fix(models): use Anthropic-native headers for model validation

The generic /v1/models probe in validate_requested_model() sent a plain
'Authorization: Bearer <key>' header, which works for OpenAI-compatible
endpoints but results in a 401 Unauthorized from Anthropic's API.
Anthropic requires x-api-key + anthropic-version headers (or Bearer for
OAuth tokens from Claude Code).

Add a provider-specific branch for normalized == 'anthropic' that calls
the existing _fetch_anthropic_models() helper, which already handles
both regular API keys and Claude Code OAuth tokens correctly.  This
mirrors the pattern already used for openai-codex, copilot, and bedrock.

The branch also includes:
- fuzzy auto-correct (cutoff 0.9) for near-exact model ID typos
- fuzzy suggestions (cutoff 0.5) when the model is not listed
- graceful fall-through when the token cannot be resolved or the
  network is unreachable (accepts with a warning rather than hard-fail)
- a note that newer/preview/snapshot model IDs can be gate-listed
  and may still work even if not returned by /v1/models

Fixes Anthropic provider users seeing 'service unreachable' errors
when running /model <claude-model> because every probe 401'd.

hermes_cli/models.py

@@ -2656,6 +2656,51 @@ def validate_requested_model(
                 ),
             }
 
+    # Native Anthropic provider: /v1/models requires x-api-key (or Bearer for
+    # OAuth) plus anthropic-version headers.  The generic OpenAI-style probe
+    # below uses plain Bearer auth and 401s against Anthropic, so dispatch to
+    # the native fetcher which handles both API keys and Claude-Code OAuth
+    # tokens.  (The api_mode=="anthropic_messages" branch below handles the
+    # Messages-API transport case separately.)
+    if normalized == "anthropic":
+        anthropic_models = _fetch_anthropic_models()
+        if anthropic_models is not None:
+            if requested_for_lookup in set(anthropic_models):
+                return {
+                    "accepted": True,
+                    "persist": True,
+                    "recognized": True,
+                    "message": None,
+                }
+            auto = get_close_matches(requested_for_lookup, anthropic_models, n=1, cutoff=0.9)
+            if auto:
+                return {
+                    "accepted": True,
+                    "persist": True,
+                    "recognized": True,
+                    "corrected_model": auto[0],
+                    "message": f"Auto-corrected `{requested}` → `{auto[0]}`",
+                }
+            suggestions = get_close_matches(requested, anthropic_models, n=3, cutoff=0.5)
+            suggestion_text = ""
+            if suggestions:
+                suggestion_text = "\n  Similar models: " + ", ".join(f"`{s}`" for s in suggestions)
+            # Accept anyway — Anthropic sometimes gates newer/preview models
+            # (e.g. snapshot IDs, early-access releases) behind accounts
+            # even though they aren't listed on /v1/models.
+            return {
+                "accepted": True,
+                "persist": True,
+                "recognized": False,
+                "message": (
+                    f"Note: `{requested}` was not found in Anthropic's /v1/models listing. "
+                    f"It may still work if you have early-access or snapshot IDs."
+                    f"{suggestion_text}"
+                ),
+            }
+        # _fetch_anthropic_models returned None — no token resolvable or
+        # network failure.  Fall through to the generic warning below.
+
     # Anthropic Messages API: many proxies don't implement /v1/models.
     # Try probing with correct auth; if it fails, accept with a warning.
     if api_mode == "anthropic_messages":