[denfry]

Problem

symbols.parent_id and chunks.symbol_id reference symbols(id) with ON DELETE SET NULL but have no index. With foreign_keys = ON, every deleted symbol scans both tables, so removing files costs O(deleted symbols x table rows) and runs into hours on a large index.

Solution

Add idx_symbols_parent and idx_chunks_symbol to schema.sql and mirror them in docs/SCHEMA.md.

Verification

• Synthetic index (3000 files, 18k symbols, 45k chunks), deleting 100 files: 4.68 s before, 0.03 s after. Creating the indexes takes 0.07 s, and foreign_key_check stays clean.
• Two new tests, both failing before the fix: every foreign-key column must lead an index, and an existing index gains the new ones on open.
• Full suite and ruff pass.

Compatibility

_apply_schema() runs on every open with IF NOT EXISTS, so existing indexes pick these up on their next open. No schema version bump, no rebuild.

Fixes #33