Adds SessionDB.get_messages_around(session_id, around_message_id, window)
which returns up to 'window' messages before the anchor, the anchor
itself, and up to 'window' after — all from the same session, ordered by
id ascending.
Used by the upcoming session_search mode='guided' (anchored drill-down)
to surface a focused conversation window without summarisation cost or
the 100k-char truncation gamble of mode='summary'.
Boundaries are honoured (fewer messages at session start/end), the
anchor is verified to exist in the named session before fetching (cheap
guard against cross-session id confusion), and content/tool_calls
decoding mirrors get_messages() so callers can swap between the two
without surprises.
Tested: 9 new cases in tests/hermes_state/test_get_messages_around.py
(middle-of-session, first-message, last-message, anchor-not-in-session,
no cross-session leakage, window > session, window=0, window negative,
content decoding parity with get_messages). 62/62 passing including the
existing 53 session_search tests.
yoniebans
2b606d20e2