diff --git a/apps/mobile/src/components/home-composer.tsx b/apps/mobile/src/components/home-composer.tsx
index 5e20b5a3..0d7a6a62 100644
--- a/apps/mobile/src/components/home-composer.tsx
+++ b/apps/mobile/src/components/home-composer.tsx
@@ -22,7 +22,6 @@ import {
   type ModelOptionDescriptor,
   type ModelOptionsMap,
 } from '@nuncio/core/model-options';
-import { modelSupportsFast } from '@nuncio/core/model-effort-options';
 import { ProviderIcon, brandForModel, type Brand } from './provider-icon';
 import {
   fetchBranches,
@@ -35,6 +34,7 @@ import {
 import { createSubmitLock } from '../lib/submit-lock';
 import { fetchDirectories, type DirListing } from '../lib/fs-api';
 import { basename } from '../lib/home-sections';
+import { composerModelOptionDescriptors } from '../lib/model-option-descriptors';
 import { Button } from './ui/button';
 import { Card } from './ui/card';
 import { Text } from './ui/text';
@@ -148,16 +148,10 @@ export function HomeComposer({ onCreated, onAdvanced }: HomeComposerProps) {
   }, [modelId, models]);
   const selectableBranchList = useMemo(() => selectableBranches(branches), [branches]);
   const sheetCopy = sheetMode ? SHEET_COPY[sheetMode] : null;
-  const modelOptionDescriptors = useMemo<ModelOptionDescriptor[]>(() => {
-    const base = selectedModel?.options ?? [];
-    // Some Codex/Cursor models expose `fast` (Priority) only as a variant, not
-    // as an options descriptor — surface it as a boolean toggle so the picker
-    // can set it, matching the web (which derives fast from variants).
-    if (selectedModel && !base.some((d) => d.id === 'fast') && modelSupportsFast(selectedModel)) {
-      return [...base, { id: 'fast', label: 'Priority', type: 'boolean', defaultValue: false }];
-    }
-    return base;
-  }, [selectedModel]);
+  const modelOptionDescriptors = useMemo<ModelOptionDescriptor[]>(
+    () => composerModelOptionDescriptors(selectedModel),
+    [selectedModel],
+  );
   const optionsSummary = optionSummaryLabel(modelOptionDescriptors, modelOptions);
   const canSend = Boolean(prompt.trim() && selectedModel && !busy);
 
diff --git a/apps/mobile/src/lib/model-option-descriptors.spec.ts b/apps/mobile/src/lib/model-option-descriptors.spec.ts
new file mode 100644
index 00000000..7eea4c1b
--- /dev/null
+++ b/apps/mobile/src/lib/model-option-descriptors.spec.ts
@@ -0,0 +1,71 @@
+import { describe, expect, it } from 'vitest';
+import type { ModelOptionDescriptor } from '@nuncio/core/model-options';
+import { composerModelOptionDescriptors } from './model-option-descriptors';
+
+const reasoning: ModelOptionDescriptor = {
+  id: 'reasoningEffort',
+  label: 'Reasoning',
+  type: 'select',
+  defaultValue: 'medium',
+  options: [
+    { id: 'low', label: 'Low' },
+    { id: 'medium', label: 'Medium', isDefault: true },
+  ],
+};
+
+const priority: ModelOptionDescriptor = {
+  id: 'fast',
+  label: 'Priority',
+  type: 'boolean',
+  defaultValue: false,
+};
+
+describe('composerModelOptionDescriptors', () => {
+  it('returns an empty list when no model is selected', () => {
+    expect(composerModelOptionDescriptors(undefined)).toEqual([]);
+    expect(composerModelOptionDescriptors(null)).toEqual([]);
+  });
+
+  it('passes through catalog options unchanged when fast is already declared', () => {
+    const options = [reasoning, priority];
+    expect(
+      composerModelOptionDescriptors({
+        options,
+        variants: [{ params: [{ id: 'fast', value: 'true' }] }],
+      }),
+    ).toEqual(options);
+  });
+
+  it('synthesizes a Priority toggle when fast exists only as a fast-only variant', () => {
+    // Regression for #146 — without this, the Options sheet hid Priority for
+    // Codex/Cursor models that only advertise fast via variants.
+    expect(
+      composerModelOptionDescriptors({
+        options: [reasoning],
+        variants: [{ params: [{ id: 'fast', value: 'true' }] }],
+      }),
+    ).toEqual([reasoning, priority]);
+  });
+
+  it('synthesizes Priority for a bare fast-only variant model with no options', () => {
+    expect(
+      composerModelOptionDescriptors({
+        variants: [{ params: [{ id: 'fast', value: 'TRUE' }] }],
+      }),
+    ).toEqual([priority]);
+  });
+
+  it('does not invent Priority when variants are mixed or absent', () => {
+    expect(
+      composerModelOptionDescriptors({
+        options: [reasoning],
+        variants: [
+          { params: [{ id: 'fast', value: 'true' }] },
+          { params: [{ id: 'reasoningEffort', value: 'high' }] },
+        ],
+      }),
+    ).toEqual([reasoning]);
+
+    expect(composerModelOptionDescriptors({ options: [reasoning] })).toEqual([reasoning]);
+  });
+});
diff --git a/apps/mobile/src/lib/model-option-descriptors.ts b/apps/mobile/src/lib/model-option-descriptors.ts
new file mode 100644
index 00000000..e09ab92c
--- /dev/null
+++ b/apps/mobile/src/lib/model-option-descriptors.ts
@@ -0,0 +1,20 @@
+import type { ModelOptionDescriptor } from '@nuncio/core/model-options';
+import { modelSupportsFast } from '@nuncio/core/model-effort-options';
+
+/**
+ * Descriptors shown in the home-composer Options sheet.
+ *
+ * Some Codex/Cursor models expose `fast` (Priority) only as a variant, not as
+ * an options descriptor — synthesize a boolean toggle so the picker can set it,
+ * matching the web (which derives fast from variants).
+ */
+export function composerModelOptionDescriptors(model: {
+  options?: ModelOptionDescriptor[];
+  variants?: Array<{ params: Array<{ id: string; value: string }> }>;
+} | null | undefined): ModelOptionDescriptor[] {
+  const base = model?.options ?? [];
+  if (model && !base.some((d) => d.id === 'fast') && modelSupportsFast(model)) {
+    return [...base, { id: 'fast', label: 'Priority', type: 'boolean', defaultValue: false }];
+  }
+  return base;
+}
diff --git a/apps/server/test/unit/agents/claude-agent.provider.spec.ts b/apps/server/test/unit/agents/claude-agent.provider.spec.ts
index c204914e..4bf5befe 100644
--- a/apps/server/test/unit/agents/claude-agent.provider.spec.ts
+++ b/apps/server/test/unit/agents/claude-agent.provider.spec.ts
@@ -1399,6 +1399,29 @@ describe('ClaudeAgentProvider', () => {
       expect(applied).toEqual([{ effortLevel: 'xhigh' }]);
     });
 
