diff --git a/cmd/ateapi/internal/store/atepg/partition_test.go b/cmd/ateapi/internal/store/atepg/partition_test.go
new file mode 100644
index 0000000000..ea7f765546
--- /dev/null
+++ b/cmd/ateapi/internal/store/atepg/partition_test.go
@@ -0,0 +1,370 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package atepg
+
+import (
+	"context"
+	"fmt"
+	"regexp"
+	"slices"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"github.com/agent-substrate/substrate/cmd/ateapi/internal/store"
+	"github.com/agent-substrate/substrate/cmd/ateapi/internal/store/storecontract"
+)
+
+// TestActorsTablePartitionable exists to keep it possible to partition the
+// actors table by atespace or by name later, with the other atespace-scoped
+// tables partitioned alongside it by atespace. It runs the store contract
+// suite against a copy of the schema partitioned that way, and fails on any
+// schema change or query that would not work in that layout.
+func TestActorsTablePartitionable(t *testing.T) {
+	// exemptions are statements allowed to read every partition even though
+	// their result lives in one. Do not add one without discussion and
+	// agreement in the community.
+	var exemptions []string
+
+	// spansPartitions are the statements whose result covers every partition
+	// by definition, under each partition key.
+	spansPartitions := map[string][]string{
+		// A global list walks every atespace.
+		"atespace": {globalList("actors"), globalList("actor_templates"), globalList("tags")},
+		// A global list walks every name, and a list within one atespace
+		// spans every name hash.
+		"name": {globalList("actors"), scopedActorList},
+	}
+
+	t.Run("by atespace", func(t *testing.T) {
+		// A nil table list partitions every table that has an atespace column.
+		runContractSuitePartitioned(t, "atespace", nil, slices.Concat(spansPartitions["atespace"], exemptions))
+	})
+	t.Run("by name", func(t *testing.T) {
+		runContractSuitePartitioned(t, "name", []string{"actors"}, slices.Concat(spansPartitions["name"], exemptions))
+	})
+
+	t.Run("rejects a unique index that omits the key", func(t *testing.T) {
+		pool := migratedPool(t, "partitioned-unique")
+		// This also rules out foreign keys onto uid, which need this index.
+		if _, err := pool.Exec(t.Context(), `CREATE UNIQUE INDEX actors_uid_key ON actors (uid)`); err != nil {
+			t.Fatal(err)
+		}
+		err := partitionTable(t.Context(), pool, "actors", "atespace")
+		if err == nil || !strings.Contains(err.Error(), "must include all partitioning columns") {
+			t.Fatalf("partitionTable error = %v, want unique index rejection", err)
+		}
+		t.Log(err)
+	})
+	t.Run("rejects a query that omits the key", func(t *testing.T) {
+		var got string
+		pool, tables := partitionedPool(t, "partitioned-fanout", "atespace", []string{"actors"})
+		check := newFanOutCheck("atespace", tables, nil, pool, func(format string, args ...any) { got = fmt.Sprintf(format, args...) })
+		var n int
+		if err := openPool(t, "partitioned-fanout", check).QueryRow(t.Context(), `SELECT count(*) FROM actors WHERE uid = $1`, "u1").Scan(&n); err != nil {
+			t.Fatal(err)
+		}
+		for i := range partitions {
+			if p := fmt.Sprintf("actors_p%d", i); !strings.Contains(got, p) {
+				t.Fatalf("fan-out check reported %q, want the uid lookup reading %s", got, p)
+			}
+		}
+		t.Log(got)
+	})
+	t.Run("rejects a multi-valued predicate", func(t *testing.T) {
+		var got string
+		pool, tables := partitionedPool(t, "partitioned-multi", "atespace", []string{"actors"})
+		check := newFanOutCheck("atespace", tables, nil, pool, func(format string, args ...any) { got = fmt.Sprintf(format, args...) })
+		var n int
+		// The suite's most used pair of atespaces, which partitions keeps apart.
+		if err := openPool(t, "partitioned-multi", check).QueryRow(t.Context(), `SELECT count(*) FROM actors WHERE atespace = ANY($1)`, []string{"team-a", "team-b"}).Scan(&n); err != nil {
+			t.Fatal(err)
+		}
+		if !strings.Contains(got, "reads partitions") {
+			t.Fatalf("fan-out check reported %q, want the two-atespace lookup reading two partitions", got)
+		}
+		t.Log(got)
+	})
+}
+
+// globalList is the statement that lists table across every atespace.
