diff --git a/docs/plans/2026-08-30-gitnexus-plan-ruby-gem-require-boundary.md b/docs/plans/2026-08-30-gitnexus-plan-ruby-gem-require-boundary.md
new file mode 100644
index 000000000..a57b8b1dd
--- /dev/null
+++ b/docs/plans/2026-08-30-gitnexus-plan-ruby-gem-require-boundary.md
@@ -0,0 +1,204 @@
+# GitNexus Engineering Plan
+
+> Task: Prevent Ruby gem requires from suffix-resolving to unrelated repository files (#2966).
+> Evidence verified at commit 170eefd4a0893be9d255dc3581d51fd448ce2e96; GitNexus index fresh at that commit with schema-4 runner identity.
+> Evidence provenance schema 2; global dirty digest 0a9c85780067d9afcd0764f307b60891e3cee927ee11eaeb5ec7826d10fd82cd; cited-path manifest 10 sorted entries; exact generated plan path excluded.
+
+## Objective (§1)
+
+Block a bare Ruby `require` before suffix matching when its first path segment is a dependency declared by Bundler/RubyGems metadata, while preserving local bare and `require_relative` resolution and failing open when no Gemfile or gemspec is available.
+
+## Current Behaviour (§2–3)
+
+- [verified] `resolveRubyImportTarget` sends every non-relative target to `resolveBare`, whose progressive suffix matching can drop `rails/` and select `lib/generators.rb` (`gitnexus/src/core/ingestion/languages/ruby/import-target.ts:34`).
+- [verified] The scope-resolution pipeline already loads each language's opaque workspace config once and passes it to every import lookup (`gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts:373`).
+- [verified] Ruby currently exposes no `loadResolutionConfig`; PHP demonstrates the established bounded manifest-scan and resolver-config seam (`gitnexus/src/core/ingestion/languages/php/import-target.ts:295`).
+- [verified] Existing parity coverage calls Ruby with no config and exercises both bare and `./`/`../` targets, pinning the fail-open and relative paths (`gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts:412`).
+
+## Findings (§4–5)
+
+- [graph] `impact resolveRubyImportTarget --direction upstream --depth 3 --include-tests` returned LOW risk with exactly two direct dependents: `rubyScopeResolver.resolveImportTarget` and `import-target-index-parity.test.ts`.
+- [graph] `context resolveRubyImportTarget --file gitnexus/src/core/ingestion/languages/ruby/import-target.ts` found calls only to `resolveBare`, `resolveRelative`, and `isHeritageMarker`; no process membership was reported.
+- [verified] The conformance fixture records `rails/generators -> lib/generators.rb` as Ruby's known external-import gap (`gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts:270`, `:375`).
+- No PDG slice is needed: this local fix adds one data gate before an existing pure resolver branch and changes no trust, persistence, concurrency, or state-mutation boundary.
+
+## Proposed Changes (§6)
+
+- Add `ruby/resolution-config.ts` with a bounded, static scanner that collects dependency names from Gemfile and gemspec declarations and transitive gem names from adjacent `Gemfile.lock` files; return `null` when no declarative manifest exists.
+- Add `rubyScopeResolver.loadResolutionConfig` so the existing one-load-per-workspace pipeline threads the Ruby dependency set into import resolution.
+- Update `resolveRubyImportTarget` to return `null` for bare targets whose first segment is in that set, before suffix matching; leave relative and no-config paths unchanged.
+- Remove Ruby from `KNOWN_GAPS`, provide `rails` config to that fixture, and add focused loader/gate tests for Gemfile, gemspec, lockfile, local bare paths, relative paths, and no-manifest fail-open behavior.
+
+## Implementation Sequence (§7)
+
+1. Add the manifest scanner and focused tests; keep parsing static and bounded, with skipped dependency/build directories. Risk: Ruby manifests are executable, so recognize only explicit literal dependency declarations and never evaluate them.
+2. Wire the config loader into `rubyScopeResolver`, then gate only non-relative targets in `resolveRubyImportTarget`. Risk: dependency-name/require-path conventions are not universal, so match only the literal first segment proven by metadata.
+3. Turn the shared conformance fixture green, run focused/full validation, refresh the local graph, and account for all changed symbols before the implementation commit.
+
+## Test Strategy (§8)
+
+- First make the `rails/generators` regression test fail on the pre-fix resolver, then implement the gate.
+- Assert declared direct and locked transitive dependencies return `null` despite decoy suffixes.
+- Assert `app/models/user`, `generators`, and `require_relative` continue resolving; assert a workspace without Gemfile/gemspec retains legacy fail-open behavior.
+- Run `npm test` and `npx tsc --noEmit` from `gitnexus`, plus targeted Vitest, formatting/lint checks, and `git diff --check`.
+
+## Implementation Context (§11)
+
+```yaml
+implementation_context:
+  task_summary: 'Prevent declared Ruby gem requires from suffix-resolving to unrelated repository files.'
