fix(cursor): map base-only CLI sku to fast=false to avoid silent variant no-op (#887)

Without an explicit -fast suffix, inferSkuParamHints returned no fast hint, so
matchCliSkuToAcpWireId tied between fast=true and fast=false wires and kept
the first one. For composer-2.5 that meant the picker's "non-fast" sku silently
resolved to composer-2.5[fast=true] — the same wire the fast sku resolves to —
producing the "selected but no response" symptom in #883.

Treat absence of -fast as fast=false so base-only skus pick the slow variant
and round-trip back to the matching radio.

Fixes #883

via [HAPI](https://hapi.run)

Co-authored-by: HAPI <noreply@hapi.run>

shared/src/cursorCliSku.test.ts

@@ -34,8 +34,14 @@ describe('matchCliSkuToAcpWireId', () => {
         expect(matchCliSkuToAcpWireId('gpt-5.5-medium', available)).toBe('gpt-5.5[context=272k,reasoning=medium,fast=false]');
     });
 
-    it('picks the best wire when multiple ACP variants exist', () => {
-        expect(matchCliSkuToAcpWireId('composer-2.5', available)).toBe('composer-2.5[fast=true]');
+    it('maps base-only SKU to fast=false when fast variants exist (cursor CLI convention)', () => {
+        expect(matchCliSkuToAcpWireId('composer-2.5', available)).toBe('composer-2.5[fast=false]');
+    });
+
+    it('still maps base-only SKU when only one variant exists', () => {
+        expect(matchCliSkuToAcpWireId('composer-2.5', [{ modelId: 'composer-2.5[fast=true]' }])).toBe(
+            'composer-2.5[fast=true]'
+        );
     });
 });
 
@@ -49,6 +55,55 @@ describe('findBestCliSkuForAcpWire', () => {
         ]);
         expect(best).toBe('gpt-5.5-medium');
     });
+
+    it('prefers base-only sku for fast=false wire over -fast sku', () => {
+        const wire = 'composer-2.5[fast=false]';
+        const best = findBestCliSkuForAcpWire(wire, ['composer-2.5', 'composer-2.5-fast']);
+        expect(best).toBe('composer-2.5');
+    });
+
+    it('prefers -fast sku for fast=true wire over base-only sku', () => {
+        const wire = 'composer-2.5[fast=true]';
+        const best = findBestCliSkuForAcpWire(wire, ['composer-2.5', 'composer-2.5-fast']);
+        expect(best).toBe('composer-2.5-fast');
+    });
+});
+
+describe('round-trip (regression for #883: "selected but no response")', () => {
+    const acpWires = [
+        { modelId: 'composer-2.5[fast=true]' },
+        { modelId: 'composer-2.5[fast=false]' }
+    ];
+    const pickerSkus = ['composer-2.5', 'composer-2.5-fast'];
+
+    function simulateRoundTrip(clickedSku: string): { sessionModel: string; radioOn: string | null } {
+        // CLI side: applyCursorAcpModel → resolveCursorAcpWireId → matchCliSkuToAcpWireId
+        const sessionModel = matchCliSkuToAcpWireId(clickedSku, acpWires);
+        if (!sessionModel) {
+            throw new Error('CLI rejected sku');
+        }
+        // Web side after refetch: cursorVariantSelectValue uses findBestCliSkuForAcpWire
+        const radioOn = findBestCliSkuForAcpWire(sessionModel, pickerSkus);
+        return { sessionModel, radioOn };
+    }
+
+    it('clicking composer-2.5 (slow) lands on the slow radio, not the fast one', () => {
+        const result = simulateRoundTrip('composer-2.5');
+        expect(result.sessionModel).toBe('composer-2.5[fast=false]');
+        expect(result.radioOn).toBe('composer-2.5');
+    });
+
+    it('clicking composer-2.5-fast lands on the fast radio', () => {
+        const result = simulateRoundTrip('composer-2.5-fast');
+        expect(result.sessionModel).toBe('composer-2.5[fast=true]');
+        expect(result.radioOn).toBe('composer-2.5-fast');
+    });
+
+    it('clicking each picker option lands on a distinct session model (no collapse)', () => {
+        const slow = simulateRoundTrip('composer-2.5').sessionModel;
+        const fast = simulateRoundTrip('composer-2.5-fast').sessionModel;
+        expect(slow).not.toBe(fast);
+    });
 });
 
 describe('isCursorAcpWireModelId', () => {

shared/src/cursorCliSku.ts

@@ -91,9 +91,10 @@ function inferSkuParamHints(slug: string): Record<string, string> {
         hints.reasoning = 'none';
     }
 
-    if (lower.endsWith('-fast') || lower.includes('-fast')) {
-        hints.fast = 'true';
-    }
+    // Cursor CLI convention: `-fast` suffix means fast=true; absence means fast=false.
+    // Without an explicit hint, base-only SKUs (e.g. `composer-2.5`) would tie-break to the
+    // first wire and silently coerce to the fast variant.
+    hints.fast = lower.includes('-fast') ? 'true' : 'false';
 
     if (lower.includes('thinking')) {
         hints.thinking = 'true';