+func globalList(table string) string {
+	return normalizeSQL(`
+		SELECT atespace, name, proto FROM ` + table + `
+		WHERE $1::text IS NULL OR (atespace, name) > ($1, $2)
+		ORDER BY atespace, name
+		LIMIT $3`)
+}
+
+// scopedActorList is the statement that lists one atespace's actors.
+var scopedActorList = normalizeSQL(`
+	SELECT name, proto FROM actors
+	WHERE atespace = $1 AND ($2::text IS NULL OR name > $2)
+	ORDER BY name
+	LIMIT $3`)
+
+// runContractSuitePartitioned runs the store contract suite with tables
+// partitioned on key and fails on any statement, other than the allowed
+// ones, whose plan reads more than one partition of a table.
+func runContractSuitePartitioned(t *testing.T, key string, tables []string, allowed []string) {
+	schema := "partitioned-by-" + key
+	pool, tables := partitionedPool(t, schema, key, tables)
+	check := newFanOutCheck(key, tables, allowed, pool, t.Errorf)
+	traced := openPool(t, schema, check)
+	storecontract.RunContractTests(t, func(t *testing.T) store.Interface {
+		p, err := NewPersistence(t.Context(), traced)
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Cleanup(p.Close)
+		clearAll(t, p)
+		return p
+	})
+	// A table the suite never reads or writes goes unchecked, so a missing
+	// contract test fails here rather than passing silently.
+	for _, table := range check.unchecked() {
+		t.Errorf("no statement on %s was checked; the store contract suite must exercise it", table)
+	}
+}
+
+// partitions is the number of hash partitions per table. A multi-valued
+// predicate, such as atespace = ANY($1), is only reported when its values
+// land in different partitions. Nine is the smallest modulus that separates
+// the atespace names the store contract suite creates. A power of two takes
+// the low bits of the hash, and any up to 32 puts team-a and team-b in one
+// partition. Every contract subtest truncates every partition, so more of
+// them cost run time.
+const partitions = 9
+
+// partitionTable rebuilds the empty, freshly migrated table as a
+// hash-partitioned table on key, keeping its indexes, constraints and
+// foreign keys. PostgreSQL rejects any of them that omits key.
+func partitionTable(ctx context.Context, pool *pgxpool.Pool, table, key string) error {
+	rows, err := pool.Query(ctx, `
+		SELECT format('ALTER TABLE %s ADD CONSTRAINT %I %s', conrelid::regclass, conname, pg_get_constraintdef(oid))
+		FROM pg_constraint
+		WHERE contype = 'f' AND conparentid = 0 AND $1::regclass IN (conrelid, confrelid)`, table)
+	if err != nil {
+		return err
+	}
+	foreignKeys, err := pgx.CollectRows(rows, pgx.RowTo[string])
+	if err != nil {
+		return err
+	}
+	ddl := []string{fmt.Sprintf(`CREATE TABLE %[1]s_partitioned (LIKE %[1]s INCLUDING ALL) PARTITION BY HASH (%[2]s)`, table, key)}
+	for i := range partitions {
+		ddl = append(ddl, fmt.Sprintf(`CREATE TABLE %[1]s_p%[2]d PARTITION OF %[1]s_partitioned FOR VALUES WITH (MODULUS %[3]d, REMAINDER %[2]d)`, table, i, partitions))
+	}
+	ddl = append(ddl, fmt.Sprintf(`DROP TABLE %[1]s CASCADE`, table), fmt.Sprintf(`ALTER TABLE %[1]s_partitioned RENAME TO %[1]s`, table))
+	if _, err := pool.Exec(ctx, strings.Join(ddl, ";\n")); err != nil {
+		return fmt.Errorf("%s cannot be partitioned by %s: %w", table, key, err)
+	}
+	for _, fk := range foreignKeys {
+		if _, err := pool.Exec(ctx, fk); err != nil {
+			return fmt.Errorf("foreign key cannot reference %s partitioned by %s: %s: %w", table, key, fk, err)
+		}
+	}
+	return nil
+}
+
+// fanOutCheck is a pgx tracer that explains every statement on the
+// partitioned tables and fails when its plan reads more than one partition
+// of any of them.
