feat(installer): warn on non-canonical module-help.csv headers

mergeModuleHelpCatalogs now compares each per-module file's header
against the canonical schema and emits a one-shot prompts.log.warn per
module on drift, naming both the expected and actual header. Data
continues to load positionally so external modules built against the
old after/before schema still install cleanly — the warning is the
maintainer signal to rename their columns.

Centralize the canonical header in modules/module-help-schema.js so the
merger and the synthesizer (PluginResolver._buildSynthesizedHelpCsv)
read the same source of truth; future column renames are one edit.

Verified by installing all four bmad-org external modules
(bmb, cis, gds, tea) — every one ships the legacy after/before header
today and now fires an advisory warning while still merging cleanly
into _bmad/_config/bmad-help.csv with the canonical column names.

tools/installer/core/installer.js

@@ -12,6 +12,7 @@ const { BMAD_FOLDER_NAME } = require('../ide/shared/path-utils');
 const { InstallPaths } = require('./install-paths');
 const { ExternalModuleManager } = require('../modules/external-manager');
 const { resolveModuleVersion } = require('../modules/version-resolver');
+const { MODULE_HELP_CSV_HEADER } = require('../modules/module-help-schema');
 
 const { ExistingInstall } = require('./existing-install');
 const { warnPreNativeSkillsLegacy } = require('./legacy-warnings');
@@ -942,8 +943,7 @@ class Installer {
    */
   async mergeModuleHelpCatalogs(bmadDir, _agentEntries = []) {
     const allRows = [];
-    const headerRow =
-      'module,skill,display-name,menu-code,description,action,args,phase,preceded-by,followed-by,required,output-location,outputs';
+    const headerRow = MODULE_HELP_CSV_HEADER;
     const COLUMN_COUNT = 13;
     const PHASE_INDEX = 7;
 
@@ -976,9 +976,19 @@ class Installer {
           const content = await fs.readFile(helpFilePath, 'utf8');
           const lines = content.split('\n').filter((line) => line.trim() && !line.startsWith('#'));
 
+          let headerWarned = false;
           for (const line of lines) {
-            // Skip header row
+            // Header row: warn on drift from canonical schema, then skip.
+            // Data rows are loaded positionally regardless, so the warning
+            // is advisory — the maintainer should rename their columns.
             if (line.startsWith('module,')) {
+              if (!headerWarned && line.trim() !== headerRow) {
+                await prompts.log.warn(
+                  `  ${moduleName}/module-help.csv header does not match canonical schema. ` +
+                    `Expected: ${headerRow} | Found: ${line.trim()} | Data loaded positionally.`,
+                );
+                headerWarned = true;
+              }
               continue;
             }
 

tools/installer/modules/module-help-schema.js

@@ -0,0 +1,13 @@
+/**
+ * Canonical schema for per-module `module-help.csv` files.
+ *
+ * Both the merger (`Installer.mergeModuleHelpCatalogs`) and the synthesizer
+ * (`PluginResolver._buildSynthesizedHelpCsv`) emit this exact header. The
+ * merger compares each per-module file's header against this string and
+ * warns on drift, so any rename here must be matched in external module
+ * authors' CSVs (or accepted as a positional fall-through with a warning).
+ */
+const MODULE_HELP_CSV_HEADER =
+  'module,skill,display-name,menu-code,description,action,args,phase,preceded-by,followed-by,required,output-location,outputs';
+
+module.exports = { MODULE_HELP_CSV_HEADER };

tools/installer/modules/plugin-resolver.js

@@ -1,6 +1,7 @@
 const fs = require('../fs-native');
 const path = require('node:path');
 const yaml = require('yaml');
+const { MODULE_HELP_CSV_HEADER } = require('./module-help-schema');
 
 /**
  * Resolves how to install a plugin from marketplace.json by analyzing
@@ -338,9 +339,7 @@ class PluginResolver {
    * @returns {string} CSV content
    */
   _buildSynthesizedHelpCsv(moduleName, skillInfos) {
-    const header =
-      'module,skill,display-name,menu-code,description,action,args,phase,preceded-by,followed-by,required,output-location,outputs';
-    const rows = [header];
+    const rows = [MODULE_HELP_CSV_HEADER];
 
     for (const info of skillInfos) {
       const displayName = this._formatDisplayName(info.name || info.dirName);