diff --git a/apps/cli/src/legacy/commands/bootstrap/bootstrap.integration.test.ts b/apps/cli/src/legacy/commands/bootstrap/bootstrap.integration.test.ts
index b01206e674..6a67e8d0aa 100644
--- a/apps/cli/src/legacy/commands/bootstrap/bootstrap.integration.test.ts
+++ b/apps/cli/src/legacy/commands/bootstrap/bootstrap.integration.test.ts
@@ -207,6 +207,7 @@ function setup(opts: SetupOpts = {}) {
           copyToCsv: () => Effect.succeed(new Uint8Array()),
           queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
           exec: () => Effect.void,
+          execBatch: () => Effect.void,
           query: () => Effect.succeed([]),
         });
       }),
diff --git a/apps/cli/src/legacy/commands/bootstrap/bootstrap.workdir-cache.integration.test.ts b/apps/cli/src/legacy/commands/bootstrap/bootstrap.workdir-cache.integration.test.ts
index f01f8d0f12..b85362575f 100644
--- a/apps/cli/src/legacy/commands/bootstrap/bootstrap.workdir-cache.integration.test.ts
+++ b/apps/cli/src/legacy/commands/bootstrap/bootstrap.workdir-cache.integration.test.ts
@@ -168,6 +168,7 @@ describe("legacy bootstrap linked-project cache location", () => {
               copyToCsv: () => Effect.succeed(new Uint8Array()),
               queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
               exec: () => Effect.void,
+              execBatch: () => Effect.void,
               query: () => Effect.succeed([]),
             };
           }),
diff --git a/apps/cli/src/legacy/commands/db/advisors/advisors.integration.test.ts b/apps/cli/src/legacy/commands/db/advisors/advisors.integration.test.ts
index f46a88aa74..c2165fcff8 100644
--- a/apps/cli/src/legacy/commands/db/advisors/advisors.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/advisors/advisors.integration.test.ts
@@ -10,6 +10,7 @@ import {
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyPlatformApi,
   mockLegacyTelemetryStateTracked,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import * as HttpClientResponse from "effect/unstable/http/HttpClientResponse";
 
