docs(skill): sync CEL function tables to 9.8.0 stdlib + drift-guard (#1967)

The authoring skills under-listed the stdlib (6 functions + "only the above"),
omitting the 14 registered in 9.8.0 (daysBetween/abs/round/min/max/upper/lower/
contains/startsWith/endsWith/matches/len/isEmpty/date/datetime) — so AI authors
never used daysBetween and kept hand-rolling workarounds.

- Rewrite objectstack-formula stdlib table (grouped + CEL built-ins); fix the
  daysFromNow/daysAgo note (keep wall-clock time, not midnight).
- Rewrite objectstack-automation "time-relative rule" anti-pattern to the precise
  one-day window pattern ($gte daysFromNow(N) / $lt daysFromNow(N+1) + $or); add
  daysBetween for days-remaining.
- Add a drift-guard test (packages/formula) pinning skill ↔ CEL_STDLIB_FUNCTIONS.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: os-zhuang

.changeset/skill-catalog-9.8-sync.md

@@ -0,0 +1,19 @@
+---
+---
+
+docs(skill): sync objectstack-formula/automation CEL function tables to the 9.8.0 stdlib
+
+The authoring skills (what the AI reads to know what's callable) under-listed the
+stdlib: they showed ~6 functions and capped with "only the stdlib above", omitting
+the 14 functions registered in 9.8.0 (`daysBetween`, `abs`, `round`, `min`, `max`,
+`upper`, `lower`, `contains`, `startsWith`, `endsWith`, `matches`, `len`, `isEmpty`,
+`date`/`datetime`). So AI authors never reached for `daysBetween` (days-remaining)
+and kept hand-rolling workarounds.
+
+Rewrites the formula stdlib table (grouped, with the CEL built-ins), fixes the
+`daysFromNow`/`daysAgo` note (they keep the wall-clock time, NOT midnight), and
+rewrites the automation "time-relative rule" anti-pattern to the precise one-day
+**window** pattern (`$gte daysFromNow(N)` / `$lt daysFromNow(N+1)` + `$or`) instead
+of the imprecise `BETWEEN TODAY and TODAY+N`. Adds a drift-guard test pinning the
+skill ↔ `CEL_STDLIB_FUNCTIONS` so the AI-facing list can't fall behind the runtime
+catalog again.

packages/formula/src/skill-catalog-sync.test.ts

@@ -0,0 +1,32 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, resolve } from 'node:path';
+
+import { CEL_STDLIB_FUNCTIONS } from './validate';
+
+/**
+ * Drift-guard (#1928 follow-up): the objectstack-formula authoring skill is what
+ * the AI author reads to know which CEL functions exist. It MUST stay in sync
+ * with the runtime catalog — a function advertised in the catalog but missing
+ * from the skill means the AI never reaches for it; one in the skill but not the
+ * catalog means the AI calls a function that faults the build. This pins the
+ * skill ↔ `CEL_STDLIB_FUNCTIONS` mapping so neither drifts silently again
+ * (mirrors the runtime drift-guard in cel-engine.test.ts).
+ */
+describe('objectstack-formula skill ↔ CEL_STDLIB_FUNCTIONS', () => {
+  const here = dirname(fileURLToPath(import.meta.url));
+  const skillPath = resolve(here, '../../../skills/objectstack-formula/SKILL.md');
+  const skill = readFileSync(skillPath, 'utf8');
+
+  it('documents every advertised stdlib function', () => {
+    // A function is "documented" if its name appears as `` `name(` `` (a call
+    // form) anywhere in the skill — robust to table layout / grouping changes.
+    const missing = CEL_STDLIB_FUNCTIONS.filter((fn) => !skill.includes(`\`${fn}(`));
+    expect(
+      missing,
+      `These CEL_STDLIB_FUNCTIONS are not documented in skills/objectstack-formula/SKILL.md:\n` +
+        `${missing.join(', ')}\nAdd them to the stdlib table so AI authors know they exist.`,
+    ).toEqual([]);
+  });
+});

skills/objectstack-automation/SKILL.md

@@ -39,7 +39,7 @@ pipelines.
 > envelope evaluated by `@objectstack/formula`. Use the `P\`...\`` and
 > `cel\`...\`` tagged templates from `@objectstack/spec`. See the
 > **objectstack-formula** skill for the full CEL contract, stdlib
-> (`now()`, `today()`, `daysFromNow(n)`, `isBlank(v)`, `coalesce(v, fb)`),
+> (`now()`, `today()`, `daysFromNow(n)`, `daysBetween(a, b)`, `isBlank(v)`, `coalesce(v, fb)`),
 > and the legacy → CEL translation table.
 
 ---
@@ -537,9 +537,22 @@ them right the first time:
 8. **Time-relative rules ("alert N days before a date") are SCHEDULE flows, not
    record-change date-equality.** `record.end_date == daysFromNow(60)` on a
    `record-*` trigger only fires if the record happens to be written on that exact
-   day — unattended rules never run.
-   ✅ A daily `schedule` flow whose `get_record` filters `end_date` BETWEEN
-   `{TODAY()}` and `{TODAY() + N}`, then loops over the results.
+   day — unattended rules never run. **And date EQUALITY never matches anyway**: a
+   `date` field carries a time component, so `field == daysFromNow(N)` (or
+   `{ $in: [daysFromNow(N), …] }`) compares two differently-timed timestamps and
+   silently returns nothing (build warns `flow-date-equality-filter`).
+   ✅ A daily `schedule` flow whose `get_record` filters each tier as a one-day
+   **window** (`$gte`/`$lt`), never an equality:
+   ```ts
+   filter: { status: 'active', $or: [
+     { end_date: { $gte: cel`daysFromNow(7)`,  $lt: cel`daysFromNow(8)`  } },
+     { end_date: { $gte: cel`daysFromNow(30)`, $lt: cel`daysFromNow(31)` } },
+     { end_date: { $gte: cel`daysFromNow(60)`, $lt: cel`daysFromNow(61)` } },
+   ] }
+   ```
+   Abutting windows tile the timeline so each record matches exactly one tier —
+   fires once, idempotent, no guard field. For "days remaining" in the message,
+   `daysBetween(today(), record.end_date)`.
 
