Problem

When upgrading from an older Hermes version to v0.14.0, existing kanban.db files lack the session_id column. SCHEMA_SQL includes:

CREATE TABLE IF NOT EXISTS tasks (...);
CREATE INDEX IF NOT EXISTS idx_tasks_session_id ON tasks(session_id);  -- 💥

CREATE TABLE IF NOT EXISTS is a no-op on existing tables (old schema, no session_id). But the CREATE INDEX on the next line references session_id before _migrate_add_optional_columns() gets a chance to add it via ALTER TABLE. Crash.

Fix

Remove the premature CREATE INDEX from SCHEMA_SQL. The index creation is already handled correctly inside _migrate_add_optional_columns() (line 1166–1178), where ALTER TABLE ADD COLUMN runs first.

One line deleted, no logic changed — the index still gets created, just at the right time.

Verification

• Fresh install: SCHEMA_SQL creates table + all columns → migration is a no-op → index created during migration ✓
• Upgrade from old DB: SCHEMA_SQL no-ops on existing table → migration adds session_id column → migration creates index ✓

Fixes #28554