+type fanOutCheck struct {
+	key       string
+	tables    []string
+	partition *regexp.Regexp // matches a partition name, capturing its table
+	allowed   []string
+	explain   *pgxpool.Pool
+	fail      func(format string, args ...any)
+	mu        sync.Mutex
+	checked   map[string]bool // tables that a checked plan has read
+	reported  map[string]bool // failures already reported, by table and statement
+}
+
+func newFanOutCheck(key string, tables []string, allowed []string, explain *pgxpool.Pool, fail func(string, ...any)) *fanOutCheck {
+	quoted := make([]string, len(tables))
+	for i, table := range tables {
+		quoted[i] = regexp.QuoteMeta(table)
+	}
+	return &fanOutCheck{
+		key:       key,
+		tables:    tables,
+		partition: regexp.MustCompile(`\b(` + strings.Join(quoted, "|") + `)_p\d+\b`),
+		allowed:   allowed,
+		explain:   explain,
+		fail:      fail,
+		checked:   map[string]bool{},
+		reported:  map[string]bool{},
+	}
+}
+
+func (c *fanOutCheck) TraceQueryStart(ctx context.Context, _ *pgx.Conn, data pgx.TraceQueryStartData) context.Context {
+	c.check(ctx, data.SQL, data.Args)
+	return ctx
+}
+
+func (c *fanOutCheck) TraceQueryEnd(context.Context, *pgx.Conn, pgx.TraceQueryEndData) {}
+
+// TraceBatchStart checks the statements of a batch, which pgx does not pass
+// to TraceQueryStart.
+func (c *fanOutCheck) TraceBatchStart(ctx context.Context, _ *pgx.Conn, data pgx.TraceBatchStartData) context.Context {
+	for _, q := range data.Batch.QueuedQueries {
+		c.check(ctx, q.SQL, q.Arguments)
+	}
+	return ctx
+}
+
+func (c *fanOutCheck) TraceBatchQuery(context.Context, *pgx.Conn, pgx.TraceBatchQueryData) {}
+
+func (c *fanOutCheck) TraceBatchEnd(context.Context, *pgx.Conn, pgx.TraceBatchEndData) {}
+
+// check explains one execution of a statement. The plan depends on the
+// arguments, for example a NULL page token turns a one-partition scan into a
+// scan of every partition, so every execution is explained rather than the
+// first one per statement.
+func (c *fanOutCheck) check(ctx context.Context, rawSQL string, args []any) {
+	sql := normalizeSQL(rawSQL)
+	if !slices.ContainsFunc(c.tables, func(t string) bool { return strings.Contains(sql, t) }) || slices.Contains(c.allowed, sql) {
+		return
+	}
+	// EXPLAIN accepts every statement that reads or writes rows, WITH and
+	// MERGE included. TRUNCATE is the one utility statement run on these
+	// tables. Any other statement EXPLAIN rejects fails the test below rather
+	// than passing unchecked.
+	if verb, _, _ := strings.Cut(strings.ToUpper(sql), " "); verb == "TRUNCATE" {
+		return
+	}
+	// EXPLAIN without ANALYZE plans but never executes, so writes are safe.
+	var plan []string
+	rows, err := c.explain.Query(ctx, "EXPLAIN "+rawSQL, args...)
+	if err == nil {
+		plan, err = pgx.CollectRows(rows, pgx.RowTo[string])
+	}
+	if err != nil {
+		c.report(sql, "explaining %s: %v", sql, err)
+		return
+	}
+	byTable := map[string][]string{}
+	for _, m := range c.partition.FindAllStringSubmatch(strings.Join(plan, "\n"), -1) {
+		byTable[m[1]] = append(byTable[m[1]], m[0])
+	}
+	for table, partitions := range byTable {
+		c.mu.Lock()
+		c.checked[table] = true
+		c.mu.Unlock()
+		if partitions = slices.Compact(slices.Sorted(slices.Values(partitions))); len(partitions) > 1 {
+			c.report(table+" "+sql, "statement on %s reads partitions %v instead of one; filter on %s or list it in TestActorsTablePartitionable:\n\t%s\n\targs=%v", table, partitions, c.key, sql, args)
+		}
+	}
+}
+
+// report fails the test once per key, so a statement the suite runs many
+// times is reported once.
