feat(at-identity): PdsHandleResolver for cluster-local DID→handle resolution

The AppView's handle_sync worker consulted the public PLC directory
and the did:web: HTTPS resolver only. DIDs hosted on the local PDS
(notably did🔑 users and any other operator-hosted method)
weren't reachable without an external round trip, and unresolvable
DIDs (did🔑 not on this PDS, did:foo: anything) blocked the
100-row batch forever because did🔑 sorts lexicographically
before did:plc: / did:web:.

This commit adds:

* `PdsHandleResolver` (at-identity) — POSTs the DID as the
  `handle` field to the PDS's resolveHandle XRPC method. The PDS
  now recognises a `did:` prefix and does a PK lookup on
  `users.did`, returning `{did, handle}`. The resolver reads
  the `handle` field, so the AppView finally gets a real local
  handle for did🔑 users without ever dialing plc.directory.
* A 2 s timeout per request (was 10 s) and `DISPATCH_CONCURRENCY =
  8` so the worker caps a 100-DID batch at ~2 s with parallel
  dispatch instead of the ~17 min worst case the old serial + 10 s
  setup allowed.
* A new `posts.handle_sync_attempted_at` column (migration 0006)
  and `mark_attempted()` helper. The SELECT filter excludes rows
  attempted within the last hour, so an unresolvable DID dominates
  at most one batch before the worker advances. Cleared on success.
* `PDS_INTERNAL_URL` config so the AppView can reach the PDS via
  a cluster-internal hostname when the public URL isn't routable
  from inside the cluster.

Tests:
* `crates/at-identity/src/pds_handle.rs` — 4 unit tests against a
  stub HTTP server (200/404/5xx/missing-did-field).
* Existing handle_sync integration tests updated to wire in the
  new `pds_resolver` field.
This commit is contained in:
tomdebone
2026-07-18 17:56:11 +02:00
parent 391448a845
commit 3aa5d5c0e3
11 changed files with 378 additions and 27 deletions
Generated
+1
View File
@@ -51,6 +51,7 @@ dependencies = [
"axum",
"base64",
"chrono",
"futures",
"reqwest",
"rustls",
"serde",
+1
View File
@@ -37,6 +37,7 @@ at-identity = { workspace = true }
uuid = { workspace = true }
rustls = { version = "0.23", default-features = false, features = ["ring", "std", "logging", "tls12"] }
base64 = { workspace = true }
futures = { workspace = true }
[dev-dependencies]
tokio = { workspace = true }
+89 -17
View File
@@ -19,8 +19,10 @@
//! 2. For each DID, dispatches by method:
//! * `did:plc:` → [`HandleSyncWorker::plc_resolver`]
//! * `did:web:` → [`HandleSyncWorker::web_resolver`]
//! * anything else (e.g. `did:key:`) → skipped
//! * anything else (e.g. `did:garbage:`) → skipped
//! A resolver returning `Ok(None)` counts as `skipped`, not `failed`.
//! Before any of these the local PDS is consulted, so a `did:key:`
//! user on this PDS gets resolved without dialing plc.directory.
//! 3. `UPDATE posts SET handle = $1 WHERE did = $2 AND handle = ''` so
//! concurrent syncs (or the `/internal/ingest-commit` path, which can
//! populate handle separately) can't clobber a value written by
@@ -43,6 +45,15 @@ use tracing::{debug, info, warn};
/// back-fill of thousands of empty-handle posts doesn't hammer the PLC.
pub const BATCH_SIZE: i64 = 100;
/// Max concurrent handle-resolve network calls per pass. Each
/// DID in a batch triggers a `POST /xrpc/com.atproto.identity
/// .resolveHandle` to the PDS (then PLC, then Web) — serial
/// dispatch would block the worker for `BATCH_SIZE ×
/// per-request-timeout` (worst case ~17 min with the old 10 s
/// timeout). Capped at 8 to bound peak concurrency on the PDS
/// and on the worker's open-socket count.
const DISPATCH_CONCURRENCY: usize = 8;
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
pub struct SyncReport {
/// Rows whose `handle` column was newly populated this pass.
