fix(memory): compact the full stored history of a limited session

[hsusul]

Summary

OpenAIResponsesCompactionSession loads compaction input with underlying_session.get_items(), which applies SessionSettings.limit. After responses.compact, it clears the entire underlying store and writes the compact result.

For a SQLite (or similar) session that stores full history but retrieves only the last N items, successful compaction therefore deletes everything older than N. The restore path already uses _get_all_underlying_session_items(); candidate loading did not.

Reproduction

from agents.memory import SQLiteSession, SessionSettings, OpenAIResponsesCompactionSession

underlying = SQLiteSession("s", session_settings=SessionSettings(limit=2))
# add 3+ items, then force input-mode compaction
# responses.compact receives only the last 2 items
# the session is then replaced with that compact output

Solution

Load candidates via the existing _get_all_underlying_session_items() helper (limit=2_147_483_647), matching the replacement/restore path.

This is a smaller version of the candidate-loading fix from closed stale #3827, without that PR's broader previous_response_id rewrite.

Test plan

• Added a SQLiteSession regression that sets SessionSettings(limit=2), stores 3 items, and asserts responses.compact receives all 3
• uv run pytest tests/memory/test_openai_responses_compaction_session.py (56 passed)
• uv run ruff format / ruff check on the changed files
• uv run pyright on the changed files
• git diff --check clean

Issue number

N/A. Related closed stale PR: #3827.

Checks

• I've added new tests, if relevant
• I've run targeted format, lint, typecheck, and tests on the changed files
• I've run .agents/skills/code-change-verification/scripts/run.sh (full make format currently fails on an unrelated pre-existing E501 in .agents/skills/implementation-final-review/scripts/test_skill_contract.py on main)
• If using Codex, I've run /review before submitting this PR

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid triggering response-ID compaction from hidden rows

When the underlying session has SessionSettings(limit=N) with N below the threshold but more than ten candidates stored, this full read now triggers default "auto" compaction; however, _resolve_compaction_mode() selects previous_response_id for a normally stored response, so the compaction request does not include these full session_items. Because that response was created using only the limited session window, its compacted output cannot represent the older rows, yet the replacement clears the entire local store. This therefore newly deletes the hidden history in the default mode; either switch to input-mode compaction when the full store differs from the retrieval window or keep hidden rows from triggering response-ID compaction.

AGENTS.md reference: AGENTS.md:L201-L203

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