Fix monorepo target-selection edge cases from #213 review (#282)

Two Cursor Bugbot Medium findings on the merged monorepo context PR:

- Excluded packages still listed: discoverTargetCandidates added every glob
  match but never applied negated workspace patterns, so an excluded package
  (e.g. "!packages/internal") showed up as a selectable target even though
  resolveWorkspaceProjectRoot sends it back to the repo root. Now filtered
  with the same isExcludedByWorkspacePattern check the resolver uses.
- Empty app list blocks root: resolveTargetSelection returned
  TARGET_SELECTION_REQUIRED whenever projectRoot === repoRoot, even with zero
  discoverable child apps (e.g. `workspaces: ["."]`), leaving an unanswerable
  prompt. It now returns null (use the repo root as the project) when there
  are no candidates.

Also documents two Greptile P2 clarity notes (the four contextSourceStatus
labels incl. the dual meaning of 'fallback', and the deliberate
isMonorepoRoot-before-hasGitBoundary ordering in findMonorepoRoot).

Adds regression tests for both behaviors.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skill/scripts/context.mjs

@@ -135,11 +135,17 @@ export function resolveTargetSelection(cwd = process.cwd(), options = {}) {
   ) {
     return null;
   }
+  const targetCandidates = discoverTargetCandidates(project.repoRoot);
+  // No discoverable child apps (e.g. `workspaces: ["."]`, a root-only workspace,
+  // or a marker file with no apps/packages children): there is nothing to choose,
+  // so treat the repo root as the active project rather than blocking on an empty
+  // selection prompt that the user cannot answer.
+  if (targetCandidates.length === 0) return null;
   return {
     targetPath: null,
     projectRoot: project.projectRoot,
     repoRoot: project.repoRoot,
-    targetCandidates: discoverTargetCandidates(project.repoRoot),
+    targetCandidates,
   };
 }
 
@@ -211,6 +217,12 @@ function findMonorepoRoot(startDir) {
   const homeDir = path.resolve(os.homedir());
   while (true) {
     if (dir === homeDir) return null;
+    // isMonorepoRoot is checked before hasGitBoundary on purpose: a workspace
+    // root that also carries its own .git is still recognized. The trade-off is
+    // deliberate — a directory with a monorepo *marker* but no workspace patterns
+    // and no apps/packages children is not a monorepo root, so its .git stops
+    // traversal and a further-up root is not searched. The nested .git is treated
+    // as an independent project boundary, which is the intended isolation.
     if (isMonorepoRoot(dir)) return dir;
     if (hasGitBoundary(dir)) return null;
     const parent = path.dirname(dir);
@@ -245,7 +257,8 @@ function hasFallbackWorkspaceChildren(dir) {
 
 function discoverTargetCandidates(repoRoot) {
   const roots = new Map();
-  for (const pattern of readWorkspacePatterns(repoRoot)) {
+  const patterns = readWorkspacePatterns(repoRoot);
+  for (const pattern of patterns) {
     for (const root of discoverRootsForPattern(repoRoot, pattern)) {
       roots.set(path.relative(repoRoot, root).split(path.sep).join('/'), root);
     }
@@ -268,6 +281,10 @@ function discoverTargetCandidates(repoRoot) {
   }
   return [...roots.entries()]
     .filter(([rel]) => rel && !rel.startsWith('..'))
+    // Honor negated workspace patterns (e.g. "!packages/internal"). resolveWorkspaceProjectRoot
+    // sends an excluded package back to the repo root, so an excluded folder must not appear as a
+    // selectable target — choosing it would silently resolve to the root instead.
+    .filter(([rel]) => !isExcludedByWorkspacePattern(rel.split('/').filter(Boolean), patterns))
     .sort(([a], [b]) => a.localeCompare(b))
     .map(([rel, root]) => {
       const targetExample = findTargetExample(repoRoot, root);
@@ -290,6 +307,12 @@ function resolveCandidateContextSummary(repoRoot, projectRoot, targetPath) {
   };
 }
 
+// Selection candidates surface one of four statuses: 'child' (a canonical
+// PRODUCT.md/DESIGN.md directly in the app root), 'inherited' (resolved from the
+// repo root in a monorepo), 'missing' (no file found), and 'fallback'. 'fallback'
+// intentionally covers two non-canonical locations: a file inside the project
+// root but in a subdirectory (FALLBACK_DIRS, e.g. `.agents/context/`), and a file
+// outside both the project and repo roots (IMPECCABLE_CONTEXT_DIR override).
 function contextSourceStatus(filePath, repoRoot, projectRoot) {
   if (!filePath) return 'missing';
   const absPath = path.resolve(filePath);