fix: prevent infinite auto-compact loop for unknown 3P models (#635) (#636)

- Raise context window fallback from 8k to 128k for unknown OpenAI-compat models.
  The 8k fallback caused effective context (8k minus output reservation) to go
  negative, making auto-compact fire on every single message.
- Add safety floor in getEffectiveContextWindowSize(): effective context is
  always at least reservedTokensForSummary + 13k buffer, ensuring the
  auto-compact threshold stays positive.
- Add missing MiniMax model entries (M2.5, M2.5-highspeed, M2.1, M2.1-highspeed)
  all at 204,800 context / 131,072 max output per MiniMax docs.
- Add tests for MiniMax variants, 128k fallback, and autoCompact floor.

Fixes #635

Co-authored-by: root <root@vm7508.lumadock.com>

src/services/compact/autoCompact.ts

@@ -45,7 +45,12 @@ export function getEffectiveContextWindowSize(model: string): number {
     }
   }
 
-  return contextWindow - reservedTokensForSummary
+  // Floor: effective context must be at least the summary reservation plus a
+  // usable buffer. If it goes lower, the auto-compact threshold becomes
+  // negative and fires on every message (issue #635).
+  const autocompactBuffer = 13_000 // must match AUTOCOMPACT_BUFFER_TOKENS
+  const effectiveContext = contextWindow - reservedTokensForSummary
+  return Math.max(effectiveContext, reservedTokensForSummary + autocompactBuffer)
 }
 
 export type AutoCompactTrackingState = {