feat(workers): pgboss claim/complete/fail via psycopg

Adds the Boss class — SELECT … FOR UPDATE SKIP LOCKED to atomically
claim, UPDATE state on completion. Retry semantics match pg-boss:
exponential backoff via retry_count / retry_delay / retry_backoff.

Forces client_encoding=UTF8 on every connection. The void2-db cluster
was initialized as SQL_ASCII so psycopg refuses to decode text by
default; UTF8 client_encoding works because the data is already UTF-8.
Node's pg lib is more forgiving and didn't surface this.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workers/tests/test_boss.py

@@ -0,0 +1,48 @@
+import json
+from void_workers.boss import Boss
+from void_workers.config import DATABASE_URL
+
+def test_claim_returns_none_when_no_jobs(boss_ready):
+    boss = Boss(dsn=DATABASE_URL)
+    assert boss.claim("echo") is None
+
+def test_claim_then_complete_round_trip(boss_ready):
+    boss_ready.execute(
+        "INSERT INTO pgboss.job(name, data) VALUES('echo', %s)",
+        (json.dumps({"ping": 1}),)
+    )
+    boss = Boss(dsn=DATABASE_URL)
+    job = boss.claim("echo")
+    assert job is not None
+    assert job["data"] == {"ping": 1}
+    boss.complete(job["id"], {"pong": 1})
+    row = boss_ready.execute(
+        "SELECT state, output FROM pgboss.job WHERE id=%s", (job["id"],)
+    ).fetchone()
+    assert row[0] == "completed"
+    assert row[1] == {"pong": 1}
+
+def test_fail_records_output_and_state(boss_ready):
+    boss_ready.execute("INSERT INTO pgboss.job(name) VALUES('echo')")
+    boss = Boss(dsn=DATABASE_URL)
+    job = boss.claim("echo")
+    boss.fail(job["id"], {"name": "BoomError", "message": "boom"})
+    row = boss_ready.execute(
+        "SELECT state, output, retry_count FROM pgboss.job WHERE id=%s",
+        (job["id"],)
+    ).fetchone()
+    # retry_limit defaults to 5 and retry_count was 0 → should move to 'retry'
+    assert row[0] == "retry"
+    assert row[2] == 1
+
+def test_fail_past_retry_limit_marks_failed(boss_ready):
+    boss_ready.execute(
+        "INSERT INTO pgboss.job(name, retry_count, retry_limit) VALUES('echo', 5, 5)"
+    )
+    boss = Boss(dsn=DATABASE_URL)
+    job = boss.claim("echo")
+    boss.fail(job["id"], {"name": "Done"})
+    row = boss_ready.execute(
+        "SELECT state FROM pgboss.job WHERE id=%s", (job["id"],)
+    ).fetchone()
+    assert row[0] == "failed"