LIKE wildcards break psycopg parameter parsing

[amiller]

Bug

SQL queries with LIKE '%...' patterns fail because psycopg interprets % in the SQL string as parameter placeholders.

Reproduction

Query: "Is there any green juice videos"

The query agent generates:

SELECT * FROM watch_history WHERE LOWER(title) LIKE '%green juice%'

psycopg rejects this with:

only '%s', '%b', '%t' are allowed as placeholders, got '%g'

The %g in %green is parsed as a psycopg format specifier instead of a SQL LIKE wildcard.

Root cause

db.execute() passes SQL through psycopg's parameter substitution. Literal % characters in SQL need to be escaped as %%, or (better) the LIKE pattern should be passed as a parameter:

SELECT * FROM watch_history WHERE LOWER(title) LIKE %s
-- params: ['%green juice%']

The query agent inlines string values directly in SQL instead of using parameterized queries.

Possible fixes

1. Agent prompt fix: instruct query agents to always use %s parameterized queries for string values
2. Engine fix: escape % in SQL before passing to psycopg (risky — could break intentional %s params)
3. Engine fix: switch psycopg to ClientCursor with mogrify() or use a different param style

Impact

Any LIKE/ILIKE query with a pattern starting with a letter after % fails silently — the agent gets an error and reports "technical error" to the user instead of results.

Found via trace logging on the live CVM deployment.