diff --git a/dist/feca_mailshots_plugin-1.1.6.zip b/dist/feca_mailshots_plugin-1.1.6.zip
new file mode 100644
index 0000000..3539afe
Binary files /dev/null and b/dist/feca_mailshots_plugin-1.1.6.zip differ
diff --git a/feca_mailshots_plugin/feca_mailshots_plugin.php b/feca_mailshots_plugin/feca_mailshots_plugin.php
index e35806c..e6537c0 100644
--- a/feca_mailshots_plugin/feca_mailshots_plugin.php
+++ b/feca_mailshots_plugin/feca_mailshots_plugin.php
@@ -3,7 +3,7 @@
  * Plugin Name: FECA Mailshots
  * Plugin URI: https://fenedge.co.uk/
  * Description: FECA mailshots plugin.
- * Version: 1.1.5
+ * Version: 1.1.6
  * Requires at least: 6.0
  * Requires PHP: 7.4
  * Author: FECA
diff --git a/feca_mailshots_plugin/src/Admin/DataSourcesAdminPage.php b/feca_mailshots_plugin/src/Admin/DataSourcesAdminPage.php
index c60c3d9..065546b 100644
--- a/feca_mailshots_plugin/src/Admin/DataSourcesAdminPage.php
+++ b/feca_mailshots_plugin/src/Admin/DataSourcesAdminPage.php
@@ -101,8 +101,7 @@ final class DataSourcesAdminPage
             $dsl = (string) ($draft['dsl_text'] ?? $dsl);
         }
         $result = $this->consumeOptionArray(self::RESULT_OPTION_KEY);
-        $sourceFieldsMap = $this->service()->sourceFields();
-        $schemaList = $this->service()->listSchemas();
+        $builtInSources = $this->service()->knownSources();
 
