fix(auxiliary): route custom:<name> through named-provider arm + Palantir Bearer auth

When the user's main provider is a named custom_providers entry exposing an
Anthropic Messages surface (e.g. Palantir Foundry's
/api/v2/llm/proxy/anthropic, custom LiteLLM/Bedrock proxies), auxiliary
tasks (title generation, compression, web extract, session search, etc.)
returned HTTP 404 NOT_FOUND for every call.

Root cause: `_resolve_auto` collapsed any `custom:<name>` main provider
to plain `"custom"` and passed runtime_base_url as explicit_base_url.
This landed in `resolve_provider_client`'s anonymous-custom arm
(`if provider == "custom":`), which unconditionally calls
`_to_openai_base_url` — that helper strips a trailing `/anthropic` and
substitutes `/v1` (designed for MiniMax/ZAI which expose both surfaces).
The result for Palantir is `/api/v2/llm/proxy/v1`, which does not exist
on the proxy — every auxiliary call 404s. The runtime `api_mode=
anthropic_messages` flag was discarded by this arm.

Fix: split the conditional so only the literal `"custom"` provider takes
the anonymous-custom path; `custom:<name>` keeps its full `custom:<name>`
string when handed to `resolve_provider_client`, where the
named-custom-provider arm (added in earlier work) honours the entry's
`api_mode` and routes through `AnthropicAuxiliaryClient` against the
original `/anthropic` URL.

Also: extend `_requires_bearer_auth` in `anthropic_adapter.py` to
recognise palantirfoundry hosts so the SDK sends `Authorization: Bearer`
instead of the default `x-api-key` (Palantir's proxy rejects x-api-key
with 401).

Verified end-to-end against a live Palantir Foundry deployment with both
claude-4-6-opus and claude-4-7-opus models — `generate_title` returns
real titles instead of 404ing.  Regression-tested:

  - anonymous `custom` (with base_url) still routes to OpenAI wire
  - built-in NVIDIA provider unchanged
  - custom-without-base_url still falls through to Step-2 chain

agent/anthropic_adapter.py

@@ -544,6 +544,7 @@ def _requires_bearer_auth(base_url: str | None) -> bool:
     return (
         normalized.startswith(("https://api.minimax.io/anthropic", "https://api.minimaxi.com/anthropic"))
         or "azure.com" in normalized
+        or "palantirfoundry" in normalized
     )
 
 

agent/auxiliary_client.py

@@ -4384,10 +4384,26 @@ def _resolve_auto(
         resolved_provider = main_provider
         explicit_base_url = runtime_base_url or None
         explicit_api_key = None
-        if runtime_base_url and (main_provider == "custom" or main_provider.startswith("custom:")):
+        if runtime_base_url and main_provider == "custom":
+            # Anonymous custom endpoint (OPENAI_BASE_URL / config.model.base_url)
+            # — pass through with explicit base_url + api_key.
             resolved_provider = "custom"
             explicit_base_url = runtime_base_url
             explicit_api_key = runtime_api_key or None
+        elif main_provider.startswith("custom:"):
+            # Named custom provider (custom_providers / providers dict entry).
+            # KEEP the full ``custom:<name>`` so resolve_provider_client lands in
+            # the named-custom-provider arm — that arm honours the entry's
+            # api_mode (e.g. anthropic_messages → AnthropicAuxiliaryClient,
+            # avoiding the /anthropic→/v1 rewrite that 404s against proxies
+            # like Palantir Foundry's Anthropic surface).  Do NOT collapse to
+            # plain "custom"; that path strips /anthropic and routes through
+            # OpenAI chat.completions.
+            resolved_provider = main_provider
+            # base_url / api_key come from the named entry itself — leave the
+            # explicit_* overrides unset so the named arm reads them from config.
+            if runtime_api_key:
+                explicit_api_key = runtime_api_key
         elif runtime_api_key:
             # Pin auxiliary to the same api_key as the active main chat session
             # so that a working key is reused instead of re-selecting from the pool