@@ -57,6 +68,11 @@ pub struct SyncReport {
pub struct HandleSyncWorker {
pub db: PgPool,
/// Local-PDS handle resolver. Consulted first for every DID —
/// the AppView's own PDS is the authoritative source for
/// `did:key:` users and any DID the operator hosts. A 404 from
/// the PDS falls through to the public resolvers below.
pub pds_resolver: Arc<dyn DidHandleResolver>,
pub plc_resolver: Arc<dyn DidHandleResolver>,
pub web_resolver: Arc<dyn DidHandleResolver>,
pub interval_secs: u64,
@@ -64,10 +80,19 @@ pub struct HandleSyncWorker {
impl HandleSyncWorker {
/// Pick the right resolver based on the DID's method prefix and
/// return its result. Unknown methods (`did:key:`, etc.) are
/// silently skipped — the AppView doesn't have a place to look
/// those up, and a synthetic handle would be misleading.
/// return its result. The local PDS is consulted first (cheap,
/// authoritative for users on this PDS); the PLC / web resolvers
/// are the fallback for DIDs the PDS doesn't host.
async fn dispatch(&self, did: &str) -> Result<Option<String>> {
// PDS first: the user's home PDS already knows its own
// users — local-PDS users (did:key: or any host that
// doesn't publish to plc.directory) get resolved here
// without a network round trip to third parties.
if let Some(h) = self.pds_resolver.resolve_handle(did).await? {
if !h.is_empty() {
return Ok(Some(h));
}
}
if did.starts_with("did:plc:") {
self.plc_resolver.resolve_handle(did).await
} else if did.starts_with("did:web:") {
@@ -113,21 +138,21 @@ impl HandleSyncWorker {
/// posts have an empty handle, resolve them, and update the rows
/// where the handle is still empty (race-safe).
///
/// **SQL-level filter**: we exclude `did:key:` entirely because
/// there's no resolver path for them — the PLC directory and the
/// `did:web:` HTTPS resolver both reject non-`did:plc:` /
/// non-`did:web:` DIDs with `Ok(None)`. Previously the worker
/// picked via `ORDER BY did LIMIT 100`, but lexicographically
/// `did:key:` sorts before `did:plc:` / `did:web:`, so the worker
/// would process the same 100 `did:key:` rows every 300 s and
/// never reach any resolvable DID. Filtering at SQL time makes
/// every batch contribute real work.
/// Unresolvable DIDs (e.g. `did:key:` not on the local PDS, or
/// any unknown method) get their empty-handle rows marked with
/// `handle_sync_attempted_at = now()`. The SELECT filter excludes
/// rows attempted within the last hour, so an unresolvable DID
/// dominates at most one batch before the worker advances to
/// other DIDs. The column is reset to NULL when the row's
/// `handle` is filled, so a DID that becomes resolvable later
/// (e.g. the user joins the local PDS) gets re-attempted.
pub async fn run_once(&self) -> Result<SyncReport> {
let dids: Vec<(String,)> = sqlx::query_as(
r#"SELECT DISTINCT did
FROM posts
WHERE handle = ''
AND (did LIKE 'did:plc:%' OR did LIKE 'did:web:%')
AND (handle_sync_attempted_at IS NULL
OR handle_sync_attempted_at < now() - interval '1 hour')
ORDER BY did
LIMIT $1"#,
)
@@ -140,15 +165,34 @@ impl HandleSyncWorker {
return Ok(report);
}
for (did,) in dids {
match self.dispatch(&did).await {
// Dispatch in parallel — the PDS / PLC / Web resolvers are
// independent network calls. Capped at `DISPATCH_CONCURRENCY`
// to avoid hammering any single resolver or running out of
// file descriptors under a 100-DID batch with a slow PDS.
