docs + guard: single 262k slot state, split-limits analysis, cache incident

- spec matrix + PP doc: production state = 1 slot @ 262144, split 0.53
  (34 blocks), KV 8192/8192, 3090 at 23460/24576. New 'Split limits
  (measured 2026-08-17)' section: 0.50/0.54/0.55 boundary data, the
  KV-per-device rounding rule (round(f x 66)), and why 35 blocks is
  unreachable (9-FA flip at f~0.538).
- PP doc: cache incident writeup - full Dankserver disk -> 0-byte cache
  entries -> corrupt weights -> degenerate output; fix + signature.
- deployment.md + AGENTS.md + index.md: numbers brought current.
- scripts/prune-rpc-cache.sh: cron guard capping the worker cache at
  40 GiB (oldest first) to prevent the disk-full recurrence.

scripts/prune-rpc-cache.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+# Bound the ggml-rpc worker tensor cache.
+#
+# The worker (frank-pp-worker on Dankserver) keys cache entries per
+# session, so each model load writes a fresh full copy (~15 GB). Left
+# unbounded, the directory filled the root disk to 100% on 2026-08-17;
+# failed cache writes left 0-byte entries, and a later reload served
+# corrupt weights -> degenerate model output (see the cache incident in
+# docs/Pipeline Parallelism/Qwen3.8 PP Deployment.md).
+#
+# This script prunes the cache to a byte cap, oldest files first. Cache
+# entries are derived data: safe to delete. Run from cron on Dankserver.
+set -euo pipefail
+
+CACHE_DIR=/home/dank/.cache/llama.cpp/rpc
+MAX_BYTES=$((40 * 1024 * 1024 * 1024))   # 40 GiB
+
+if [[ ! -d "$CACHE_DIR" ]]; then
+    exit 0
+fi
+
+total=$(du -sb "$CACHE_DIR" | cut -f1)
+if (( total <= MAX_BYTES )); then
+    exit 0
+fi
+
+while (( total > MAX_BYTES )); do
+    oldest=$(ls -1t "$CACHE_DIR" | tail -1)
+    if [[ -z "$oldest" ]]; then
+        break
+    fi
+    rm -f -- "$CACHE_DIR/$oldest"
+    total=$(du -sb "$CACHE_DIR" | cut -f1)
+done
+
+echo "prune-rpc-cache: pruned to $(du -sh "$CACHE_DIR" | cut -f1)"