perf(server): stop thread search from scanning every turn

apps/server/src/orchestration/Layers/ProjectionSnapshotQuery.test.ts

@@ -1954,6 +1954,16 @@ projectionSnapshotLayer("ProjectionSnapshotQuery", (it) => {
             0,
             '2026-05-01T00:00:16.000Z',
             '2026-05-01T00:00:16.000Z'
+          ),
+          (
+            'message-assistant-decoy',
+            'thread-percent-decoy',
+            NULL,
+            'assistant',
+            'Unreferenced assistant needle must not be searchable.',
+            0,
+            '2026-05-01T00:00:17.000Z',
+            '2026-05-01T00:00:17.000Z'
           )
       `;
 
@@ -2009,6 +2019,10 @@ projectionSnapshotLayer("ProjectionSnapshotQuery", (it) => {
         (yield* snapshotQuery.searchThreads({ query: "system needle" })).matches,
         [],
       );
+      assert.deepStrictEqual(
+        (yield* snapshotQuery.searchThreads({ query: "unreferenced assistant needle" })).matches,
+        [],
+      );
       assert.deepStrictEqual(
         (yield* snapshotQuery.searchThreads({ query: "hidden needle" })).matches,
         [],

apps/server/src/orchestration/Layers/ProjectionSnapshotQuery.ts

@@ -904,10 +904,10 @@ const makeProjectionSnapshotQuery = Effect.gen(function* () {
               messages.role = 'user'
               OR (
                 messages.role = 'assistant'
-                AND messages.message_id IN (
-                  SELECT turns.assistant_message_id
+                AND EXISTS (
+                  SELECT 1
                   FROM projection_turns AS turns
-                  WHERE turns.assistant_message_id IS NOT NULL
+                  WHERE turns.assistant_message_id = messages.message_id
                 )
               )
             )

apps/server/src/persistence/Migrations.ts

@@ -59,6 +59,7 @@ import Migration0044 from "./Migrations/044_ClearAutomaticProjectModelDefaults.t
 import Migration0045 from "./Migrations/045_ProjectionProjectsAutoPull.ts";
 import Migration0046 from "./Migrations/046_RepairAutomaticSettlementTimestamps.ts";
 import Migration0047 from "./Migrations/047_ProjectionProjectIcon.ts";
+import Migration0048 from "./Migrations/048_ProjectionTurnsAssistantMessageIndex.ts";
 
 /**
  * Migration loader with all migrations defined inline.
@@ -118,6 +119,7 @@ export const migrationEntries = [
   [45, "ProjectionProjectsAutoPull", Migration0045],
   [46, "RepairAutomaticSettlementTimestamps", Migration0046],
   [47, "ProjectionProjectIcon", Migration0047],
+  [48, "ProjectionTurnsAssistantMessageIndex", Migration0048],
 ] as const;
 
 export const migrationManifest = migrationEntries.map(([id, name]) => [id, name] as const);

apps/server/src/persistence/Migrations/048_ProjectionTurnsAssistantMessageIndex.test.ts

@@ -0,0 +1,63 @@
+import { assert, it } from "@effect/vitest";
+import * as Effect from "effect/Effect";
+import * as Layer from "effect/Layer";
+import * as SqlClient from "effect/unstable/sql/SqlClient";
+
+import { runMigrations } from "../Migrations.ts";
+import * as NodeSqliteClient from "@t3tools/shared/nodeSqliteClient";
+
+const layer = it.layer(Layer.mergeAll(NodeSqliteClient.layerMemory()));
+
+layer("048_ProjectionTurnsAssistantMessageIndex", (it) => {
+  it.effect("indexes correlated canonical assistant lookups", () =>
+    Effect.gen(function* () {
+      const sql = yield* SqlClient.SqlClient;
+
+      yield* runMigrations({ toMigrationInclusive: 47 });
+      yield* runMigrations({ toMigrationInclusive: 48 });
+
+      const indexes = yield* sql<{
+        readonly seq: number;
+        readonly name: string;
+        readonly unique: number;
+        readonly origin: string;
+        readonly partial: number;
+      }>`
+        PRAGMA index_list(projection_turns)
+      `;
+      const assistantMessageIndex = indexes.find(
+        (index) => index.name === "idx_projection_turns_assistant_message_id",
+      );
+      assert.equal(assistantMessageIndex?.partial, 1);
+
+      const indexColumns = yield* sql<{
+        readonly seqno: number;
+        readonly cid: number;
+        readonly name: string;
+      }>`
+        PRAGMA index_info('idx_projection_turns_assistant_message_id')
+      `;
+      assert.deepStrictEqual(
+        indexColumns.map((column) => column.name),
+        ["assistant_message_id"],
+      );
+
+      const plan = yield* sql<{ readonly detail: string }>`
+        EXPLAIN QUERY PLAN
+        SELECT messages.message_id
+        FROM projection_thread_messages AS messages
+        WHERE messages.role = 'assistant'
+          AND EXISTS (
+            SELECT 1
+            FROM projection_turns AS turns
+            WHERE turns.assistant_message_id = messages.message_id
+          )
+      `;
+      assert.ok(
+        plan.some((step) => step.detail.includes("idx_projection_turns_assistant_message_id")),
+      );
+      assert.ok(plan.every((step) => !step.detail.includes("SCAN turns")));
+      assert.ok(plan.every((step) => !step.detail.includes("LIST SUBQUERY")));
+    }),
+  );
+});

apps/server/src/persistence/Migrations/048_ProjectionTurnsAssistantMessageIndex.ts

@@ -0,0 +1,11 @@
+import * as Effect from "effect/Effect";
+import * as SqlClient from "effect/unstable/sql/SqlClient";
+
+export default Effect.gen(function* () {
+  const sql = yield* SqlClient.SqlClient;
+  yield* sql`
+    CREATE INDEX IF NOT EXISTS idx_projection_turns_assistant_message_id
+    ON projection_turns(assistant_message_id)
+    WHERE assistant_message_id IS NOT NULL
+  `;
+});