         echo '<div class="wrap feca-mailshots-admin">';
         echo $this->renderAdminUiStyles();
@@ -184,16 +183,13 @@ final class DataSourcesAdminPage
         echo '<div class="feca-builder-grid">';
         echo '<div class="feca-builder-col-left">';
         echo '<h3 class="feca-modal-title">Data Sources</h3>';
-        foreach (array_keys($sourceFieldsMap) as $builtInSource) {
+        foreach ($builtInSources as $builtInSource) {
             $escapedSource = htmlspecialchars((string) $builtInSource, ENT_QUOTES);
             echo '<label><input type="checkbox" class="ds-source-built" value="' . $escapedSource . '"> ' . $escapedSource . '</label><br>';
         }
         echo '<br>';
         echo '<strong>Add custom source</strong><br>';
         echo '<label>Schema <select id="ds-builder-schema"><option value="">Select schema</option>';
-        foreach ($schemaList as $schema) {
-            echo '<option value="' . htmlspecialchars((string) $schema, ENT_QUOTES) . '">' . htmlspecialchars((string) $schema) . '</option>';
-        }
         echo '</select></label> ';
         echo '<label>Table <select id="ds-builder-table"><option value="">Select table</option></select></label> ';
         echo '<button type="button" class="button button-small" id="ds-builder-add-custom">Add</button>';
@@ -285,7 +281,7 @@ final class DataSourcesAdminPage
         echo '</div></div>';
         echo '<script>';
         echo 'window.fecaDataSourcesBuilderConfig = ' . json_encode([
-            'sourceFields' => $sourceFieldsMap,
+            'sourceFields' => [],
             'restBase' => '/wp-json/mailshots/v1/data-sources',
             'adminPostApi' => $this->wp->adminUrl('admin-post.php?action=feca_mailshots_data_sources_api'),
         ], JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) . ';';
@@ -320,6 +316,9 @@ final class DataSourcesAdminPage
         echo 'var customSources=[];';
         echo 'var sourceOrder=[];';
         echo 'var constraints=[];';
+        echo 'var sourceFieldRequests={};';
+        echo 'var schemasLoaded=false;';
+        echo 'var schemasLoading=false;';
         echo 'var isDirty=false;';
         echo 'function confirmDiscard(){if(!isDirty){return true;}return window.confirm("You have unsaved changes. Close without saving?");}';
         echo 'if(editorForm){editorForm.querySelectorAll("input,select,textarea").forEach(function(el){el.addEventListener("input",function(){isDirty=true;});el.addEventListener("change",function(){isDirty=true;});});editorForm.addEventListener("submit",function(){isDirty=false;});}';
@@ -329,7 +328,57 @@ final class DataSourcesAdminPage
         echo 'function noteSourceDeselected(src){sourceOrder=sourceOrder.filter(function(v){return v!==src;});}';
         echo 'function updateCustomList(){customList.innerHTML="";customSources.forEach(function(src,i){var li=document.createElement("li");li.textContent=src+" ";var b=document.createElement("button");b.type="button";b.className="button-link-delete";b.textContent="Remove";b.onclick=function(){noteSourceDeselected(src);customSources.splice(i,1);updateCustomList();renderRows();updateDsl();};li.appendChild(b);customList.appendChild(li);});}';
         echo 'function fetchTables(schema){tableSel.innerHTML="<option value=\"\">Loading...</option>";tableSel.style.color="#1d2327";if(tableErr){tableErr.textContent="";}var pickLabel=function(t){if(typeof t==="string"){return t.trim();}if(t===null||t===undefined){return "";}if(typeof t==="number"){return String(t);}if(typeof t==="object"){var direct=[t.table_name,t.name,t.table,t.label];for(var i=0;i<direct.length;i++){var dv=String(direct[i]||"").trim();if(dv){return dv;}}var keys=Object.keys(t||{});for(var k=0;k<keys.length;k++){var key=String(keys[k]||"").trim();if(/^Tables_in_/i.test(key)){var vv=String(t[key]||"").trim();if(vv){return vv;}}}var vals=Object.values(t||{});for(var j=0;j<vals.length;j++){var v=String(vals[j]||"").trim();if(v){return v;}}}return "";};var fill=function(items){tableSel.innerHTML="<option value=\"\">Select table</option>";var invalid=0;(items||[]).forEach(function(t){var label=pickLabel(t);if(!label){invalid++;return;}var o=document.createElement("option");o.value=label;o.textContent=label;tableSel.appendChild(o);});if((items||[]).length===0&&tableErr){tableErr.textContent="No tables returned for this schema. Check DB grants: SELECT and SHOW VIEW on schema tables.";}if(invalid>0&&tableErr){tableErr.textContent="Received "+invalid+" table entries without names; showing only valid table names.";}};var showErr=function(msg){tableSel.innerHTML="<option value=\"\">Select table</option>";if(tableErr){tableErr.textContent=msg||"Table lookup failed. Resolve the error before continuing.";}if(err){err.textContent="Table lookup failed: "+(msg||"unknown error");}};var u=(cfg.adminPostApi||"/wp-admin/admin-post.php?action=feca_mailshots_data_sources_api")+"&op=tables&schema="+encodeURIComponent(schema);fetch(u,{credentials:"same-origin"}).then(function(r){if(!r.ok){throw new Error("API "+r.status);}return r.json();}).then(function(j){if(!j||j.ok===false){throw new Error((j&&j.error)||"API error");}fill((j&&j.items)||[]);}).catch(function(e){showErr(e&&e.message?e.message:"Need MySQL grants on the selected schema.");});}';
