fix(installer): address third-round PR #2353 review comments

(J) Prototype pollution guard (CodeRabbit major).
`--set __proto__.x=1` previously mutated Object.prototype because
`overrides.__proto__` returned Object.prototype on a plain object,
and assigning `[key]=value` polluted every plain object in the process.
Verified the attack reproduces on f1c9e12 and is now blocked: parser
rejects __proto__/prototype/constructor segments, and the maps are
Object.create(null) for defense-in-depth.

(I) Non-zero exit when --list-options <module>'s yaml is unparseable
(CodeRabbit major). formatOptionsList tracks moduleScopedFailure and
returns ok:false in that case; install.js exits 1.

(F) Dynamic defaults can now see --set sibling values (Augment medium).
buildQuestion's function default falls back to
`this.collectedConfig[mod][otherKey]`, but overrides were only in
`allAnswers` (local) at default-evaluation time. Pre-write override
raw values to collectedConfig before the prompt batch so the
fallback resolves. Post-prompt template processing overwrites with
the rendered version.

(E) applyOverridesAfterSeeding no longer bypasses carry-forward when
the schema can't be loaded (Augment low). Restructured: schema-load
is now best-effort; without schema, declaredKeys is an empty Set, so
all overrides are flagged as "unknown" and carry-forward runs against
every prior key. Comment now matches behavior.

(G) Flag placeholder --set <spec> instead of <module.key=value>
(Augment low) — angle brackets in the placeholder were misleading;
the description spells out the spec format.

(H) README wording: "every available key" → "locally-known official
keys (built-in modules plus any external officials cached on this
machine)" (CodeRabbit minor) — accurately reflects scope.

Tests: +2 cases for prototype-pollution rejection. Total 343 passing.

README.md

@@ -52,7 +52,7 @@ Follow the installer prompts, then open your AI IDE (Claude Code, Cursor, etc.)
 npx bmad-method install --directory /path/to/project --modules bmm --tools claude-code --yes
 ```
 
-Override any module config option with `--set <module>.<key>=<value>` (repeatable). Run `--list-options` to see every available key:
+Override any module config option with `--set <module>.<key>=<value>` (repeatable). Run `--list-options [module]` to see locally-known official keys (built-in modules plus any external officials cached on this machine):
 
 ```bash
 npx bmad-method install --yes \

test/test-installation-components.js

@@ -3030,6 +3030,25 @@ async function runTests() {
     const empty = parseSetEntries();
     assert(empty && Object.keys(empty).length === 0, 'parseSetEntries() returns empty object when called without args');
 
+    // parseSetEntries — prototype-pollution guard. `--set __proto__.x=1` would
+    // otherwise reach `overrides.__proto__[x] = 1` and pollute Object.prototype.
+    const polluteProbe = {};
+    let pollutionThrown = false;
+    try {
+      parseSetEntries(['__proto__.polluted=1']);
+    } catch {
+      pollutionThrown = true;
+    }
+    assert(pollutionThrown, 'parseSetEntries rejects __proto__ as a module name');
+    assert(polluteProbe.polluted === undefined, 'Object.prototype is not polluted by __proto__ in --set entries');
+    let constructorThrown = false;
+    try {
+      parseSetEntries(['bmm.constructor=evil']);
+    } catch {
+      constructorThrown = true;
+    }
+    assert(constructorThrown, 'parseSetEntries rejects "constructor" as a key name');
+
     // discoverOfficialModuleYamls + formatOptionsList read the on-disk
     // external-module cache. Point that env at a temp dir so test results
     // don't depend on whatever the developer / CI runner has cached.

tools/installer/commands/install.js

@@ -19,8 +19,8 @@ module.exports = {
     ],
     ['--list-tools', 'Print all supported tool/IDE IDs (with target directories) and exit.'],
     [
-      '--set <module.key=value>',
-      'Set a module config option non-interactively (e.g. --set bmm.project_knowledge=research). Repeatable. Run --list-options to see available keys.',
+      '--set <spec>',
+      'Set a module config option non-interactively. Spec format: <module>.<key>=<value> (e.g. bmm.project_knowledge=research). Repeatable. Run --list-options to see available keys.',
       (value, prev) => [...(prev || []), value],
       [],
     ],

tools/installer/list-options.js

@@ -175,6 +175,11 @@ async function formatOptionsList(moduleCode) {
   }
 
   const sections = [];
+  // Track when a module-scoped lookup couldn't actually be rendered (yaml
+  // unparseable or empty after parse). The full `--list-options` output is
+  // tolerant of one bad entry, but `--list-options <module>` against a single
+  // unreadable module should still fail tooling so a CI script catches it.
+  let moduleScopedFailure = false;
   sections.push('Available --set keys', 'Format: --set <module>.<key>=<value> (repeatable)', '');
   for (const { code, yamlPath, source } of filtered) {
     let parsed;
@@ -182,9 +187,13 @@ async function formatOptionsList(moduleCode) {
       parsed = yaml.parse(await fs.readFile(yamlPath, 'utf8'));
     } catch {
       sections.push(`${code} (${source}): could not parse module.yaml`, '');
+      if (moduleCode) moduleScopedFailure = true;
+      continue;
+    }
+    if (!parsed || typeof parsed !== 'object') {
+      if (moduleCode) moduleScopedFailure = true;
       continue;
     }
-    if (!parsed || typeof parsed !== 'object') continue;
     sections.push(formatModuleOptions(code, parsed, source));
   }
 