@@ -29,6 +30,7 @@ import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.t
 import {
   LegacyDbConnection,
   type LegacyPgConnInput,
+  type LegacyDbSession,
 } from "../../../shared/legacy-db-connection.service.ts";
 import {
   LegacyDbAdvisorsFailOnError,
@@ -103,8 +105,8 @@ function mockConnection(opts: {
 }) {
   const execs: Array<string> = [];
   const layer = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
@@ -123,7 +125,12 @@ function mockConnection(opts: {
             }
             return Effect.succeed(opts.rows ?? []);
           }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
   return {
     layer,
diff --git a/apps/cli/src/legacy/commands/db/diff/diff.integration.test.ts b/apps/cli/src/legacy/commands/db/diff/diff.integration.test.ts
index d2f0ae0564..9d9fcff873 100644
--- a/apps/cli/src/legacy/commands/db/diff/diff.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/diff/diff.integration.test.ts
@@ -16,6 +16,7 @@ import {
   mockLegacyShadowContainerCliSpawner,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { mockOutput, mockRuntimeInfo } from "../../../../../tests/helpers/mocks.ts";
 import { dockerfileServiceImage } from "../../../../shared/services/dockerfile-images.ts";
@@ -149,6 +150,7 @@ function fakeShadowDbConnection() {
               execCalls.push(sql);
             }),
           query: () => Effect.succeed([]),
+          execBatch: (statements) => legacySequentialExecBatch(session)(statements),
           extensionExists: () => Effect.succeed(false),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
           queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
diff --git a/apps/cli/src/legacy/commands/db/lint/lint.integration.test.ts b/apps/cli/src/legacy/commands/db/lint/lint.integration.test.ts
index 63e2aa49ff..d69277424e 100644
--- a/apps/cli/src/legacy/commands/db/lint/lint.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/lint/lint.integration.test.ts
@@ -6,6 +6,7 @@ import {
   LEGACY_VALID_REF,
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyTelemetryStateTracked,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
 import { LegacyDnsResolverFlag } from "../../../../shared/legacy/global-flags.ts";
@@ -19,6 +20,7 @@ import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.t
 import {
   LegacyDbConnection,
   type LegacyPgConnInput,
+  type LegacyDbSession,
 } from "../../../shared/legacy-db-connection.service.ts";
 import { LegacyDbLintFailOnError } from "./lint.errors.ts";
 import { encodeLegacyLintResults, parseLegacyLintResult } from "./lint.format.ts";
@@ -81,8 +83,8 @@ function mockConnection(opts: {
   const linted: Array<string> = [];
   let listParams: ReadonlyArray<unknown> | undefined;
   const layer = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
@@ -122,7 +124,12 @@ function mockConnection(opts: {
             }
             return Effect.succeed([]);
           }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
   return {
     layer,
diff --git a/apps/cli/src/legacy/commands/db/pull/pull.integration.test.ts b/apps/cli/src/legacy/commands/db/pull/pull.integration.test.ts
index 412cea0a16..53db82f60e 100644
--- a/apps/cli/src/legacy/commands/db/pull/pull.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/pull/pull.integration.test.ts
@@ -37,7 +37,10 @@ import {
   PROJECT_NOT_LINKED_MESSAGE,
 } from "../../../config/legacy-project-ref.service.ts";
 import { LegacyDbConfigResolver } from "../../../shared/legacy-db-config.service.ts";
-import { LegacyDbConnection } from "../../../shared/legacy-db-connection.service.ts";
+import {
+  type LegacyDbSession,
+  LegacyDbConnection,
+} from "../../../shared/legacy-db-connection.service.ts";
 import {
   LegacyDockerRun,
   type LegacyDockerRunOpts,
@@ -327,19 +330,30 @@ function setup(workdir: string, opts: SetupOpts = {}) {
   // ALSO issues a parameterized `INSERT_MIGRATION_VERSION` query, into its own
   // separate in-shadow history table).
   const TARGET_PORT = 5432;
-  const makeSession = (isShadow: boolean) => ({
-    exec: (sql: string) => Effect.sync(() => void execLog.push(sql)),
-    query: (sql: string, params?: ReadonlyArray<unknown>) => {
+  const makeSession = (isShadow: boolean): LegacyDbSession => {
+    const exec = (sql: string) => Effect.sync(() => void execLog.push(sql));
+    const query = (sql: string, params?: ReadonlyArray<unknown>) => {
       if (/SELECT version/u.test(sql)) {
         return Effect.succeed((opts.remoteVersions ?? []).map((v) => ({ version: v })));
       }
       if (!isShadow && params !== undefined) historyUpserts.push(params);
       return Effect.succeed([] as ReadonlyArray<Record<string, unknown>>);
-    },
-    extensionExists: () => Effect.die("extensionExists unused"),
-    copyToCsv: () => Effect.die("copyToCsv unused"),
-    queryRaw: () => Effect.die("queryRaw unused"),
-  });
+    };
+    return {
+      exec,
+      query,
+      // A migration batch carries exactly the statements (and the parameterized
+      // history insert) the sequential path would run, so route each operation
+      // through the same recording.
+      execBatch: (statements) =>
+        Effect.forEach(statements, ({ sql, params }) =>
+          params === undefined ? exec(sql) : query(sql, params),
+        ).pipe(Effect.asVoid),
+      extensionExists: () => Effect.die("extensionExists unused"),
+      copyToCsv: () => Effect.die("copyToCsv unused"),
+      queryRaw: () => Effect.die("queryRaw unused"),
+    };
+  };
   const targetSession = makeSession(false);
   const shadowSession = makeSession(true);
   const dbConnection = Layer.succeed(LegacyDbConnection, {
diff --git a/apps/cli/src/legacy/commands/db/pull/pull.sync.integration.test.ts b/apps/cli/src/legacy/commands/db/pull/pull.sync.integration.test.ts
index f626ab565e..333f6398f0 100644
--- a/apps/cli/src/legacy/commands/db/pull/pull.sync.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/pull/pull.sync.integration.test.ts
@@ -20,6 +20,9 @@ function mockSession(opts: { readonly failUpsertAt?: number } = {}) {
   let upsertCount = 0;
   const session: LegacyDbSession = {
     exec: (sql: string) => Effect.sync(() => void calls.push(sql)),
+    // `legacyUpdateMigrationHistory` owns its transaction envelope statement by
+    // statement; it never batches.
+    execBatch: () => Effect.die("execBatch unused"),
     query: (sql: string) => {
       if (/INSERT INTO supabase_migrations/u.test(sql)) {
         upsertCount += 1;
diff --git a/apps/cli/src/legacy/commands/db/push/push.integration.test.ts b/apps/cli/src/legacy/commands/db/push/push.integration.test.ts
index 55bea9eece..f8b411d56c 100644
--- a/apps/cli/src/legacy/commands/db/push/push.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/push/push.integration.test.ts
@@ -13,6 +13,7 @@ import {
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
 import { LegacyDnsResolverFlag, LegacyYesFlag } from "../../../../shared/legacy/global-flags.ts";
@@ -28,6 +29,7 @@ import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.t
 import {
   LegacyDbConnection,
   type LegacyPgConnInput,
+  type LegacyDbSession,
 } from "../../../shared/legacy-db-connection.service.ts";
 import { LegacyEdgeRuntimeScriptError } from "../../../shared/legacy-edge-runtime-script.errors.ts";
 import {
@@ -96,8 +98,8 @@ function mockConnection(opts: {
   const execs: Array<string> = [];
   const queries: Array<{ sql: string; params?: ReadonlyArray<unknown> }> = [];
   const layer = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
@@ -144,7 +146,12 @@ function mockConnection(opts: {
               return Effect.succeed([]);
             },
           ),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
   return {
     layer,
diff --git a/apps/cli/src/legacy/commands/db/query/query.integration.test.ts b/apps/cli/src/legacy/commands/db/query/query.integration.test.ts
index 05e0f0a143..6b54b09ca1 100644
--- a/apps/cli/src/legacy/commands/db/query/query.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/query/query.integration.test.ts
@@ -81,6 +81,7 @@ function mockDbConnection(opts: {
     connect: () =>
       Effect.succeed({
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         query: () => Effect.succeed([]),
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/db/reset/reset.integration.test.ts b/apps/cli/src/legacy/commands/db/reset/reset.integration.test.ts
index 8924889d0c..4addec1d0e 100644
--- a/apps/cli/src/legacy/commands/db/reset/reset.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/reset/reset.integration.test.ts
@@ -22,6 +22,7 @@ import {
   mockLegacyPlatformApiService,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { LegacyPlatformApi } from "../../../auth/legacy-platform-api.service.ts";
 import { LegacyPlatformApiFactory } from "../../../auth/legacy-platform-api-factory.service.ts";
@@ -56,6 +57,7 @@ import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.t
 import {
   LegacyDbConnection,
   type LegacyPgConnInput,
+  type LegacyDbSession,
 } from "../../../shared/legacy-db-connection.service.ts";
 import { legacyDbReset } from "./reset.handler.ts";
 import type { LegacyDbResetFlags } from "./reset.command.ts";
@@ -163,8 +165,8 @@ function mockConnection(
   const queries: Array<{ sql: string; params?: ReadonlyArray<unknown> }> = [];
   let replicationCallIndex = 0;
   const layer = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
@@ -211,7 +213,12 @@ function mockConnection(
               return Effect.succeed([]);
             },
           ),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
   return {
     layer,
diff --git a/apps/cli/src/legacy/commands/db/schema/declarative/declarative.orchestrate.integration.test.ts b/apps/cli/src/legacy/commands/db/schema/declarative/declarative.orchestrate.integration.test.ts
index 47788d9346..62c85f1f7c 100644
--- a/apps/cli/src/legacy/commands/db/schema/declarative/declarative.orchestrate.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/schema/declarative/declarative.orchestrate.integration.test.ts
@@ -82,6 +82,7 @@ function mockShadowInfra() {
         connectedDatabases.push(cfg.database);
         const session: LegacyDbSession = {
           exec: () => Effect.void,
+          execBatch: () => Effect.void,
           query: () => Effect.succeed([]),
           extensionExists: () => Effect.succeed(false),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/db/schema/declarative/generate/generate.integration.test.ts b/apps/cli/src/legacy/commands/db/schema/declarative/generate/generate.integration.test.ts
index 49787250b1..74c0597144 100644
--- a/apps/cli/src/legacy/commands/db/schema/declarative/generate/generate.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/schema/declarative/generate/generate.integration.test.ts
@@ -26,6 +26,7 @@ import {
   mockLegacyPlatformApiService,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../../../../shared/cli/cli-args.service.ts";
 import {
@@ -40,7 +41,10 @@ import { LegacyPlatformApi } from "../../../../../auth/legacy-platform-api.servi
 import { LegacyPlatformApiFactory } from "../../../../../auth/legacy-platform-api-factory.service.ts";
 import { legacyDockerRunLayer } from "../../../../../shared/legacy-docker-run.layer.ts";
 import { LegacyDbConfigResolver } from "../../../../../shared/legacy-db-config.service.ts";
-import { LegacyDbConnection } from "../../../../../shared/legacy-db-connection.service.ts";
+import {
+  type LegacyDbSession,
+  LegacyDbConnection,
+} from "../../../../../shared/legacy-db-connection.service.ts";
 import {
   type LegacyEdgeRuntimeRunOpts,
   LegacyEdgeRuntimeScript,
@@ -112,8 +116,8 @@ function setup(workdir: string, opts: SetupOpts = {}) {
   );
   const dbExec: string[] = [];
   const dbConn = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         exec: (sql: string) =>
           Effect.sync(() => {
             dbExec.push(sql);
@@ -126,7 +130,12 @@ function setup(workdir: string, opts: SetupOpts = {}) {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
   const seam = Layer.succeed(LegacyDeclarativeSeam, {
     exportCatalog: ({ mode, projectRef }) => {
diff --git a/apps/cli/src/legacy/commands/db/shared/legacy-pgdelta.seam.integration.test.ts b/apps/cli/src/legacy/commands/db/shared/legacy-pgdelta.seam.integration.test.ts
index 9171739c15..ec0927af3c 100644
--- a/apps/cli/src/legacy/commands/db/shared/legacy-pgdelta.seam.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/shared/legacy-pgdelta.seam.integration.test.ts
@@ -58,6 +58,7 @@ function fakeShadowDbConnection() {
       Effect.sync(() => {
         const session: LegacyDbSession = {
           exec: () => Effect.void,
+          execBatch: () => Effect.void,
           query: () => Effect.succeed([]),
           extensionExists: () => Effect.succeed(false),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/db/shared/legacy-shadow-source.ts b/apps/cli/src/legacy/commands/db/shared/legacy-shadow-source.ts
index bfc54450bf..19fbf800b1 100644
--- a/apps/cli/src/legacy/commands/db/shared/legacy-shadow-source.ts
+++ b/apps/cli/src/legacy/commands/db/shared/legacy-shadow-source.ts
@@ -643,6 +643,18 @@ function legacyMigrateBaseDatabase(
         path,
         absolutePaths,
         (message) => new LegacyDeclarativeShadowDbError({ message }),
+      ).pipe(
+        // A batch runs on its own pooled connection, so failing to acquire it is a
+        // connection failure, not a statement failure: it wears this seam's own error
+        // class (like the `connect` mapping above) and keeps the driver's suggestion.
+        Effect.catchTag("LegacyDbConnectError", (cause) =>
+          Effect.fail(
+            new LegacyDeclarativeShadowDbError({
+              message: cause.message,
+              ...(cause.suggestion === undefined ? {} : { suggestion: cause.suggestion }),
+            }),
+          ),
+        ),
       );
     }),
   );
diff --git a/apps/cli/src/legacy/commands/db/start/start.integration.test.ts b/apps/cli/src/legacy/commands/db/start/start.integration.test.ts
index 94ef016d04..5f5244be1f 100644
--- a/apps/cli/src/legacy/commands/db/start/start.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/start/start.integration.test.ts
@@ -18,6 +18,7 @@ import {
   mockLegacyCliConfig,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
 import {
@@ -248,6 +249,7 @@ function fakeDbSession() {
         calls.push({ kind: "query", sql });
         return [];
       }),
+    execBatch: (statements) => legacySequentialExecBatch(session)(statements),
     extensionExists: () => Effect.succeed(false),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
     queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
diff --git a/apps/cli/src/legacy/commands/db/test/test.integration.test.ts b/apps/cli/src/legacy/commands/db/test/test.integration.test.ts
index 38fd0c105c..2e18a09c61 100644
--- a/apps/cli/src/legacy/commands/db/test/test.integration.test.ts
+++ b/apps/cli/src/legacy/commands/db/test/test.integration.test.ts
@@ -48,6 +48,7 @@ import {
 import {
   mockLegacyCliConfig,
   mockLegacyTelemetryStateTracked,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
 import { commandRuntimeLayer } from "../../../../shared/runtime/command-runtime.layer.ts";
@@ -124,6 +125,7 @@ function mockDbConnection() {
       Effect.sync(() => {
         execCalls.push(sql);
       }),
+    execBatch: (statements) => legacySequentialExecBatch(session)(statements),
     extensionExists: () => Effect.succeed(false),
     queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-deprecated.integration.test.ts b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-deprecated.integration.test.ts
index 55c1c4793e..1ab158ec48 100644
--- a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-deprecated.integration.test.ts
+++ b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-deprecated.integration.test.ts
@@ -61,6 +61,7 @@ function setup() {
       connect: () =>
         Effect.succeed({
           exec: () => Effect.void,
+          execBatch: () => Effect.void,
           extensionExists: () => Effect.succeed(false),
           queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-query.integration.test.ts b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-query.integration.test.ts
index 2e83f36d2c..41c6a5098e 100644
--- a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-query.integration.test.ts
+++ b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-query.integration.test.ts
@@ -110,6 +110,7 @@ function mockDbConnection(opts: {
       }
       return Effect.succeed({
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         extensionExists: () => Effect.succeed(false),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-specs.integration.test.ts b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-specs.integration.test.ts
index 4ed65417fe..14d58b7f06 100644
--- a/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-specs.integration.test.ts
+++ b/apps/cli/src/legacy/commands/inspect/db/legacy-inspect-specs.integration.test.ts
@@ -52,6 +52,7 @@ function setup(rows: ReadonlyArray<Record<string, unknown>>) {
       connect: () =>
         Effect.succeed({
           exec: () => Effect.void,
+          execBatch: () => Effect.void,
           extensionExists: () => Effect.succeed(false),
           queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/commands/inspect/report/report.integration.test.ts b/apps/cli/src/legacy/commands/inspect/report/report.integration.test.ts
index e7a95a7559..ef0fe2a072 100644
--- a/apps/cli/src/legacy/commands/inspect/report/report.integration.test.ts
+++ b/apps/cli/src/legacy/commands/inspect/report/report.integration.test.ts
@@ -91,6 +91,7 @@ function mockReportConnection(opts: {
       }
       return Effect.succeed({
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         extensionExists: () => Effect.succeed(false),
         query: () => Effect.succeed([]),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
diff --git a/apps/cli/src/legacy/commands/migration/down/down.integration.test.ts b/apps/cli/src/legacy/commands/migration/down/down.integration.test.ts
index 92a5e14a4a..6f1acb1bca 100644
--- a/apps/cli/src/legacy/commands/migration/down/down.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/down/down.integration.test.ts
@@ -12,6 +12,7 @@ import {
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { mockOutput, mockStdin, mockTty } from "../../../../../tests/helpers/mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
@@ -25,7 +26,10 @@ import type {
   LegacyResolvedDbConfig,
 } from "../../../shared/legacy-db-config.types.ts";
 import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.ts";
-import { LegacyDbConnection } from "../../../shared/legacy-db-connection.service.ts";
+import {
+  type LegacyDbSession,
+  LegacyDbConnection,
+} from "../../../shared/legacy-db-connection.service.ts";
 import { LegacyMigrationDropError } from "../../../shared/legacy-drop-objects.ts";
 import { LegacyMigrationSeedError } from "../../../shared/legacy-seed.ts";
 import { legacyMigrationDown } from "./down.handler.ts";
@@ -87,8 +91,8 @@ function setup(workdir: string, opts: SetupOpts = {}) {
   });
 
