fix(agent): pass config_context_length in fallback activation path

Try to activate fallback model after errors was calling get_model_context_length()
without the config_context_length parameter, causing it to fall through to
DEFAULT_FALLBACK_CONTEXT (128K) even when config.yaml has an explicit
model.context_length value (e.g. 204800 for MiniMax-M2.7).

This mirrors the fix already present in switch_model() at line 1988, which
correctly passes config_context_length. The fallback path was missed.

Fixes: context_length forced to 128K on fallback activation

run_agent.py

@@ -6430,11 +6430,15 @@ class AIAgent:
             # Without this, compression decisions use the primary model's
             # context window (e.g. 200K) instead of the fallback's (e.g. 32K),
             # causing oversized sessions to overflow the fallback.
+            # Also pass _config_context_length so the explicit config override
+            # (model.context_length in config.yaml) is respected — without this,
+            # the fallback activation drops to 128K even when config says 204800.
             if hasattr(self, 'context_compressor') and self.context_compressor:
                 from agent.model_metadata import get_model_context_length
                 fb_context_length = get_model_context_length(
                     self.model, base_url=self.base_url,
                     api_key=self.api_key, provider=self.provider,
+                    config_context_length=getattr(self, "_config_context_length", None),
                 )
                 self.context_compressor.update_model(
                     model=self.model,