Subject: [PATCH 0004] chat: LLM_DEFAULT_CONTEXT_WINDOW for model names the OpenAI table does not know

OpenAIService.GetContextWindow knows only OpenAI's own names (gpt-4o, gpt-4, gpt-3.5)
and returns 4096 for anything else. Behind an OpenAI-compatible gateway every model is
"anything else" (here LiteLLM's summarizer and gen-large, 262k-context vLLM seats), so
chat refuses any transcript the handler estimates above 3,596 tokens (chars/4, minus 500
kept for the reply): a 22k-character meeting was refused on 2026-10-19 with "limit 4096".
The default branch now reads LLM_DEFAULT_CONTEXT_WINDOW (a positive integer) and keeps
4096 when it is unset or invalid; the known OpenAI names are unchanged.

---
--- a/internal/llm/openai.go
+++ b/internal/llm/openai.go
@@ -9,6 +9,8 @@
 	"io"
 	"log"
 	"net/http"
+	"os"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -337,7 +339,11 @@
 	case strings.HasPrefix(model, "gpt-3.5-turbo"):
 		return 16385, nil // Most recent gpt-3.5-turbo is 16k
 	default:
-		// Default fallback
+		// Not an OpenAI model name (a LiteLLM alias, a vLLM served name): the operator's
+		// LLM_DEFAULT_CONTEXT_WINDOW when set to a positive integer, else upstream's 4096.
+		if v, err := strconv.Atoi(strings.TrimSpace(os.Getenv("LLM_DEFAULT_CONTEXT_WINDOW"))); err == nil && v > 0 {
+			return v, nil
+		}
 		return 4096, nil
 	}
 }