+  evidence_provenance:
+    schema_version: 2
+    head_commit: '170eefd4a0893be9d255dc3581d51fd448ce2e96'
+    generated_plan_path: 'docs/plans/2026-08-30-gitnexus-plan-ruby-gem-require-boundary.md'
+    global_dirty_digest:
+      algorithm: 'sha256'
+      canonicalization: 'gitnexus-evidence-provenance-v2 NUL-framed UTF-8 records'
+      value: '0a9c85780067d9afcd0764f307b60891e3cee927ee11eaeb5ec7826d10fd82cd'
+    cited_path_manifest:
+      - path: 'gitnexus/package.json'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:157760d8e69666e9e228091077a8c62787d15c1e9e43b059601093d90c081976'
+        index_digest: 'sha256:157760d8e69666e9e228091077a8c62787d15c1e9e43b059601093d90c081976'
+        worktree_digest: 'sha256:157760d8e69666e9e228091077a8c62787d15c1e9e43b059601093d90c081976'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/languages/php/import-target.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:4e73c2e3f1322defaafcd543d715ab351c2d4f5af0fa481c3c81b3543e7618de'
+        index_digest: 'sha256:4e73c2e3f1322defaafcd543d715ab351c2d4f5af0fa481c3c81b3543e7618de'
+        worktree_digest: 'sha256:4e73c2e3f1322defaafcd543d715ab351c2d4f5af0fa481c3c81b3543e7618de'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/languages/ruby/import-target.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:326155551dda5d759e6d6e21b09b4e8b5c90b956ed11905568b146e8cc8a3fb8'
+        index_digest: 'sha256:326155551dda5d759e6d6e21b09b4e8b5c90b956ed11905568b146e8cc8a3fb8'
+        worktree_digest: 'sha256:326155551dda5d759e6d6e21b09b4e8b5c90b956ed11905568b146e8cc8a3fb8'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/languages/ruby/resolution-config.ts'
+        object_kind: { head: 'absent', index: 'absent', worktree: 'absent', untracked: 'absent' }
+        state: 'absent'
+        rename_from: null
+        rename_to: null
+        head_digest: 'absent'
+        index_digest: 'absent'
+        worktree_digest: 'absent'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:d6b77df3b87b341f3cd7b30576e8fd9b89fbc78dec55a71cf4788c15deebc1bf'
+        index_digest: 'sha256:d6b77df3b87b341f3cd7b30576e8fd9b89fbc78dec55a71cf4788c15deebc1bf'
+        worktree_digest: 'sha256:d6b77df3b87b341f3cd7b30576e8fd9b89fbc78dec55a71cf4788c15deebc1bf'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/scope-resolution/contract/scope-resolver.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:84c8a5edc9776551df216cf3159fdbb0a68ebfb7b2f6d317cc0dd6e8522d93ab'
+        index_digest: 'sha256:84c8a5edc9776551df216cf3159fdbb0a68ebfb7b2f6d317cc0dd6e8522d93ab'
+        worktree_digest: 'sha256:84c8a5edc9776551df216cf3159fdbb0a68ebfb7b2f6d317cc0dd6e8522d93ab'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/src/core/ingestion/scope-resolution/pipeline/phase.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:911f7cd3d76fc0c47db7498f93c163571440f7dd1d2c6bd9e23f1423465a1398'
+        index_digest: 'sha256:911f7cd3d76fc0c47db7498f93c163571440f7dd1d2c6bd9e23f1423465a1398'
+        worktree_digest: 'sha256:911f7cd3d76fc0c47db7498f93c163571440f7dd1d2c6bd9e23f1423465a1398'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:faa3f40d302ea7e4b9914aeb91b3ef3a32c511a4c4be16cea966ee0d0e92de55'
+        index_digest: 'sha256:faa3f40d302ea7e4b9914aeb91b3ef3a32c511a4c4be16cea966ee0d0e92de55'
+        worktree_digest: 'sha256:faa3f40d302ea7e4b9914aeb91b3ef3a32c511a4c4be16cea966ee0d0e92de55'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts'
+        object_kind: { head: 'regular', index: 'regular', worktree: 'regular', untracked: 'absent' }
+        state: 'clean'
+        rename_from: null
+        rename_to: null
+        head_digest: 'sha256:0154615b77157bbfd413867b6c83a837d7fa5d2bf03ecbc969cca873021cf51c'
+        index_digest: 'sha256:0154615b77157bbfd413867b6c83a837d7fa5d2bf03ecbc969cca873021cf51c'
+        worktree_digest: 'sha256:0154615b77157bbfd413867b6c83a837d7fa5d2bf03ecbc969cca873021cf51c'
+        untracked_digest: 'absent'
+      - path: 'gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts'
+        object_kind: { head: 'absent', index: 'absent', worktree: 'absent', untracked: 'absent' }
+        state: 'absent'
+        rename_from: null
+        rename_to: null
+        head_digest: 'absent'
+        index_digest: 'absent'
+        worktree_digest: 'absent'
+        untracked_digest: 'absent'
+  files_to_modify:
+    - file: 'gitnexus/src/core/ingestion/languages/ruby/resolution-config.ts'
+      symbols: ['RubyResolutionConfig', 'loadRubyResolutionConfig']
+      intended_change: 'Statically collect declared and locked gem names with bounded traversal; return null without Gemfile/gemspec evidence.'
+    - file: 'gitnexus/src/core/ingestion/languages/ruby/import-target.ts'
+      symbols: ['resolveRubyImportTarget']
+      intended_change: 'Reject declared external-gem roots before bare suffix resolution.'
+    - file: 'gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts'
+      symbols: ['rubyScopeResolver']
+      intended_change: 'Load Ruby resolution config once per workspace.'
+    - file: 'gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts'
+      symbols: ['CASES', 'KNOWN_GAPS']
+      intended_change: 'Provide rails dependency evidence and remove the Ruby gap.'
+    - file: 'gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts'
+      symbols: []
+      intended_change: 'Cover manifest parsing, gate behavior, local positives, relative behavior, and fail-open mode.'
+  tests:
+    - file: 'gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts'
+      scenarios:
+        - "declared rails + require rails/generators + local generators.rb decoy -> null"
+        - "same workspace + require generators -> lib/generators.rb"
+    - file: 'gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts'
+      scenarios:
+        - 'Gemfile/gemspec direct dependency and Gemfile.lock transitive name -> collected roots'
+        - 'no Gemfile/gemspec -> null config and legacy bare resolution remains available'
+        - 'declared dependency target -> null; local app/models/user -> local file'
+        - 'require_relative target -> importer-relative file despite matching dependency name'
+  verification_commands:
+    - 'cd gitnexus && npx vitest run test/unit/scope-resolution/external-import-conformance.test.ts test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts test/unit/scope-resolution/import-target-index-parity.test.ts'
+    - 'cd gitnexus && npm test'
+    - 'cd gitnexus && npx tsc --noEmit'
+    - 'cd gitnexus && npx eslint src/core/ingestion/languages/ruby test/unit/scope-resolution/external-import-conformance.test.ts test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts'
+    - 'cd gitnexus && npx prettier --check src/core/ingestion/languages/ruby/import-target.ts src/core/ingestion/languages/ruby/resolution-config.ts src/core/ingestion/languages/ruby/scope-resolver.ts test/unit/scope-resolution/external-import-conformance.test.ts test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts'
+    - 'git diff --check'
+  assumptions:
+    - 'Recheck immediately before implementation that #2966 is open and has no overlapping PR.'
