fix(vsearch): skip missing vec tables instead of aborting (#161)

[J0nd1sk]

Closes #161.

Problem

cmd_vsearch defaults to tables = ["memories", "events", "context"] (_impl.py:8081), but vec_events / vec_context are never created or populated anywhere in the codebase. The inner _vsearch_table (_impl.py:8091) ran the MATCH query with no guard, so the first missing table raised OperationalError, which the CLI surfaced as:

{"error": "Database table missing: no such table: vec_events", "hint": "Run 'brainctl init' ..."}

— discarding results from vec_memories, which exists and has hits. So the default brainctl vsearch <query> failed on any real brain.db (and the hint is wrong: init doesn't create those tables either).

Fix

Catch sqlite3.OperationalError for a missing table in _vsearch_table and return [] for that source, so vsearch returns hits from the tables that exist. Any other OperationalError re-raises unchanged.

This is the minimal correctness fix. The deeper question — events/context are in the default table set but nothing ever indexes them — is called out in #161 as a separate change (implement the indexing, or drop them from the default set). Happy to follow up on whichever you prefer.

Test

tests/test_vsearch_missing_vec_table.py builds a full-schema DB (via the cli_db fixture) with a populated real vec_memories and no vec_events, then drives cmd_vsearch(tables="memories,events") and asserts it returns the memory hit with events == [] and never raises. Skips if the sqlite-vec dylib isn't available.

Verification

$ pytest tests/test_mcp_tools_vsearch.py tests/test_vsearch_missing_vec_table.py -q
14 passed

# end-to-end: default vsearch (memories,events,context) against a DB with only
# vec_memories present now returns memory hits instead of erroring.