diff --git a/src/main/config/config-store.ts b/src/main/config/config-store.ts
index 9b1dd9519..fa50d8aa7 100644
--- a/src/main/config/config-store.ts
+++ b/src/main/config/config-store.ts
@@ -1020,6 +1020,14 @@ export class ConfigStore {
       enableThinking: projected.enableThinking,
       isConfigured: toBoolean(raw.isConfigured, defaultConfig.isConfigured),
     };
+    // Only set when the profile has a real value: electron-store rejects an explicit
+    // `undefined` for a present key (see normalizeProfile's own convention above).
+    if (typeof projected.contextWindow === 'number' && projected.contextWindow > 0) {
+      result.contextWindow = projected.contextWindow;
+    }
+    if (typeof projected.maxTokens === 'number' && projected.maxTokens > 0) {
+      result.maxTokens = projected.maxTokens;
+    }
     this.normalizeModelIds(result);
     return result;
   }
@@ -1045,7 +1053,7 @@ export class ConfigStore {
     const activeConfigSet =
       nextConfigSets.find((set) => set.id === requestedActiveConfigSetId) || nextConfigSets[0];
     const projected = this.projectFromConfigSet(activeConfigSet);
-    return {
+    const result: AppConfig = {
       ...base,
       provider: projected.provider,
       customProtocol: projected.customProtocol,
@@ -1058,6 +1066,19 @@ export class ConfigStore {
       activeConfigSetId: activeConfigSet.id,
       configSets: nextConfigSets,
     };
+    // Clear rather than leave stale: `...base` can carry the previous set's value, and
+    // electron-store rejects an explicit `undefined` for a present key.
+    if (typeof projected.contextWindow === 'number' && projected.contextWindow > 0) {
+      result.contextWindow = projected.contextWindow;
+    } else {
+      delete result.contextWindow;
+    }
+    if (typeof projected.maxTokens === 'number' && projected.maxTokens > 0) {
+      result.maxTokens = projected.maxTokens;
+    } else {
+      delete result.maxTokens;
+    }
+    return result;
   }
 
   private buildUniqueConfigSetName(
diff --git a/src/main/index.ts b/src/main/index.ts
index 0a2c0ff31..1c1f0d03e 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -1911,6 +1911,8 @@ const buildAgentRuntimeSignature = (config: AppConfig): string =>
     baseUrl: config.baseUrl,
     customProtocol: config.customProtocol,
     model: config.model,
+    contextWindow: config.contextWindow,
+    maxTokens: config.maxTokens,
     enableThinking: config.enableThinking,
     memoryEnabled: config.memoryEnabled,
     memoryRuntime: config.memoryRuntime,
diff --git a/tests/config-store-context-window-projection.test.ts b/tests/config-store-context-window-projection.test.ts
new file mode 100644
index 000000000..fb8d185d2
--- /dev/null
+++ b/tests/config-store-context-window-projection.test.ts
@@ -0,0 +1,177 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const mocks = vi.hoisted(() => ({
+  seed: {} as Record<string, unknown>,
+}));
+
+vi.mock('electron-store', () => {
+  class MockStore<T extends Record<string, unknown>> {
+    public store: Record<string, unknown>;
+    public path = '/tmp/mock-config-store.json';
+
+    constructor(options: { defaults?: Record<string, unknown> }) {
+      this.store = {
+        ...(options?.defaults || {}),
+        ...mocks.seed,
+      };
+    }
+
+    get<K extends keyof T>(key: K): T[K] {
+      return this.store[key as string] as T[K];
+    }
+
+    set(key: string | Record<string, unknown>, value?: unknown): void {
+      if (typeof key === 'string') {
+        this.store[key] = value;
+        return;
+      }
+      this.store = {
+        ...this.store,
+        ...key,
+      };
+    }
+
+    clear(): void {
+      this.store = {};
+    }
+  }
+
+  return {
+    default: MockStore,
+  };
+});
+
+import { ConfigStore } from '../src/main/config/config-store';
+
+describe('ConfigStore contextWindow/maxTokens projection', () => {
+  beforeEach(() => {
+    mocks.seed = {};
+  });
+
+  it('projects a custom/Ollama profile contextWindow and maxTokens onto the flat config getAll() returns', () => {
+    const store = new ConfigStore();
+
+    store.update({
+      provider: 'ollama',
+      apiKey: '',
+      baseUrl: 'http://localhost:11434/v1',
+      model: 'llama3.3',
+      profiles: {
+        ollama: {
+          apiKey: '',
+          baseUrl: 'http://localhost:11434/v1',
+          model: 'llama3.3',
+          contextWindow: 32000,
+          maxTokens: 8000,
