docs(meta_llama): verify API access; defer t4_3 to follow-up track

The Meta Llama developer docs URL (https://llama.developer.meta.com/docs/overview)
IS now reachable (200 OK; was 400 in the parent session). However,
the actual API endpoints are not publicly accessible:

  - https://api.meta.ai/v1/chat/completions -> 404 (no public surface)
  - https://llama-api.meta.com -> (no response)
  - https://api.llama.com -> 403 (auth-required)

Decision: defer t4_3 (Meta Llama API adapter) to a separate
follow-up track. The local-backend need is fully covered by
the Ollama native adapter (t4_2); Meta Llama via cloud is
out of scope for this track.

The follow-up track would require:
1. A public Meta OpenAI-compat API URL (not yet available)
2. Test target with a real key
3. A new PROVIDERS entry

See docs/reports/meta_llama_api_verification_20260611.md
for the full probe results and reasoning.

docs/reports/meta_llama_api_verification_20260611.md

@@ -0,0 +1,61 @@
+# Meta Llama API — 2026-06-11 Verification
+
+## TL;DR
+
+**The Meta Llama API is not publicly accessible.** The Meta Llama
+developer docs page is reachable (200 OK), but the actual API
+endpoints either 404 (no public surface) or 403 (auth-required).
+A 4th Llama backend (`meta_llama_chat`) cannot be implemented
+in this track.
+
+## Probe results (2026-06-11, from this session)
+
+| URL | Status | Notes |
+|---|---|---|
+| `https://llama.developer.meta.com` | 200 OK | landing page; JS-rendered docs |
+| `https://llama.developer.meta.com/docs/overview` | 200 OK | the URL the parent track tried; was 400 in parent session, now 200 |
+| `https://api.meta.ai/v1/chat/completions` | 404 Not Found | no public OpenAI-compat surface |
+| `https://llama-api.meta.com` | (no response) | DNS or connection failure |
+| `https://api.llama.com` | 403 Forbidden | requires auth |
+
+## Decision
+
+`t4_3` (Meta Llama API adapter) is DEFERRED. Three reasons:
+
+1. **No public API contract**: Meta does not publish a public
+   OpenAI-compat endpoint. The 4th Llama backend would need
+   either a partnership API key (out of scope for this OSS tool)
+   or a custom protocol that doesn't exist.
+2. **No test target**: Even if I implemented a stub, the
+   `live_gui` / integration tests couldn't verify it without
+   a real key.
+3. **Scope discipline**: The user's directive in this track is
+   "local models as first-class". The Ollama native adapter
+   (shipped in t4_2) covers the local-backend need. Meta Llama
+   via cloud is out of scope.
+
+## Where to add it later (separate track)
+
+If Meta publishes a public OpenAI-compat endpoint in the
+future, the follow-up would:
+
+1. Add `meta_llama_chat(model, messages, *, base_url, api_key)`
+   to `src/ai_client.py` (per the naming convention HARD RULE
+   on no new `src/*.py` files)
+2. Add a 4th `if base_url contains "meta.com"` branch in
+   `_send_llama` (or a new backend detection helper)
+3. Add `meta-llama/*` registry entries to `src/vendor_capabilities.py`
+4. Add a "Meta" provider in the provider combo (currently
+   `PROVIDERS` only lists Ollama-compatible URLs under `llama`)
+
+The follow-up track would be 1-2 days of work; it cannot
+ship without the public API URL.
+
+## Source
+
+This decision was made on 2026-06-11 in the
+`qwen_llama_grok_followup_20260611` track, Phase 4. The
+session-end report (`docs/reports/qwen_llama_grok_followup_session_end_20260611.md`)
+had marked t4_3 as "DEFER if URL still 400". The URL is
+now 200, but the actual API is not accessible, so the
+deferral stands on different grounds.