fix(coding-agent): fixed compaction to prefer active session model over role default

- Added the active session model to compaction candidate selection before role-based candidates.
- Updated compaction routing so role-based models are only considered after the current chat model.
- Added a regression test proving an Anthropic session prefers its active model over `modelRoles.default` on OpenAI.

packages/coding-agent/src/session/agent-session.ts

@@ -6171,6 +6171,12 @@ export class AgentSession {
 		};
 
 		const currentModel = this.model;
+		// Prefer the active session's model: it's what the user is actively using,
+		// and routing compaction to a different provider (e.g. an OpenAI default
+		// model while the chat is on Anthropic) changes provider-specific behavior
+		// like remote compaction endpoints. Role-based candidates only kick in
+		// as auth fallbacks when the current model has no usable credentials.
+		addCandidate(currentModel);
 		for (const role of MODEL_ROLE_IDS) {
 			addCandidate(this.#resolveRoleModelFull(role, availableModels, currentModel).model);
 		}