Document Depot/sccache cache as jllama-only in cross-repo scope

Add a 'Cross-repo scope' note to the CI build cache section explaining the sccache+Depot compiler cache benefits only this repo's native build, and link the workspace crossrepostatus.md non-parity entry. No build/CI behaviour change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Claude-Session: https://claude.ai/code/session_01LjWiKSyNzqqpobSKYRiew5

Author: claude

CLAUDE.md

@@ -206,6 +206,17 @@ container), the Windows jobs (sccache supports MSVC), and the Linux-host `test-c
 extend a job: install `sccache`, set the two `SCCACHE_WEBDAV_*` env vars, and (for
 RAM-limited runners) `BUILD_JOBS`.
 
+**Cross-repo scope — this is java-llama.cpp-only by nature.** `sccache` caches *compiler*
+output (C/C++/Rust/CUDA), and jllama is the only sibling repo with a native (C++/JNI) build,
+so it is the only one that benefits. The pure-Maven siblings (BitcoinAddressFinder,
+streambuffer, llamacpp-ai-index-maven-plugin) have no C/C++ to cache, run on **GitHub-hosted**
+runners (Depot's *GitHub Actions* cache backend activates only on **Depot-hosted** runners),
+and already cache their Maven dependencies via `actions/setup-java`'s `cache: maven`. The
+`DEPOT_TOKEN` organization secret is present in every repo but is **inert** outside jllama, and
+the README "Build cache by Depot" badge is intentionally kept here only — advertising it on the
+Maven repos would claim a capability they do not have. Recorded as deliberate non-parity in
+[`../workspace/crossrepostatus.md`](../workspace/crossrepostatus.md).
+
 ## Upgrading/Downgrading llama.cpp Version
 
 To change the llama.cpp version, update the following **three** files: