fix(opencode): use ACP-reported reasoning effort options (#853)

* fix(opencode): use ACP-reported reasoning effort options

Expose thought_level options from OpenCode ACP to the web UI via RPC/API
instead of hardcoded presets, and validate effort values before setConfigOption.

Fixes #852

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(opencode): sync hub effort after coerced setConfigOption

When resolveThoughtLevelEffort falls back to a different supported value,
roll back session state after a successful ACP update so keepalive and the
web UI do not keep advertising the rejected effort.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

cli/src/opencode/thoughtLevelEffort.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from 'vitest';
+import { resolveThoughtLevelEffort } from './thoughtLevelEffort';
+
+const thoughtLevelOption = {
+    id: 'effort',
+    category: 'thought_level',
+    currentValue: 'low',
+    options: [
+        { value: 'low', name: 'Low' },
+        { value: 'medium', name: 'Medium' }
+    ]
+};
+
+describe('resolveThoughtLevelEffort', () => {
+    it('returns the requested value when it is supported', () => {
+        expect(resolveThoughtLevelEffort('medium', thoughtLevelOption, 'low')).toBe('medium');
+    });
+
+    it('falls back to the current backend effort when the request is unsupported', () => {
+        expect(resolveThoughtLevelEffort('high', thoughtLevelOption, 'low')).toBe('low');
+    });
+
+    it('falls back to the ACP current value when the backend effort is also unsupported', () => {
+        expect(resolveThoughtLevelEffort('high', thoughtLevelOption, 'max')).toBe('low');
+    });
+
+    it('falls back to the first supported option when nothing else matches', () => {
+        const option = {
+            ...thoughtLevelOption,
+            currentValue: 'high'
+        };
+        expect(resolveThoughtLevelEffort('max', option, null)).toBe('low');
+    });
+});