-- AppView database schema 0006: handle-sync attempt tracking.
--
-- Why
-- The `handle_sync` worker SELECTs DIDs whose `posts.handle` is empty
-- and tries to resolve them via the local PDS → PLC directory →
-- `did:web:` resolver. Some DIDs are *unresolvable* (e.g. a `did:key:`
-- user not hosted on the local PDS, or any `did:foo:` method that
-- neither PLC nor Web understands). Without tracking these, every
-- pass re-selects them and they dominate the 100-row batch — and
-- since `did:key:` sorts lexicographically before `did:plc:` /
-- `did:web:`, the worker would process the same 100 unresolvable
-- `did:key:` rows forever and never reach any resolvable DID.
--
-- With this column the worker marks each empty-handle row with the
-- time of its last attempt. The SELECT filter excludes rows
-- attempted within the last hour, so an unresolvable DID gets at
-- most one attempt per hour and stops blocking forward progress.
-- Rows whose `handle` later gets filled (by another code path) are
-- naturally no longer in the candidate set.
--
-- The column is per-post (not per-DID) because the candidate set is
-- already per-post and the update is cheap (the empty-handle slice
-- is small in steady state).

ALTER TABLE posts ADD COLUMN IF NOT EXISTS handle_sync_attempted_at TIMESTAMPTZ;