feat(model-settings-compat): add variant/reasoningEffort compatibility resolver

- Registry-based model family detection (provider-agnostic)
- Variant and reasoningEffort ladder downgrade logic
- Three-tier resolution: metadata override → family heuristic → unknown drop
- Comprehensive test suite covering all model families

src/shared/session-prompt-params-helpers.ts

@@ -0,0 +1,31 @@
+import { clearSessionPromptParams, setSessionPromptParams } from "./session-prompt-params-state"
+
+type PromptParamModel = {
+  temperature?: number
+  top_p?: number
+  reasoningEffort?: string
+  maxTokens?: number
+  thinking?: { type: "enabled" | "disabled"; budgetTokens?: number }
+}
+
+export function applySessionPromptParams(
+  sessionID: string,
+  model: PromptParamModel | undefined,
+): void {
+  if (!model) {
+    clearSessionPromptParams(sessionID)
+    return
+  }
+
+  const promptOptions: Record<string, unknown> = {
+    ...(model.reasoningEffort ? { reasoningEffort: model.reasoningEffort } : {}),
+    ...(model.thinking ? { thinking: model.thinking } : {}),
+    ...(model.maxTokens !== undefined ? { maxTokens: model.maxTokens } : {}),
+  }
+
+  setSessionPromptParams(sessionID, {
+    ...(model.temperature !== undefined ? { temperature: model.temperature } : {}),
+    ...(model.top_p !== undefined ? { topP: model.top_p } : {}),
+    ...(Object.keys(promptOptions).length > 0 ? { options: promptOptions } : {}),
+  })
+}