diff --git a/src/resources/extensions/sf/sf-db.js b/src/resources/extensions/sf/sf-db.js
index b90f9e5c5..edadf35ff 100644
--- a/src/resources/extensions/sf/sf-db.js
+++ b/src/resources/extensions/sf/sf-db.js
@@ -78,7 +78,7 @@ function openRawDb(path) {
 	loadProvider();
 	return new DatabaseSync(path);
 }
-const SCHEMA_VERSION = 38;
+const SCHEMA_VERSION = 39;
 function indexExists(db, name) {
 	return !!db
 		.prepare(
@@ -576,6 +576,16 @@ function initSchema(db, fileBacked) {
         tags TEXT NOT NULL DEFAULT '[]'
       )
     `);
+		// content_hash is queried on every insert for deduplication; without an
+		// index the lookup becomes a full table scan as ingestion volume grows.
+		db.exec(
+			"CREATE INDEX IF NOT EXISTS idx_memory_sources_content_hash ON memory_sources(content_hash)",
+		);
+		// Category GROUP BY queries (e.g. /sf memory stats) need a covering
+		// index that filters active memories and groups by category.
+		db.exec(
+			"CREATE INDEX IF NOT EXISTS idx_memories_category ON memories(superseded_by, category)",
+		);
 		db.exec(`
       CREATE TABLE IF NOT EXISTS milestones (
         id TEXT PRIMARY KEY,
@@ -2046,6 +2056,20 @@ function migrateSchema(db) {
 				":applied_at": new Date().toISOString(),
 			});
 		}
+		if (currentVersion < 39) {
+			db.exec(
+				"CREATE INDEX IF NOT EXISTS idx_memory_sources_content_hash ON memory_sources(content_hash)",
+			);
+			db.exec(
+				"CREATE INDEX IF NOT EXISTS idx_memories_category ON memories(superseded_by, category)",
+			);
+			db.prepare(
+				"INSERT INTO schema_version (version, applied_at) VALUES (:version, :applied_at)",
+			).run({
+				":version": 39,
+				":applied_at": new Date().toISOString(),
+			});
+		}
 		db.exec("COMMIT");
 	} catch (err) {
 		db.exec("ROLLBACK");
diff --git a/src/resources/extensions/sf/tests/sf-db-migration.test.mjs b/src/resources/extensions/sf/tests/sf-db-migration.test.mjs
index 4774328e5..122e86603 100644
--- a/src/resources/extensions/sf/tests/sf-db-migration.test.mjs
+++ b/src/resources/extensions/sf/tests/sf-db-migration.test.mjs
@@ -201,7 +201,7 @@ test("openDatabase_migrates_v27_tasks_without_created_at_through_spec_backfill",
 	const version = db
 		.prepare("SELECT MAX(version) AS version FROM schema_version")
 		.get();
-	assert.equal(version.version, 38);
+	assert.equal(version.version, 39);
 	const taskSpec = db
 		.prepare(
 			"SELECT milestone_id, slice_id, task_id, verify FROM task_specs WHERE task_id = 'T01'",
@@ -285,3 +285,26 @@ test("openDatabase_memories_table_has_tags_column", () => {
 	assert.equal(tagsCol.type, "TEXT");
 	assert.equal(tagsCol.dflt_value, "'[]'");
 });
+
+test("openDatabase_memory_indexes_exist", () => {
+	assert.equal(openDatabase(":memory:"), true);
+	const db = getDatabase();
+	const indexes = db
+		.prepare(
+			"SELECT name FROM sqlite_master WHERE type = 'index' AND tbl_name IN ('memories', 'memory_sources')",
+		)
+		.all();
+	const names = indexes.map((r) => r.name);
+	assert.ok(
+		names.includes("idx_memories_active"),
+		"should have idx_memories_active",
+	);
+	assert.ok(
+		names.includes("idx_memories_category"),
+		"should have idx_memories_category",
+	);
+	assert.ok(
+		names.includes("idx_memory_sources_content_hash"),
+		"should have idx_memory_sources_content_hash",
+	);
+});
diff --git a/src/resources/extensions/sf/tests/uok-message-bus.test.mjs b/src/resources/extensions/sf/tests/uok-message-bus.test.mjs
index 97bfe700b..9fb2ea3b3 100644
--- a/src/resources/extensions/sf/tests/uok-message-bus.test.mjs
+++ b/src/resources/extensions/sf/tests/uok-message-bus.test.mjs
@@ -6,7 +6,9 @@ import { afterEach, test } from "vitest";
 import {
 	closeDatabase,
 	getUokMessageBusMetrics,
+	getUokMessagesForAgent,
 	insertUokMessage,
+	openDatabase,
 } from "../sf-db.js";
 import { AgentInbox, MessageBus } from "../uok/message-bus.js";
 
@@ -274,3 +276,24 @@ test("getUokMessageBusMetrics_ignores_reads_by_non_recipient_for_unread_count",
 	assert.equal(m.totalMessages, 1);
 	assert.equal(m.totalUnread, 1);
 });
+
+test("messageBus_send_when_switching_projects_uses_current_project_db", () => {
+	const first = makeProject();
+	const second = makeProject();
+
+	new MessageBus(first).send("agent-a", "agent-b", "first");
+	new MessageBus(second).send("agent-a", "agent-b", "second");
+
+	closeDatabase();
+	openDatabase(join(first, ".sf", "sf.db"));
+	assert.deepEqual(
+		getUokMessagesForAgent("agent-b").map((message) => message.body),
+		["first"],
+	);
+	closeDatabase();
+	openDatabase(join(second, ".sf", "sf.db"));
+	assert.deepEqual(
+		getUokMessagesForAgent("agent-b").map((message) => message.body),
+		["second"],
+	);
+});
diff --git a/src/resources/extensions/sf/uok/message-bus.js b/src/resources/extensions/sf/uok/message-bus.js
index e80d72b5c..05d2a3fba 100644
--- a/src/resources/extensions/sf/uok/message-bus.js
+++ b/src/resources/extensions/sf/uok/message-bus.js
@@ -20,7 +20,6 @@ import {
 	getUokMessageReadIds,
 	getUokMessagesForAgent,
 	insertUokMessage,
-	isDbAvailable,
 	markUokMessageRead,
 	openDatabase,
 } from "../sf-db.js";
@@ -34,7 +33,6 @@ function deterministicMessageId(key) {
 }
 
 function ensureDb(basePath) {
-	if (isDbAvailable()) return;
 	const dir = sfRoot(basePath);
 	mkdirSync(dir, { recursive: true });
 	openDatabase(join(dir, "sf.db"));