   const connection = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         exec: (sql: string) =>
           Effect.suspend(() => {
             execs.push(sql);
@@ -111,7 +115,12 @@ function setup(workdir: string, opts: SetupOpts = {}) {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
 
   // `loadProjectRef` gives an explicit `--project-ref` flag top precedence, same
diff --git a/apps/cli/src/legacy/commands/migration/fetch/fetch.integration.test.ts b/apps/cli/src/legacy/commands/migration/fetch/fetch.integration.test.ts
index 188b419f19..1af8b5b187 100644
--- a/apps/cli/src/legacy/commands/migration/fetch/fetch.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/fetch/fetch.integration.test.ts
@@ -81,6 +81,7 @@ function setup(workdir: string, opts: SetupOpts = {}) {
     connect: () =>
       Effect.succeed({
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         query: (sql: string) =>
           Effect.suspend(() =>
             sql === SELECT_SQL
diff --git a/apps/cli/src/legacy/commands/migration/list/list.integration.test.ts b/apps/cli/src/legacy/commands/migration/list/list.integration.test.ts
index 618740a95d..c5eccee980 100644
--- a/apps/cli/src/legacy/commands/migration/list/list.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/list/list.integration.test.ts
@@ -66,6 +66,7 @@ function setup(workdir: string, opts: SetupOpts = {}) {
     connect: () =>
       Effect.succeed({
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         query: (sql: string) =>
           Effect.suspend(() => {
             if (sql === LIST_SQL) {
diff --git a/apps/cli/src/legacy/commands/migration/repair/repair.integration.test.ts b/apps/cli/src/legacy/commands/migration/repair/repair.integration.test.ts
index fa14041e82..34ed94bb7b 100644
--- a/apps/cli/src/legacy/commands/migration/repair/repair.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/repair/repair.integration.test.ts
@@ -11,6 +11,7 @@ import {
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { mockOutput, mockStdin, mockTty } from "../../../../../tests/helpers/mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
@@ -24,7 +25,10 @@ import type {
   LegacyResolvedDbConfig,
 } from "../../../shared/legacy-db-config.types.ts";
 import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.ts";
-import { LegacyDbConnection } from "../../../shared/legacy-db-connection.service.ts";
+import {
+  type LegacyDbSession,
+  LegacyDbConnection,
+} from "../../../shared/legacy-db-connection.service.ts";
 import { legacyMigrationRepair, type LegacyMigrationRepairInput } from "./repair.handler.ts";
 
 interface SetupOpts {
@@ -72,8 +76,8 @@ function setup(workdir: string, opts: SetupOpts = {}) {
   });
 
   const connection = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         exec: (sql: string) =>
           Effect.suspend(() => {
             execs.push(sql);
@@ -91,7 +95,12 @@ function setup(workdir: string, opts: SetupOpts = {}) {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
 
