fix: Claude Code model vars not updated when switching providers

ANTHROPIC_DEFAULT_*_MODEL and CLAUDE_CODE_SUBAGENT_MODEL were using
${VAR:-default} syntax which preserved stale values from previous
sessions instead of updating to the new provider's model.

Author: samestrin

llm-env

@@ -1015,11 +1015,11 @@ set_single_provider() {
         # Export Anthropic-specific variables (only set what's configured)
         export ANTHROPIC_BASE_URL="$base"
         export ANTHROPIC_MODEL="$model"
-        # Set Claude Code specific model variables to the same model for fallback during Anthropic outage
-        export ANTHROPIC_DEFAULT_OPUS_MODEL="${ANTHROPIC_DEFAULT_OPUS_MODEL:-$model}"
-        export ANTHROPIC_DEFAULT_SONNET_MODEL="${ANTHROPIC_DEFAULT_SONNET_MODEL:-$model}"
-        export ANTHROPIC_DEFAULT_HAIKU_MODEL="${ANTHROPIC_DEFAULT_HAIKU_MODEL:-$model}"
-        export CLAUDE_CODE_SUBAGENT_MODEL="${CLAUDE_CODE_SUBAGENT_MODEL:-$model}"
+        # Set Claude Code specific model variables to the provider's model
+        export ANTHROPIC_DEFAULT_OPUS_MODEL="$model"
+        export ANTHROPIC_DEFAULT_SONNET_MODEL="$model"
+        export ANTHROPIC_DEFAULT_HAIKU_MODEL="$model"
+        export CLAUDE_CODE_SUBAGENT_MODEL="$model"
         export CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC="${CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC:-false}"
 
         if [[ -n "$key" ]]; then