+    - 'Verify the loader returns null when no Gemfile/gemspec is found, even if a lockfile exists.'
+  open_questions: []
+  avoid:
+    - 'Do not evaluate Ruby manifest code.'
+    - 'Do not classify undeclared require roots as external.'
+    - 'Do not change suffix-matching order, WorkspaceFileIndex reuse, or require_relative semantics.'
+    - 'Do not expand this PR to conventional-load-root heuristics beyond the accepted dependency gate.'
+```
+
+## Assumptions and Open Questions (§12)
+
+- [assumed] Literal dependency declarations cover the accepted gate; dynamic Gemfile/gemspec logic remains fail-open and is explicitly deferred.
+- [assumed] A lockfile contributes transitive names only when at least one Gemfile/gemspec proves the repository is Bundler/RubyGems-managed.
+- No blocking open question remains; first-segment aliases for gems whose require path differs from their package name are deferred because metadata alone cannot prove them safely.
+
+## Definition of Done (§13)
+
+- `rails/generators` is unresolved with declared `rails`; local bare and relative fixtures still resolve.
+- Ruby is removed from `KNOWN_GAPS`; focused, full, typecheck, lint, formatting, diff, and graph-change gates pass.
+- No Ruby code is executed while reading manifests, and no-config workspaces retain existing behavior.
diff --git a/gitnexus/src/core/ingestion/languages/ruby/import-target.ts b/gitnexus/src/core/ingestion/languages/ruby/import-target.ts
index 62d6fca3d..462a47e08 100644
--- a/gitnexus/src/core/ingestion/languages/ruby/import-target.ts
+++ b/gitnexus/src/core/ingestion/languages/ruby/import-target.ts
@@ -10,6 +10,11 @@
 import { resolveRubyImportInternal } from '../../import-resolvers/ruby.js';
 import { getWorkspaceFileIndex } from '../../import-resolvers/workspace-file-index.js';
 import { isHeritageMarker } from '../../utils/heritage-marker.js';
+import {
+  findRubyResolutionScope,
+  type RubyResolutionConfig,
+  type RubyResolutionScope,
+} from './resolution-config.js';
 
 export interface RubyResolveContext {
   readonly fromFile: string;
@@ -35,7 +40,7 @@ export function resolveRubyImportTarget(
   targetRaw: string,
   fromFile: string,
   allFilePaths: ReadonlySet<string>,
-  _resolutionConfig?: unknown,
+  resolutionConfig?: unknown,
 ): string | readonly string[] | null {
   if (!targetRaw) return null;
   if (isHeritageMarker(targetRaw)) return null;
@@ -51,7 +56,16 @@ export function resolveRubyImportTarget(
     return resolved;
   }
 
-  // ── require: bare/gem-style suffix matching ─────────────────────────
+  // ── require: scoped gem evidence before repository-wide fallback ────
+  const config = resolutionConfig as RubyResolutionConfig | null | undefined;
+  const scope =
+    config === null || config === undefined ? undefined : findRubyResolutionScope(config, fromFile);
+  if (scope !== undefined) {
+    const localGemTarget = resolveLocalGemTarget(targetRaw, scope, allFilePaths);
+    if (localGemTarget !== null) return localGemTarget;
+    if (matchesRequirePrefix(targetRaw, scope.externalRequirePrefixes)) return null;
+  }
+
   return resolveBare(targetRaw, allFilePaths);
 }
 
@@ -95,6 +109,47 @@ function resolveRelative(
   return null;
 }
 
+/**
+ * Yield the target itself, then each slash-delimited ancestor. This makes both
+ * local-root and external-gem lookup O(require path depth), not O(gem count).
+ */
+function requirePrefixCandidates(targetRaw: string): readonly string[] {
+  const candidates = [targetRaw];
+  let slash = targetRaw.lastIndexOf('/');
+  while (slash !== -1) {
+    candidates.push(targetRaw.slice(0, slash));
+    slash = targetRaw.lastIndexOf('/', slash - 1);
+  }
+  return candidates;
+}
+
+function matchesRequirePrefix(targetRaw: string, prefixes: ReadonlySet<string>): boolean {
+  return requirePrefixCandidates(targetRaw).some((candidate) => prefixes.has(candidate));
+}
+
+/** Resolve a path/gemspec-backed gem against its declared Ruby load roots. */
+function resolveLocalGemTarget(
+  targetRaw: string,
+  scope: RubyResolutionScope,
+  allFilePaths: ReadonlySet<string>,
+): string | null {
+  for (const prefix of requirePrefixCandidates(targetRaw)) {
+    const loadRoots = scope.localLoadRootsByPrefix.get(prefix);
+    if (loadRoots === undefined) continue;
+
+    for (const loadRoot of loadRoots) {
+      const base = loadRoot ? `${loadRoot}/${targetRaw}` : targetRaw;
+      if (base.endsWith('.rb')) {
+        if (allFilePaths.has(base)) return base;
+        continue;
+      }
+      const rbFile = `${base}.rb`;
+      if (allFilePaths.has(rbFile)) return rbFile;
+    }
+  }
+  return null;
+}
+
 /**
  * Resolve a bare require path (`'serializable'`, `'json'`, `'net/http'`)
  * via suffix matching using the existing Ruby import resolver.