   // `loadProjectRef` gives an explicit `--project-ref` flag top precedence, same
diff --git a/apps/cli/src/legacy/commands/migration/squash/squash.integration.test.ts b/apps/cli/src/legacy/commands/migration/squash/squash.integration.test.ts
index cac1d8f1d9..5d1f5dcb75 100644
--- a/apps/cli/src/legacy/commands/migration/squash/squash.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/squash/squash.integration.test.ts
@@ -16,6 +16,7 @@ import {
   mockLegacyShadowContainerCliSpawner,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import {
   mockOutput,
@@ -286,6 +287,9 @@ function setup(workdir: string, opts: SetupOpts = {}) {
                 ? Effect.fail(new LegacyDbExecError({ message: "boom" }))
                 : Effect.succeed<ReadonlyArray<Record<string, unknown>>>([]);
             }),
+          // A migration file's statements arrive as one batch; replay them through
+          // `exec`/`query` so the call-order log and failure injection still apply.
+          execBatch: (batch) => legacySequentialExecBatch(session)(batch),
           extensionExists: () => Effect.succeed(false),
           copyToCsv: () => Effect.succeed(new Uint8Array()),
           queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
diff --git a/apps/cli/src/legacy/commands/migration/up/up.integration.test.ts b/apps/cli/src/legacy/commands/migration/up/up.integration.test.ts
index 27979f452d..e903a225c2 100644
--- a/apps/cli/src/legacy/commands/migration/up/up.integration.test.ts
+++ b/apps/cli/src/legacy/commands/migration/up/up.integration.test.ts
@@ -11,6 +11,7 @@ import {
   mockLegacyLinkedProjectCacheTracked,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../../tests/helpers/legacy-mocks.ts";
 import { mockOutput } from "../../../../../tests/helpers/mocks.ts";
 import { CliArgs } from "../../../../shared/cli/cli-args.service.ts";
@@ -23,7 +24,10 @@ import type {
   LegacyResolvedDbConfig,
 } from "../../../shared/legacy-db-config.types.ts";
 import { LegacyDbExecError } from "../../../shared/legacy-db-connection.errors.ts";
-import { LegacyDbConnection } from "../../../shared/legacy-db-connection.service.ts";
+import {
+  type LegacyDbSession,
+  LegacyDbConnection,
+} from "../../../shared/legacy-db-connection.service.ts";
 import { LegacyMigrationVaultError } from "../../../shared/legacy-vault.ts";
 import { legacyMigrationUp } from "./up.handler.ts";
 import type { LegacyMigrationUpFlags } from "./up.command.ts";
@@ -69,8 +73,8 @@ function setup(workdir: string, opts: SetupOpts = {}) {
   });
 
   const connection = Layer.succeed(LegacyDbConnection, {
-    connect: () =>
-      Effect.succeed({
+    connect: () => {
+      const session: LegacyDbSession = {
         exec: (sql: string) =>
           Effect.suspend(() => {
             execs.push(sql);
@@ -94,7 +98,12 @@ function setup(workdir: string, opts: SetupOpts = {}) {
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
         queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
-      }),
+        // A migration file's statements arrive as one batch; replay them through
+        // `exec`/`query` so this suite's recordings and failure injection still apply.
+        execBatch: (statements) => legacySequentialExecBatch(session)(statements),
+      };
+      return Effect.succeed(session);
+    },
   });
 
