feat(acp): list named custom providers in the ACP model selector

Named endpoints from the providers: mapping (and legacy custom_providers:
list) never appear in the ACP model selector: _build_model_state lists
only the canonical current provider's catalog, and canonical provider
enumeration does not include user-defined named endpoints. The TUI
/model picker already renders these entries (#47039, implemented for the
TUI surface only), so editor clients silently hide endpoints the user
configured — e.g. an OpenAI-compatible Bedrock Mantle Responses provider.

Add _named_custom_provider_catalogs(), sourcing entries from
get_compatible_custom_providers() (covers both config shapes), and append
its models to the selector payload. Choice ids use the custom:<name>
slug shape so custom:<name>:<model> selections round-trip through
parse_model_input / resolve_runtime_provider unchanged on set_session_model.

Declared models (default_model + models) survive failed live /models
discovery — some OpenAI-compatible endpoints expose no /models route yet
serve their declared models fine. Honors providers.<name>.enabled: false
and discover_models: false.

Verified: scripts/run_tests.sh tests/acp/ — 318 passed, 0 failed;
scripts/check-windows-footguns.py clean.

acp_adapter/server.py

@@ -85,6 +85,110 @@ from tools.approval import (
 
 logger = logging.getLogger(__name__)
 
+
+def _named_custom_provider_catalogs() -> list[tuple[str, str, list[tuple[str, str]]]]:
+    """Return ``(slug, label, [(model_id, description), ...])`` for named endpoints.
+
+    Covers both the v12 ``providers:`` mapping and the legacy
+    ``custom_providers:`` list.  These endpoints never appear in canonical
+    provider enumeration, so without this the ACP model selector hides every
+    named endpoint that the TUI ``/model`` picker already renders (#47039
+    implemented named-endpoint rows for the TUI surface only).
+
+    Model lists come from the entry's declared models (``default_model`` +
+    ``models``), refreshed from the endpoint's live ``/models`` listing when a
+    credential is available and ``discover_models`` is not disabled.  Declared
+    models are kept even when live discovery fails — some OpenAI-compatible
+    endpoints (e.g. Bedrock Mantle Responses) expose no ``/models`` route at
+    all yet serve the declared models fine.
+
+    Slugs use the ``custom:<name>`` shape that ``parse_model_input`` and
+    ``resolve_runtime_provider`` already resolve, so encoded choice ids
+    (``custom:<name>:<model>``) round-trip through ``set_session_model``
+    unchanged.
+    """
+    try:
+        from hermes_cli.config import (
+            get_compatible_custom_providers,
+            is_provider_enabled,
+            load_config,
+        )
+        from hermes_cli.models import fetch_api_models
+    except ImportError:
+        return []
+
+    try:
+        cfg = load_config()
+        entries = get_compatible_custom_providers(cfg)
+    except Exception:
+        logger.debug("Could not load named custom providers", exc_info=True)
+        return []
+
+    # ``get_compatible_custom_providers`` drops the ``enabled`` flag during
+    # normalization, so collect explicitly disabled provider keys from the
+    # raw config and skip their entries below.
+    disabled_keys: set[str] = set()
+    raw_providers = cfg.get("providers") if isinstance(cfg, dict) else None
+    if isinstance(raw_providers, dict):
+        for raw_key, raw_entry in raw_providers.items():
+            if isinstance(raw_entry, dict) and not is_provider_enabled(raw_entry):
+                disabled_keys.add(str(raw_key).strip().lower())
+
+    catalogs: list[tuple[str, str, list[tuple[str, str]]]] = []
+    for entry in entries:
+        if not isinstance(entry, dict):
+            continue
+        provider_key = str(entry.get("provider_key", "") or "").strip()
+        if provider_key.lower() in disabled_keys:
+            continue
+        name = str(entry.get("name", "") or "").strip()
+        base_url = str(entry.get("base_url", "") or "").strip()
+        if not name or not base_url:
+            continue
+        slug_source = provider_key or name
+        slug = "custom:" + slug_source.strip().lower().replace(" ", "-")
+
+        api_key = str(entry.get("api_key", "") or "").strip()
+        if not api_key:
+            key_env = str(entry.get("key_env", "") or "").strip()
+            api_key = os.environ.get(key_env, "").strip() if key_env else ""
+
+        declared: list[str] = []
+        default_model = str(entry.get("model", "") or "").strip()
+        if default_model:
+            declared.append(default_model)
+        models_cfg = entry.get("models")
+        if isinstance(models_cfg, dict):
+            for mid in models_cfg:
+                mid = str(mid or "").strip()
+                if mid and mid not in declared:
+                    declared.append(mid)
+
+        if not api_key and not declared:
+            # No credential to discover with and nothing declared:
+            # not addressable from the selector.
+            continue
+
+        model_ids = list(declared)
+        discover = entry.get("discover_models", True)
+        if isinstance(discover, str):
+            discover = discover.lower() not in {"false", "no", "0"}
+        if discover and api_key:
+            try:
+                live = fetch_api_models(
+                    api_key, base_url, api_mode=entry.get("api_mode")
+                )
+            except Exception:
+                live = None
+            if live:
+                model_ids = declared + [m for m in live if m not in declared]
+
+        if not model_ids:
+            continue
+        catalogs.append((slug, name, [(mid, "") for mid in model_ids]))
+
+    return catalogs
+
 try:
     from hermes_cli import __version__ as HERMES_VERSION
 except Exception:
@@ -664,6 +768,28 @@ class HermesACPAgent(acp.Agent):
                     )
                     seen_ids.add(choice_id)
 