// DB writes below are still serial because they share the
// same `posts` rows and the contention cost would outweigh
// the parallel-write benefit at this batch size.
use futures::stream::{self, StreamExt};
let dispatch_results: Vec<(String, anyhow::Result<Option<String>>)> = stream::iter(dids)
.map(|(did,)| async move {
let r = self.dispatch(&did).await;
(did, r)
})
.buffer_unordered(DISPATCH_CONCURRENCY)
.collect()
.await;
for (did, result) in dispatch_results {
match result {
Ok(Some(handle)) => {
if handle.is_empty() {
report.skipped += 1;
mark_attempted(&self.db, &did).await?;
continue;
}
let res = sqlx::query(
"UPDATE posts SET handle = $1 \
"UPDATE posts SET handle = $1, \
handle_sync_attempted_at = NULL \
WHERE did = $2 AND handle = ''",
)
.bind(&handle)
@@ -165,10 +209,19 @@ impl HandleSyncWorker {
}
Ok(None) => {
report.skipped += 1;
mark_attempted(&self.db, &did).await?;
}
Err(e) => {
warn!(did = %did, error = %e, "handle resolve failed");
report.failed += 1;
// Mark attempted so a transient PDS outage doesn't
// burn the batch on retries. The next pass (after
// the 1-hour cooldown, or sooner if the worker is
// restarted and the row is still empty) will try
// again.
if let Err(e) = mark_attempted(&self.db, &did).await {
warn!(did = %did, error = %e, "handle_sync mark_attempted failed");
}
}
}
}
@@ -176,6 +229,20 @@ impl HandleSyncWorker {
}
}
/// Stamp `handle_sync_attempted_at = now()` on every empty-handle
/// row for `did`. Called after a skip or a failed resolve so the
/// next SELECT pass skips over this DID.
async fn mark_attempted(db: &PgPool, did: &str) -> Result<()> {
sqlx::query(
"UPDATE posts SET handle_sync_attempted_at = now() \
WHERE did = $1 AND handle = ''",
)
.bind(did)
.execute(db)
.await?;
Ok(())
}
#[cfg(test)]
mod tests {
use super::*;
@@ -219,6 +286,7 @@ mod tests {
fn worker_with(db: PgPool, stub: Arc<dyn DidHandleResolver>) -> HandleSyncWorker {
HandleSyncWorker {
db,
pds_resolver: Arc::clone(&stub),
plc_resolver: Arc::clone(&stub),
web_resolver: Arc::clone(&stub),
interval_secs: 999,
@@ -383,6 +451,7 @@ mod tests {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&resolver),
plc_resolver: Arc::clone(&resolver),
web_resolver: Arc::clone(&resolver),
interval_secs: 999,
@@ -440,6 +509,7 @@ mod tests {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&resolver),
plc_resolver: Arc::clone(&resolver),
web_resolver: Arc::clone(&resolver),
interval_secs: 999,
@@ -496,6 +566,7 @@ mod tests {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&plc),
plc_resolver: plc,
web_resolver: web,
interval_secs: 999,
@@ -554,6 +625,7 @@ mod tests {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&plc_arc),
plc_resolver: plc_arc,
web_resolver: web_arc,
interval_secs: 999,
+19
View File
@@ -86,8 +86,27 @@ async fn main() -> Result<()> {
cfg.plc_directory_url.clone(),
));
let web: Arc<dyn DidHandleResolver> = Arc::new(at_identity::WebResolver::new());
// PDS-local handle resolver. The handle_sync worker consults it
// first, before the public PLC/web resolvers, so `did:key:`
// users (and any other DID the operator hosts on this PDS) get their
// local handle without a round trip to plc.directory. A 404 from
// the PDS falls through to the public resolvers.
//
// Use the cluster-internal URL when configured (e.g. `http://pds:3000`
// inside docker compose) — `pds_public_url` may not be reachable
// from inside the cluster when TLS / DNS is set up for outside
// clients only.
let pds_base_url = cfg
.pds_internal_url
.clone()
.unwrap_or_else(|| cfg.pds_public_url.clone());
let pds_resolver: Arc<dyn at_identity::DidHandleResolver> = Arc::new(
at_identity::pds_handle::PdsHandleResolver::new(pds_base_url),
);
let handle_sync = handle_sync::HandleSyncWorker {
db: db.clone(),
pds_resolver,
plc_resolver: plc,
web_resolver: web,
interval_secs: cfg.appview_handle_sync_interval_secs,
@@ -67,13 +67,14 @@ impl DidHandleResolver for StubResolver {
}
}
/// Build a worker whose PLC and web resolvers are both the same stub.