   // `loadProjectRef` gives an explicit `--project-ref` flag top precedence, same
diff --git a/apps/cli/src/legacy/commands/start/start.integration.test.ts b/apps/cli/src/legacy/commands/start/start.integration.test.ts
index 94132e5939..3a73df184d 100644
--- a/apps/cli/src/legacy/commands/start/start.integration.test.ts
+++ b/apps/cli/src/legacy/commands/start/start.integration.test.ts
@@ -22,6 +22,7 @@ import {
   mockLegacyCliConfig,
   mockLegacyTelemetryStateTracked,
   useLegacyTempWorkdir,
+  legacySequentialExecBatch,
 } from "../../../../tests/helpers/legacy-mocks.ts";
 import { CliArgs } from "../../../shared/cli/cli-args.service.ts";
 import { classifyCliCauseActionability } from "../../../shared/telemetry/error-actionability.ts";
@@ -378,6 +379,7 @@ function fakeDbSession() {
         calls.push({ kind: "query", sql });
         return [];
       }),
+    execBatch: (statements) => legacySequentialExecBatch(session)(statements),
     extensionExists: () => Effect.succeed(false),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
     queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
diff --git a/apps/cli/src/legacy/shared/db-bootstrap/db-setup.ts b/apps/cli/src/legacy/shared/db-bootstrap/db-setup.ts
index 510f9dee39..9378a2d360 100644
--- a/apps/cli/src/legacy/shared/db-bootstrap/db-setup.ts
+++ b/apps/cli/src/legacy/shared/db-bootstrap/db-setup.ts
@@ -1032,7 +1032,13 @@ export const legacySetupDatabase = (
   options: LegacySetupDatabaseOptions = {},
 ): Effect.Effect<
   void,
-  LegacyDbSetupError | LegacyMigrationVaultError | LegacyImagePrepullError,
+  | LegacyDbSetupError
+  | LegacyMigrationVaultError
+  | LegacyImagePrepullError
+  // A batched SQL file whose pooled connection cannot be acquired fails with the
+  // driver's own connect error, surfaced verbatim (never relabeled as a setup
+  // failure) like every other connection failure on this path.
+  | LegacyDbConnectError,
   Output | LegacyDockerRun | RuntimeInfo
 > =>
   Effect.gen(function* () {
@@ -1118,7 +1124,10 @@ export const legacyStartSetupLocalDatabase = (
   input: LegacyStartSetupLocalDatabaseInput,
 ): Effect.Effect<
   void,
-  LegacyStartSetupLocalDatabaseError,
+  // `LegacyDbConnectError` rides alongside the alias (as in `legacyRunFreshDbSetup`)
+  // because a batch that cannot check a connection out of the pool fails with the
+  // driver's connect error verbatim, suggestion included.
+  LegacyStartSetupLocalDatabaseError | LegacyDbConnectError,
   | Output
   | LegacyDockerRun
   | RuntimeInfo
diff --git a/apps/cli/src/legacy/shared/db-bootstrap/db-setup.unit.test.ts b/apps/cli/src/legacy/shared/db-bootstrap/db-setup.unit.test.ts
index 12fd879112..0c3d2bad12 100644
--- a/apps/cli/src/legacy/shared/db-bootstrap/db-setup.unit.test.ts
+++ b/apps/cli/src/legacy/shared/db-bootstrap/db-setup.unit.test.ts
@@ -59,6 +59,14 @@ function fakeSession() {
       Effect.sync(() => {
         calls.push({ kind: "exec", sql });
       }),
+    // A batched file records the same way a statement-at-a-time run would, so the
+    // fingerprint assertions below read the SQL regardless of how it was sent.
+    execBatch: (statements) =>
+      Effect.sync(() => {
+        for (const { sql, params } of statements) {
+          calls.push(params === undefined ? { kind: "exec", sql } : { kind: "query", sql, params });
+        }
+      }),
     query: (sql, params) =>
       Effect.sync(() => {
         calls.push({ kind: "query", sql, params });
@@ -935,6 +943,10 @@ describe("legacyRunDatabaseWebhooksSetup", () => {
         Effect.sync(() => {
           execSql.push(sql);
         }),
+      execBatch: (statements) =>
+        Effect.sync(() => {
+          for (const { sql } of statements) execSql.push(sql);
+        }),
       query: (sql) =>
         sql.includes("supabase_migrations.schema_migrations")
           ? opts.historyUnavailable === true
diff --git a/apps/cli/src/legacy/shared/db-bootstrap/recreate-local-database.unit.test.ts b/apps/cli/src/legacy/shared/db-bootstrap/recreate-local-database.unit.test.ts
index c57b08ad80..6c2e3051bf 100644
--- a/apps/cli/src/legacy/shared/db-bootstrap/recreate-local-database.unit.test.ts
+++ b/apps/cli/src/legacy/shared/db-bootstrap/recreate-local-database.unit.test.ts
@@ -26,6 +26,7 @@ function mockSession(opts: {
   let callIndex = 0;
   const session: LegacyDbSession = {
     exec: () => Effect.void,
+    execBatch: () => Effect.void,
     query: (sql): Effect.Effect<ReadonlyArray<Record<string, unknown>>, LegacyDbExecError> =>
       Effect.suspend(() => {
         queries.push(sql);
diff --git a/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.ts b/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.ts
index 0fe542c3e7..dd31042f69 100644
--- a/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.ts
+++ b/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.ts
@@ -554,7 +554,14 @@ export const legacySetupShadowConn = (
   Output | LegacyDockerRun | RuntimeInfo
 > =>
   Effect.gen(function* () {
-    yield* legacySetupDatabase(spawner, input, options);
+    yield* legacySetupDatabase(spawner, input, options).pipe(
+      // The baseline's batched SQL files check their own connection out of the pool;
+      // failing to acquire one is a shadow CONNECT failure, like
+      // `legacyConnectShadowDatabase`'s, never a setup/statement failure.
+      Effect.catchTag("LegacyDbConnectError", (cause) =>
+        Effect.fail(new LegacyShadowDbError({ message: cause.message, reason: "connect" })),
+      ),
+    );
     yield* input.session.exec(LEGACY_SHADOW_CREATE_TEMPLATE_SQL).pipe(
       Effect.mapError(
         (cause) =>
@@ -720,6 +727,13 @@ const migrateShadowDatabase = <E>(
         input.path,
         pending,
         (message) => new LegacyShadowDbError({ message, reason: "database" }),
+      ).pipe(
+        // A batch runs on its own pooled connection: failing to acquire it is a
+        // shadow CONNECT failure (same classification as `legacyConnectShadowDatabase`),
+        // never a `"database"` statement failure.
+        Effect.catchTag("LegacyDbConnectError", (cause) =>
+          Effect.fail(new LegacyShadowDbError({ message: cause.message, reason: "connect" })),
+        ),
       );
     }),
   );
diff --git a/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.unit.test.ts b/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.unit.test.ts
index 10fe3c93ec..7249ea4ab0 100644
--- a/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.unit.test.ts
+++ b/apps/cli/src/legacy/shared/db-bootstrap/shadow-database.unit.test.ts
@@ -44,6 +44,10 @@ function fakeSession() {
       Effect.sync(() => {
         calls.push({ kind: "exec", sql });
       }),
+    execBatch: (statements) =>
+      Effect.sync(() => {
+        for (const { sql } of statements) calls.push({ kind: "exec", sql });
+      }),
     query: (sql) =>
       Effect.sync(() => {
         calls.push({ kind: "query", sql });
diff --git a/apps/cli/src/legacy/shared/legacy-db-config.integration.test.ts b/apps/cli/src/legacy/shared/legacy-db-config.integration.test.ts
index 1a37ac0d34..6fc666c141 100644
--- a/apps/cli/src/legacy/shared/legacy-db-config.integration.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-db-config.integration.test.ts
@@ -422,6 +422,7 @@ describe("legacyDbConfigResolver (linked config ordering)", () => {
     }> = [];
     const session: LegacyDbSession = {
       exec: () => Effect.void,
+      execBatch: () => Effect.void,
       query: () => Effect.succeed([]),
       extensionExists: () => Effect.succeed(false),
       copyToCsv: () => Effect.succeed(new Uint8Array()),
@@ -575,6 +576,7 @@ describe("legacyDbConfigResolver (linked config ordering)", () => {
       }> = [];
       const session: LegacyDbSession = {
         exec: () => Effect.void,
+        execBatch: () => Effect.void,
         query: () => Effect.succeed([]),
         extensionExists: () => Effect.succeed(false),
         copyToCsv: () => Effect.succeed(new Uint8Array()),
@@ -730,6 +732,7 @@ describe("legacyDbConfigResolver (linked config ordering)", () => {
     }> = [];
     const session: LegacyDbSession = {
       exec: () => Effect.void,
+      execBatch: () => Effect.void,
       query: () => Effect.succeed([]),
       extensionExists: () => Effect.succeed(false),
       copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/shared/legacy-db-connection.service.ts b/apps/cli/src/legacy/shared/legacy-db-connection.service.ts
index c5da489124..73d471b2a6 100644
--- a/apps/cli/src/legacy/shared/legacy-db-connection.service.ts
+++ b/apps/cli/src/legacy/shared/legacy-db-connection.service.ts
@@ -101,10 +101,15 @@ export interface LegacyDbSession {
    * Run statements as one extended-protocol batch with a single final Sync.
    * On failure, {@link LegacyDbExecError.statementIndex} is the number of
    * statements that completed before the error.
+   *
+   * A batch runs on its own pooled connection, which the driver checks out per
+   * call. Failing to acquire it raises `LegacyDbConnectError` (a connection-setup
+   * failure, surfaced verbatim — not masked as an exec error), consistent with
+   * {@link queryRaw}; only the batch's own execution raises `LegacyDbExecError`.
    */
-  readonly execBatch?: (
+  readonly execBatch: (
     statements: ReadonlyArray<LegacyDbBatchStatement>,
-  ) => Effect.Effect<void, LegacyDbExecError>;
+  ) => Effect.Effect<void, LegacyDbExecError | LegacyDbConnectError>;
   /**
    * Run a parameterized SQL query and return the result rows as plain objects
    * keyed by the query's column names (snake_case is preserved — the driver
diff --git a/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.integration.test.ts b/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.integration.test.ts
index a6de9eb86b..1193d02ebf 100644
--- a/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.integration.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.integration.test.ts
@@ -8,7 +8,7 @@
  */
 import * as net from "node:net";
 import { describe, expect, it } from "@effect/vitest";
-import { Effect } from "effect";
+import { Duration, Effect } from "effect";
 
 import { LEGACY_SUGGEST_ENV_VAR, LEGACY_SUGGEST_LOCAL_STACK } from "./legacy-connect-errors.ts";
 import type { LegacyDbConnectError, LegacyDbExecError } from "./legacy-db-connection.errors.ts";
@@ -174,6 +174,8 @@ const fakeBatchServer = (
     readonly failExecuteAt?: number;
     readonly failOnSync?: boolean;
     readonly emptyAt?: number;
+    /** Never answer an extended-protocol frame, so a batch hangs until interrupted. */
+    readonly stall?: boolean;
   } = {},
 ): Promise<{
   readonly port: number;
@@ -219,6 +221,7 @@ const fakeBatchServer = (
             continue;
           }
           state.frameTypes.push(type);
+          if (options.stall === true) continue;
           if (type === "P") {
             activeIndex += 1;
             const [, sqlOffset] = readCString(body, 0);
@@ -506,6 +509,16 @@ describe("legacyDbConnectionSqlPgLayer exec failures", () => {
 });
 
