fix: handle RemoteEvalParameters in eval dev /list endpoint

[Alex Jean-Baptiste (justcodebruh)]

Summary

• Fix AttributeError: 'RemoteEvalParameters' object has no attribute 'items' raised by build_eval_definitions when an Eval(...) is declared with parameters=load_parameters(...).
• The dev server's /list endpoint was masking this as a generic 500 (Eval runner exited with an error.), so the Playground Remote evals settings page just said "could not connect to the dev server" with no actionable trace.
• Branch on RemoteEvalParameters in the runner and pass through its already-resolved .schema, matching what the SDK itself does at braintrust/framework.py:1515 and braintrust/parameters.py:357.

Bug path

1. Customer calls params = load_parameters(project=..., slug=...) → returns a RemoteEvalParameters object.
2. Customer passes parameters=params into Eval(...).
3. UI hits /list on the dev server → bt spawns eval-runner.py with BT_EVAL_DEV_MODE=list.
4. build_eval_definitions (was eval-runner.py:570) calls parameters_to_json_schema(evaluator.parameters) unconditionally; that helper calls parameters.items(), which RemoteEvalParameters does not implement → uncaught AttributeError.
5. Runner exits non-zero. Rust dev_server_list returns a generic 500 with no error detail (the traceback goes to stderr, not through sse.send(\"error\", ...)).

Verification (local)

• BT_EVAL_DEV_MODE=list python scripts/eval-runner.py eval_repro_15895.py --local against the same Eval(..., parameters=load_parameters(project=\"repro-15895\", slug=\"eval-config\")) repro: previously crashed with the AttributeError at line 570 → now emits the correctly-serialized JSON schema.
• Built cargo build --release and ran the patched binary against the same eval file. curl http://localhost:8301/list (with Authorization: Bearer + x-bt-org-name) previously returned 500 {\"error\":\"Eval runner exited with an error.\"}; now returns 200 with the full param schema (model + eval_prompt + temperature + system_prompt all resolved).

Test plan

• CI green
• Manual repro from Pylon #15895: bt eval <file>.py --language=python --dev --dev-port 8301 against an Eval(..., parameters=load_parameters(...)) no longer crashes the dev server, and the Playground Remote evals settings page lists the eval with all saved parameters visible
• Sanity: existing inline Eval(parameters={\"prefix\": PrefixParam, \"main\": {\"type\": \"prompt\", ...}}) flow is unchanged

Pylon: #15895

🤖 Generated with Claude Code

[github-actions]

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