diff --git a/gitnexus/src/core/ingestion/languages/ruby/resolution-config.ts b/gitnexus/src/core/ingestion/languages/ruby/resolution-config.ts
new file mode 100644
index 000000000..52c213af3
--- /dev/null
+++ b/gitnexus/src/core/ingestion/languages/ruby/resolution-config.ts
@@ -0,0 +1,380 @@
+import { readdirSync, readFileSync, type Dirent } from 'node:fs';
+import { isAbsolute, join, relative, resolve } from 'node:path';
+
+export interface RubyResolutionScope {
+  /** Require prefixes provided by gems whose source is outside this repository. */
+  readonly externalRequirePrefixes: ReadonlySet<string>;
+  /** Require prefix -> repository-relative Ruby load roots for local gems. */
+  readonly localLoadRootsByPrefix: ReadonlyMap<string, readonly string[]>;
+}
+
+export interface RubyResolutionConfig {
+  /** Manifest directory (repository-relative POSIX path) -> dependency scope. */
+  readonly scopesByDirectory: ReadonlyMap<string, RubyResolutionScope>;
+}
+
+interface MutableRubyResolutionScope {
+  readonly externalRequirePrefixes: Set<string>;
+  readonly localLoadRootsByPrefix: Map<string, Set<string>>;
+}
+
+interface GemspecMetadata {
+  readonly name: string | null;
+  readonly requirePaths: readonly string[];
+}
+
+const MAX_VISITED_DIRECTORIES = 20_000;
+const SKIP_DIRECTORIES = new Set([
+  '.git',
+  '.gitnexus',
+  'node_modules',
+  'vendor',
+  'dist',
+  'build',
+  'coverage',
+]);
+
+const GEMFILE_DEPENDENCY = /^\s*gem\s*(?:\(\s*)?(['"])([A-Za-z0-9_.-]+)\1(?<options>.*)$/;
+const GEMSPEC_DEPENDENCY =
+  /^\s*(?:[A-Za-z_]\w*\.)?(?:add_dependency|add_runtime_dependency|add_development_dependency)\s*(?:\(\s*)?(['"])([A-Za-z0-9_.-]+)\1/;
+const GEMSPEC_NAME = /^\s*(?:[A-Za-z_]\w*\.)?name\s*=\s*(['"])([A-Za-z0-9_.-]+)\1/;
+const GEMSPEC_REQUIRE_PATHS = /^\s*(?:[A-Za-z_]\w*\.)?require_paths\s*=\s*\[([^\]]*)\]/;
+const QUOTED_LITERAL = /(['"])([^'"]+)\1/g;
+const LOCKFILE_SECTION = /^([A-Z][A-Z ]*)\s*$/;
+const LOCKFILE_REMOTE = /^ {2}remote:\s*(.+?)\s*$/;
+const LOCKFILE_SPECS_HEADER = /^ {2}specs:\s*$/;
+const LOCKFILE_SPEC = /^ {4}([A-Za-z0-9_.-]+) \(/;
+
+function createMutableScope(): MutableRubyResolutionScope {
+  return {
+    externalRequirePrefixes: new Set<string>(),
+    localLoadRootsByPrefix: new Map<string, Set<string>>(),
+  };
+}
+
+function normalizeRepoPath(filePath: string): string {
+  return filePath.replace(/\\/g, '/').replace(/^\.\//, '').replace(/\/$/, '');
+}
+
+function repoRelativePath(repoPath: string, candidate: string): string | null {
+  const rel = relative(resolve(repoPath), resolve(candidate));
+  if (rel === '') return '';
+  if (rel === '..' || rel.startsWith(`..\\`) || rel.startsWith('../') || isAbsolute(rel)) {
+    return null;
+  }
+  return normalizeRepoPath(rel);
+}
+
+function requirePrefixes(gemName: string, requireAs?: string): readonly string[] {
+  const prefixes = new Set<string>([gemName]);
+  if (gemName.includes('-')) prefixes.add(gemName.replaceAll('-', '/'));
+  if (requireAs !== undefined && requireAs.length > 0) prefixes.add(requireAs);
+  return [...prefixes];
+}
+
+function literalOption(options: string, name: string): string | undefined {
+  const modern = new RegExp(`(?:^|[,\\s])${name}\\s*:\\s*(['"])([^'"]+)\\1`).exec(options);
+  if (modern !== null) return modern[2];
+  const hashRocket = new RegExp(`(?:^|[,\\s]):${name}\\s*=>\\s*(['"])([^'"]+)\\1`).exec(options);
+  return hashRocket?.[2];
+}
+
+function hasOption(options: string, name: string): boolean {
+  return (
+    new RegExp(`(?:^|[,\\s])${name}\\s*:`).test(options) ||
+    new RegExp(`(?:^|[,\\s]):${name}\\s*=>`).test(options)
+  );
+}
+
+function addExternalGem(
+  scope: MutableRubyResolutionScope,
+  gemName: string,
+  requireAs?: string,
+): void {
+  for (const prefix of requirePrefixes(gemName, requireAs)) {
+    if (!scope.localLoadRootsByPrefix.has(prefix)) scope.externalRequirePrefixes.add(prefix);
+  }
+}
+
+function addLocalGem(
+  scope: MutableRubyResolutionScope,
+  gemName: string,
+  loadRoots: readonly string[],
+  requireAs?: string,
+): void {
+  for (const prefix of requirePrefixes(gemName, requireAs)) {
+    scope.externalRequirePrefixes.delete(prefix);
+    let roots = scope.localLoadRootsByPrefix.get(prefix);
+    if (roots === undefined) {
+      roots = new Set<string>();
+      scope.localLoadRootsByPrefix.set(prefix, roots);
+    }
+    for (const loadRoot of loadRoots) roots.add(loadRoot);
+  }
+}
+
+function parseGemspecMetadata(contents: string): GemspecMetadata {
+  let name: string | null = null;
+  let requirePaths: string[] | null = null;
+
+  for (const line of contents.split(/\r?\n/)) {
+    const nameMatch = GEMSPEC_NAME.exec(line);
+    if (nameMatch !== null) name = nameMatch[2];
+
+    const requirePathsMatch = GEMSPEC_REQUIRE_PATHS.exec(line);
+    if (requirePathsMatch === null) continue;
+    const paths: string[] = [];
+    for (const match of requirePathsMatch[1].matchAll(QUOTED_LITERAL)) paths.push(match[2]);
+    if (paths.length > 0) requirePaths = paths;
+  }
+
+  return { name, requirePaths: requirePaths ?? ['lib'] };
+}
+
+function loadLocalGemRoots(
+  repoPath: string,
+  gemRoot: string,
+  expectedGemName: string,
+): readonly string[] | null {
+  const gemRootRelative = repoRelativePath(repoPath, gemRoot);
+  if (gemRootRelative === null) return null;
+
+  let requirePaths: readonly string[] = ['lib'];
+  try {
+    const gemspecs = readdirSync(gemRoot, { withFileTypes: true })
+      .filter((entry) => entry.isFile() && entry.name.endsWith('.gemspec'))
+      .map((entry) => join(gemRoot, entry.name))
+      .sort();
+    for (const gemspec of gemspecs) {
+      const metadata = parseGemspecMetadata(readFileSync(gemspec, 'utf8'));
+      if (metadata.name === expectedGemName) {
+        requirePaths = metadata.requirePaths;
+        break;
+      }
+    }
+  } catch {
+    // An unreadable local gem stays local; the conventional lib root is a
+    // bounded best effort, and resolution falls through if no file matches.
+  }
+
+  return requirePaths
+    .map((requirePath) => repoRelativePath(repoPath, resolve(gemRoot, requirePath)))
+    .filter((loadRoot): loadRoot is string => loadRoot !== null);
+}
+
+function addGemfileDependencies(
+  contents: string,
+  manifestDirectory: string,
+  repoPath: string,
+  scope: MutableRubyResolutionScope,
+): void {
+  for (const line of contents.split(/\r?\n/)) {
+    const match = GEMFILE_DEPENDENCY.exec(line);
+    if (match === null) continue;
+
+    const gemName = match[2];
+    const options = match.groups?.options ?? '';
+    const requireAs = literalOption(options, 'require');
+    const localPath = literalOption(options, 'path');
+
+    if (localPath !== undefined) {
+      const loadRoots = loadLocalGemRoots(repoPath, resolve(manifestDirectory, localPath), gemName);
+      if (loadRoots === null) addExternalGem(scope, gemName, requireAs);
+      else addLocalGem(scope, gemName, loadRoots, requireAs);
+      continue;
+    }
+
+    // A dynamic path expression cannot be classified without evaluating Ruby.
+    // Fail open instead of deleting a potentially real in-repo import edge.
+    if (hasOption(options, 'path')) continue;
+
+    addExternalGem(scope, gemName, requireAs);
+  }
+}
+
+function addGemspecDependencies(
+  contents: string,
+  gemspecDirectory: string,
+  repoPath: string,
+  scope: MutableRubyResolutionScope,
+): void {
+  const metadata = parseGemspecMetadata(contents);
+  if (metadata.name !== null) {
+    if (repoRelativePath(repoPath, gemspecDirectory) !== null) {
+      const loadRoots = metadata.requirePaths
+        .map((requirePath) => repoRelativePath(repoPath, resolve(gemspecDirectory, requirePath)))
+        .filter((loadRoot): loadRoot is string => loadRoot !== null);
+      addLocalGem(scope, metadata.name, loadRoots);
+    }
+  }
+
+  for (const line of contents.split(/\r?\n/)) {
+    const match = GEMSPEC_DEPENDENCY.exec(line);
+    if (match !== null) addExternalGem(scope, match[2]);
+  }
+}
+
+function addLockedDependencies(
+  contents: string,
+  lockfileDirectory: string,
+  repoPath: string,
+  scope: MutableRubyResolutionScope,
+): void {
+  let section = '';
+  let remote: string | null = null;
+  let inSpecs = false;
+
+  for (const line of contents.split(/\r?\n/)) {
+    const sectionMatch = LOCKFILE_SECTION.exec(line);
+    if (sectionMatch !== null) {
+      section = sectionMatch[1];
+      remote = null;
+      inSpecs = false;
+      continue;
+    }
+
+    const remoteMatch = LOCKFILE_REMOTE.exec(line);
+    if (remoteMatch !== null) {
+      remote = remoteMatch[1];
+      continue;
+    }
+
+    if (LOCKFILE_SPECS_HEADER.test(line)) {
+      inSpecs = true;
+      continue;
+    }
+    if (!inSpecs) continue;
+
+    const specMatch = LOCKFILE_SPEC.exec(line);
+    if (specMatch === null) continue;
+    const gemName = specMatch[1];
+
+    if (section === 'GEM' || section === 'GIT') {
+      addExternalGem(scope, gemName);
+      continue;
+    }
+
+    if (section !== 'PATH' && section !== 'GEMSPEC') continue;
+    if (remote === null) continue;
+
+    const loadRoots = loadLocalGemRoots(repoPath, resolve(lockfileDirectory, remote), gemName);
+    if (loadRoots === null) addExternalGem(scope, gemName);
+    else addLocalGem(scope, gemName, loadRoots);
+  }
+}
+
+function freezeScope(scope: MutableRubyResolutionScope): RubyResolutionScope {
+  const localLoadRootsByPrefix = new Map<string, readonly string[]>();
+  for (const [prefix, roots] of scope.localLoadRootsByPrefix) {
+    localLoadRootsByPrefix.set(prefix, [...roots].sort());
+  }
+  return {
+    externalRequirePrefixes: new Set(scope.externalRequirePrefixes),
+    localLoadRootsByPrefix,
+  };
+}
+
+/**
+ * Select the nearest manifest directory that owns `fromFile`.
+ *
+ * Walking ancestors makes lookup O(path depth), independent of how many
+ * sibling Gemfiles a monorepo contains.
+ */
+export function findRubyResolutionScope(
+  config: RubyResolutionConfig,
+  fromFile: string,
+): RubyResolutionScope | undefined {
+  const normalized = normalizeRepoPath(fromFile);
+  let directory = normalized.includes('/') ? normalized.slice(0, normalized.lastIndexOf('/')) : '';
+
+  for (;;) {
+    const scope = config.scopesByDirectory.get(directory);
+    if (scope !== undefined) return scope;
+    if (directory === '') return undefined;
+    const slash = directory.lastIndexOf('/');
+    directory = slash === -1 ? '' : directory.slice(0, slash);
+  }
+}
+
+/**
+ * Statically collect Ruby dependency sources without evaluating Gemfile or
+ * gemspec code. Scopes stay separate by manifest directory so sibling projects
+ * in a monorepo cannot suppress one another's local imports. Lockfiles
+ * contribute remote GEM/GIT specs and local PATH/GEMSPEC load roots only when
+ * an adjacent Gemfile or gemspec establishes a Bundler/RubyGems project.
+ *
+ * No declarative manifest means no safe gate, so return null and preserve the
+ * resolver's existing fail-open behavior for loose script directories.
+ */
+export function loadRubyResolutionConfig(repoPath: string): RubyResolutionConfig | null {
+  const pending = [repoPath];
+  const manifestsByDirectory = new Map<string, string[]>();
+  const lockfilesByDirectory = new Map<string, string>();
+  let visitedDirectories = 0;
+
+  while (pending.length > 0 && visitedDirectories < MAX_VISITED_DIRECTORIES) {
+    const directory = pending.pop();
+    if (directory === undefined) break;
+    visitedDirectories++;
+
+    let entries: Dirent[];
+    try {
+      entries = readdirSync(directory, { withFileTypes: true }).sort((left, right) =>
+        left.name.localeCompare(right.name),
+      );
+    } catch {
+      continue;
+    }
+
+    for (const entry of entries) {
+      if (entry.isDirectory() && !SKIP_DIRECTORIES.has(entry.name)) {
+        pending.push(join(directory, entry.name));
+      } else if (entry.isFile() && (entry.name === 'Gemfile' || entry.name.endsWith('.gemspec'))) {
+        const manifests = manifestsByDirectory.get(directory) ?? [];
+        manifests.push(join(directory, entry.name));
+        manifestsByDirectory.set(directory, manifests);
+      } else if (entry.isFile() && entry.name === 'Gemfile.lock') {
+        lockfilesByDirectory.set(directory, join(directory, entry.name));
+      }
+    }
+  }
+
+  if (manifestsByDirectory.size === 0) return null;
+
+  const mutableScopes = new Map<string, MutableRubyResolutionScope>();
+  for (const [directory, manifests] of [...manifestsByDirectory].sort(([left], [right]) =>
+    left.localeCompare(right),
+  )) {
+    const directoryRelative = repoRelativePath(repoPath, directory);
+    if (directoryRelative === null) continue;
+    const scope = createMutableScope();
+    mutableScopes.set(directoryRelative, scope);
+
+    for (const manifest of manifests.sort()) {
+      try {
+        const contents = readFileSync(manifest, 'utf8');
+        if (manifest.endsWith('.gemspec')) {
+          addGemspecDependencies(contents, directory, repoPath, scope);
+        } else {
+          addGemfileDependencies(contents, directory, repoPath, scope);
+        }
+      } catch {
+        // A partially readable scope remains fail-open for unknown gems.
+      }
+    }
+
+    const lockfile = lockfilesByDirectory.get(directory);
+    if (lockfile === undefined) continue;
+    try {
+      addLockedDependencies(readFileSync(lockfile, 'utf8'), directory, repoPath, scope);
+    } catch {
+      // Direct declarations still provide bounded evidence when the lock is unreadable.
+    }
+  }
+
+  const scopesByDirectory = new Map<string, RubyResolutionScope>();
+  for (const [directory, scope] of mutableScopes) {
+    scopesByDirectory.set(directory, freezeScope(scope));
+  }
+  return { scopesByDirectory };
+}
diff --git a/gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts b/gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts
index 160bec94e..02035bc4f 100644
--- a/gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts
+++ b/gitnexus/src/core/ingestion/languages/ruby/scope-resolver.ts
@@ -10,6 +10,7 @@ import type { GraphNodeLookup } from '../../scope-resolution/graph-bridge/node-l
 import type { KnowledgeGraph } from '../../../graph/types.js';
 import { generateId } from '../../../../lib/utils.js';
 import { decodeMarker } from '../../utils/heritage-marker.js';
+import { loadRubyResolutionConfig } from './resolution-config.js';
 
 /**
  * #1991: resolve a BARE mixin reference (`include Loggable`) to a nested module by
@@ -268,6 +269,8 @@ export const rubyScopeResolver: ScopeResolver = {
   resolveImportTarget: (targetRaw, fromFile, allFilePaths, resolutionConfig) =>
     resolveRubyImportTarget(targetRaw, fromFile, allFilePaths, resolutionConfig),
 
+  loadResolutionConfig: (repoPath) => loadRubyResolutionConfig(repoPath),
+
   expandsWildcardTo: (targetModuleScope, parsedFiles) =>
     expandRubyWildcardNames(targetModuleScope, parsedFiles),
 
diff --git a/gitnexus/test/integration/ruby-pipeline-benchmark.test.ts b/gitnexus/test/integration/ruby-pipeline-benchmark.test.ts
index e43dc37d7..350e34f9f 100644
--- a/gitnexus/test/integration/ruby-pipeline-benchmark.test.ts
+++ b/gitnexus/test/integration/ruby-pipeline-benchmark.test.ts
@@ -3,8 +3,9 @@
  *
  * Generates synthetic Ruby codebases at increasing scales and measures
  * wall-clock time and peak heap through the full pipeline — parsing,
- * scope extraction, heritage (include/extend/prepend), MRO construction,
- * and call resolution via the registry-primary scope-resolution path.
+ * scope extraction, manifest-scoped external require resolution, heritage
+ * (include/extend/prepend), MRO construction, and call resolution via the
+ * registry-primary scope-resolution path.
  *
  * Run: GITNEXUS_BENCH=1 npx vitest run test/integration/ruby-pipeline-benchmark.test.ts
  *
@@ -38,6 +39,10 @@ function generateRubyFixture(
   modulesPerLevel: number,
 ): { dir: string; classCount: number; moduleCount: number; mixinModuleCount: number } {
   const dir = fs.mkdtempSync(path.join(os.tmpdir(), `ruby-bench-${fileCount}-`));
+  fs.writeFileSync(
+    path.join(dir, 'Gemfile'),
+    ["source 'https://rubygems.org'", "gem 'rails'"].join('\n'),
+  );
 
   // Three families of mixins: one for include, one for extend, one for prepend.
