Fix #373: fallback_model blank fields no longer trigger gateway warnings

When users blank fallback_model fields or set enabled: false, the validation
and gateway now treat this as intentionally disabling fallback instead of
showing warnings.

Changes:
- hermes_cli/config.py: Skip warnings when both provider and model are blank
  or when enabled: false is set
- gateway/run.py: Return None for disabled fallback configs
- tests: Added 8 new tests for blank/disabled fallback scenarios

Behavior:
- Both fields blank: no warnings (intentional disable)
- enabled: false: no warnings (explicit disable)
- One field blank: warning shown (likely misconfiguration)
- Valid config: no warnings

Fixes #373

gateway/run.py

@@ -1026,6 +1026,16 @@ class GatewayRunner:
                     cfg = _y.safe_load(_f) or {}
                 fb = cfg.get("fallback_providers") or cfg.get("fallback_model") or None
                 if fb:
+                    # Treat empty dict / disabled fallback as "not configured"
+                    if isinstance(fb, dict):
+                        _enabled = fb.get("enabled")
+                        if _enabled is False or (
+                            isinstance(_enabled, str)
+                            and _enabled.strip().lower() in ("false", "0", "no", "off")
+                        ):
+                            return None
+                        if not fb.get("provider") and not fb.get("model"):
+                            return None
                     return fb
         except Exception:
             pass

hermes_cli/config.py

@@ -1421,6 +1421,7 @@ def validate_config_structure(config: Optional[Dict[str, Any]] = None) -> List["
                     ))
 
     # ── fallback_model must be a top-level dict with provider + model ────
+    # Blank or explicitly disabled fallback is intentional — skip validation.
     fb = config.get("fallback_model")
     if fb is not None:
         if not isinstance(fb, dict):
@@ -1430,21 +1431,40 @@ def validate_config_structure(config: Optional[Dict[str, Any]] = None) -> List["
                 "Change to:\n"
                 "  fallback_model:\n"
                 "    provider: openrouter\n"
-                "    model: anthropic/claude-sonnet-4",
+                "    model: anthropic/claude-sonnet-4\n"
+                "Or disable with:\n"
+                "  fallback_model:\n"
+                "    enabled: false",
             ))
         elif fb:
-            if not fb.get("provider"):
-                issues.append(ConfigIssue(
-                    "warning",
-                    "fallback_model is missing 'provider' field — fallback will be disabled",
-                    "Add: provider: openrouter (or another provider)",
-                ))
-            if not fb.get("model"):
-                issues.append(ConfigIssue(
-                    "warning",
-                    "fallback_model is missing 'model' field — fallback will be disabled",
-                    "Add: model: anthropic/claude-sonnet-4 (or another model)",
-                ))
+            # Skip warnings when fallback is explicitly disabled (enabled: false)
+            _enabled = fb.get("enabled")
+            if _enabled is False or (isinstance(_enabled, str) and _enabled.strip().lower() in ("false", "0", "no", "off")):
+                pass  # intentionally disabled — no warnings
+            else:
+                # Check if both fields are blank (intentional disable)
+                provider = fb.get("provider")
+                model = fb.get("model")
+                provider_blank = not provider or (isinstance(provider, str) and not provider.strip())
+                model_blank = not model or (isinstance(model, str) and not model.strip())
+                
+                # Only warn if at least one field is set (user might be trying to configure)
+                # If both are blank, treat as intentionally disabled
+                if not provider_blank or not model_blank:
+                    if provider_blank:
+                        issues.append(ConfigIssue(
+                            "warning",
+                            "fallback_model is missing 'provider' field — fallback will be disabled",
+                            "Add: provider: openrouter (or another provider)\n"
+                            "Or disable with: enabled: false",
+                        ))
+                    if model_blank:
+                        issues.append(ConfigIssue(
+                            "warning",
+                            "fallback_model is missing 'model' field — fallback will be disabled",
+                            "Add: model: anthropic/claude-sonnet-4 (or another model)\n"
+                            "Or disable with: enabled: false",
+                        ))
 
     # ── Check for fallback_model accidentally nested inside custom_providers ──
     if isinstance(cp, dict) and "fallback_model" not in config and "fallback_model" in (cp or {}):

tests/hermes_cli/test_config_validation.py

@@ -136,6 +136,83 @@ class TestFallbackModelValidation:
         fb_issues = [i for i in issues if "fallback" in i.message.lower()]
         assert len(fb_issues) == 0
 
+    def test_blank_fallback_fields_no_issues(self):
+        """Blank fallback_model fields (both empty) should not trigger warnings."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "provider": "",
+                "model": "",
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
+    def test_blank_fallback_fields_with_whitespace_no_issues(self):
+        """Blank fallback_model fields with whitespace should not trigger warnings."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "provider": "  ",
+                "model": "  ",
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
+    def test_none_fallback_fields_no_issues(self):
+        """None fallback_model fields should not trigger warnings."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "provider": None,
+                "model": None,
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
+    def test_enabled_false_no_issues(self):
+        """enabled: false should suppress warnings."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "enabled": False,
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
+    def test_enabled_false_string_no_issues(self):
+        """enabled: 'false' (string) should suppress warnings."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "enabled": "false",
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
+    def test_partial_blank_fallback_warns(self):
+        """Partial blank fallback (only one field blank) should warn."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "provider": "",
+                "model": "anthropic/claude-sonnet-4",
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 1
+        assert "provider" in fb_issues[0].message
+
+    def test_valid_fallback_with_enabled_true(self):
+        """Valid fallback with enabled: true should not warn."""
+        issues = validate_config_structure({
+            "fallback_model": {
+                "enabled": True,
+                "provider": "openrouter",
+                "model": "anthropic/claude-sonnet-4",
+            },
+        })
+        fb_issues = [i for i in issues if "fallback" in i.message.lower()]
+        assert len(fb_issues) == 0
+
 
 class TestMissingModelSection:
     """Warn when custom_providers exists but model section is missing."""