 describe("legacyDbConnectionSqlPgLayer extended batches", () => {
+  /**
+   * Narrow a batch failure to its statement-execution error. `execBatch` also fails
+   * with `LegacyDbConnectError` when it cannot check a connection out of the pool,
+   * which the server-side statement failures below never produce.
+   */
+  const asBatchExecError = (error: LegacyDbConnectError | LegacyDbExecError): LegacyDbExecError => {
+    if (error._tag === "LegacyDbExecError") return error;
+    throw new Error(`expected a batch exec failure, got ${error._tag}`);
+  };
+
   const runWithBatchServer = <A>(
     server: Awaited<ReturnType<typeof fakeBatchServer>>,
     use: (session: LegacyDbSession) => Effect.Effect<A, unknown>,
@@ -519,6 +532,8 @@ describe("legacyDbConnectionSqlPgLayer extended batches", () => {
           user: "postgres",
           password: "postgres",
           database: "postgres",
+          // Set so a batch-connection failure can assert the suggestion survives.
+          suggestionContext: SUGGESTION_CONTEXT,
         },
         { isLocal: true, dnsResolver: "native" },
       );
@@ -533,17 +548,16 @@ describe("legacyDbConnectionSqlPgLayer extended batches", () => {
     Effect.gen(function* () {
       const server = yield* Effect.promise(() => fakeBatchServer({ emptyAt: 1 }));
       const values = ["plain", 'quote"', "slash\\", "comma,", "{brace}", "line\nbreak", "NULL", ""];
-      yield* runWithBatchServer(server, (session) => {
-        if (session.execBatch === undefined) return Effect.die("execBatch is unavailable");
-        return session.execBatch([
+      yield* runWithBatchServer(server, (session) =>
+        session.execBatch([
           { sql: "SELECT 1" },
           { sql: "-- comment only" },
           {
             sql: "INSERT INTO history(version, name, statements) VALUES($1, $2, $3)",
             params: ["v'1", "name\\two", values],
           },
-        ]);
-      });
+        ]),
+      );
       expect(server.state.statements).toEqual([
         "SELECT 1",
         "-- comment only",
@@ -580,22 +594,20 @@ describe("legacyDbConnectionSqlPgLayer extended batches", () => {
   it.live("maps a later parse failure to its statement and keeps its local position", () =>
     Effect.gen(function* () {
       const server = yield* Effect.promise(() => fakeBatchServer({ emptyAt: 1, failAt: 2 }));
-      yield* runWithBatchServer(server, (session) => {
-        const execBatch = session.execBatch;
-        if (execBatch === undefined) return Effect.die("execBatch is unavailable");
-        return Effect.gen(function* () {
-          const error = yield* execBatch([
-            { sql: "SELECT 1" },
-            { sql: "-- comment only" },
-            { sql: "SELECT bad" },
-          ]).pipe(Effect.flip);
+      yield* runWithBatchServer(server, (session) =>
+        Effect.gen(function* () {
+          const error = asBatchExecError(
+            yield* session
+              .execBatch([{ sql: "SELECT 1" }, { sql: "-- comment only" }, { sql: "SELECT bad" }])
+              .pipe(Effect.flip),
+          );
           expect(error.statementIndex).toBe(2);
           expect(error.code).toBe("42601");
           expect(error.detail).toBe("batch detail");
           expect(error.position).toBe(10);
           yield* session.exec("SELECT after_error");
-        });
-      });
+        }),
+      );
       expect(server.state.syncs).toBe(1);
     }),
   );
@@ -603,40 +615,69 @@ describe("legacyDbConnectionSqlPgLayer extended batches", () => {
   it.live("maps a position-less runtime failure from completed commands", () =>
     Effect.gen(function* () {
       const server = yield* Effect.promise(() => fakeBatchServer({ failExecuteAt: 1 }));
-      yield* runWithBatchServer(server, (session) => {
-        if (session.execBatch === undefined) return Effect.die("execBatch is unavailable");
-        return session
+      yield* runWithBatchServer(server, (session) =>
+        session
           .execBatch([{ sql: "SELECT 1" }, { sql: "INSERT duplicate" }, { sql: "SELECT 3" }])
           .pipe(
             Effect.flip,
-            Effect.tap((error) =>
+            Effect.tap((cause) =>
               Effect.sync(() => {
+                const error = asBatchExecError(cause);
                 expect(error.statementIndex).toBe(1);
                 expect(error.code).toBe("23505");
                 expect(error.detail).toBe("runtime detail");
                 expect(error.position).toBeUndefined();
               }),
             ),
-          );
-      });
+          ),
+      );
     }),
   );
 
   it.live("reports a deferred Sync failure after every completed statement", () =>
     Effect.gen(function* () {
       const server = yield* Effect.promise(() => fakeBatchServer({ failOnSync: true }));
-      yield* runWithBatchServer(server, (session) => {
-        if (session.execBatch === undefined) return Effect.die("execBatch is unavailable");
-        return session.execBatch([{ sql: "SELECT 1" }, { sql: "SELECT 2" }]).pipe(
+      yield* runWithBatchServer(server, (session) =>
+        session.execBatch([{ sql: "SELECT 1" }, { sql: "SELECT 2" }]).pipe(
           Effect.flip,
-          Effect.tap((error) =>
+          Effect.tap((cause) =>
             Effect.sync(() => {
+              const error = asBatchExecError(cause);
               expect(error.statementIndex).toBe(2);
               expect(error.code).toBe("23514");
             }),
           ),
+        ),
+      );
+    }),
+  );
+
+  it.live("classifies a failed batch-connection acquisition as a connect error", () =>
+    // A batch checks its own connection out of the pool, so a refused checkout is a
+    // CONNECTION failure — not statement 0 failing. Misclassifying it as an exec error
+    // would drop the connect suggestion and make the migration-apply formatter blame
+    // the migration's first statement for the database being unreachable.
+    Effect.gen(function* () {
+      const server = yield* Effect.promise(() => fakeBatchServer({ stall: true }));
+      const error = yield* runWithBatchServer(server, (session) =>
+        Effect.gen(function* () {
+          // Interrupting a batch discards its pooled connection, so the next batch has
+          // to dial again — and by then the server has stopped listening.
+          yield* session
+            .execBatch([{ sql: "SELECT 1" }])
+            .pipe(Effect.timeout(Duration.millis(100)), Effect.ignore);
+          yield* Effect.sync(server.close);
+          return yield* session.execBatch([{ sql: "SELECT 1" }]).pipe(Effect.flip);
+        }),
+      );
+      expect(error._tag).toBe("LegacyDbConnectError");
+      if (error._tag === "LegacyDbConnectError") {
+        expect(error.message).toBe(
+          "failed to connect to postgres: failed to connect to `host=127.0.0.1 user=postgres database=postgres`: " +
+            `dial error (connect ECONNREFUSED 127.0.0.1:${server.port})`,
         );
-      });
+        expect(error.suggestion).toBe(LEGACY_SUGGEST_LOCAL_STACK);
+      }
     }),
   );
 });
diff --git a/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.layer.ts b/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.layer.ts
index 3da257ab63..8f56cb1166 100644
--- a/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.layer.ts
+++ b/apps/cli/src/legacy/shared/legacy-db-connection.sql-pg.layer.ts
@@ -961,7 +961,15 @@ const connect = (
       return fresh;
     });
 
-    const acquireBatchClient = Effect.callback<Pg.PoolClient, LegacyDbExecError>((resume) => {
+    // Checking a connection out of the pool for a batch is a connection-setup
+    // concern, so it fails with `LegacyDbConnectError` — the same classification
+    // `acquireRawClient` uses above, and for the same reason: the pool may have to
+    // redial (its single connection is discarded after an interrupted or poisoned
+    // batch), and a refused/auth/DNS failure there is not a statement failure. Mapping
+    // it to `LegacyDbExecError` would lose the connect suggestion and make the
+    // migration-apply formatter blame the batch's first statement for a connectivity
+    // problem. Only the batch's own execution (below) raises `LegacyDbExecError`.
+    const acquireBatchClient = Effect.callback<Pg.PoolClient, LegacyDbConnectError>((resume) => {
       let done = false;
       try {
         pool.connect((error, activeClient) => {
@@ -971,10 +979,12 @@ const connect = (
           }
           done = true;
           if (error !== undefined) {
-            resume(Effect.fail(legacyToExecError(error)));
+            resume(Effect.fail(legacyToConnectError(cfg, options.isLocal, error)));
           } else if (activeClient === undefined) {
             resume(
-              Effect.fail(new LegacyDbExecError({ message: "failed to acquire batch connection" })),
+              Effect.fail(
+                new LegacyDbConnectError({ message: "failed to acquire batch connection" }),
+              ),
             );
           } else {
             resume(Effect.succeed(activeClient));
@@ -982,7 +992,7 @@ const connect = (
         });
       } catch (error) {
         done = true;
-        resume(Effect.fail(legacyToExecError(error)));
+        resume(Effect.fail(legacyToConnectError(cfg, options.isLocal, error)));
       }
       return Effect.sync(() => {
         done = true;
diff --git a/apps/cli/src/legacy/shared/legacy-migrate-and-seed.unit.test.ts b/apps/cli/src/legacy/shared/legacy-migrate-and-seed.unit.test.ts
index 5d0b9aca0c..ee50793394 100644
--- a/apps/cli/src/legacy/shared/legacy-migrate-and-seed.unit.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-migrate-and-seed.unit.test.ts
@@ -22,11 +22,17 @@ const isRoot = typeof process.getuid === "function" && process.getuid() === 0;
 
 function fakeSession() {
   const execs: Array<string> = [];
+  // A file's statements travel as one batch, so both entry points record into
+  // `execs` — the assertions below only care about which SQL reached the database.
   const session: LegacyDbSession = {
     exec: (sql) =>
       Effect.sync(() => {
         execs.push(sql);
       }),
+    execBatch: (statements) =>
+      Effect.sync(() => {
+        for (const { sql } of statements) execs.push(sql);
+      }),
     query: () => Effect.succeed([]),
     extensionExists: () => Effect.succeed(false),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
@@ -35,16 +41,20 @@ function fakeSession() {
   return { session, execs };
 }
 
