fix(session): strip reasoning item ids from session history

[Epochex]

Fixes #2020

Session-backed runs can end up replaying reasoning items with server-assigned rs_... IDs from prior turns. Those IDs are not guaranteed to be stable across turns, and replaying them can trigger a 404 ("Item with id 'rs_...' not found") in a subsequent responses.create call.

This change strips the id field from reasoning items loaded from non-Conversations sessions before building model input, so the reasoning payload can still be replayed without relying on server-side item retention.

Tests:

• uv run ruff format src/agents/run_internal/session_persistence.py tests/test_agent_runner.py
• uv run ruff check src/agents/run_internal/session_persistence.py tests/test_agent_runner.py
• uv run pyright --project pyrightconfig.json src/agents/run_internal/session_persistence.py tests/test_agent_runner.py
• uv run pytest tests/test_agent_runner.py -q

[bombert]

Hi Epochex:

Could you add this check in the _strip_reasoning_item_ids_from_history_item for this case?

# Drop the item entirely if summary is missing or empty if not sanitized.get("summary"): return None

`
{
"input":[
{
"content":"User id is u_123. Help me choose the best subscription plan.",
"role":"user"
},
{
"id":"rs_0b61d86498c245ce016a17c138fc588199b2a78d6a1b3a6776",
"summary":[

     ],
     "type":"reasoning"
  }

]
}
`

[Epochex]

Done in 13e004c. I changed the session-history sanitizer to drop replayed reasoning items when summary is missing or empty, while still preserving reasoning items that have a summary and stripping only their id.

Ran:
uv run pytest tests/test_agent_runner.py::test_prepare_input_with_session_strips_reasoning_item_ids_from_history tests/test_agent_runner.py::test_prepare_input_with_session_drops_reasoning_items_without_summary