Builds the system prompt injected at the start of every session.
search_enabled controls whether search_web instructions are included.
memory_context is an optional markdown block from the project memory store.
auto_test_cmd is the test command that will run automatically after changes, if any.
symbol_summary is an optional one-line summary of the indexed symbol count, e.g.
“Symbol index: 4 312 symbols across 187 files — use find_symbol to navigate.”