build(paged): stacking patch-series scaffolding for llama.cpp paged attention

Numbered patches under backend/cpp/llama-cpp/patches/ applied in order against
the pinned LLAMA_VERSION (build hook in the llama.cpp: target). Each phase is one
small, independently-buildable patch so the work rebases cleanly across llama.cpp
bumps (anti-drift). README defines the series (0001 vendor manager -> 0006 prefix
caching) + the regen workflow.

Assisted-by: Claude:opus-4.8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/cpp/llama-cpp/Makefile

@@ -137,7 +137,12 @@ llama.cpp:
 	git remote add origin $(LLAMA_REPO)  && \
 	git fetch --all --tags && \
 	git checkout -b build $(LLAMA_VERSION) && \
-	git submodule update --init --recursive --depth 1 --single-branch
+	git submodule update --init --recursive --depth 1 --single-branch && \
+	for p in $(CURRENT_MAKEFILE_DIR)patches/0*.patch; do \
+		[ -e "$$p" ] || continue; \
+		echo "applying llama.cpp patch: $$p"; \
+		git apply --verbose "$$p" || { echo "patch failed: $$p"; exit 1; }; \
+	done
 
 llama.cpp/tools/grpc-server: llama.cpp
 	mkdir -p llama.cpp/tools/grpc-server

backend/cpp/llama-cpp/patches/README.md

@@ -0,0 +1,58 @@
+# llama.cpp patch series — paged attention (vLLM-parity engine)
+
+A **stacking** series: each patch is a small, self-contained, independently-buildable step toward an
+in-model paged-attention engine. They apply in numeric order on top of the pinned `LLAMA_VERSION`
+(`backend/cpp/llama-cpp/Makefile`). The build applies them automatically after checkout (see the
+`llama.cpp:` target). Keeping the work as ordered patches — rather than one big diff — is what lets us
+**rebase cleanly across llama.cpp bumps and avoid drift**: when a patch stops applying, only that small
+patch needs fixing, and the failure points at exactly which step the upstream change touched.
+
+## Base
+
+- `LLAMA_VERSION` pin in `../Makefile`. **All patches are generated against that exact commit.** Bumping
+  the pin = re-run the regen workflow below and fix only the patches that no longer apply.
+
+## The series (phases → patches)
+
+| # | Patch | What | Verifies |
+|---|-------|------|----------|
+| 0001 | `0001-vendor-paged-kv-manager.patch` | Add `src/paged-kv-manager.{h,cpp}` (vLLM-parity block manager, CPU foundation) + CMake; no behavior change | builds; unit-tested separately under `../paged/` |
+| 0002 | `0002-paged-kv-storage.patch` | Shared block-pool KV tensor + `set_rows`-by-slot writes, behind `LLAMA_KV_PAGED` | builds; write/gather round-trip |
+| 0003 | `0003-paged-gather-read.patch` | `build_attn_paged` gather-read in `llama-graph.cpp` | **Gate 0**: token-identical greedy gen, single + multi-seq |
+| 0004 | `0004-paged-ondemand-alloc.patch` | On-demand block allocation via PagedKVManager | max concurrent seqs before OOM |
+| 0005 | `0005-paged-continuous-batching.patch` | Block-granular admit/evict in the server slot path | tok/s vs concurrency, mixed-length |
+| 0006 | `0006-paged-prefix-caching.patch` | Block-hash cross-request prefix dedup | TTFT + memory on shared prefixes |
+
+Each row is a separate `git commit` on the dev branch (below), exported 1:1 as a patch. Default off
+(`LLAMA_KV_PAGED`) until Gate 0 (0003) is green, so partial series never changes stock behavior.
+
+## Regen workflow (the anti-drift recipe)
+
+```sh
+# 1. check out the exact pin into a dev tree
+git -C /tmp clone https://github.com/ggml-org/llama.cpp llama-dev && cd /tmp/llama-dev
+git checkout <LLAMA_VERSION from ../Makefile>
+git checkout -b paged
+
+# 2. apply the current series (each becomes a commit), or develop the next patch
+git am /path/to/backend/cpp/llama-cpp/patches/00*.patch     # or `git apply` + commit per patch
+
+# 3. iterate a phase as ONE commit, then export the whole series 1:1
+git format-patch <LLAMA_VERSION>..paged -o /path/to/backend/cpp/llama-cpp/patches/ --zero-commit -N
+
+# 4. on a pin bump: rebase `paged` onto the new pin; only conflicting patches need edits; re-export.
+```
+
+## Build integration
+
+`../Makefile`'s `llama.cpp:` target runs, after `git checkout -b build $(LLAMA_VERSION)`:
+```
+for p in $(CURRENT_MAKEFILE_DIR)/patches/0*.patch; do git apply --verbose "$p"; done
+```
+All variants (avx/avx2/avx512/cuda/…) copy the patched `llama.cpp/` tree, so the series ships everywhere.
+
+## Status
+
+0001 in progress. The CPU foundation (the block manager + ggml write/gather + attention numerics) is
+already built and verified under `../paged/` (`paged_kv_manager.*`, tests, `README.md`); these patches
+vendor it into the llama.cpp tree and wire it in-model phase by phase.