-        echo 'function sourceFields(source){var map=cfg.sourceFields||{};if(map[source]){return map[source];}if(source&&source.indexOf(".")!==-1){var u=(cfg.adminPostApi||"/wp-admin/admin-post.php?action=feca_mailshots_data_sources_api")+"&op=source_fields&source="+encodeURIComponent(source);fetch(u,{credentials:"same-origin"}).then(function(r){if(!r.ok){throw new Error("API "+r.status);}return r.json();}).then(function(j){if(!j||j.ok===false){throw new Error((j&&j.error)||"API error");}var fields=(j&&j.fields)||[];if(fields&&fields.length){map[source]=fields;cfg.sourceFields=map;renderRows();updateDsl();return;}if(err){err.textContent="Source field lookup returned no fields for "+source+".";}}).catch(function(e){if(err){err.textContent="Source field lookup failed for "+source+": "+(e&&e.message?e.message:"unknown error");}});}return [];}';
+        $lazyMetadataJs = <<<'JS'
+function loadSchemas(){
+    if(schemasLoaded||schemasLoading||!schemaSel){return;}
+    schemasLoading=true;
+    var u=(cfg.adminPostApi||"/wp-admin/admin-post.php?action=feca_mailshots_data_sources_api")+"&op=schemas";
+    fetch(u,{credentials:"same-origin"}).then(function(r){
+        if(!r.ok){throw new Error("API "+r.status);}
+        return r.json();
+    }).then(function(j){
+        if(!j||j.ok===false){throw new Error((j&&j.error)||"API error");}
+        schemaSel.innerHTML="<option value=\"\">Select schema</option>";
+        (j.items||[]).forEach(function(schema){
+            var value=String(schema||"").trim();
+            if(!value){return;}
+            var option=document.createElement("option");
+            option.value=value;
+            option.textContent=value;
+            schemaSel.appendChild(option);
+        });
+        schemasLoaded=true;
+        schemasLoading=false;
+    }).catch(function(e){
+        schemasLoading=false;
+        if(err){err.textContent="Schema lookup failed: "+(e&&e.message?e.message:"unknown error");}
+    });
+}
+function sourceFields(source){
+    var map=cfg.sourceFields||{};
+    if(Object.prototype.hasOwnProperty.call(map,source)){return map[source];}
+    if(!source||sourceFieldRequests[source]){return [];}
+    sourceFieldRequests[source]=true;
+    var u=(cfg.adminPostApi||"/wp-admin/admin-post.php?action=feca_mailshots_data_sources_api")+"&op=source_fields&source="+encodeURIComponent(source);
+    fetch(u,{credentials:"same-origin"}).then(function(r){
+        if(!r.ok){throw new Error("API "+r.status);}
+        return r.json();
+    }).then(function(j){
+        delete sourceFieldRequests[source];
+        if(!j||j.ok===false){throw new Error((j&&j.error)||"API error");}
+        var fields=(j&&j.fields)||[];
+        map[source]=fields;
+        cfg.sourceFields=map;
+        if(fields.length){renderRows();updateDsl();return;}
+        if(err){err.textContent="Source field lookup returned no fields for "+source+".";}
+    }).catch(function(e){
+        delete sourceFieldRequests[source];
+        if(err){err.textContent="Source field lookup failed for "+source+": "+(e&&e.message?e.message:"unknown error");}
+    });
+    return [];
+}
+JS;
+        echo $lazyMetadataJs;
         echo 'function mkSelect(options,value){var s=document.createElement("select");options.forEach(function(opt){var o=document.createElement("option");o.value=opt[0];o.textContent=opt[1];if(opt[0]===value){o.selected=true;}s.appendChild(o);});return s;}';
         echo 'function filterArgType(name){for(var i=0;i<filters.length;i++){if(filters[i][0]===name){return filters[i][2]||"none";}}return "none";}';
         echo 'function addConstraint(){constraints.push({kind:"filter",negate:false,filter:"selected-renewal",filterArg:"",lhsSource:"",lhsField:"",op:"=",rhsMode:"literal",rhsLiteral:"",rhsSource:"",rhsField:""});renderRows();updateDsl();}';
@@ -350,7 +399,7 @@ final class DataSourcesAdminPage
         echo 'if(addCustomBtn){addCustomBtn.onclick=function(){if(!schemaSel.value||!tableSel.value){return;}var src=schemaSel.value+"."+tableSel.value;if(customSources.indexOf(src)===-1){customSources.push(src);}noteSourceSelected(src);updateCustomList();renderRows();updateDsl();};}';
         echo 'builtChecks.forEach(function(c){c.onchange=function(){if(c.checked){noteSourceSelected(c.value);}else{noteSourceDeselected(c.value);}renderRows();updateDsl();};});';
         echo 'if(addRowBtn){addRowBtn.onclick=addConstraint;}';
-        echo 'if(openBtn){openBtn.onclick=function(){resetBuilder();prefillFromDsl();modal.style.display="block";};}';
+        echo 'if(openBtn){openBtn.onclick=function(){loadSchemas();resetBuilder();prefillFromDsl();modal.style.display="block";};}';
         echo 'if(cancelBtn){cancelBtn.onclick=function(){modal.style.display="none";};}';
         echo 'if(applyBtn){applyBtn.onclick=function(){if(dslInput){dslInput.value=out.value;}modal.style.display="none";};}';
         echo 'if(openNew){openNew.onclick=function(){if(!confirmDiscard()){return;}if(editorId){editorId.value="";}if(editorName){editorName.value="";}if(dslInput){dslInput.value="";}isDirty=false;editorModal.style.display="block";};}';
diff --git a/feca_mailshots_plugin/src/Admin/SetupAdminPage.php b/feca_mailshots_plugin/src/Admin/SetupAdminPage.php
index a6f879e..6482349 100644
--- a/feca_mailshots_plugin/src/Admin/SetupAdminPage.php
+++ b/feca_mailshots_plugin/src/Admin/SetupAdminPage.php
@@ -141,6 +141,7 @@ final class SetupAdminPage
 