@@ -194,7 +203,7 @@ async function formatOptionsList(moduleCode) {
     );
   }
 
-  return { text: sections.join('\n'), ok: true };
+  return { text: sections.join('\n'), ok: !moduleScopedFailure };
 }
 
 module.exports = { formatOptionsList, discoverOfficialModuleYamls };

tools/installer/modules/official-modules.js

@@ -56,27 +56,29 @@ class OfficialModules {
       this.collectedConfig[moduleName][key] = value;
     }
 
-    // Load schema so we can flag unknown keys. If the schema can't be loaded,
-    // we skip key-existence validation but still apply overrides + carry-forward.
+    if (!this.setOverrideKeys) this.setOverrideKeys = {};
+    if (!this.setOverrideKeys[moduleName]) this.setOverrideKeys[moduleName] = new Set();
+
+    // Try to load the module's schema. When available we can distinguish
+    // declared keys from unknown ones; when not (built-in is missing or
+    // unparseable — rare for `core`), we treat every prior + override key as
+    // unknown so carry-forward still runs and writeCentralConfig keeps them.
     let schema = null;
     const schemaPath = path.join(getModulePath(moduleName), 'module.yaml');
     if (await fs.pathExists(schemaPath)) {
       try {
         schema = yaml.parse(await fs.readFile(schemaPath, 'utf8'));
       } catch {
-        // schema unparseable — skip key-existence validation
+        // schema unparseable — fall through to no-schema behavior
       }
     }
-    if (!schema || typeof schema !== 'object') return;
-
     const declaredKeys = new Set();
-    for (const [key, decl] of Object.entries(schema)) {
-      if (decl && typeof decl === 'object' && 'prompt' in decl) declaredKeys.add(key);
+    if (schema && typeof schema === 'object') {
+      for (const [key, decl] of Object.entries(schema)) {
+        if (decl && typeof decl === 'object' && 'prompt' in decl) declaredKeys.add(key);
+      }
     }
 
-    if (!this.setOverrideKeys) this.setOverrideKeys = {};
-    if (!this.setOverrideKeys[moduleName]) this.setOverrideKeys[moduleName] = new Set();
-
     // Warn + track unknown keys from this run's --set entries.
     for (const key of Object.keys(overrides)) {
       if (!declaredKeys.has(key)) {
@@ -1634,6 +1636,19 @@ class OfficialModules {
     for (const key of seededOverrideKeys) {
       allAnswers[`${moduleName}_${key}`] = moduleOverrides[key];
     }
+    // Pre-write raw override values into collectedConfig so dynamic-default
+    // resolvers (`buildQuestion`'s function default) can see them when a
+    // sibling key uses a `{other_key}` placeholder. The fallback chain in
+    // that closure is: current prompt batch → `this.collectedConfig[mod]`,
+    // and overridden keys are removed from the prompt batch — without this
+    // pre-write the placeholder lookup would miss them. The raw value is
+    // overwritten with the template-rendered version after prompts complete.
+    if (seededOverrideKeys.size > 0) {
+      if (!this.collectedConfig[moduleName]) this.collectedConfig[moduleName] = {};
+      for (const key of seededOverrideKeys) {
+        this.collectedConfig[moduleName][key] = moduleOverrides[key];
+      }
+    }
     // Drop pre-seeded questions so the user is not re-prompted and so
     // skipPrompts mode doesn't overwrite the override with the default.
     // In-place mutation keeps the rest of this method's `questions` references

tools/installer/set-overrides.js

@@ -1,3 +1,12 @@
+// Names that, when used as object keys, can mutate `Object.prototype` and
+// cascade into every plain-object lookup in the process. The whole `--set`
+// pipeline assigns into plain `{}` maps keyed by user input, so a flag like
+// `--set __proto__.polluted=1` would otherwise reach
+// `overrides.__proto__[key] = value`, which assigns onto Object.prototype.
+// We reject both segments at parse time and harden the maps in
+// `parseSetEntries` with `Object.create(null)`.
+const PROTOTYPE_POLLUTING_NAMES = new Set(['__proto__', 'prototype', 'constructor']);
+
 /**
  * Parse a single `--set <module>.<key>=<value>` entry.
  * @param {string} entry - raw flag value
@@ -26,21 +35,32 @@ function parseSetEntry(entry) {
   if (!moduleCode || !key) {
     throw new Error(`--set "${entry}": empty module or key. Expected <module>.<key>=<value>`);
   }
+  if (PROTOTYPE_POLLUTING_NAMES.has(moduleCode) || PROTOTYPE_POLLUTING_NAMES.has(key)) {
+    throw new Error(
+      `--set "${entry}": '__proto__', 'prototype', and 'constructor' are reserved and cannot be used as a module or key name.`,
+    );
+  }
   return { module: moduleCode, key, value };
 }
 
 /**
  * Parse repeated `--set` entries into a `{ module: { key: value } }` map.
  * Later entries overwrite earlier ones for the same key.
+ *
+ * Both the outer map and the per-module inner maps are `Object.create(null)`
+ * so that even if a future caller bypasses `parseSetEntry`'s reserved-name
+ * check, lookups can't traverse `Object.prototype` and pollution-style writes
+ * land on the map's own properties (not the global prototype).
+ *
  * @param {string[]} entries
  * @returns {Object<string, Object<string, string>>}
  */
 function parseSetEntries(entries) {
-  const overrides = {};
+  const overrides = Object.create(null);
   if (!Array.isArray(entries)) return overrides;
   for (const entry of entries) {
     const { module: moduleCode, key, value } = parseSetEntry(entry);
-    if (!overrides[moduleCode]) overrides[moduleCode] = {};
+    if (!overrides[moduleCode]) overrides[moduleCode] = Object.create(null);
     overrides[moduleCode][key] = value;
   }
   return overrides;