemas/attack';
@@ -1285,7 +1286,7 @@ export const useSessionStore = create<SessionState>()(
     }),
     {
       name: 'debate-trainer-storage',
-      storage: createJSONStorage(() => localStorage),
+      storage: resilientLocalStorage(),
       // v1 scopes saved work and sources to debates. Drop lists persisted by
       // older clients: the server replaces them on hydrate, and keeping them
       // would resurrect purged legacy rows and debate-less sources.
diff --git a/src/test/stores/resilient-local-storage.test.ts b/src/test/stores/resilient-local-storage.test.ts
new file mode 100644
index 000000000..ebc65535e
--- /dev/null
+++ b/src/test/stores/resilient-local-storage.test.ts
@@ -0,0 +1,55 @@
+import { describe, expect, it } from 'vitest';
+import { resilientSetItem, withoutBulkyLists, withoutSourceText } from '@/lib/stores/resilient-local-storage';
+
+const saved = JSON.stringify({
+  state: {
+    sourceLibrary: [{ id: 'src-1', title: 'Buses', content: 'a very long article' }],
+    savedCases: [{ id: 'case-1', data: { contentions: ['cost'] } }],
+    generateForm: { motion: 'Free buses' },
+    generateResult: { title: 'Open case' },
+  },
+  version: 1,
+});
+
+describe('resilient local storage', () => {
+  it('removes source text before it removes saved lists', () => {
+    const stripped = withoutSourceText(saved);
+    expect(stripped).toContain('"title":"Buses"');
+    expect(stripped).not.toContain('a very long article');
+    expect(stripped).toContain('Free buses');
+
+    const emptied = withoutBulkyLists(saved)!;
+    const parsed = JSON.parse(emptied) as { state: Record<string, unknown> };
+    expect(parsed.state.sourceLibrary).toBeUndefined();
+    expect(parsed.state.savedCases).toBeUndefined();
+    expect(parsed.state.generateForm).toEqual({ motion: 'Free buses' });
+    expect(parsed.state.generateResult).toEqual({ title: 'Open case' });
+  });
+
+  it('retries a quota failure and does not throw when every copy is still too big', () => {
+    const writes: string[] = [];
+    const storage = {
+      setItem: (key: string, value: string) => {
+        writes.push(value);
+        if (value.includes('a very long article') || value.includes('savedCases')) {
+          throw new DOMException('quota', 'QuotaExceededError');
+        }
+      },
+    };
+    resilientSetItem(storage, 'debate-trainer-storage', saved);
+    expect(writes).toHaveLength(3);
+    expect(writes[1]).not.toContain('a very long article');
+    expect(writes[2]).not.toContain('savedCases');
+    expect(writes[2]).toContain('Free buses');
+
+    const alwaysFull = {
+      setItem: () => { throw new DOMException('quota', 'QuotaExceededError'); },
+    };
+    expect(() => resilientSetItem(alwaysFull, 'debate-trainer-storage', saved)).not.toThrow();
+  });
+
+  it('still throws errors that are not a full disk', () => {
+    const storage = { setItem: () => { throw new Error('blocked'); } };
+    expect(() => resilientSetItem(storage, 'debate-trainer-storage', saved)).toThrow('blocked');
+  });
+});