fix(mail-index): local AI retrieval returned 0 hits for real questions — AND-every-token FTS matching killed on stop words

Found by a new real Electron e2e test built specifically to prove the
`local` AI class genuinely works end-to-end in the packaged desktop shell:
a real local Ollama model answering a real question, grounded in the real
encrypted SQLite/FTS5 mail index — not a browser tab, not a mock.

First run surfaced a genuine bug: toFtsMatchQuery() AND-joins every token,
which is right for a deliberate search-box query but wrong for the natural-
language questions the AI retrieval surface (/api/offline/search — see its
own module header, "THE RETRIEVAL SURFACE") actually receives. "When is
check-in for the Villa sul Lago booking, and what time?" shares almost none
of its own function words with the email that answers it, so ANDing every
token — including "when"/"is"/"for"/"the"/"and"/"what" — returned 0 hits
against an index that correctly returns the right email for "Villa sul Lago
check-in".

Fix: new toFtsMatchQueryAny() (lib/mail-index/store.ts) — drops a small,
well-known English stop-word list, OR-joins what's left, and lets the
existing bm25 ranking pick the winner among partial matches. Deliberately a
NEW function, not a change to toFtsMatchQuery itself: that one's own tests
rely on "AND"/"OR"/"NOT" surviving verbatim as literal search terms
(FTS5-keyword-injection safety) — a different guarantee than this one's job
of turning a question into a good search. search() gains a `mode: 'and' |
'any'` option (default 'and', so every existing caller is unaffected); the
offline-search route passes 'any', since its one real caller is exactly
this AI-question shape.

Also added, to make the e2e test possible at all: electron/main.ts's
VNCMAIL_TEST_FIXED_PORT — a narrow, off-by-default escape hatch so
DEV_MOCK_JMAP's JMAP_SERVER_URL can point at this same standalone server's
own /api/dev-jmap. Needed because the encrypted index's key channel
(fd-3/safeStorage) only gets wired up in startStandaloneServer()'s own
random-port launch path, never when ELECTRON_LOAD_URL bypasses it for a
plain `next dev` target — so this was the only way to exercise the real
index without a full Stalwart+SMTP Docker fixture.

Verified live in the real packaged Electron shell, not just unit tests:
real dev-mode login, real multi-round /api/offline/sync + /api/offline/reindex
(39 mail/35 calendar/23 contacts indexed), real local-discovery banner
(11 real Ollama models on this machine), real "Connect", a real question
through the real Settings UI, a real direct renderer->Ollama /api/chat call
(confirmed via network log, never proxied through this app's backend), and
the model's own answer citing the exact right fact: "Saturday 28 March at
15:00" — a fact that exists nowhere except in the one indexed email.

4 new unit tests for toFtsMatchQueryAny. Full gate: tsc clean, eslint
clean, 2502/2502 tests passing, build clean, e2e/electron-ai-local-index.spec.ts
passing against the real standalone server + real Electron + real Ollama.

lib/mail-index/__tests__/store.test.ts

@@ -6,7 +6,7 @@ import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 import { isSqlcipherAvailable } from '../binding';
 import type { SqlcipherConstructor, SqlcipherDatabase, SqlcipherStatement } from '../binding';
 import { accountFileToken, getStoreDir, indexDbPath, STORE_DIR_ENV } from '../paths';
-import { MailIndex, openKeyed, toFtsMatchQuery, type IndexDoc } from '../store';
+import { MailIndex, openKeyed, toFtsMatchQuery, toFtsMatchQueryAny, type IndexDoc } from '../store';
 
 describe('toFtsMatchQuery', () => {
   it('quotes every token so FTS5 operators in user input cannot break the query', () => {
@@ -48,6 +48,62 @@ describe('toFtsMatchQuery', () => {
   });
 });
 
+describe('toFtsMatchQueryAny', () => {
+  it('drops English function words and OR-joins what is left - the confirmed-live failure this fixes', () => {
+    // AND-every-token (toFtsMatchQuery) returns 0 hits for this exact
+    // question against a document that only contains "Villa sul Lago" and
+    // "check-in" - see app/api/offline/search/route.ts's comment and the
+    // e2e electron-ai-local-index.spec.ts run that first caught this.
+    const result = toFtsMatchQueryAny('When is check-in for the Villa sul Lago booking, and what time?');
+    expect(result).not.toBeNull();
+    expect(result).not.toContain(' AND ');
+    expect(result).toContain('"check-in"');
+    expect(result).toContain('"Villa"');
+    expect(result).toContain('"sul"');
+    expect(result).toContain('"Lago"');
+    expect(result).toContain('"booking"');
+    // "time" is the last surviving content word, so it gets the
+    // prefix-match star - not "Lago", which is merely the last one this
+    // test happens to name first.
+    expect(result).toContain('"time"*');
+    // Pure stop words, correctly dropped rather than OR-joined as noise that
+    // would otherwise match almost every document in a mailbox.
+    expect(result).not.toMatch(/"When"|"is"|"for"|"the"|"and"|"what"/i);
+  });
+
+  it('falls back to the unfiltered text when every word is a stop word, rather than searching for nothing', () => {
+    // "What is this" is 100% stop words - dropping all of them would leave
+    // zero tokens (a null match, meaning "return everything" is wrong for a
+    // question shaped like this); falling back to the original text at
+    // least keeps a real, if weak, query.
+    const result = toFtsMatchQueryAny('What is this');
+    expect(result).not.toBeNull();
+  });
+
+  it('still safely quotes FTS5 syntax characters even after stop-word filtering removes the surrounding noise', () => {
+    // "OR"/"NEAR" themselves are common enough as English words that this
+    // builder's stop-word list intentionally drops bare "or" (unlike
+    // toFtsMatchQuery, which preserves it verbatim - see that test's own
+    // comment on why: different concern, different guarantee). The safety
+    // property that DOES still apply here is the one that matters for a
+    // 500: whatever tokens survive filtering are always quoted before
+    // reaching FTS5, so a stray `"`/`*`/`(` in real question text can never
+    // raise a syntax error.
+    const result = toFtsMatchQueryAny('a" NEAR(bar) baz*');
+    expect(result).not.toBeNull();
+    expect(result).toContain('"NEAR"');
+    expect(result).toContain('"bar"');
+    expect(result).toContain('"baz"');
+    expect(result).not.toMatch(/fts5|syntax/i);
+  });
+
+  it('returns null for input with no usable tokens', () => {
+    expect(toFtsMatchQueryAny('')).toBeNull();
+    expect(toFtsMatchQueryAny('***')).toBeNull();
+    expect(toFtsMatchQueryAny(undefined as unknown as string)).toBeNull();
+  });
+});
+
 describe('paths', () => {
   const original = process.env[STORE_DIR_ENV];
   afterEach(() => {