+            # Named user-defined endpoints (providers: / custom_providers:)
+            # are invisible to canonical provider enumeration — append them
+            # so editor clients can select them like the TUI /model picker.
+            for named_slug, named_label, named_catalog in _named_custom_provider_catalogs():
+                for named_model, named_desc in named_catalog:
+                    named_choice = self._encode_model_choice(named_slug, named_model)
+                    if not named_choice or named_choice in seen_ids:
+                        continue
+                    named_parts = [f"Provider: {named_label}"]
+                    if named_desc:
+                        named_parts.append(str(named_desc).strip())
+                    if named_slug == normalized_provider and named_model == model:
+                        named_parts.append("current")
+                    available_models.append(
+                        ModelInfo(
+                            model_id=named_choice,
+                            name=named_model,
+                            description=" • ".join(part for part in named_parts if part),
+                        )
+                    )
+                    seen_ids.add(named_choice)
+
             current_model_id = self._encode_model_choice(normalized_provider, model)
             if current_model_id and current_model_id not in seen_ids:
                 provider_name = provider_label(normalized_provider)

tests/acp/test_named_provider_catalogs.py

@@ -0,0 +1,203 @@
+"""Tests for named user-defined provider entries in the ACP model selector.
+
+Named endpoints from the ``providers:`` mapping (and legacy
+``custom_providers:`` list) are invisible to canonical provider enumeration,
+so ``_build_model_state`` must append them explicitly for ACP clients to
+offer them — the TUI ``/model`` picker already renders these entries
+(#47039 implemented named endpoints for the TUI surface only).
+"""
+
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import pytest
+
+from acp_adapter.server import HermesACPAgent, _named_custom_provider_catalogs
+from acp_adapter.session import SessionManager
+from acp.schema import SessionModelState
+
+
+MANTLE_URL = "https://bedrock-mantle.us-east-1.api.aws/openai/v1"
+
+
+def _cfg(providers=None, custom_providers=None):
+    cfg = {}
+    if providers is not None:
+        cfg["providers"] = providers
+    if custom_providers is not None:
+        cfg["custom_providers"] = custom_providers
+    return cfg
+
+
+class TestNamedCustomProviderCatalogs:
+    def test_declared_default_model_survives_failed_discovery(self, monkeypatch):
+        """Endpoints without a /models route keep their declared models."""
+        monkeypatch.setenv("BEDROCK_MANTLE_API_KEY", "test-key")
+        cfg = _cfg(
+            providers={
+                "bedrock-mantle": {
+                    "name": "AWS Bedrock Mantle",
+                    "base_url": MANTLE_URL,
+                    "key_env": "BEDROCK_MANTLE_API_KEY",
+                    "api_mode": "codex_responses",
+                    "default_model": "openai.gpt-5.5",
+                }
+            }
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models", return_value=None
+        ):
+            catalogs = _named_custom_provider_catalogs()
+
+        assert catalogs == [
+            (
+                "custom:bedrock-mantle",
+                "AWS Bedrock Mantle",
+                [("openai.gpt-5.5", "")],
+            )
+        ]
+
+    def test_live_discovery_extends_declared_models(self, monkeypatch):
+        monkeypatch.setenv("SOME_KEY", "k")
+        cfg = _cfg(
+            providers={
+                "relay": {
+                    "name": "Relay",
+                    "base_url": "https://relay.example/v1",
+                    "key_env": "SOME_KEY",
+                    "default_model": "model-a",
+                }
+            }
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models",
+            return_value=["model-a", "model-b"],
+        ):
+            catalogs = _named_custom_provider_catalogs()
+
+        assert len(catalogs) == 1
+        slug, label, models = catalogs[0]
+        assert slug == "custom:relay"
+        assert [m for m, _ in models] == ["model-a", "model-b"]
+
+    def test_declared_models_dict_included(self, monkeypatch):
+        monkeypatch.setenv("SOME_KEY", "k")