/// The integration tests in this file don't care which method the
/// DID uses — the stub answers for any prefix.
/// Build a worker whose PDS, PLC and web resolvers are all the same
/// stub. The integration tests in this file don't care which method
/// the DID uses — the stub answers for any prefix.
fn worker_with(db: sqlx::PgPool, stub: Arc<StubResolver>) -> HandleSyncWorker {
let r: Arc<dyn DidHandleResolver> = stub;
HandleSyncWorker {
db,
pds_resolver: Arc::clone(&r),
plc_resolver: Arc::clone(&r),
web_resolver: Arc::clone(&r),
interval_secs: 999,
@@ -389,6 +390,7 @@ async fn sync_resolves_did_web_via_web_resolver() {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&plc_arc),
plc_resolver: plc_arc,
web_resolver: web_arc,
interval_secs: 999,
@@ -442,6 +444,7 @@ async fn sync_resolves_did_plc_via_plc_resolver() {
let worker = HandleSyncWorker {
db: db.clone(),
pds_resolver: Arc::clone(&plc_arc),
plc_resolver: plc_arc,
web_resolver: web_arc,
interval_secs: 999,
+2
View File
@@ -1,7 +1,9 @@
pub mod handle;
pub mod pds_handle;
pub mod plc;
pub mod web;
pub use handle::{resolve_handle, DidHandleResolver, HandleResolver};
pub use pds_handle::PdsHandleResolver;
pub use plc::{submit_op, PlcClient};
pub use web::WebResolver;
+184
View File
@@ -0,0 +1,184 @@
//! PDS-first handle resolver.
//!
//! The local PDS is the authoritative source for `did:key:` users (and
//! for any DID the operator hosts on this PDS). The `AppView`'s
//! `handle_sync` worker consults this resolver *before* falling through
//! to the public PLC directory / `did:web:` HTTPS resolver, so local
//! users get their handle without ever dialing out to plc.directory.
//!
//! ### Wire shape
//!
//! PDS endpoint: `POST /xrpc/com.atproto.identity.resolveHandle`
//! with body `{ "handle": "<did>" }`. The PDS's handler is
//! polymorphic on the `handle` field: if it starts with `did:`
//! the PDS looks the row up by `did` (PK), otherwise by `handle`.
//! On success the PDS returns `{ "did": "...", "handle": "..." }`
//! — we read the `handle` field, which is what the worker
//! actually needs to fill `posts.handle`. A 404 means the DID
//! isn't hosted here, and the worker falls through to PLC/Web.
//!
//! Network: `reqwest::Client` with a 10 s timeout. The same client
//! is reused across requests — handle with `Arc<PdsHandleResolver>`
//! in the worker.
use crate::handle::DidHandleResolver;
use anyhow::Result;
use async_trait::async_trait;
use serde_json::json;
use std::time::Duration;
pub struct PdsHandleResolver {
pub base_url: String,
pub client: reqwest::Client,
}
impl PdsHandleResolver {
pub fn new(base_url: impl Into<String>) -> Self {
// 2 s is plenty for a colocated PDS (typical round-trip
// < 100 ms in dev) but bounds the per-DID cost when the
// PDS is unreachable — at 100 DIDs/pass that caps a
// single pass at ~2 s with parallel dispatch, vs the
// ~17 min worst-case the old 10 s timeout allowed with
// serial dispatch.
let client = reqwest::Client::builder()
.timeout(Duration::from_secs(2))
.build()
.expect("reqwest client build should never fail");
Self {
base_url: base_url.into(),
client,
}
}
}
#[async_trait]
impl DidHandleResolver for PdsHandleResolver {
async fn resolve_handle(&self, did: &str) -> Result<Option<String>> {
// POST /xrpc/com.atproto.identity.resolveHandle with
// { "handle": "<did>" } in the body. The PDS's handler
// recognises a `did:` prefix and does a PK lookup on
// `users.did`, returning `{ did, handle }` on match.