-/** Every statement fails except the `BEGIN`/`COMMIT`/`ROLLBACK` transaction control Go wraps it in. */
+/** Every statement fails, whether it runs standalone or inside a batch. */
 function failingExecSession(): { session: LegacyDbSession; execs: Array<string> } {
   const execs: Array<string> = [];
-  const TRANSACTION_CONTROL = new Set(["BEGIN", "COMMIT", "ROLLBACK"]);
+  const syntaxError = () => new LegacyDbExecError({ message: "syntax error" });
   const session: LegacyDbSession = {
     exec: (sql) => {
       execs.push(sql);
-      return TRANSACTION_CONTROL.has(sql)
-        ? Effect.sync(() => {})
-        : Effect.fail(new LegacyDbExecError({ message: "syntax error" }));
+      return Effect.fail(syntaxError());
+    },
+    execBatch: (statements) => {
+      for (const { sql } of statements) execs.push(sql);
+      // The batch dies on its first statement, like a server ErrorResponse before
+      // any command completed.
+      return Effect.fail(new LegacyDbExecError({ message: "syntax error", statementIndex: 0 }));
     },
     query: () => Effect.succeed([]),
     extensionExists: () => Effect.succeed(false),
@@ -55,8 +65,11 @@ function failingExecSession(): { session: LegacyDbSession; execs: Array<string>
 }
 
 function pgNetFailureSession(error: LegacyDbExecError): LegacyDbSession {
+  const failsOnPgNet = (sql: string): boolean => sql.includes("net.http_post");
   return {
-    exec: (sql) => (sql.includes("net.http_post") ? Effect.fail(error) : Effect.void),
+    exec: (sql) => (failsOnPgNet(sql) ? Effect.fail(error) : Effect.void),
+    execBatch: (statements) =>
+      statements.some(({ sql }) => failsOnPgNet(sql)) ? Effect.fail(error) : Effect.void,
     query: () => Effect.succeed([]),
     extensionExists: () => Effect.succeed(false),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/src/legacy/shared/legacy-migration-apply.ts b/apps/cli/src/legacy/shared/legacy-migration-apply.ts
index f0f12f38cd..6fb99cac7c 100644
--- a/apps/cli/src/legacy/shared/legacy-migration-apply.ts
+++ b/apps/cli/src/legacy/shared/legacy-migration-apply.ts
@@ -2,7 +2,7 @@ import { Data, Effect, type FileSystem, type Path } from "effect";
 
 import { Output } from "../../shared/output/output.service.ts";
 import { legacyBold } from "./legacy-colors.ts";
-import { LegacyDbExecError } from "./legacy-db-connection.errors.ts";
+import { LegacyDbConnectError, LegacyDbExecError } from "./legacy-db-connection.errors.ts";
 import {
   actionability,
   type CliErrorActionabilityDeclaration,
@@ -505,8 +505,7 @@ const formattedExecBatchDbError = (error: unknown): LegacyDbExecError | undefine
  * cannot run in a transaction block: the open batch is flushed (committed), the
  * statement runs standalone, then batching resumes (supabase/cli#5156). The history
  * insert goes in the final batch, so the migration is recorded only after every
- * statement succeeds. A file with no such statements uses one batch and one Sync
- * (a session without `execBatch` falls back to an explicit `BEGIN`/`COMMIT`).
+ * statement succeeds. A file with no such statements uses one batch and one Sync.
  * Pg-delta files whose first line is `-- pg-delta: transaction=false` instead run
  * every statement sequentially without a CLI-owned transaction. This keeps their
  * session preamble, nontransactional action, and cleanup on the same connection.
@@ -529,7 +528,7 @@ const execMigrationBatch = <E>(
   forceNoVersion: boolean,
   displayPath: string = migrationPath,
   projectEnv: Readonly<Record<string, string>> = {},
-): Effect.Effect<void, E> =>
+): Effect.Effect<void, E | LegacyDbConnectError> =>
   Effect.gen(function* () {
     // Receives an already-read/parsed file (the read
     // happens earlier, which wraps the open
@@ -648,31 +647,15 @@ const execMigrationBatch = <E>(
             });
           }
           const base = executed;
-          let completed = 0;
-          const execute =
-            session.execBatch === undefined
-              ? Effect.gen(function* () {
-                  yield* session.exec("BEGIN");
-                  const body = Effect.gen(function* () {
-                    for (const operation of operations) {
-                      if (operation.params === undefined) {
-                        yield* session.exec(operation.sql);
-                      } else {
-                        yield* session.query(operation.sql, operation.params);
-                      }
-                      completed += 1;
-                    }
-                    yield* session.exec("COMMIT");
-                  });
-                  yield* body.pipe(
-                    Effect.tapError(() => session.exec("ROLLBACK").pipe(Effect.ignore)),
-                  );
-                })
-              : session.execBatch(operations);
-
-          yield* execute.pipe(
+          yield* session.execBatch(operations).pipe(
             Effect.mapError((cause) => {
-              const globalIndex = base + (cause.statementIndex ?? completed);
+              // Acquiring the batch's connection failed: there is no failing
+              // statement to name, so the connect error (and its suggestion) is
+              // surfaced verbatim instead of being rendered as `At statement: N`.
+              if (cause instanceof LegacyDbConnectError) return cause;
+              // `statementIndex` is set by every batch failure the driver raises; a
+              // session that omits it can only have failed before the first statement.
+              const globalIndex = base + (cause.statementIndex ?? 0);
               return legacyFormatExecBatchError(
                 cause,
                 globalIndex,
@@ -701,7 +684,13 @@ const execMigrationBatch = <E>(
       yield* flushBatch(version.length > 0);
     }).pipe(
       Effect.mapError((error) =>
-        mapError(legacyErrorMessage(error), "exec", formattedExecBatchDbError(error)),
+        // A batch connection failure is not an execution failure: it keeps its own
+        // error class (and `suggestion`) all the way out, exactly like the connect
+        // failure a caller would have seen from `connect` itself, instead of being
+        // relabeled as this file's statement-execution failure.
+        error instanceof LegacyDbConnectError
+          ? error
+          : mapError(legacyErrorMessage(error), "exec", formattedExecBatchDbError(error)),
       ),
     );
   });
@@ -737,7 +726,7 @@ export const legacyApplyMigrationFile = <E>(
   path: Path.Path,
   migrationPath: string,
   mapError: (message: string, dbError?: LegacyDbExecError) => E,
-): Effect.Effect<void, E> =>
+): Effect.Effect<void, E | LegacyDbConnectError> =>
   Effect.gen(function* () {
     yield* resetConnectionState(session, mapError);
     yield* legacyCreateMigrationTable(session).pipe(
@@ -765,7 +754,7 @@ export const legacyApplyMigrations = <E>(
   path: Path.Path,
   pending: ReadonlyArray<string>,
   mapError: (message: string) => E,
-): Effect.Effect<void, E, Output> =>
+): Effect.Effect<void, E | LegacyDbConnectError, Output> =>
   Effect.gen(function* () {
     const output = yield* Output;
     if (pending.length === 0) return;
@@ -793,7 +782,7 @@ export const legacySeedGlobals = <E>(
   path: Path.Path,
   globals: ReadonlyArray<string>,
   mapError: (message: string) => E,
-): Effect.Effect<void, E, Output> =>
+): Effect.Effect<void, E | LegacyDbConnectError, Output> =>
   Effect.gen(function* () {
     const output = yield* Output;
     for (const globalPath of globals) {
@@ -829,7 +818,7 @@ export const legacyExecSqlFile = <E>(
   mapError: (message: string, phase: "read" | "exec") => E,
   displayPath?: string,
   projectEnv?: Readonly<Record<string, string>>,
-): Effect.Effect<void, E> =>
+): Effect.Effect<void, E | LegacyDbConnectError> =>
   execMigrationBatch(session, fs, path, filePath, mapError, true, displayPath, projectEnv);
 
