feat: support session-scoped model overrides

Model selection was acting like a provider-level preference.

That made resumed sessions drift back to a default or request-time model.

Users expect /models changes made inside a conversation to affect that session.

Store explicit session choices in app-owned ~/.cloudcli state.

This avoids editing provider transcripts or native provider config.

Resolve the effective model before launching each provider runtime.

Claude, Cursor, Codex, Gemini, and OpenCode now honor stored resume choices.

Expose a backend active-model change endpoint for existing sessions.

The models modal can now distinguish default changes from session overrides.

It also shows when a selected model will apply on the next response.

For Claude, stop probing active model state by resuming with a dummy prompt.

Read the indexed JSONL transcript from the end instead.

This preserves provider history while honoring /model stdout or model fields.

Add service tests for adapter delegation and resume-model precedence.

The tests keep cache state, override state, and requested fallback separate.

server/shared/interfaces.ts

@@ -7,9 +7,11 @@ import type {
   ProviderSkill,
   ProviderSkillListOptions,
   ProviderAuthStatus,
+  ProviderChangeActiveModelInput,
   ProviderCurrentActiveModel,
   ProviderModelsDefinition,
   ProviderMcpServer,
+  ProviderSessionActiveModelChange,
   UpsertProviderMcpServerInput,
 } from '@/shared/types.js';
 
@@ -55,6 +57,19 @@ export interface IProviderModels {
    * no active model can be resolved.
    */
   getCurrentActiveModel(sessionId?: string): Promise<ProviderCurrentActiveModel>;
+
+  /**
+   * Persists a session-scoped model override that the next resumed turn should
+   * honor for this provider.
+   *
+   * This does not require the provider to mutate an already running remote
+   * session in-place. Instead, adapters store the user's explicit model choice
+   * so the backend resume path can add the correct provider-native model option
+   * on the next CLI/SDK invocation for the same session.
+   */
+  changeActiveModel(
+    input: ProviderChangeActiveModelInput,
+  ): Promise<ProviderSessionActiveModelChange>;
 }
 
 // ---------------------------