+    it("skips mid-session applyFlagSettings for Codex 'ultra' (not a Claude effortLevel)", async () => {
+      // Claude Settings.effortLevel has no 'ultra'; Codex-sub catalog rows can
+      // still carry it historically — mid-session must no-op, not send an invalid flag.
+      const applied: Array<Record<string, unknown>> = [];
+      provider.queryFactory = () => ({
+        async interrupt() {},
+        async setModel() {},
+        async applyFlagSettings(settings: Record<string, unknown>) {
+          applied.push(settings);
+        },
+        async *[Symbol.asyncIterator](): AsyncIterator<ClaudeSdkMessage> {
+          yield { type: 'system', subtype: 'init', session_id: 't1' };
+          yield { type: 'result', subtype: 'success', result: 'ok' };
+        },
+      });
+      const created = sessions.create({ prompt: 'hi', provider: 'claude', model: 'claude:sonnet' });
+      await provider.run(created.id, 'hi', { cwd: '/tmp/ws', model: 'claude:sonnet' });
+      await provider.setModel(created.id, 'claude:sonnet', { effort: 'ultra' });
+      expect(applied).toEqual([]);
+      await provider.setModel(created.id, 'claude:sonnet', { reasoningEffort: 'ultra' });
+      expect(applied).toEqual([]);
+    });
+
     it('does not throw on setModel when the query has no applyFlagSettings', async () => {
       const created = sessions.create({ prompt: 'hi', provider: 'claude', model: 'claude:haiku' });
       await provider.run(created.id, 'hi', { cwd: '/tmp/ws', model: 'claude:haiku' });
diff --git a/apps/server/test/unit/agents/codex-model-options.spec.ts b/apps/server/test/unit/agents/codex-model-options.spec.ts
index ca0433d6..b31cdf56 100644
--- a/apps/server/test/unit/agents/codex-model-options.spec.ts
+++ b/apps/server/test/unit/agents/codex-model-options.spec.ts
@@ -44,6 +44,20 @@ describe('codex-model-options', () => {
       );
       expect(option.options?.filter((o) => o.isDefault)).toHaveLength(1);
     });
+
+    it('drops ultra when excludeUltra is set (Claude Codex-sub catalog rows)', () => {
+      // Native Codex CLI can run Multi-agent ultra; Claude-routed Codex-sub cannot.
+      const option = defaultCodexReasoningEffortOption({ excludeUltra: true });
+      expect(option.options?.map((o) => o.id)).toEqual([
+        'low',
+        'medium',
+        'high',
+        'xhigh',
+      ]);
+      expect(option.options?.some((o) => o.id === 'ultra')).toBe(false);
+      expect(option.defaultValue).toBe('medium');
+      expect(option.options?.find((o) => o.id === 'medium')?.isDefault).toBe(true);
+    });
   });
 
   describe('codexFastOption / defaultCodexModelOptions', () => {