   // Each family has modulesPerLevel² modules so the MRO partitioning logic is
@@ -120,6 +125,7 @@ function generateRubyFixture(
     const crossClass = `Model${crossIdx}`;
 
     const requireLines = [
+      `require 'rails/generators'`,
       `require_relative '../concerns/${incMixin.toLowerCase()}'`,
       `require_relative '../concerns/${incMixin2.toLowerCase()}'`,
       `require_relative '../concerns/${extMixin.toLowerCase()}'`,
diff --git a/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts b/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
index dca6f187d..7ba1e5efa 100644
--- a/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
+++ b/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
@@ -53,6 +53,18 @@ import {
 const PHP_COMPOSER: ComposerConfig = { psr4: new Map([['App', 'app']]) };
 /** The value `loadGoModulePath` produces for a repo with a `go.mod`. */
 const GO_MODULE = { modulePath: 'example.com/mod' };
+/** The root dependency scope `loadRubyResolutionConfig` would have produced. */
+const RUBY_GEMS = {
+  scopesByDirectory: new Map([
+    [
+      '',
+      {
+        externalRequirePrefixes: new Set(['rails']),
+        localLoadRootsByPrefix: new Map(),
+      },
+    ],
+  ]),
+};
 /** What `scanCSharpProject` would report for the C# workspace below — the
  *  in-repo namespace evidence the #1881 suffix-fallback gate reads. */
 const CSHARP_NAMESPACES = {
@@ -272,7 +284,7 @@ const CASES: ReadonlyMap<SupportedLanguages, ConformanceCase> = new Map([
     {
       files: ['lib/app/models/user.rb', 'lib/generators.rb', 'lib/main.rb'],
       fromFile: 'lib/main.rb',
-      resolutionConfig: undefined,
+      resolutionConfig: RUBY_GEMS,
       external: 'rails/generators',
       decoy: 'lib/generators.rb',
       reachesDecoy: 'generators',
@@ -389,7 +401,6 @@ const CASES: ReadonlyMap<SupportedLanguages, ConformanceCase> = new Map([
  * TypeScript one, then deleting its line here.
  */
 const KNOWN_GAPS: ReadonlyMap<SupportedLanguages, string> = new Map<SupportedLanguages, string>([
-  [SupportedLanguages.Ruby, '`rails/generators` -> `lib/generators.rb`'],
   [SupportedLanguages.Dart, '`package:http/http.dart` -> `lib/http.dart`'],
   [SupportedLanguages.Swift, '`Foundation` -> `Sources/Foundation/Thing.swift`'],
   [SupportedLanguages.C, '`stdio.h` -> `src/stdio.h`'],
diff --git a/gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts b/gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts
new file mode 100644
index 000000000..b61b8b393
--- /dev/null
+++ b/gitnexus/test/unit/scope-resolution/ruby/ruby-resolution-config.test.ts
@@ -0,0 +1,193 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+
+import { resolveRubyImportTarget } from '../../../../src/core/ingestion/languages/ruby/import-target.js';
+import { loadRubyResolutionConfig } from '../../../../src/core/ingestion/languages/ruby/resolution-config.js';
+import { rubyScopeResolver } from '../../../../src/core/ingestion/languages/ruby/scope-resolver.js';
+
+const temporaryRepos: string[] = [];
+
+afterEach(() => {
+  for (const repo of temporaryRepos.splice(0)) rmSync(repo, { recursive: true, force: true });
+});
+
+function makeRepo(): string {
+  const repo = mkdtempSync(join(tmpdir(), 'gitnexus-ruby-dependencies-'));
+  temporaryRepos.push(repo);
+  return repo;
+}
+
+describe('Ruby dependency resolution config (#2966)', () => {
+  it('keeps manifest directories separate and records conventional require prefixes', () => {
+    const repo = makeRepo();
+    writeFileSync(
+      join(repo, 'Gemfile'),
+      ["source 'https://rubygems.org'", "gem 'rails'", 'gem("pg")', "# gem 'commented'"].join('\n'),
+    );
+    writeFileSync(
+      join(repo, 'Gemfile.lock'),
+      [
+        'GEM',
+        '  specs:',
+        '    actionpack (8.0.0)',
+        '      rack (~> 3.0)',
+        '    rack (3.0.0)',
+        'DEPENDENCIES',
+      ].join('\n'),
+    );
+    mkdirSync(join(repo, 'packages', 'widget'), { recursive: true });
+    writeFileSync(
+      join(repo, 'packages', 'widget', 'widget.gemspec'),
+      [
+        "spec.name = 'widget'",
+        "spec.require_paths = ['src']",
+        "spec.add_dependency 'dry-types'",
+        'spec.add_development_dependency("rspec")',
+      ].join('\n'),
+    );
+
+    const config = loadRubyResolutionConfig(repo);
+    const root = config?.scopesByDirectory.get('');
+    const widget = config?.scopesByDirectory.get('packages/widget');
+
+    expect(root?.externalRequirePrefixes).toEqual(new Set(['rails', 'pg', 'actionpack', 'rack']));
+    expect(widget?.externalRequirePrefixes).toEqual(new Set(['dry-types', 'dry/types', 'rspec']));
+    expect(widget?.localLoadRootsByPrefix.get('widget')).toEqual(['packages/widget/src']);
+  });
+
+  it('fails open when a lockfile exists without a Gemfile or gemspec', () => {
+    const repo = makeRepo();
+    writeFileSync(join(repo, 'Gemfile.lock'), ['GEM', '  specs:', '    rails (8.0.0)'].join('\n'));
+
+    expect(loadRubyResolutionConfig(repo)).toBeNull();
+  });
+
+  it('gates external gems without changing local bare, relative, or no-config resolution', async () => {
+    const repo = makeRepo();
