fix: add _ExceptionTranslatingRoute to prevent keep-alive breakage on Linux - #4886

The OpenAI Python SDK parses error responses as body["error"]["message"].
The global exception handler was using "detail" which the SDK could not
surface in exception messages, breaking client error handling.

This keeps _ExceptionTranslatingRoute in fastapi_routes.py (from ogx-ai#4886)
to avoid keep-alive breakage on Linux. Route-level 400 responses use
"detail"; the global handler uses {"error": {"message": ...}}.

Unit tests updated: route-level ValueError->400 assert on detail; global
handler path (RuntimeError) asserts on error in json().

Co-authored-by: Cursor <cursoragent@cursor.com>

The OpenAI Python SDK parses error responses as body["error"]["message"].
The global exception handler was using "detail" which the SDK could not
surface in exception messages, breaking client error handling.

This keeps _ExceptionTranslatingRoute in fastapi_routes.py (from ogx-ai#4886)
to avoid keep-alive breakage on Linux. Route-level 400 responses use
"detail"; the global handler uses {"error": {"message": ...}}.

Unit tests updated: route-level ValueError->400 assert on detail; global
handler path (RuntimeError) asserts on error in json().

Co-authored-by: Cursor <cursoragent@cursor.com>

Depends on: #4886

## Summary
- Introduce `LlamaStackError` base class with `status_code` attribute
for automatic HTTP status code translation in the server error handler
- Add `ClientListCommand` for consistent "not found" help messages and
new named error types: `BatchNotFoundError`,
`OpenAIFileObjectNotFoundError`, `ResponseNotFoundError`,
`InvalidParameterError`, `ServiceNotEnabledError`, `InternalServerError`
- Extract `translate_exception` into `core/exceptions` module with a
shared `EXCEPTION_MAP` for single-source-of-truth status code mapping
- Update file/batch providers to use specific error types instead of
generic `ResourceNotFoundError` with hardcoded strings

## Stack
This is PR 1/4 in the error message consistency series (split from
#3913):
1. **This PR** - Error types foundation
2. Responses API error handling (targets this branch)
3. Record/replay error support (targets this branch)
4. Integration tests (targets PR 2)

## Test plan
- [x] Unit tests for `ClientListCommand` and `ResourceNotFoundError` (7
tests pass)
- [x] All pre-commit hooks pass (ruff, mypy, API spec codegen, etc.)

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

…uter (#5057)

## Summary

PR #4886 added `ExceptionTranslatingRoute` to the agents router to
prevent TCP connection resets on Linux. When known exceptions (like
`ValueError` or `LlamaStackError` subclasses) are thrown from a route
handler, `ServerErrorMiddleware` can close the transport before the
global exception handler has a chance to format a JSON response. The
route class catches these exceptions earlier and converts them to
`HTTPException`, which FastAPI handles gracefully without dropping the
connection.

The conversations router raises the same exception types
(`ConversationNotFoundError`, `InvalidParameterError`, etc.) but was
missing this route class, leaving it vulnerable to the same issue. This
PR:

- Moves `ExceptionTranslatingRoute` and
`try_translate_to_http_exception` to the shared `router_utils` module so
they can be reused across routers
- Applies `route_class=ExceptionTranslatingRoute` to the conversations
router
- Adds a unit test verifying consecutive errors on the conversations
router return proper JSON without breaking the connection

## Test plan
- [x] All 66 existing router tests pass (no regressions from moving to
shared module)
- [x] New unit test verifies keep-alive behavior on the conversations
router

---------

Co-authored-by: Francisco Javier Arceo <farceo@redhat.com>
Co-authored-by: Francisco Javier Arceo <arceofrancisco@gmail.com>