         $this->wp->updateOption(self::OPTION_KEY, $settings);
         $this->wp->updateOption(self::DOWNLOAD_MEMORY_LIMIT_OPTION, $downloadMemoryLimit);
+        $this->wp->deleteOption(\FecaMailshots\Infrastructure\MailshotSchemaInstaller::STATE_OPTION_KEY);
 
         if (!headers_sent()) {
             $location = $this->wp->adminUrl('admin.php?page=feca-mailshots-setup&saved=1');
diff --git a/feca_mailshots_plugin/src/Application/DataSourceService.php b/feca_mailshots_plugin/src/Application/DataSourceService.php
index 662912e..9a3ee64 100644
--- a/feca_mailshots_plugin/src/Application/DataSourceService.php
+++ b/feca_mailshots_plugin/src/Application/DataSourceService.php
@@ -191,6 +191,12 @@ final class DataSourceService
         return $result;
     }
 
+    /** @return list<string> */
+    public function knownSources(): array
+    {
+        return $this->metadata->allKnownSources();
+    }
+
     /** @return list<string> */
     public function listSchemas(): array
     {
diff --git a/feca_mailshots_plugin/src/Infrastructure/MailshotSchemaInstaller.php b/feca_mailshots_plugin/src/Infrastructure/MailshotSchemaInstaller.php
index 16df009..130f5b8 100644
--- a/feca_mailshots_plugin/src/Infrastructure/MailshotSchemaInstaller.php
+++ b/feca_mailshots_plugin/src/Infrastructure/MailshotSchemaInstaller.php
@@ -8,6 +8,9 @@ use PDO;
 
 final class MailshotSchemaInstaller
 {
+    public const SCHEMA_VERSION = '1';
+    public const STATE_OPTION_KEY = 'feca_mailshots_schema_state';
+
     private DatabaseRouter $router;
 
     public function __construct(DatabaseRouter $router)
@@ -26,6 +29,16 @@ final class MailshotSchemaInstaller
         $this->ensureMailshotQueriesColumns($pdo);
     }
 
+    /** @param array<string,string> $dbConfig @return array{version:string,config_hash:string} */
+    public static function migrationTarget(array $dbConfig): array
+    {
+        ksort($dbConfig);
+        return [
+            'version' => self::SCHEMA_VERSION,
+            'config_hash' => hash('sha256', json_encode($dbConfig, JSON_UNESCAPED_SLASHES) ?: ''),
+        ];
+    }
+
     /** @return list<string> */
     private function createTableSql(): array
     {
diff --git a/feca_mailshots_plugin/src/Infrastructure/SchemaEnsuringDatabaseRouter.php b/feca_mailshots_plugin/src/Infrastructure/SchemaEnsuringDatabaseRouter.php
deleted file mode 100644
index 2e49b7d..0000000
--- a/feca_mailshots_plugin/src/Infrastructure/SchemaEnsuringDatabaseRouter.php
+++ /dev/null
@@ -1,53 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace FecaMailshots\Infrastructure;
-
-use PDO;
-
-final class SchemaEnsuringDatabaseRouter implements DatabaseRouter
-{
-    private DatabaseRouter $inner;
-    private bool $installed = false;
-
-    public function __construct(DatabaseRouter $inner)
-    {
-        $this->inner = $inner;
-    }
-
-    public function mailshotsPdo(): PDO
-    {
-        $this->installOnce();
-        return $this->inner->mailshotsPdo();
-    }
-
-    public function membersPdo(): PDO
-    {
-        return $this->inner->membersPdo();
-    }
-
-    public function mailshotsDbName(): string
-    {
-        return $this->inner->mailshotsDbName();
-    }
-
-    public function membersDbName(): string
-    {
-        return $this->inner->membersDbName();
-    }
-
-    public function fenDbName(): string
-    {
-        return $this->inner->fenDbName();
-    }
-
-    private function installOnce(): void
-    {
-        if ($this->installed) {
-            return;
-        }
-        (new MailshotSchemaInstaller($this->inner))->install();
-        $this->installed = true;
-    }
-}
diff --git a/feca_mailshots_plugin/src/Plugin.php b/feca_mailshots_plugin/src/Plugin.php
index 4e7d18e..a798830 100644
--- a/feca_mailshots_plugin/src/Plugin.php
+++ b/feca_mailshots_plugin/src/Plugin.php
@@ -32,7 +32,6 @@ use FecaMailshots\Infrastructure\MailshotSchemaInstaller;
 use FecaMailshots\Infrastructure\DatabaseSourceMetadataProvider;
 use FecaMailshots\Infrastructure\PhpImapAppender;
 use FecaMailshots\Infrastructure\PdoDatabaseRouter;
-use FecaMailshots\Infrastructure\SchemaEnsuringDatabaseRouter;
 use FecaMailshots\Infrastructure\WordPressSaltSecretKeyProvider;
 use FecaMailshots\Repository\AttachmentRepository;
 use FecaMailshots\Repository\LastRunRepository;
@@ -54,7 +53,7 @@ final class Plugin
 