+        cfg = _cfg(
+            providers={
+                "relay": {
+                    "name": "Relay",
+                    "base_url": "https://relay.example/v1",
+                    "key_env": "SOME_KEY",
+                    "default_model": "model-a",
+                    "models": {"model-b": {}, "model-c": {}},
+                }
+            }
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models", return_value=None
+        ):
+            catalogs = _named_custom_provider_catalogs()
+
+        assert [m for m, _ in catalogs[0][2]] == ["model-a", "model-b", "model-c"]
+
+    def test_disabled_provider_skipped(self, monkeypatch):
+        monkeypatch.setenv("SOME_KEY", "k")
+        cfg = _cfg(
+            providers={
+                "off": {
+                    "name": "Disabled Endpoint",
+                    "base_url": "https://off.example/v1",
+                    "key_env": "SOME_KEY",
+                    "default_model": "m",
+                    "enabled": False,
+                }
+            }
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models", return_value=None
+        ):
+            assert _named_custom_provider_catalogs() == []
+
+    def test_no_credential_and_no_declared_models_skipped(self, monkeypatch):
+        monkeypatch.delenv("MISSING_KEY", raising=False)
+        cfg = _cfg(
+            providers={
+                "bare": {
+                    "name": "Bare",
+                    "base_url": "https://bare.example/v1",
+                    "key_env": "MISSING_KEY",
+                }
+            }
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models", return_value=None
+        ):
+            assert _named_custom_provider_catalogs() == []
+
+    def test_legacy_custom_providers_list_included(self, monkeypatch):
+        monkeypatch.setenv("SOME_KEY", "k")
+        cfg = _cfg(
+            custom_providers=[
+                {
+                    "name": "Legacy Endpoint",
+                    "base_url": "https://legacy.example/v1",
+                    "key_env": "SOME_KEY",
+                    "model": "legacy-model",
+                }
+            ]
+        )
+        with patch("hermes_cli.config.load_config", return_value=cfg), patch(
+            "hermes_cli.models.fetch_api_models", return_value=None
+        ):
+            catalogs = _named_custom_provider_catalogs()
+
+        assert catalogs == [
+            ("custom:legacy-endpoint", "Legacy Endpoint", [("legacy-model", "")])
+        ]
+
+
+class TestModelStateIncludesNamedProviders:
+    @pytest.mark.asyncio
+    async def test_named_provider_models_appear_in_model_state(self):
+        manager = SessionManager(
+            agent_factory=lambda: SimpleNamespace(
+                model="gpt-5.4", provider="openai-codex"
+            )
+        )
+        acp_agent = HermesACPAgent(session_manager=manager)
+
+        with patch(
+            "hermes_cli.models.curated_models_for_provider",
+            return_value=[("gpt-5.4", "recommended")],
+        ), patch(
+            "acp_adapter.server._named_custom_provider_catalogs",
+            return_value=[
+                (
+                    "custom:bedrock-mantle",
+                    "AWS Bedrock Mantle",
+                    [("openai.gpt-5.5", "")],
+                )
+            ],
+        ):
+            resp = await acp_agent.new_session(cwd="/tmp")
+
+        assert isinstance(resp.models, SessionModelState)
+        ids = [m.model_id for m in resp.models.available_models]
+        # Current provider's models come first, named endpoints after.
+        assert ids[0] == "openai-codex:gpt-5.4"
+        assert "custom:bedrock-mantle:openai.gpt-5.5" in ids
+        named = next(
+            m
+            for m in resp.models.available_models
+            if m.model_id == "custom:bedrock-mantle:openai.gpt-5.5"
+        )
+        assert "AWS Bedrock Mantle" in (named.description or "")
+
+    def test_selector_choice_id_round_trips_through_parse_model_input(self):
+        """The encoded choice id must resolve back to the named provider."""
+        from hermes_cli.models import parse_model_input
+
+        choice_id = "custom:bedrock-mantle:openai.gpt-5.5"
+        provider, model = parse_model_input(choice_id, "bedrock")
+        assert provider == "custom:bedrock-mantle"
+        assert model == "openai.gpt-5.5"