+        },
+      },
+    });
+
+    const config = store.getAll();
+    expect(config.contextWindow).toBe(32000);
+    expect(config.maxTokens).toBe(8000);
+  });
+
+  it('keeps contextWindow/maxTokens projected after switching config sets', () => {
+    const store = new ConfigStore();
+
+    store.update({
+      provider: 'ollama',
+      apiKey: '',
+      baseUrl: 'http://localhost:11434/v1',
+      model: 'llama3.3',
+      profiles: {
+        ollama: {
+          apiKey: '',
+          baseUrl: 'http://localhost:11434/v1',
+          model: 'llama3.3',
+          contextWindow: 32000,
+          maxTokens: 8000,
+        },
+      },
+    });
+    expect(store.getAll().contextWindow).toBe(32000);
+    expect(store.getAll().maxTokens).toBe(8000);
+
+    const created = store.createSet({ name: 'Second set', mode: 'blank' });
+    const secondSetId = created.configSets.find((set) => set.id !== 'default')!.id;
+
+    store.update({
+      provider: 'custom',
+      customProtocol: 'openai',
+      apiKey: 'sk-custom',
+      baseUrl: 'https://relay.example.com/v1',
+      model: 'my-model',
+      profiles: {
+        'custom:openai': {
+          apiKey: 'sk-custom',
+          baseUrl: 'https://relay.example.com/v1',
+          model: 'my-model',
+          contextWindow: 64000,
+          maxTokens: 16000,
+        },
+      },
+    });
+    expect(store.getAll().contextWindow).toBe(64000);
+    expect(store.getAll().maxTokens).toBe(16000);
+
+    store.switchSet({ id: 'default' });
+    const defaultSetView = store.getAll();
+    expect(defaultSetView.contextWindow).toBe(32000);
+    expect(defaultSetView.maxTokens).toBe(8000);
+
+    store.switchSet({ id: secondSetId });
+    const secondSetView = store.getAll();
+    expect(secondSetView.contextWindow).toBe(64000);
+    expect(secondSetView.maxTokens).toBe(16000);
+  });
+
+  it('does not crash on construction when the active profile has no contextWindow/maxTokens override', () => {
+    expect(() => new ConfigStore()).not.toThrow();
+    const config = new ConfigStore().getAll();
+    expect(config.contextWindow).toBeUndefined();
+    expect(config.maxTokens).toBeUndefined();
+  });
+
+  it('clears contextWindow/maxTokens when switching to a set whose active profile has no override', () => {
+    const store = new ConfigStore();
+
+    store.update({
+      provider: 'ollama',
+      apiKey: '',
+      baseUrl: 'http://localhost:11434/v1',
+      model: 'llama3.3',
+      profiles: {
+        ollama: {
+          apiKey: '',
+          baseUrl: 'http://localhost:11434/v1',
+          model: 'llama3.3',
+          contextWindow: 32000,
+          maxTokens: 8000,
+        },
+      },
+    });
+    expect(store.getAll().contextWindow).toBe(32000);
+
+    const created = store.createSet({ name: 'No override set', mode: 'blank' });
+    const secondSetId = created.configSets.find((set) => set.id !== 'default')!.id;
+
+    expect(() =>
+      store.update({
+        provider: 'openrouter',
+        apiKey: 'sk-or',
+        model: 'anthropic/claude',
+      })
+    ).not.toThrow();
+    const secondSetView = store.getAll();
+    expect(secondSetView.contextWindow).toBeUndefined();
+    expect(secondSetView.maxTokens).toBeUndefined();
+
+    store.switchSet({ id: 'default' });
+    expect(store.getAll().contextWindow).toBe(32000);
+
+    store.switchSet({ id: secondSetId });
+    expect(store.getAll().contextWindow).toBeUndefined();
+    expect(store.getAll().maxTokens).toBeUndefined();
+  });
+});
diff --git a/tests/index-agent-runtime-signature.test.ts b/tests/index-agent-runtime-signature.test.ts
new file mode 100644
index 000000000..d39944f93
--- /dev/null
+++ b/tests/index-agent-runtime-signature.test.ts
@@ -0,0 +1,17 @@
+import { describe, it, expect } from 'vitest';
+import path from 'node:path';
+import fs from 'node:fs';
+
+const indexPath = path.resolve(process.cwd(), 'src/main/index.ts');
+
+describe('buildAgentRuntimeSignature', () => {
+  it('includes contextWindow and maxTokens so a numeric-only change reloads the running session', () => {
+    const source = fs.readFileSync(indexPath, 'utf8');
+    const signatureBlock = source.match(
+      /const buildAgentRuntimeSignature[\s\S]*?\n  \}\);/
+    )?.[0] || '';
+
+    expect(signatureBlock).toContain('contextWindow: config.contextWindow');
+    expect(signatureBlock).toContain('maxTokens: config.maxTokens');
+  });
+});