fix(custom-model): warn when parallel llama.cpp slots leave too little context per request (#658)

Squash of PR #658. Discovery records each llama.cpp model's parallel slot
count (from --parallel/-np, or /props total_slots when the launch command
states none), and a Claude launch warns when the context split across
those slots leaves less than 40K tokens per request. An explicit
--parallel beside a /props context records a slot count of 1, so a later
round overwrites an earlier count, and a non-2xx /props is remembered per
launch command while a network error is retried.

Merge-time fix by the maintainer: the architecture-invariants sentence on
the explicit --parallel case now says it records a slot count of 1.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -996,7 +996,10 @@ confirmed? } | { clear: true }` applies (or clears) the session's
     just because a swap is needed at all — only when it would disrupt
     someone else.
   - `{requiresContextWarning: true, modelId, contextLength,
-minSafeContextTokens}` — Claude Code's own fixed per-turn overhead
+minSafeContextTokens, slotCount?}` — `slotCount` is present whenever the model runs more than
+    one parallel llama.cpp slot, and the warning also fires when the context
+    divided across those slots is below the floor even though the whole context
+    is not. Claude Code's own fixed per-turn overhead
     (system prompt + tool schemas) can exceed a small model's entire
     discovered context on its own, before any conversation history exists
     to compact, guaranteeing the very first message fails regardless of