         $c->set('logger', static fn() => new ErrorLogLogger());
 
-        $c->set(DatabaseRouter::class, static fn() => $router ?? new SchemaEnsuringDatabaseRouter(new PdoDatabaseRouter($dbConfig)));
+        $c->set(DatabaseRouter::class, static fn() => $router ?? new PdoDatabaseRouter($dbConfig));
         $c->set(MailshotSchemaInstaller::class, static fn(Container $c) => new MailshotSchemaInstaller($c->get(DatabaseRouter::class)));
 
         $c->set(DatabaseSourceMetadataProvider::class, static fn(Container $c) => new DatabaseSourceMetadataProvider($c->get(DatabaseRouter::class)));
diff --git a/feca_mailshots_plugin/src/autoload.php b/feca_mailshots_plugin/src/autoload.php
index 81a73a2..d3d2980 100644
--- a/feca_mailshots_plugin/src/autoload.php
+++ b/feca_mailshots_plugin/src/autoload.php
@@ -2,21 +2,37 @@
 
 declare(strict_types=1);
 
-// Load Composer dependencies (Twig, Dompdf, etc.) when available.
-$autoloadCandidates = [
-    dirname(__DIR__) . '/vendor/autoload.php',       // Preferred: packaged/deployed plugin-local vendor
-    dirname(__DIR__, 2) . '/vendor/autoload.php',    // Backward-compatible: workspace/shared vendor
-];
-foreach ($autoloadCandidates as $composerAutoload) {
-    if (is_file($composerAutoload) && feca_mailshots_composer_autoload_is_usable($composerAutoload)) {
-        try {
-            require_once $composerAutoload;
-        } catch (\Throwable $e) {
-            error_log('FECA Mailshots skipped unusable Composer autoload: ' . $e->getMessage());
+/** @return object|null Composer class loader when runtime dependencies are available. */
+function feca_mailshots_load_composer_dependencies(): ?object
+{
+    static $attempted = false;
+    static $loader = null;
+
+    if ($attempted) {
+        return is_object($loader) ? $loader : null;
+    }
+    $attempted = true;
+
+    $autoloadCandidates = [
+        dirname(__DIR__) . '/vendor/autoload.php',
+        dirname(__DIR__, 2) . '/vendor/autoload.php',
+    ];
+    foreach ($autoloadCandidates as $composerAutoload) {
+        if (!is_file($composerAutoload) || !feca_mailshots_composer_autoload_is_usable($composerAutoload)) {
             continue;
         }
-        break;
+        try {
+            $candidate = require $composerAutoload;
+            if (is_object($candidate)) {
+                $loader = $candidate;
+                return $loader;
+            }
+        } catch (\Throwable $e) {
+            error_log('FECA Mailshots skipped unusable Composer autoload: ' . $e->getMessage());
+        }
     }
+
+    return null;
 }
 
