[chengyongru]

Summary

Remove the model-facing [Message Time: ...] replay prefix from session history.

The session still persists message timestamps in session.messages[], so this does not discard stored metadata. It only stops rewriting replayed user content before sending history to the model.

Why

The previous timestamp injection changed historical user message content between turns, which made provider-facing prompt prefixes unstable and reduced prompt/KV cache friendliness. Runtime current-time context remains available separately, so normal turn metadata is still represented without polluting every historical message.

Changes

• Remove Session.get_history(include_timestamps=...) and the timestamp annotation helper.
• Stop agent loop and consolidation token probes from requesting timestamp-prefixed history.
• Update focused tests to assert timestamps remain persisted but replay content does not contain [Message Time: ...].

Validation

• python -m pytest tests/agent/test_session_manager_history.py tests/agent/test_loop_save_turn.py::test_system_subagent_followup_is_persisted_before_prompt_assembly tests/agent/test_auto_compact.py::TestAgentLoopTTLParam::test_process_message_reads_history_with_token_budget tests/agent/test_context_prompt_cache.py -q --cache-clear
• python -m ruff check nanobot/agent/loop.py nanobot/agent/memory.py nanobot/session/manager.py tests/agent/test_auto_compact.py tests/agent/test_loop_save_turn.py tests/agent/test_session_manager_history.py

[Re-bin]

LGTM. This removes the model-facing [Message Time: ...] replay prefix without dropping persisted timestamps, which makes historical prompts more stable and friendlier to provider prompt/KV caching. The change is narrowly scoped to replay/context assembly and consolidation estimation; storage metadata remains intact.

Validated locally:

• python -m pytest tests/agent/test_session_manager_history.py tests/agent/test_loop_save_turn.py::test_system_subagent_followup_is_persisted_before_prompt_assembly tests/agent/test_auto_compact.py::TestAgentLoopTTLParam::test_process_message_reads_history_with_token_budget tests/agent/test_context_prompt_cache.py -q
• python -m ruff check nanobot/agent/loop.py nanobot/agent/memory.py nanobot/session/manager.py tests/agent/test_auto_compact.py tests/agent/test_loop_save_turn.py tests/agent/test_session_manager_history.py

GitHub Actions is green.