+    writeFileSync(join(repo, 'Gemfile'), "gem 'rails'\n");
+    const files = new Set(['lib/app/models/user.rb', 'lib/generators.rb', 'lib/main.rb']);
+    const config = await rubyScopeResolver.loadResolutionConfig?.(repo);
+
+    expect(
+      rubyScopeResolver.resolveImportTarget('rails/generators', 'lib/main.rb', files, config),
+    ).toBeNull();
+    expect(
+      rubyScopeResolver.resolveImportTarget('app/models/user', 'lib/main.rb', files, config),
+    ).toBe('lib/app/models/user.rb');
+    expect(resolveRubyImportTarget('generators', 'lib/main.rb', files, config)).toBe(
+      'lib/generators.rb',
+    );
+    expect(resolveRubyImportTarget('./generators', 'lib/main.rb', files, config)).toBe(
+      'lib/generators.rb',
+    );
+    expect(resolveRubyImportTarget('rails/generators', 'lib/main.rb', files)).toBe(
+      'lib/generators.rb',
+    );
+  });
+
+  it('gates the conventional slash prefix of a hyphenated gem', () => {
+    const repo = makeRepo();
+    writeFileSync(join(repo, 'Gemfile'), "gem 'dry-types'\n");
+    const files = new Set(['lib/types.rb', 'lib/main.rb']);
+    const config = loadRubyResolutionConfig(repo);
+
+    expect(resolveRubyImportTarget('dry/types', 'lib/main.rb', files, config)).toBeNull();
+    expect(resolveRubyImportTarget('dry-types', 'lib/main.rb', files, config)).toBeNull();
+    expect(resolveRubyImportTarget('types', 'lib/main.rb', files, config)).toBe('lib/types.rb');
+  });
+
+  it('resolves a Gemfile path gem through its local load root', () => {
+    const repo = makeRepo();
+    mkdirSync(join(repo, 'engines', 'my_engine'), { recursive: true });
+    writeFileSync(join(repo, 'Gemfile'), "gem 'my_engine', path: 'engines/my_engine'\n");
+    writeFileSync(
+      join(repo, 'engines', 'my_engine', 'my_engine.gemspec'),
+      ["spec.name = 'my_engine'", "spec.require_paths = ['lib']"].join('\n'),
+    );
+    const files = new Set([
+      'engines/my_engine/lib/my_engine.rb',
+      'lib/my_engine.rb',
+      'lib/main.rb',
+    ]);
+    const config = loadRubyResolutionConfig(repo);
+
+    expect(resolveRubyImportTarget('my_engine', 'lib/main.rb', files, config)).toBe(
+      'engines/my_engine/lib/my_engine.rb',
+    );
+    expect(config?.scopesByDirectory.get('')?.externalRequirePrefixes).not.toContain('my_engine');
+  });
+
+  it('recognizes the Gemfile hashrocket path syntax as local', () => {
+    const repo = makeRepo();
+    mkdirSync(join(repo, 'engines', 'my_engine'), { recursive: true });
+    writeFileSync(join(repo, 'Gemfile'), "gem 'my_engine', :path => 'engines/my_engine'\n");
+    writeFileSync(
+      join(repo, 'engines', 'my_engine', 'my_engine.gemspec'),
+      "spec.name = 'my_engine'\n",
+    );
+    const files = new Set(['engines/my_engine/lib/my_engine.rb', 'lib/main.rb']);
+    const config = loadRubyResolutionConfig(repo);
+
+    expect(resolveRubyImportTarget('my_engine', 'lib/main.rb', files, config)).toBe(
+      'engines/my_engine/lib/my_engine.rb',
+    );
+    expect(config?.scopesByDirectory.get('')?.externalRequirePrefixes).not.toContain('my_engine');
+  });
+
+  it('keeps lockfile PATH specs local while gating GEM specs', () => {
+    const repo = makeRepo();
+    writeFileSync(
+      join(repo, 'mygem.gemspec'),
+      ["spec.name = 'mygem'", "spec.require_paths = ['lib']"].join('\n'),
+    );
+    writeFileSync(
+      join(repo, 'Gemfile.lock'),
+      [
+        'PATH',
+        '  remote: .',
+        '  specs:',
+        '    mygem (1.0.0)',
+        '',
+        'GEM',
+        '  remote: https://rubygems.org/',
+        '  specs:',
+        '    rails (8.0.0)',
+        '',
+        'DEPENDENCIES',
+        '  mygem!',
+        '  rails',
+      ].join('\n'),
+    );
+    const files = new Set(['lib/mygem.rb', 'lib/generators.rb', 'lib/main.rb']);
+    const config = loadRubyResolutionConfig(repo);
+    const root = config?.scopesByDirectory.get('');
+
+    expect(resolveRubyImportTarget('mygem', 'lib/main.rb', files, config)).toBe('lib/mygem.rb');
+    expect(resolveRubyImportTarget('rails/generators', 'lib/main.rb', files, config)).toBeNull();
+    expect(root?.externalRequirePrefixes).toContain('rails');
+    expect(root?.externalRequirePrefixes).not.toContain('mygem');
+  });
+
+  it('uses the nearest manifest instead of a repository-wide monorepo union', () => {
+    const repo = makeRepo();
+    mkdirSync(join(repo, 'packages', 'a'), { recursive: true });
+    mkdirSync(join(repo, 'packages', 'b'), { recursive: true });
+    writeFileSync(join(repo, 'packages', 'a', 'Gemfile'), "gem 'rails'\n");
+    writeFileSync(join(repo, 'packages', 'b', 'Gemfile'), "source 'https://rubygems.org'\n");
+    const files = new Set([
+      'packages/a/lib/main.rb',
+      'packages/b/lib/main.rb',
+      'packages/b/lib/rails/generators.rb',
+    ]);
+    const config = loadRubyResolutionConfig(repo);
+
+    expect(
+      resolveRubyImportTarget('rails/generators', 'packages/a/lib/main.rb', files, config),
+    ).toBeNull();
+    expect(
+      resolveRubyImportTarget('rails/generators', 'packages/b/lib/main.rb', files, config),
+    ).toBe('packages/b/lib/rails/generators.rb');
+  });
+});