fix: stabilization pass — fail-closed auth, ai flag validation, lint/config/security hardening, regression tests

17-point code-level audit executed via Explorer->Architect->Builder->Tester->Reviewer;
Reviewer accepted (APPROVE_WITH_NOTES; 3 block-list items resolved):

- security: telegram sender-owner AND-gate + TELEGRAM_OWNER_ID, matrix
  MATRIX_ROOM_ID fail-closed, gpg --passphrase-fd 3 (no argv secret),
  /dev/tcp positional-arg form (checkport/smb-client/share-lib/NET_PROBE),
  eval deny-by-default + --no-command-execution carried by both chat bridges,
  tty-gated --trust; config/{telegram,matrix}.env reference templates
- ai: all ExecStart flags validated against installed llama.cpp
  (requested->error, default->omit+warn, CONFIG_REQUESTED_FLAGS); single-file
  hf download failure rc=1 + no .hf-meta; LLAMACPP_HOST coherent;
  POS_SUBCMDS + metadata gaps closed
- tooling: lint-conventions Bash-native rewrite (~24-30x faster, rules and
  output byte-identical, :num restored); pos system uninstall covers all 12
  libs + scale-tail + flags dir + systemd user units (|| true) + plugin
  markers; anchored .bash_completion/.bashrc removal replaces sed -i '/pos/d'
- config: canonical load_env_file in lib/config-ui.sh (CRLF strip, env-wins,
  XDG, LOADED_ENV_KEYS); 9 tools migrated; entertainment-lib collapsed to
  wrappers; docker-compose deliberately unmigrated (source semantics)
- tests: first committed regression suite — tests/run-tests.sh zero-dep
  runner + make test; 12 files / 179 checks / 0 skip / ~52s; hard skip
  contract; systemd-analyze verify on generated unit PASS

Verified: make gen idempotent; make check green; make lint 0 FAIL, 0 WARN;
make test green; bash -n clean; git diff --check clean. Audit deliverables +
agent reports + AGENT_TODO Done entry included.

apps/ai/llamacpp.sh

@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+set -euo pipefail
+source "$(dirname "$0")/../../lib/common.sh"
+
+# llama.cpp — Local LLM inference server (llama-server) + CLI tools.
+#
+# Asset-naming note (probed live 2026-09-06): the vX.Y.Z milestone
+# releases carry NO binary assets (only nightly-tag.txt); the prebuilt
+# Ubuntu binaries ship on the nightly bNNNNN releases as
+#   llama-<tag>-bin-ubuntu-x64.tar.gz    /    llama-<tag>-bin-ubuntu-arm64.tar.gz
+# so we scan the newest releases for the first one that ships our arch
+# instead of hitting /releases/latest.
+RELEASES_URL="https://api.github.com/repos/ggml-org/llama.cpp/releases?per_page=10"
+
+install_llamacpp() {
+    command -v llama-server &>/dev/null && { log "llama.cpp already installed"; return 0; }
+
+    local arch
+    case "$(uname -m)" in
+        x86_64)  arch="x64" ;;
+        aarch64) arch="arm64" ;;
+        *) err "Unsupported architecture: $(uname -m) (llama.cpp publishes x64/arm64 Ubuntu builds)" ;;
+    esac
+
+    spawn "Fetching latest llama.cpp release info" bash -c "
+        curl -fsSL '$RELEASES_URL' -o /tmp/llamacpp-releases.json
+    "
+
+    local tag asset_url
+    if ! { read -r tag && read -r asset_url; } < <(python3 -c "
+import json, sys
+rels = json.load(open('/tmp/llamacpp-releases.json'))
+suffix = '-bin-ubuntu-$arch.tar.gz'
+for r in rels:
+    for a in r['assets']:
+        if a['name'].endswith(suffix):
+            print(r['tag_name'])
+            print(a['browser_download_url'])
+            sys.exit(0)
+sys.exit(1)
+" 2>/dev/null); then
+        rm -f /tmp/llamacpp-releases.json
+        err "No llama.cpp Ubuntu $arch binary release found — see https://github.com/ggml-org/llama.cpp/releases"
+    fi
+
+    spawn "Installing llama.cpp $tag ($arch)" bash -c "
+        install_dir=/usr/local/lib/llama.cpp-$tag
+        curl -fsSL '$asset_url' -o /tmp/llamacpp.tar.gz
+        sudo rm -rf \$install_dir
+        sudo mkdir -p \$install_dir
+        sudo tar xzf /tmp/llamacpp.tar.gz -C \$install_dir --strip-components=1
+        for bin in \$install_dir/llama*; do
+            [ -f \"\$bin\" ] && [ -x \"\$bin\" ] || continue
+            sudo ln -sf \"\$bin\" /usr/local/bin/\$(basename \"\$bin\")
+        done
+        rm -f /tmp/llamacpp.tar.gz /tmp/llamacpp-releases.json
+    "
+
+    log "llama.cpp $tag installed — run the server with 'pos ai server start <model.gguf>'"
+}
+
+uninstall_llamacpp() {
+    command -v llama-server &>/dev/null || { log "llama.cpp not installed"; return 0; }
+
+    spawn "Removing llama.cpp files" sudo rm -rf /usr/local/lib/llama.cpp-*
+
+    # Remove only the symlinks we created (targets inside the install dir);
+    # unrelated /usr/local/bin/llama* files are left alone.
+    spawn "Removing llama.cpp symlinks" bash -c "
+        for link in /usr/local/bin/llama*; do
+            [ -L \"\$link\" ] || continue
+            target=\$(readlink \"\$link\")
+            case \"\$target\" in
+                /usr/local/lib/llama.cpp-*) sudo rm -f \"\$link\" ;;
+            esac
+        done
+    "
+
+    log "llama.cpp removed"
+}
+
+case "${1:-}" in
+    uninstall) uninstall_llamacpp ;;
+    *)         install_llamacpp ;;
+esac