docs(automation): document the time-relative trigger (#1874)

Follow-up to the merged #1874 feature. Adds the declarative time-relative
trigger to the two hand-written surfaces authors consult (the auto-generated
reference and the trigger-schedule README already landed with the feature):

- skills/objectstack-automation/SKILL.md — a "Time-relative triggers" section
  under Triggers, framed as the declarative replacement for the fragile
  date-equality-on-record-change anti-pattern (flows are heavily AI-authored, so
  this is where an author reaches for the wrong pattern). Cross-linked from the
  schedule flow-type row.
- content/docs/automation/flows.mdx — a "Time-relative flow" example right after
  the hand-rolled scheduled get_record example it replaces.

Doc gates verified locally: check:doc-authoring, check:skill-docs, check:docs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AHzW68suiFuu6GdJyea8U4

Author: claude

content/docs/automation/flows.mdx

@@ -735,6 +735,51 @@ export const contractExpirationCheck: Flow = {
 };
 ```
 
+### Time-relative flow (declarative date sweep)
+
+Instead of hand-writing the "find records, then act" query above — and far more
+robust than a `record_change` flow gated on date-equality (`end_date ==
+daysFromNow(60)`), which only fires if the record is edited on the exact day — a
+`schedule` flow whose `start` node declares a `timeRelative` descriptor is swept
+on a schedule (daily by default) and runs **once per matching record**:
+
+```typescript
+export const renewalReminder: Flow = {
+  name: 'renewal_reminder',
+  label: 'Renewal Reminder',
+  type: 'schedule',
+  status: 'active',
+  runAs: 'system', // a sweep has no trigger user — elevate explicitly
+  nodes: [
+    {
+      id: 'start',
+      type: 'start',
+      label: 'Start',
+      config: {
+        timeRelative: {
+          object: 'contract',
+          dateField: 'end_date',
+          offsetDays: [60, 30, 7], // — or — withinDays: 30 (negative = overdue lookback)
+          filter: { status: 'active' }, // optional, ANDed with the date window
+        },
+        // schedule: { type: 'cron', expression: '0 8 * * *' } // optional; defaults to daily 08:00 UTC
+      },
+    },
+    { id: 'notify_owner', type: 'notify', label: 'Notify Owner' },
+    { id: 'end', type: 'end', label: 'End' },
+  ],
+  edges: [
+    { id: 'e1', source: 'start', target: 'notify_owner' },
+    { id: 'e2', source: 'notify_owner', target: 'end' },
+  ],
+};
+```
+
+Exactly one of `offsetDays` (discrete T-minus days) or `withinDays` (a range) is
+required. Requires the `triggers` **and** `job` capabilities. The record is on
+the flow context (`record.*`), so the start `condition` and `{record.*}`
+interpolation work as in a record-change flow.
+
 ### Update-triggered flow
 
 Trigger on a record update and compare against the previous value:

skills/objectstack-automation/SKILL.md

@@ -55,7 +55,7 @@ parallel. Flows are the primary automation building block in ObjectStack.
 |:-----|:------------|
 | `autolaunched` | Runs without user interaction — triggered by events, APIs, or other flows |
 | `screen` | Interactive — presents UI screens to the user (wizards, forms) |
-| `schedule` | Runs on a cron schedule (daily cleanup, weekly reports) |
+| `schedule` | Runs on a cron schedule (daily cleanup, weekly reports) — or a **per-record date sweep** via `config.timeRelative`, see *Time-relative triggers* |
 | `record_change` | Fires automatically on record create/update/delete (bind via the `start` node's `triggerType`) |
 | `api` | Invoked explicitly via the API / `engine.execute()`, **or** bound as an inbound **webhook**: `POST /api/v1/automation/hooks/:flowName/:hookId` (see *Inbound webhook triggers* below) |
 
@@ -509,6 +509,47 @@ read at runtime, not Zod-validated):
 > value after. (Salesforce-flavor `OLD` / `NEW` were removed in M9.5 and now
 > evaluate to `null`.) See [objectstack-formula](../objectstack-formula/SKILL.md).
 
+### Time-relative triggers — scheduled per-record date sweep
+
+**Don't** express "act N days before/after a date" (renewal reminders, "expiring
+soon", overdue sweeps) as a `record_change` flow gated on date-equality
+(`end_date == daysFromNow(60)`) — that predicate is only evaluated when the
+record *happens to change*, so unattended it almost never fires. Use a
+**declarative time-relative trigger**: a `schedule`-type flow whose `start` node
+carries a **`timeRelative`** descriptor is swept on a schedule (daily by default)
+and launched **once per record** whose date field falls in the window. The record
+is on the context, so the start `condition` and `{record.*}` interpolation work
+exactly as for a record-change flow — and because the window is evaluated every
+day, a threshold is never missed.
+
+```typescript
+{
+  name: 'renewal_alert',
+  type: 'schedule',
+  runAs: 'system',              // a sweep has no trigger user — elevate explicitly
+  nodes: [{
+    id: 'start', type: 'start',
+    config: {
+      timeRelative: {
+        object: 'contracts',
+        dateField: 'end_date',
+        offsetDays: [60, 30, 7],   // fire exactly at T-60 / T-30 / T-7
+        // — or — withinDays: 30    // "expiring within 30 days" (negative = overdue lookback)
+        filter: { status: 'active' },  // optional, ANDed with the date window
+        // maxRecords: 1000            // optional per-sweep cap (default 1000)
+      },
+      // schedule: cron`0 8 * * *`     // optional sweep cadence; omit for daily 08:00 UTC
+    },
+  }, /* …downstream nodes, connected via `edges` */],
+}
+```
+
+Exactly one of `offsetDays` (discrete T-minus days) or `withinDays` (a range;
+negative = overdue) is required. Ships in `@objectstack/trigger-schedule` —
+needs `requires: ['automation', 'triggers']` **plus `'job'`** (the sweep cadence
+runs on the job service). See the
+[Time Relative Trigger reference](/docs/references/automation/time-relative-trigger).
+
 ---
 
 ## Best Practices