 /**
@@ -876,7 +865,7 @@ export const legacyApplySchemaFiles = <E>(
   schemaPaths: ReadonlyArray<string>,
   mapError: (message: string, suggestion?: string) => E,
   projectEnv: Readonly<Record<string, string>> = {},
-): Effect.Effect<void, E> =>
+): Effect.Effect<void, E | LegacyDbConnectError> =>
   Effect.gen(function* () {
     const { files, warnings } = yield* legacySqlFilesGlob(fs, path, schemaPaths, workdir);
     if (files.length === 0) {
diff --git a/apps/cli/src/legacy/shared/legacy-migration-apply.unit.test.ts b/apps/cli/src/legacy/shared/legacy-migration-apply.unit.test.ts
index 07cb9120af..aceab90bed 100644
--- a/apps/cli/src/legacy/shared/legacy-migration-apply.unit.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-migration-apply.unit.test.ts
@@ -11,6 +11,7 @@ import {
   type CliErrorActionabilityDeclaration,
   ErrorActionabilityId,
 } from "../../shared/telemetry/error-actionability.ts";
+import type { LegacyDbConnectError } from "./legacy-db-connection.errors.ts";
 import type { LegacyDbBatchStatement, LegacyDbSession } from "./legacy-db-connection.service.ts";
 import {
   legacyApplyMigrationFile,
@@ -101,7 +102,10 @@ const executedSql = (
         : [],
   );
 
-const run = (session: LegacyDbSession, migrationPath: string): Effect.Effect<void, TestError> =>
+const run = (
+  session: LegacyDbSession,
+  migrationPath: string,
+): Effect.Effect<void, TestError | LegacyDbConnectError> =>
   Effect.gen(function* () {
     const fs = yield* FileSystem.FileSystem;
     const path = yield* Path.Path;
diff --git a/apps/cli/src/legacy/shared/legacy-migration-history.unit.test.ts b/apps/cli/src/legacy/shared/legacy-migration-history.unit.test.ts
index ac972b435d..7666fd518f 100644
--- a/apps/cli/src/legacy/shared/legacy-migration-history.unit.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-migration-history.unit.test.ts
@@ -18,6 +18,7 @@ const mig = (version: string) => `supabase/migrations/${version}_test.sql`;
 /** Minimal session whose `query` fails with the given error. */
 const failingSession = (error: LegacyDbExecError): LegacyDbSession => ({
   exec: () => Effect.die("unused"),
+  execBatch: () => Effect.die("unused"),
   query: () => Effect.fail(error),
   extensionExists: () => Effect.die("unused"),
   copyToCsv: () => Effect.die("unused"),
diff --git a/apps/cli/src/legacy/shared/legacy-seed-ops.unit.test.ts b/apps/cli/src/legacy/shared/legacy-seed-ops.unit.test.ts
index abbb82f506..f5288ffebb 100644
--- a/apps/cli/src/legacy/shared/legacy-seed-ops.unit.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-seed-ops.unit.test.ts
@@ -18,6 +18,10 @@ function fakeSeedSession() {
       calls.push({ kind: "exec", sql });
       return Effect.void;
     },
+    execBatch: (statements) => {
+      for (const { sql } of statements) calls.push({ kind: "exec", sql });
+      return Effect.void;
+    },
     query: (sql) => {
       calls.push({ kind: "query", sql });
       return Effect.succeed([]);
diff --git a/apps/cli/src/legacy/shared/legacy-seed.unit.test.ts b/apps/cli/src/legacy/shared/legacy-seed.unit.test.ts
index a42e208211..eb04c5bc8e 100644
--- a/apps/cli/src/legacy/shared/legacy-seed.unit.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-seed.unit.test.ts
@@ -13,6 +13,7 @@ function fakeSession() {
   const queries: Array<{ sql: string; params?: ReadonlyArray<unknown> }> = [];
   const session: LegacyDbSession = {
     exec: () => Effect.void,
+    execBatch: () => Effect.void,
     query: (sql, params) =>
       Effect.sync(() => {
         queries.push({ sql, params });
diff --git a/apps/cli/src/legacy/shared/legacy-test-db.integration.test.ts b/apps/cli/src/legacy/shared/legacy-test-db.integration.test.ts
index 359340ff9e..8b466567c4 100644
--- a/apps/cli/src/legacy/shared/legacy-test-db.integration.test.ts
+++ b/apps/cli/src/legacy/shared/legacy-test-db.integration.test.ts
@@ -84,6 +84,8 @@ function mockDbConnection(opts: {
           return yield* Effect.fail(new LegacyDbExecError({ message: "cannot drop" }));
         }
       }),
+    // `test db` never runs a migration batch; keep the seam explicit rather than silent.
+    execBatch: () => Effect.die("execBatch unused"),
     extensionExists: () => Effect.succeed(opts.existed ?? false),
     queryRaw: () => Effect.succeed({ fields: [], rows: [], commandTag: "" }),
     copyToCsv: () => Effect.succeed(new Uint8Array()),
diff --git a/apps/cli/tests/helpers/legacy-mocks.ts b/apps/cli/tests/helpers/legacy-mocks.ts
index 71e72f3959..fd9b230930 100644
--- a/apps/cli/tests/helpers/legacy-mocks.ts
+++ b/apps/cli/tests/helpers/legacy-mocks.ts
@@ -16,6 +16,11 @@ import * as UrlParams from "effect/unstable/http/UrlParams";
 import { afterEach, beforeEach } from "vitest";
 
 import { LegacyCredentials } from "../../src/legacy/auth/legacy-credentials.service.ts";
+import { LegacyDbExecError } from "../../src/legacy/shared/legacy-db-connection.errors.ts";
+import type {
+  LegacyDbBatchStatement,
+  LegacyDbSession,
+} from "../../src/legacy/shared/legacy-db-connection.service.ts";
 import {
   LegacyCredentialDeleteError,
   LegacyDeleteTokenError,
@@ -667,6 +672,36 @@ export function mockLegacyPlatformApiService(
   return { layer, requests };
 }
 
+/**
+ * A `LegacyDbSession.execBatch` fake for mocks that only model statement-level
+ * behavior: it replays a batch's operations one at a time through the mock's own
+ * `exec` (no params) / `query` (params) fakes, and attaches the failing
+ * statement's index the way the real driver does. Mocks stay free of batch
+ * protocol details while `execs`/`queries` recordings and per-suite failure
+ * injection keep working for batched migration files.
+ */
+export function legacySequentialExecBatch(
+  session: Pick<LegacyDbSession, "exec" | "query">,
+): (statements: ReadonlyArray<LegacyDbBatchStatement>) => Effect.Effect<void, LegacyDbExecError> {
+  return (statements) =>
+    Effect.forEach(statements, ({ sql, params }, index) =>
+      (params === undefined ? session.exec(sql) : session.query(sql, params)).pipe(
+        Effect.asVoid,
+        Effect.mapError((cause) =>
+          cause.statementIndex !== undefined
+            ? cause
+            : new LegacyDbExecError({
+                message: cause.message,
+                ...(cause.code === undefined ? {} : { code: cause.code }),
+                ...(cause.detail === undefined ? {} : { detail: cause.detail }),
+                ...(cause.position === undefined ? {} : { position: cause.position }),
+                statementIndex: index,
+              }),
+        ),
+      ),
+    ).pipe(Effect.asVoid);
+}
+
 // ---------------------------------------------------------------------------
 // Temp workdir lifecycle — calls vitest beforeEach/afterEach internally, so
 // the helper must be invoked at module scope (or inside the surrounding