Add daily activity digest — Phase B (v0.1.0:77)

Sends a once-a-day internal email to all active admins summarizing each team
member's email activity per investor, plus a team-wide by-investor view
(inbound + outbound, deduped). Narratives are generated on the LOCAL Spark
model, never Claude — the digest is intentionally un-anonymized, so substance
stays on Ten31 infra. This is an internal ops email, exempt from the
'agents draft, humans send' rule (which governs outward LP contact).

- backend/digest_builder.py: per-user + per-investor activity queries
  (soft-delete filtered), per-user Spark narrative with a deterministic
  fallback, two-section plain-text body, and the DB-backed policy resolver.
- backend/email_integration/digest_scheduler.py: always-on daily thread that
  re-reads the policy each cycle and sends once/day; window cursor in
  app_settings so a missed day rolls forward.
- server.py: POST /api/admin/digest/send-now and GET/PATCH
  /api/admin/digest/policy; scheduler wired into main().
- Control lives in Settings -> Admin (enable toggle + send-time dropdown),
  not StartOS actions; env vars only seed the first-boot default.
- Tests: backend/test_digest_builder.py.

docs/guides/email.md

@@ -40,8 +40,45 @@ different category. **Never extend this path to send to LPs/prospects.**
   independent of any StartOS system-wide SMTP.
 - The admin **`POST /api/admin/digest/test-email`** restricts recipients to the active-admin
   set (not an open relay), and logs send failures rather than echoing them (an auth error can
-  carry a token/credential). Digest *content* generation (Phase B) runs on **Spark, never
-  Claude** — the digest is deliberately un-anonymized.
+  carry a token/credential).
+
+### Phase B — the daily digest itself (built)
+
+- **Content builder: `backend/digest_builder.py`** (top-level). `build_digest(conn, since_iso,
+  until_iso, chat_fn=None)` returns `{subject, body, has_activity, user_count, email_count,
+  investor_count}` and composes **two sections**:
+  - **By team member** — `collect_user_activity`: per registered user, both directions
+    (per-mailbox `eam.is_sent`), with **one Spark narrative paragraph** per user
+    (`ingest/llm.py` → Spark Control `/v1/chat/completions`), **never Claude** (the digest is
+    deliberately un-anonymized — real LP names + substance stay local). Deterministic
+    count-only fallback if Spark is unreachable (always-send must not fail).
+  - **By investor** — `collect_investor_activity`: re-pivots the same window across the whole
+    team, **deduped per email** (a reply to several teammates counts once), direction decided
+    at the **email level** (outbound if `from_email` is one of our mailboxes, else inbound).
+    Structured list, no extra Spark calls.
+  - Soft-delete filters: `email_account_messages.deleted_at IS NULL` + `users.is_active = 1`,
+    and the org/contact name joins drop soft-deleted rows (falling back to the matched address).
+- **Control is DB-backed, set from the admin panel** — `digest_builder.load_digest_policy(conn)`
+  reads `app_settings.digest_policy` = `{enabled, send_hour}`. Precedence: **DB row wins**
+  (the Settings → Admin toggle + send-time dropdown), else `CRM_DIGEST_ENABLED`/
+  `CRM_DIGEST_SEND_HOUR` seed a first-boot default, else `{false, 18}`. `GET`/`PATCH
+  /api/admin/digest/policy` (admin-only) read/write it. **Not a StartOS action** — it's an
+  operational toggle, so it lives in-app where it's discoverable and takes effect live.
+- **Scheduler: `backend/email_integration/digest_scheduler.py`** (co-located with the sync
+  scheduler). One daemon thread, **always started**; each cycle (60s) re-reads the DB policy
+  and sends once per local day at/after `send_hour` **only when `enabled`** — so toggling in
+  the panel takes effect with no restart. Content window = (last send, now]; cursor
+  (`digest_last_sent_at`) + once-per-day guard (`digest_last_sent_date`) live in `app_settings`,
+  so a missed day rolls into the next digest. Recipients = all active admins.
+- **On-demand: `POST /api/admin/digest/send-now`** (admin-only) → `maybe_send_digest(force=True)`
+  builds the real last-24h digest and sends to the admin set regardless of the policy and
+  **without** touching the daily cursor (a preview never suppresses the scheduled send).
+  Surfaced as a "Send Digest Now" button in Settings → Admin, beside "Send Test Digest Email".
+- **Decisions (locked):** 6 PM default send · always-send (empty days get a "no activity"
+  note) · per-user narrative + by-investor structured section · enable/time controlled in the
+  admin panel. Tests: `backend/test_digest_builder.py` (per-user + per-investor queries,
+  soft-delete, inbound dedup, two-section compose, fallback, policy resolver, scheduler guards
+  — stubbed LLM + transport).
 
 ## Known gap