 function feca_mailshots_composer_autoload_is_usable(string $composerAutoload): bool
@@ -55,3 +71,15 @@ spl_autoload_register(static function (string $class): void {
         require_once $path;
     }
 });
+
+// Composer's generated function files are expensive to load. Load them only
+// when Twig or Dompdf is first requested, then delegate that initial class load.
+spl_autoload_register(static function (string $class): void {
+    if (strncmp($class, 'Twig\\', 5) !== 0 && strncmp($class, 'Dompdf\\', 7) !== 0) {
+        return;
+    }
+    $loader = feca_mailshots_load_composer_dependencies();
+    if ($loader !== null && method_exists($loader, 'loadClass')) {
+        $loader->loadClass($class);
+    }
+});
diff --git a/feca_mailshots_plugin/src/bootstrap.php b/feca_mailshots_plugin/src/bootstrap.php
index 31a9771..3bc5066 100644
--- a/feca_mailshots_plugin/src/bootstrap.php
+++ b/feca_mailshots_plugin/src/bootstrap.php
@@ -3,25 +3,28 @@
 declare(strict_types=1);
 
 use FecaMailshots\Plugin;
+use FecaMailshots\Infrastructure\MailshotSchemaInstaller;
+use FecaMailshots\Infrastructure\PdoDatabaseRouter;
 use FecaMailshots\WordPress\ProductionWordPressFacade;
 
 require_once __DIR__ . '/autoload.php';
 
+if (!function_exists('get_option')) {
+    throw new \RuntimeException('WordPress get_option() is unavailable while bootstrapping mailshots plugin.');
+}
+
 $setupErrors = [];
-$getOption = static function (string $key) use (&$setupErrors): string {
-    if (!function_exists('get_option')) {
-        throw new \RuntimeException('WordPress get_option() is unavailable while bootstrapping mailshots plugin.');
-    }
-    $raw = get_option(\FecaMailshots\Admin\SetupAdminPage::OPTION_KEY, []);
-    if (!is_array($raw)) {
-        $setupErrors[] = 'Mailshots setup option is missing or invalid.';
-        return '';
-    }
-    if (!array_key_exists($key, $raw)) {
+$rawSetup = get_option(\FecaMailshots\Admin\SetupAdminPage::OPTION_KEY, []);
+if (!is_array($rawSetup)) {
+    $setupErrors[] = 'Mailshots setup option is missing or invalid.';
+    $rawSetup = [];
+}
+$readSetupValue = static function (string $key) use (&$setupErrors, $rawSetup): string {
+    if (!array_key_exists($key, $rawSetup)) {
         $setupErrors[] = 'Missing setup configuration key: ' . $key;
         return '';
     }
-    $value = trim((string) $raw[$key]);
+    $value = trim((string) $rawSetup[$key]);
     if ($value === '') {
         $setupErrors[] = 'Empty setup configuration value: ' . $key;
     }
@@ -29,16 +32,37 @@ $getOption = static function (string $key) use (&$setupErrors): string {
 };
 
 $dbConfig = [
-    'MYSQL_HOST' => $getOption('db_host'),
-    'MYSQL_PORT' => $getOption('db_port'),
-    'MYSQL_USER' => $getOption('db_user'),
-    'MYSQL_PASSWORD' => $getOption('db_password'),
-    'MAILSHOTS_REMOTE_MYSQL_DB' => $getOption('mailshots_db_name'),
-    'MEMBERS_REMOTE_MYSQL_DB' => $getOption('members_db_name'),
-    'FEN_REMOTE_MYSQL_DB' => $getOption('fen_db_name'),
+    'MYSQL_HOST' => $readSetupValue('db_host'),
+    'MYSQL_PORT' => $readSetupValue('db_port'),
+    'MYSQL_USER' => $readSetupValue('db_user'),
+    'MYSQL_PASSWORD' => $readSetupValue('db_password'),
+    'MAILSHOTS_REMOTE_MYSQL_DB' => $readSetupValue('mailshots_db_name'),
+    'MEMBERS_REMOTE_MYSQL_DB' => $readSetupValue('members_db_name'),
+    'FEN_REMOTE_MYSQL_DB' => $readSetupValue('fen_db_name'),
 ];
 
