Schema

CREATE TABLE chat_sessions (
	id         TEXT PRIMARY KEY,
	user_id    INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
	title      TEXT NOT NULL DEFAULT 'New chat',
	created_at TEXT NOT NULL,
	updated_at TEXT NOT NULL,
	archived   INTEGER NOT NULL DEFAULT 0
);

Semantics

• id is a random hex string, not a sequence. It is a lookup key, not a capability: every route resolves it through GetChatSession(id, userID), so a correct id in the wrong session is a 404.
• title is derived from the first prompt and never regenerated — a title that rewrites itself is worse than a boring one.
• archived hides a thread from the rail without deleting it. Archiving is per-user by construction, because the row belongs to one user.
• updated_at orders the rail and drives the "2m ago" label; a finished run touches it.

Invariants

• A thread cannot change owner: no code path writes user_id after insert.
• Deleting a user removes their threads and, through the thread, their messages.

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