fix(learnings): use token-OR matching in gstack-learnings-search --query

Split the query on whitespace into tokens; a learning matches if ANY
token appears as a substring in ANY of key/insight/files. Previously
the whole query was a single substring, so multi-word queries like
"debug investigation" only matched learnings whose insight contained
that exact contiguous phrase, which is usually nothing.

Whitespace-only query falls through to no-query (matches today's no-flag
behavior). Single-word queries behave exactly as before.

Adds test/gstack-learnings-search.test.ts: 3 assertions covering
multi-token, single-token, and no-query backwards compat.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

test/gstack-learnings-search.test.ts

@@ -0,0 +1,60 @@
+import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+import { execFileSync } from 'child_process';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const BIN = path.join(ROOT, 'bin', 'gstack-learnings-search');
+
+const tmpHome = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-search-test-'));
+const tmpCwd = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-search-cwd-'));
+// gstack-slug derives slug from git remote (none here) → falls back to basename of cwd.
+const slug = path.basename(tmpCwd).replace(/[^a-zA-Z0-9._-]/g, '');
+const projDir = path.join(tmpHome, 'projects', slug);
+
+function run(args: string[]): string {
+  return execFileSync(BIN, args, {
+    env: { ...process.env, GSTACK_HOME: tmpHome },
+    cwd: tmpCwd,
+    encoding: 'utf-8',
+  });
+}
+
+beforeAll(() => {
+  fs.mkdirSync(projDir, { recursive: true });
+  const entries = [
+    { ts: '2026-05-01T00:00:00Z', skill: 'test', type: 'pattern', key: 'foo-pattern', insight: 'A foo-related insight', confidence: 8, source: 'observed', files: [] },
+    { ts: '2026-05-02T00:00:00Z', skill: 'test', type: 'pitfall', key: 'bar-pitfall', insight: 'A bar-related insight', confidence: 8, source: 'observed', files: [] },
+    { ts: '2026-05-03T00:00:00Z', skill: 'test', type: 'pattern', key: 'baz-pattern', insight: 'A baz-related insight', confidence: 8, source: 'observed', files: [] },
+  ];
+  fs.writeFileSync(path.join(projDir, 'learnings.jsonl'), entries.map(e => JSON.stringify(e)).join('\n') + '\n');
+});
+
+afterAll(() => {
+  fs.rmSync(tmpHome, { recursive: true, force: true });
+  fs.rmSync(tmpCwd, { recursive: true, force: true });
+});
+
+describe('gstack-learnings-search token-OR query semantics', () => {
+  test('multi-token query returns entries matching ANY token', () => {
+    const out = run(['--query', 'foo bar']);
+    expect(out).toContain('foo-pattern');
+    expect(out).toContain('bar-pitfall');
+    expect(out).not.toContain('baz-pattern');
+  });
+
+  test('single-token query returns only entries matching that token', () => {
+    const out = run(['--query', 'foo']);
+    expect(out).toContain('foo-pattern');
+    expect(out).not.toContain('bar-pitfall');
+    expect(out).not.toContain('baz-pattern');
+  });
+
+  test('no --query flag returns all entries (backwards-compat)', () => {
+    const out = run(['--limit', '10']);
+    expect(out).toContain('foo-pattern');
+    expect(out).toContain('bar-pitfall');
+    expect(out).toContain('baz-pattern');
+  });
+});