[AI] Add file.folder support for Obsidian-compatible filtering

Author: intellectronica

AGENTS.md

@@ -106,6 +106,7 @@ When asked to create commits in this repository:
 ## Compatibility Notes
 
 - `this` context is deterministic CLI/library metadata (`filePath`, `name`) rather than Obsidian embed-location semantics.
+- `file.folder` is supported and resolves to the vault-relative parent directory (`""` for root-level notes).
 - `file.backlinks` is not implemented in v0 (reserved for future opt-in indexing pass).
 - CSV serialisation uses the selected/declared column list as the canonical header order.
 
@@ -120,3 +121,8 @@ When asked to create commits in this repository:
   - Context: Query portability requires predictable failures on unknown symbols.
   - Decision: Enable strict mode by default in API and CLI.
   - Consequence: Users must opt out (`--no-strict`) for permissive behaviour.
+
+- 2026-02-18 - `file.folder` compatibility support
+  - Context: Real-world Base filters often rely on `file.folder` to scope notes by directory.
+  - Decision: Add `file.folder` to indexed file metadata as the vault-relative parent path.
+  - Consequence: Queries depending on folder-based filtering now evaluate correctly without strict-mode property errors.

src/core/vault-index.ts

@@ -40,6 +40,16 @@ function isMarkdown(path: string): boolean {
   return path.toLowerCase().endsWith(".md");
 }
 
+function folderFromPath(path: string): string {
+  const slashIndex = path.lastIndexOf("/");
+
+  if (slashIndex === -1) {
+    return "";
+  }
+
+  return path.slice(0, slashIndex);
+}
+
 function sortEntries(entries: RuntimeFileEntry[]): RuntimeFileEntry[] {
   return [...entries].sort((left, right) => left.path.localeCompare(right.path));
 }
@@ -73,6 +83,7 @@ export async function indexVault(options: VaultIndexOptions): Promise<VaultIndex
       file: {
         name: options.adapter.basename(relativePath),
         path: relativePath,
+        folder: folderFromPath(relativePath),
         ext: options.adapter.extname(relativePath),
         size: entry.stat.size,
         ctime: entry.stat.ctime,

src/types.ts

@@ -71,6 +71,7 @@ export interface QueryRow {
 export interface FileRecord {
   name: string;
   path: string;
+  folder: string;
   ext: string;
   size: number;
   ctime: Date;

tests/query-engine.test.ts

@@ -105,4 +105,35 @@ views:
     expect(result.rows[1].projected.title).toBe("Alpha");
     expect(result.groups?.length).toBe(1);
   });
+
+  test("supports file.folder in filters and projections", async () => {
+    const spec = parseBaseYaml(`
+filters: file.folder == "nested"
+views:
+  - type: table
+    name: folders
+    properties:
+      - file.name
+      - file.folder
+`.trim());
+
+    const compiled = compileQuery(spec);
+    const indexed = await indexVault({
+      rootDir: vaultDir,
+      include: ["**/*.md"],
+      exclude: [],
+      adapter: nodeAdapter,
+    });
+
+    const result = executeCompiledQuery({
+      compiled,
+      documents: indexed.documents,
+      view: "folders",
+    });
+
+    expect(result.rows).toHaveLength(1);
+    expect(result.rows[0].projected["file.name"]).toBe("gamma.md");
+    expect(result.rows[0].projected["file.folder"]).toBe("nested");
+    expect(result.diagnostics.errors).toHaveLength(0);
+  });
 });

tests/serialize.test.ts

@@ -10,6 +10,7 @@ const fixtureResult: QueryResult = {
       file: {
         name: "alpha.md",
         path: "alpha.md",
+        folder: "",
         ext: ".md",
         size: 10,
         ctime: new Date("2024-01-01"),