+func (c *fanOutCheck) report(key, format string, args ...any) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.reported[key] {
+		return
+	}
+	c.reported[key] = true
+	c.fail(format, args...)
+}
+
+// unchecked lists the partitioned tables no checked plan has read.
+func (c *fanOutCheck) unchecked() []string {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return slices.DeleteFunc(slices.Clone(c.tables), func(table string) bool { return c.checked[table] })
+}
+
+func normalizeSQL(sql string) string {
+	return strings.Join(strings.Fields(sql), " ")
+}
+
+// migratedPool opens a pool on a fresh schema with the migrations applied.
+func migratedPool(t *testing.T, schema string) *pgxpool.Pool {
+	t.Helper()
+	admin := requirePool(t)
+	quoted := pgx.Identifier{schema}.Sanitize()
+	if _, err := admin.Exec(t.Context(), `DROP SCHEMA IF EXISTS `+quoted+` CASCADE; CREATE SCHEMA `+quoted); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _, _ = admin.Exec(context.Background(), `DROP SCHEMA IF EXISTS `+quoted+` CASCADE`) })
+	pool := openPool(t, schema, nil)
+	p, err := NewPersistence(t.Context(), pool)
+	if err != nil {
+		t.Fatal(err)
+	}
+	p.Close()
+	return pool
+}
+
+// partitionedPool opens a pool on a fresh schema with tables partitioned on
+// key, and returns the tables it partitioned. A nil tables partitions every
+// table that has a column named key.
+func partitionedPool(t *testing.T, schema, key string, tables []string) (*pgxpool.Pool, []string) {
+	t.Helper()
+	pool := migratedPool(t, schema)
+	if tables == nil {
+		tables = tablesWithColumn(t, pool, key)
+	}
+	for _, table := range tables {
+		if err := partitionTable(t.Context(), pool, table, key); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return pool, tables
+}
+
+// tablesWithColumn lists the tables in the pool's schema that have column.
+func tablesWithColumn(t *testing.T, pool *pgxpool.Pool, column string) []string {
+	t.Helper()
+	rows, err := pool.Query(t.Context(), `
+		SELECT table_name FROM information_schema.columns
+		WHERE table_schema = current_schema() AND column_name = $1
+		ORDER BY table_name`, column)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tables, err := pgx.CollectRows(rows, pgx.RowTo[string])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(tables) == 0 {
+		t.Fatalf("no table has a %s column", column)
+	}
+	return tables
+}
+
+// openPool opens a pool on schema, tracing every statement with tracer.
+func openPool(t *testing.T, schema string, tracer pgx.QueryTracer) *pgxpool.Pool {
+	t.Helper()
+	cfg, err := pgxpool.ParseConfig(containerDSN)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cfg.ConnConfig.RuntimeParams["search_path"] = pgx.Identifier{schema}.Sanitize()
+	cfg.ConnConfig.Tracer = tracer
+	pool, err := pgxpool.NewWithConfig(t.Context(), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(pool.Close)
+	return pool
+}
diff --git a/docs/dev/postgresql-schema-evolution.md b/docs/dev/postgresql-schema-evolution.md
index 19a77b3b5a..4b60280fc8 100644
--- a/docs/dev/postgresql-schema-evolution.md
+++ b/docs/dev/postgresql-schema-evolution.md
@@ -27,6 +27,14 @@ If two schema structures hold the same data, keep them consistent while both bin
 
 Do not run a large data backfill during startup. Propose a separate migration process before you add such a change.
 
+## Keep the actors table partitionable
+
+To preserve the option to partition the `actors` table by `atespace` or by `name`, and every other table with an `atespace` column by `atespace`, do not add a schema change or a query that introduces:
+
+- A unique index or constraint on one of these tables that omits `atespace`, or on `actors` that omits `name`.
+- A foreign key that references one of these tables by columns that omit `atespace`, or `actors` by anything other than `(atespace, name)`.
+- A query on one of these tables that does not filter on `atespace`, or a query on `actors` that does not also filter on `name`. A statement whose result spans every partition by definition, such as a global list, must be listed in `TestActorsTablePartitionable`. Anything else that reads more than one partition needs an exemption there, agreed with the community.
+
 ## Expand and contract
 
 Use an expand and contract sequence for a schema replacement or removal: