stage-313 absorb: gate _resolve_configured_provider_id alias resolution + harden bootstrap test isolation

Two in-stage fixes for v0.51.19 batch:

1) api/config.py — add resolve_alias=False param to
   _resolve_configured_provider_id() and pass it from
   resolve_model_provider(). The PR #1818 swap from
   _resolve_provider_alias() to _resolve_configured_provider_id()
   was correct for active-provider/badge surfaces but broke #1625's
   local-server-provider literal-preservation contract: 'ollama' →
   'custom' and 'lm-studio' → 'lmstudio' alias-collapse caused
   _LOCAL_SERVER_PROVIDERS membership check to miss, breaking the
   model-id full-path preservation for LM Studio/Ollama. The new
   flag preserves the raw provider value when called from
   resolve_model_provider, and named-custom-slug + base-url
   fallback both still run unchanged.

2) tests/test_bootstrap_discover_agent.py — pin Path.home() in
   _isolate_discover_agent_dir so the hard-coded
   'Path.home() / .hermes / hermes-agent' / 'Path.home() /
   hermes-agent' candidates in discover_agent_dir() can't pick up
   the dev machine's real install. The original PR #1817 isolation
   helper covered HERMES_HOME, HERMES_WEBUI_AGENT_DIR, and
   REPO_ROOT but missed the Path.home() leak.

Both surfaced on full pytest pre-release gate, fixed in stage,
ship in v0.51.19. Tests: full suite green.

api/config.py

@@ -789,11 +789,34 @@ def _resolve_configured_provider_id(
     config_obj: dict | None = None,
     *,
     base_url: object = None,
+    resolve_alias: bool = True,
 ) -> str:
+    """Normalize a configured provider id.
+
+    When ``resolve_alias`` is True (default, used for active-provider /
+    badge surfaces), falls through to ``_resolve_provider_alias`` after the
+    named-custom check. When False (used by ``resolve_model_provider``),
+    preserves the raw provider value so downstream local-server detection
+    (`_LOCAL_SERVER_PROVIDERS` membership in #1625) sees the original name
+    like ``ollama`` / ``lm-studio`` rather than alias-collapsed ``custom`` /
+    ``lmstudio``. The base-url-to-named-slug fallback still runs in both
+    modes when applicable.
+
+    See in-stage absorption note on stage-313 for the #1625 regression that
+    motivated the ``resolve_alias`` flag.
+    """
     named_slug = _named_custom_provider_slug_for_provider(provider, config_obj)
     if named_slug:
         return named_slug
 
+    if not resolve_alias:
+        raw = str(provider or "").strip().lower()
+        if base_url and raw == "custom":
+            by_base_url = _named_custom_provider_slug_for_base_url(base_url, config_obj)
+            if by_base_url:
+                return by_base_url
+        return str(provider or "")
+
     resolved = _resolve_provider_alias(provider)
     if (
         base_url
@@ -1423,6 +1446,7 @@ def resolve_model_provider(model_id: str) -> tuple:
             model_cfg.get("provider"),
             cfg,
             base_url=config_base_url,
+            resolve_alias=False,
         )
 
     # Heal legacy ``provider: local`` entries (written by WebUI < v0.50.252)

tests/test_bootstrap_discover_agent.py

@@ -54,6 +54,13 @@ def _isolate_discover_agent_dir(monkeypatch, tmp_path, hermes_path):
     # Force REPO_ROOT.parent to a dir that won't accidentally contain a
     # `hermes-agent` sibling on the dev machine running these tests.
     monkeypatch.setattr(bootstrap, "REPO_ROOT", tmp_path / "isolated-repo-root")
+    # Pin Path.home() to a directory with no `.hermes/hermes-agent` or
+    # `hermes-agent` so the hard-coded `Path.home() / ".hermes" / "hermes-agent"`
+    # / `Path.home() / "hermes-agent"` candidates in `discover_agent_dir()`
+    # cannot pick up the dev machine's real install. Stage-313 absorbed
+    # this in-stage after the original test file isolated only env vars
+    # and REPO_ROOT, missing the Path.home() leakage.
+    monkeypatch.setattr(bootstrap.Path, "home", classmethod(lambda cls: tmp_path / "isolated-home"))
 
 
 def test_discovers_agent_dir_from_hermes_shebang(monkeypatch, tmp_path):