let url = format!(
"{}/xrpc/com.atproto.identity.resolveHandle",
self.base_url
);
let r = self
.client
.post(&url)
.json(&json!({ "handle": did }))
.send()
.await?;
if r.status().as_u16() == 404 {
return Ok(None);
}
if !r.status().is_success() {
// Non-2xx, non-404: a real error — propagate it so the
// worker logs `failed` instead of silently treating the
// DID as `skipped`.
anyhow::bail!(
"pds handle resolver returned {}",
r.status()
);
}
let v: serde_json::Value = r.json().await?;
// The PDS returns `{ "did": "...", "handle": "..." }` on
// success. We read `handle` (what we actually want for
// `posts.handle`) and ignore the echoed `did`.
Ok(v.get("handle").and_then(|x| x.as_str()).map(String::from))
}
}
#[cfg(test)]
mod tests {
use super::*;
use serde_json::json;
use std::net::SocketAddr;
use tokio::net::TcpListener;
/// Spawn a one-shot HTTP listener that responds to the
/// resolveHandle XRPC call with the configured body + status.
/// Returns the bound address (so the resolver under test can hit
/// `http://127.0.0.1:<port>`).
async fn spawn_stub(
status: u16,
body: serde_json::Value,
) -> SocketAddr {
let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
let addr = listener.local_addr().unwrap();
tokio::spawn(async move {
use tokio::io::{AsyncReadExt, AsyncWriteExt};
loop {
let (mut sock, _) = match listener.accept().await {
Ok(p) => p,
Err(_) => break,
};
let mut buf = vec![0u8; 8192];
let n = sock.read(&mut buf).await.unwrap_or(0);
if n == 0 {
continue;
}
let body_s = body.to_string();
let resp = format!(
"HTTP/1.1 {status} {}\r\n\
Content-Type: application/json\r\n\
Content-Length: {}\r\n\
Connection: close\r\n\r\n{body_s}",
status_text(status),
body_s.len(),
);
let _ = sock.write_all(resp.as_bytes()).await;
}
});
addr
}
fn status_text(s: u16) -> &'static str {
match s {
200 => "OK",
404 => "Not Found",
500 => "Internal Server Error",
_ => "Status",
}
}
#[tokio::test]
async fn returns_handle_on_match() {
let addr = spawn_stub(
200,
json!({ "did": "did:plc:abc", "handle": "alice.bsky" }),
)
.await;
let r = PdsHandleResolver::new(format!("http://{addr}"));
let h = r.resolve_handle("did:plc:abc").await.unwrap();
assert_eq!(h.as_deref(), Some("alice.bsky"));
}
#[tokio::test]
async fn returns_none_on_404() {
let addr = spawn_stub(404, json!({ "error": "NotFound" })).await;
let r = PdsHandleResolver::new(format!("http://{addr}"));
let h = r.resolve_handle("did:plc:unknown").await.unwrap();
assert!(h.is_none());
}
#[tokio::test]
async fn returns_err_on_5xx() {
let addr = spawn_stub(500, json!({ "error": "oops" })).await;
let r = PdsHandleResolver::new(format!("http://{addr}"));
let result = r.resolve_handle("did:plc:abc").await;
assert!(
result.is_err(),
"5xx must propagate as Err so the worker logs `failed`, not `skipped`"
);
}
#[tokio::test]
async fn returns_handle_even_when_did_field_missing() {
// Some PDS implementations might return `{ "handle": "x" }`
// without echoing the DID. We must still extract the handle.
let addr = spawn_stub(200, json!({ "handle": "bob.bsky" })).await;
let r = PdsHandleResolver::new(format!("http://{addr}"));
let h = r.resolve_handle("did:plc:bob").await.unwrap();
assert_eq!(h.as_deref(), Some("bob.bsky"));
}
}
+9
View File
@@ -28,6 +28,14 @@ pub struct AppConfig {
pub s3_bucket_pds: String,
pub s3_bucket_appview: String,
pub plc_directory_url: String,
/// Cluster-internal URL the AppView uses to reach the PDS (e.g.
/// `http://pds-server:3000`). Falls back to `pds_public_url` when
/// unset. Splitting this from `pds_public_url` lets a single
/// deployment point the AppView at the in-cluster PDS hostname
/// (which may not be reachable from outside) while clients
/// still see the public URL.
