-- 0003_chat_history: persistent chat sessions + message stream (DevDocs/design/16 §2.1, §3.1).
-- chat_sessions records the persistent sessions: one fixed main session plus arbitrarily
-- many secondary (sub) sessions. chat_messages is the raw, durable message stream in
-- millisecond-timestamp cursor order. The two are the backend truth for the Web frontend;
-- they are NOT memory (design/16 §3.2 separates memory from the raw stream).
--
-- Its canonical schema is owned by internal/runtime/history, which reuses these tables. The
-- migration is the authoritative path; internal/runtime/history.NewStore re-issues the same
-- DDL idempotently so the store is self-contained (matching memory/session).

CREATE TABLE IF NOT EXISTS chat_sessions (
    id         TEXT PRIMARY KEY,            -- main = fixed id ("web"); sub = "web:<uuid>"
    type       TEXT NOT NULL,               -- 'main' | 'sub'
    title      TEXT NOT NULL DEFAULT '',
    created_at INTEGER NOT NULL             -- ms timestamp
);

CREATE TABLE IF NOT EXISTS chat_messages (
    id         TEXT PRIMARY KEY,            -- message unique id (uuid)
    session_id TEXT NOT NULL,               -- owning session (main or sub)
    role       TEXT NOT NULL,               -- user / assistant / system
    content    TEXT NOT NULL,               -- raw message body (incl. <p>/<action>)
    mode       TEXT,                        -- behavior mode (optional, bubble render)
    mood       TEXT,                        -- mood (optional)
    image      TEXT,                        -- attachment base64/URL (optional)
    thinking   TEXT,                        -- chain of thought (optional, stored, not echoed by default)
    created_at INTEGER NOT NULL             -- ms timestamp (pagination cursor)
);

CREATE INDEX IF NOT EXISTS idx_chat_msgs_session_created
    ON chat_messages (session_id, created_at DESC);