 $wp = new ProductionWordPressFacade();
+if ($setupErrors === [] && function_exists('is_admin') && is_admin()) {
+    $target = MailshotSchemaInstaller::migrationTarget($dbConfig);
+    $state = get_option(MailshotSchemaInstaller::STATE_OPTION_KEY, []);
+    $sameTarget = is_array($state)
+        && ($state['version'] ?? '') === $target['version']
+        && ($state['config_hash'] ?? '') === $target['config_hash'];
+    if ($sameTarget && ($state['status'] ?? '') === 'failed') {
+        $setupErrors[] = 'Mailshots database schema setup failed: ' . (string) ($state['error'] ?? 'unknown error');
+    } elseif (!$sameTarget || ($state['status'] ?? '') !== 'complete') {
+        try {
+            (new MailshotSchemaInstaller(new PdoDatabaseRouter($dbConfig)))->install();
+            update_option(MailshotSchemaInstaller::STATE_OPTION_KEY, $target + ['status' => 'complete']);
+        } catch (\Throwable $e) {
+            update_option(MailshotSchemaInstaller::STATE_OPTION_KEY, $target + [
+                'status' => 'failed',
+                'error' => $e->getMessage(),
+            ]);
+            $setupErrors[] = 'Mailshots database schema setup failed: ' . $e->getMessage();
+        }
+    }
+}
 if ($setupErrors !== []) {
     $setupPage = new \FecaMailshots\Admin\SetupAdminPage($wp, array_values(array_unique($setupErrors)), true);
     $setupPage->register();
diff --git a/requirements/environment.md b/requirements/environment.md
index c9fe3c7..6bfcdf0 100644
--- a/requirements/environment.md
+++ b/requirements/environment.md
@@ -84,6 +84,10 @@ Hard constraints for this task:
 
 ## Dependency Installation Scripts
 
+Runtime Composer dependencies must be autoloaded lazily when Twig or Dompdf is first used. Ordinary WordPress/admin bootstrap requests must not load Composer-generated runtime function files.
+
+Mailshot database schema installation/checking must run only when the schema version or database configuration changes. Normal page reads must not execute `CREATE TABLE`, `ALTER TABLE`, or `information_schema` migration checks.
+
 - `scripts/install_dependencies.sh`
   - Installs Composer dependencies (`vendor/`) for plugin runtime.
   - Installs/bundles editor assets (Jodit + Ace) into `feca_mailshots_plugin/assets/vendor/`.
diff --git a/requirements/mailshot_data_source.md b/requirements/mailshot_data_source.md
index 95b862f..850f9fd 100644
--- a/requirements/mailshot_data_source.md
+++ b/requirements/mailshot_data_source.md
@@ -300,6 +300,8 @@ Optional:
 
 Provide a UI to view, create, update, validate, and preview DSL sentences.
 
+The initial Data Sources page GET must load only the saved query list and built-in source names. Schema enumeration and source-column discovery must be requested lazily within the Build DSL dialog when the user opens or uses the relevant controls; failures must be displayed inside that dialog.
+
 ### Mailshot data source page
 
 Add a dedicated page "Data Sources" under FECA Mailshots admin page for managing data source sentences.
diff --git a/tests/e2e/specs/data-sources.spec.mjs b/tests/e2e/specs/data-sources.spec.mjs
index 0b4a22e..4efd2af 100644
--- a/tests/e2e/specs/data-sources.spec.mjs
+++ b/tests/e2e/specs/data-sources.spec.mjs
@@ -1,6 +1,43 @@
 import { test, expect } from '@playwright/test';
 import { adminPath, apiPost, cleanupByNames, ensureDataSource } from './helpers.mjs';
 
