feat(llm-inference-multimodel): codify Phi-3.5-mini + Llama-3.1-8B GGUF staging (t_730f9584)

Adds idempotent, data-driven GGUF staging for the two new router models on
astro-orbiter alongside the production Qwen3.6-35B-A3B-UD-Q4_K_S. Both files
were already staged live (byte-exact); this commit codifies them in Ansible so
future re-runs and any new model adds are version-controlled and audit-friendly.

Changes:
- roles/llm-inference-multimodel/tasks/stage_model.yml (NEW)
  Idempotent per-model task: stat -> exact byte-size guard -> conditional
  get_url -> ownership/mode ensure -> notify router restart handler only on
  actual download. Loops from models.yml; nothing hardcoded.

- roles/llm-inference-multimodel/tasks/models.yml
  Appends the stage_model.yml loop (tagged: models) after the existing Qwen3.6
  download tasks. Data driven from host_vars/astro-orbiter/vars.yml.

- roles/llm-inference-multimodel/defaults/main.yml
  Adds llm_staged_models: [] default (empty = safe no-op for hosts with no
  staged model list defined).

- roles/llm-inference-multimodel/handlers/main.yml
  Adds 'restart llama-server-router on new GGUF' handler. Only fires when
  stage_model.yml performs an actual download or corrects ownership/mode.
  Normal idempotent re-runs (files already correct) do NOT fire this handler.

- host_vars/astro-orbiter/vars.yml
  Adds llm_staged_models list with the two new models:
    * Phi-3.5-mini-instruct-Q8_0.gguf (4,061,222,688 bytes,
      bartowski/Phi-3.5-mini-instruct-GGUF)
    * Meta-Llama-3.1-8B-Instruct-Q4_K_M.gguf (4,920,739,232 bytes,
      bartowski/Meta-Llama-3.1-8B-Instruct-GGUF)

- playbooks/day1_deploy_llm_inference_multimodel.yml
  Updates header comment: removes stale 'Semaphore broken' note, documents
  the correct execution channel (Semaphore template
  llm_inference_multimodel_stage_models, --tags models).

- group_vars/all/semaphore.yml
  Adds llm_inference_multimodel_stage_models template entry (config-as-code).
  Template is scoped to --tags models explicitly. Phase 4 (verify) is
  EXCLUDED: verify.yml starts llama-server-qwen on :8002, which would collide
  with the production llama-server-router.service already running on :8002.

Semaphore template created via API: project 1 / template id 19.
Execution: triggered immediately after this commit via Semaphore REST API.

ansible/roles/llm-inference-multimodel/tasks/models.yml

@@ -59,3 +59,18 @@
       Expected URL (bartowski UD-Q4_K_S):
       https://huggingface.co/bartowski/Qwen3.6-35B-A3B-UD-Q4_K_S-GGUF/resolve/main/Qwen3.6-35B-A3B-UD-Q4_K_S.gguf
   when: not (llm_qwen_model_stat.stat.exists | default(false))
+
+# --- Staged GGUF models (data-driven, idempotent) ----------------------------
+# Ensure every entry in llm_staged_models is present in llm_models_dir with the
+# EXACT expected byte size. When present AND size matches, this is a pure
+# no-op: no download, no service touch. When a genuine new/mismatched GGUF is
+# detected, it is downloaded + ownership/mode corrected and the router restart
+# handler is notified so the llama.cpp router re-discovers the models_dir.
+# Driven entirely by inventory vars (host_vars) — nothing hardcoded here, so
+# adding a future model = append to llm_staged_models in host_vars.
+- name: Stage data-driven GGUF models into {{ llm_models_dir }}
+  ansible.builtin.include_tasks: stage_model.yml
+  loop: "{{ llm_staged_models | default([]) }}"
+  loop_control:
+    loop_var: staged_model
+  tags: [models]

ansible/roles/llm-inference-multimodel/tasks/stage_model.yml

@@ -0,0 +1,67 @@
+---
+# ------------------------------------------------------------------------------
+# FILE: roles/llm-inference-multimodel/tasks/stage_model.yml
+# DESCRIPTION: Idempotent staging of a SINGLE GGUF listed in llm_staged_models.
+#              Looped from tasks/models.yml (one include per entry).
+#
+#              GUARD (idempotency):
+#                - stat the target path in llm_models_dir
+#                - get_url ONLY when the file is MISSING or its on-disk size
+#                  != the exact HF manifest size (staged_model.size_bytes)
+#                - when present AND size matches -> pure no-op (no download,
+#                  no service touch)
+#
+#              SIDE EFFECT ON CHANGE:
+#                When a genuine new/mismatched GGUF is downloaded (or its
+#                ownership/mode corrected), this task notifies the
+#                "restart llama-server-router on new GGUF" handler so the
+#                llama.cpp router re-discovers the models_dir. A normal
+#                re-run that finds the files already correct will NOT fire
+#                the handler — the live router is left untouched.
+#
+#              Driven entirely by inventory vars (host_vars), nothing
+#              hardcoded here, so adding a future model = append to the list.
+# ------------------------------------------------------------------------------
+
+- name: "Check if {{ staged_model.filename }} is present on disk"
+  ansible.builtin.stat:
+    path: "{{ llm_models_dir }}/{{ staged_model.filename }}"
+  register: _staged_stat
+
+- name: "Report {{ staged_model.filename }} presence (source: {{ staged_model.source_repo | default('n/a') }})"
+  ansible.builtin.debug:
+    msg: >-
+      {{ staged_model.filename }}:
+      exists={{ _staged_stat.stat.exists | default(false) }},
+      size={{ (_staged_stat.stat.size | default(0) | int) }},
+      expected={{ staged_model.size_bytes | int }},
+      match={{ (_staged_stat.stat.exists | default(false)) and
+               ((_staged_stat.stat.size | default(0) | int) == (staged_model.size_bytes | int)) }}
+  when: _staged_stat.stat.exists | default(false)
+
+- name: "Download {{ staged_model.filename }} (missing or size mismatch)"
+  ansible.builtin.get_url:
+    url: "{{ staged_model.url }}"
+    dest: "{{ llm_models_dir }}/{{ staged_model.filename }}"
+    owner: "{{ llm_service_user }}"
+    group: "{{ llm_service_user }}"
+    mode: "0664"
+    timeout: 600
+  become: true
+  when: >-
+    not (_staged_stat.stat.exists | default(false))
+    or (_staged_stat.stat.size | default(0) | int != (staged_model.size_bytes | int))
+  register: _staged_download
+  notify: restart llama-server-router on new GGUF
+
+- name: "Ensure ownership/mode on {{ staged_model.filename }}"
+  ansible.builtin.file:
+    path: "{{ llm_models_dir }}/{{ staged_model.filename }}"
+    owner: "{{ llm_service_user }}"
+    group: "{{ llm_service_user }}"
+    mode: "0664"
+  become: true
+  when: >-
+    (_staged_stat.stat.exists | default(false))
+    or (_staged_download is changed | default(false))
+  notify: restart llama-server-router on new GGUF