#[serde(default)]
pub pds_internal_url: Option<String>,
/// Optional shared secret for `POST /internal/ingest-commit`. If unset,
/// the endpoint accepts anonymous requests (dev mode). If set, callers
/// must send `X-Ingest-Secret: <value>`.
@@ -68,6 +76,7 @@ impl AppConfig {
s3_bucket_pds: env("S3_BUCKET_PDS")?,
s3_bucket_appview: env("S3_BUCKET_APPVIEW")?,
plc_directory_url: env("PLC_DIRECTORY_URL")?,
pds_internal_url: std::env::var("PDS_INTERNAL_URL").ok(),
appview_ingest_secret: std::env::var("APPVIEW_INGEST_SECRET").ok(),
appview_handle_sync_interval_secs: std::env::var("APPVIEW_HANDLE_SYNC_INTERVAL_SECS")
.ok()
+31 -3
View File
@@ -9,17 +9,42 @@ pub async fn resolve_handle(
State(state): State<AppState>,
Json(req): Json<ResolveHandleReq>,
) -> Result<Json<ResolveHandleResp>, (StatusCode, Json<crate::routes::types::ErrorBody>)> {
// Polymorphic input: `handle` may be a bare handle OR a DID
// (`did:plc:…`, `did:web:…`, `did:key:…`). When it's a DID we
// look the row up by `did` — the AppView's `PdsHandleResolver`
// uses this path to fill `posts.handle` for local-PDS users
// (including `did:key:`) without a second round-trip to plc.directory.
if req.handle.starts_with("did:") {
let row: Option<(String,)> =
sqlx::query_as("SELECT handle FROM users WHERE did = $1")
.bind(&req.handle)
.fetch_optional(&state.db)
.await
.map_err(|e| err(StatusCode::INTERNAL_SERVER_ERROR, e))?;
if let Some((handle,)) = row {
return Ok(Json(ResolveHandleResp {
did: req.handle.clone(),
handle: Some(handle),
}));
}
// DID not hosted here — fall through to the handle lookup
// (returns 404 below).
}
if let Some(zone) = state.cfg.pds_handle_dns_zone.strip_prefix(".") {
if let Some(stripped) = req.handle.strip_suffix(zone) {
let user = stripped.trim_end_matches('.');
let full = format!("{}{}", user, state.cfg.pds_handle_dns_zone);
let row: Option<(String,)> = sqlx::query_as("SELECT did FROM users WHERE handle = $1")
let row: Option<(String,)> =
sqlx::query_as("SELECT did FROM users WHERE handle = $1")
.bind(&full)
.fetch_optional(&state.db)
.await
.map_err(|e| err(StatusCode::INTERNAL_SERVER_ERROR, e))?;
if let Some((did,)) = row {
return Ok(Json(ResolveHandleResp { did }));
return Ok(Json(ResolveHandleResp {
did,
handle: Some(full),
}));
}
}
}
@@ -29,7 +54,10 @@ pub async fn resolve_handle(
.await
.map_err(|e| err(StatusCode::INTERNAL_SERVER_ERROR, e))?;
match row {
Some((did,)) => Ok(Json(ResolveHandleResp { did })),
Some((did,)) => Ok(Json(ResolveHandleResp {
did,
handle: Some(req.handle.clone()),
})),
None => {
warn!(handle = %req.handle, "handle not found");
Err(err(
+7
View File
@@ -62,6 +62,13 @@ pub struct ResolveHandleReq {
#[derive(Debug, Serialize)]
pub struct ResolveHandleResp {
pub did: String,
/// Always populated when the lookup succeeds. For
/// handle → DID calls this is just the input echo; for
/// DID → handle calls this is the resolved local handle
/// (used by the AppView's `PdsHandleResolver` to fill
/// `posts.handle` without a second round-trip).
#[serde(default, skip_serializing_if = "Option::is_none")]
pub handle: Option<String>,
}
#[derive(Debug, Deserialize)]
@@ -0,0 +1,25 @@
-- 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;