9ab5aba6b3
The reworked bundle's PORT.md makes row-level last-write-wins conditional
on three gates, each learned by losing real data. The port's sync broke
all three, and had four more ways to lose or stall work. Both ends change,
so this is one protocol version, refused by the other side if mismatched.
Gate 1, hydration. A device now pulls every page the server holds before
it may push anything; it used to push first. The 14 Sep laptop — a
week-old copy re-stamped at boot and pushed over a week of phone work —
is now a test, and the phone's week survives it. Boot writes nothing
syncable either: the lesson opens with the app's own words (the artifact's
seeded turn) and waits for Start, instead of stamping a reply and a
progress edit before a server can even be configured.
Gate 2, a counter. Every row remembers the change_seq it last agreed with
(base_seq). The server applies a write only if that still matches —
compare-and-swap under an advisory lock — and otherwise returns its copy
as a conflict. No clock is compared anywhere: a device an hour fast used
to win every conflict for an hour, and a slow one's newer edit was
silently dropped with HTTP 200. dirty and rev replace the timestamp
watermark, which lost edits whenever a clock moved backwards.
Gate 3, no silent shrinking. A conflict is settled by what each copy
holds (sync/resolve.ts): more reviews, more evidence, a finished unit, the
further roadmap position, the union of learned grammar. A deliberate
shrink is explicit: a reset or a cleared lesson raises a marker every
device obeys, including its own unsynced edits, so a reset is not undone
by a device that had not heard of it. Trimming the transcript is local
and tombstones nothing — it used to delete the other device's turns.
Also fixed on the way:
· keys travel as JSON arrays — a space in 몇 명 used to stop every
device's pull at that row, permanently;
· pulls take a shared lock against pushes, so a change_seq committed
out of order can no longer be skipped;
· study_log and peek are per device and summed, so two devices' reviews
of one day both count;
· each user's data has an epoch; a server that lost it is detected,
and the device re-hydrates and offers its data back;
· a protocol-1 client is refused with 426 rather than half-understood.
Migration 9 adds the columns, re-keys the counters and tombstones; the
server drops protocol-1 rows once (none were deployed). Verified: 14
two-device scenarios against a real Postgres, and two browser profiles
syncing a lesson through the UI.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
33 lines
1.2 KiB
SQL
33 lines
1.2 KiB
SQL
-- Sync protocol 2.
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--
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-- Rows are now written only by compare-and-swap on change_seq (see
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-- server/src/db.ts), keyed by a JSON array of the key's values, and every
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-- user's data belongs to an epoch: a random id that changes whenever the
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-- server's copy is thrown away, so a client can tell it is talking to a
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-- server that no longer holds what it pushed and must hydrate from scratch.
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CREATE TABLE IF NOT EXISTS sync_meta (
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k TEXT PRIMARY KEY,
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v TEXT NOT NULL
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);
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CREATE TABLE IF NOT EXISTS sync_epoch (
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user_id TEXT PRIMARY KEY,
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epoch TEXT NOT NULL
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);
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-- Protocol 1 rows cannot be read as protocol 2: their keys were joined with
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-- a space and every one was ordered by a client's clock. They are dropped
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-- once, and each user's epoch with them — so every client re-hydrates and
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-- offers its own database back, which is the copy that was always the
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-- source of truth. No deployment held protocol 1 data when this shipped.
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DO $$
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BEGIN
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IF NOT EXISTS (SELECT 1 FROM sync_meta WHERE k = 'protocol' AND v = '2') THEN
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DELETE FROM sync_row;
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DELETE FROM sync_epoch;
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INSERT INTO sync_meta (k, v) VALUES ('protocol', '2')
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ON CONFLICT (k) DO UPDATE SET v = EXCLUDED.v;
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END IF;
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END $$;
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