+test('data sources: builder metadata is lazy and browser runtime is clean', async ({ page }) => {
+  const runtimeErrors = [];
+  const metadataRequests = [];
+  page.on('pageerror', error => runtimeErrors.push(error.message));
+  page.on('console', message => {
+    if (message.type() === 'error') {
+      runtimeErrors.push(message.text());
+    }
+  });
+  page.on('request', request => {
+    const url = request.url();
+    if (url.includes('op=schemas') || url.includes('op=source_fields')) {
+      metadataRequests.push(url);
+    }
+  });
+
+  await page.goto(adminPath('feca-mailshot-data-sources'));
+  await expect(page.getByRole('heading', { name: 'Mailshot Data Sources' })).toBeVisible();
+  expect(metadataRequests).toHaveLength(0);
+
+  await page.getByRole('button', { name: 'New Data Source' }).click();
+  await page.locator('#ds-build-dsl-open').click();
+  await expect(page.locator('#ds-builder-modal')).toBeVisible();
+  await expect.poll(() => metadataRequests.filter(url => url.includes('op=schemas')).length).toBe(1);
+  await expect(page.locator('#ds-builder-schema option')).not.toHaveCount(1);
+
+  await page.locator('.ds-source-built[value="contacts"]').check();
+  await page.locator('#ds-builder-add-row').click();
+  const row = page.locator('.feca-builder-row').first();
+  await row.locator('select').first().selectOption('compare');
+  await row.locator('select').nth(1).selectOption('contacts');
+  await expect.poll(() => metadataRequests.filter(url => url.includes('op=source_fields')).length).toBe(1);
+  await expect(row.locator('select').nth(2).locator('option')).not.toHaveCount(1);
+
+  expect(runtimeErrors).toEqual([]);
+});
+
 test('data sources: create + preview + validation failure path', async ({ page, request }) => {
   const uniq = `${Date.now()}_${Math.floor(Math.random() * 100000)}`;
   const dsName = `e2e_ds_${uniq}`;
diff --git a/tests/unit/test_bootstrap_full_setup_no_db_touch.php b/tests/unit/test_bootstrap_full_setup_no_db_touch.php
index 6f2c79a..1e7b195 100644
--- a/tests/unit/test_bootstrap_full_setup_no_db_touch.php
+++ b/tests/unit/test_bootstrap_full_setup_no_db_touch.php
@@ -7,13 +7,11 @@ if (!defined('ABSPATH')) {
 }
 
 $GLOBALS['feca_bootstrap_actions'] = [];
+$GLOBALS['feca_setup_option_reads'] = 0;
 
 function get_option($key, $default = null)
 {
-    if ($key !== \FecaMailshots\Admin\SetupAdminPage::OPTION_KEY) {
-        return $default;
-    }
-    return [
+    $config = [
         'db_host' => 'invalid-host.local.test',
         'db_port' => '3306',
         'db_user' => 'mailshots',
@@ -22,6 +20,28 @@ function get_option($key, $default = null)
         'members_db_name' => 'members',
         'fen_db_name' => 'fen',
     ];
+    if ($key === \FecaMailshots\Admin\SetupAdminPage::OPTION_KEY) {
+        $GLOBALS['feca_setup_option_reads']++;
+        return $config;
+    }
+    if ($key === \FecaMailshots\Infrastructure\MailshotSchemaInstaller::STATE_OPTION_KEY) {
+        $dbConfig = [
+            'MYSQL_HOST' => $config['db_host'],
+            'MYSQL_PORT' => $config['db_port'],
+            'MYSQL_USER' => $config['db_user'],
+            'MYSQL_PASSWORD' => $config['db_password'],
+            'MAILSHOTS_REMOTE_MYSQL_DB' => $config['mailshots_db_name'],
+            'MEMBERS_REMOTE_MYSQL_DB' => $config['members_db_name'],
+            'FEN_REMOTE_MYSQL_DB' => $config['fen_db_name'],
+        ];
+        return \FecaMailshots\Infrastructure\MailshotSchemaInstaller::migrationTarget($dbConfig) + ['status' => 'complete'];
+    }
+    return $default;
+}
+
+function is_admin(): bool
+{
+    return true;
 }
 
 function add_action(string $hook, callable $callback): void
@@ -47,5 +67,15 @@ if (!isset($actions['admin_post_feca_mailshots_data_sources_api'], $actions['adm
     fwrite(STDERR, "Expected normal handlers to register without touching the database\n");
     exit(1);
 }
+if ($GLOBALS['feca_setup_option_reads'] !== 1) {
+    fwrite(STDERR, "Expected setup configuration to be read exactly once during bootstrap\n");
+    exit(1);
+}
+foreach (get_included_files() as $includedFile) {
+    if (strpos($includedFile, '/vendor/thecodingmachine/safe/') !== false) {
+        fwrite(STDERR, "Composer runtime function files should remain unloaded during admin bootstrap\n");
+        exit(1);
+    }
+}
 
 echo "Bootstrap full setup no DB touch regression test passed\n";