 9. **`script` nodes must name a callable.** Set `config.actionType` to a built-in
    side-effect (`email` / `slack`) **or** `config.function` to a function
@@ -573,8 +586,9 @@ them right the first time:
    that's an L2 **hook** (objectstack-data) — hooks get `ctx.api`; flow functions don't.
 
 10. **Conditions are bare CEL — only the stdlib is callable.** `now()`,
-    `today()`, `daysFromNow(n)`, `daysAgo(n)`, `isBlank(v)`, `coalesce(a, b)`,
-    `trim(s)`, plus CEL built-ins (`has`, `size`, `contains`, `startsWith`, …).
+    `today()`, `daysFromNow(n)`, `daysAgo(n)`, `daysBetween(a, b)`, `isBlank(v)`,
+    `coalesce(a, b)`, `abs/round/min/max`, `upper/lower/contains/matches`, plus CEL
+    built-ins (`has`, `size`, `int`, `string`, …) — see **objectstack-formula** for the full table.
     An UNKNOWN function (`PRIOR()`, a typo'd name) **fails the build**. And never
     wrap a field reference in `{…}` inside a condition — that's a template brace
     and fails as CEL: write `record.x`, not `{record.x}`.

skills/objectstack-formula/SKILL.md

@@ -126,24 +126,59 @@ in `coalesce(..., '')`.
 Registered automatically. Source:
 [`packages/formula/src/stdlib.ts`](../../packages/formula/src/stdlib.ts).
 
+The canonical list is `CEL_STDLIB_FUNCTIONS` in
+[`packages/formula/src/validate.ts`](../../packages/formula/src/validate.ts) — a
+test asserts every entry resolves at runtime, so this table stays in sync with it.
+
+**Dates**
+
+| Function | Returns | Notes |
+|:---|:---|:---|
+| `now()` | timestamp | Current instant. Pinned per evaluation run; deterministic in build |
+| `today()` | timestamp | UTC **start-of-day** (midnight) |
+| `daysFromNow(n)` | timestamp | `now()` + `n` days — **keeps the current time-of-day** (NOT midnight) |
+| `daysAgo(n)` | timestamp | `now()` − `n` days — keeps the current time-of-day |
+| `daysBetween(a, b)` | int | Whole days from `a` to `b` (negative if `b` precedes `a`). `daysBetween(today(), record.due)` = days remaining |
+| `date(s)` / `datetime(s)` | timestamp | Parse an ISO date / date-time string to a timestamp |
+
+**Numbers**
+
+| Function | Returns | Notes |
+|:---|:---|:---|
+| `abs(x)` | double | Absolute value |
+| `round(x)` | int | Round to the nearest integer |
+| `min(a, b)` / `max(a, b)` | dyn | Smaller / larger operand (numeric comparison) |
+
+**Strings**
+
+| Function | Returns | Notes |
+|:---|:---|:---|
+| `upper(s)` / `lower(s)` | string | Case conversion |
+| `trim(s)` | string | Strip surrounding whitespace (`''` for null) |
+| `contains(s, sub)` | bool | Substring test |
+| `startsWith(s, p)` / `endsWith(s, p)` | bool | Prefix / suffix test |
+| `matches(s, re)` | bool | Regex test |
+| `joinNonEmpty(list, sep)` | string | Join, dropping null/empty entries |
+
+**Collections / null-ish**
+
 | Function | Returns | Notes |
 |:---|:---|:---|
-| `now()` | timestamp | Pinned per evaluation run; deterministic in build |
-| `today()` | timestamp | UTC start-of-day |
-| `daysFromNow(n)` | timestamp | `today() + n*24h` |
-| `daysAgo(n)` | timestamp | `today() - n*24h` |
 | `isBlank(v)` | bool | true for `null`, `undefined`, `''`, `[]` |
+| `isEmpty(v)` | bool | true for `null`, `undefined`, empty string / list / map |
 | `coalesce(v, fallback)` | dyn | `v` when non-null, else `fallback` |
+| `len(v)` | int | Length of a string / list / map |
+
+Plus CEL built-ins: `has(x)`, `size(x)`, `int(x)`, `string(x)`, `bool(x)`,
+`double(x)`, `timestamp(s)`, `duration(s)`.
 
 If you need a helper that doesn't exist, prefer adding it to the stdlib
 (small, pure, dependency-free) over inlining a complex CEL expression.
 
-> **Only the stdlib above + CEL built-ins (`has`, `size`, `contains`,
-> `startsWith`, `endsWith`, `matches`, `min`, `max`, …) are callable.** An
-> UNKNOWN function — `PRIOR()`, a legacy `ISBLANK()`, a typo'd `isBlnk()` — now
-> **fails `objectstack build`** with a "no matching overload" type error (#1877),
-> rather than silently no-op'ing the predicate at run time. Use `previous.x`
-> (not `PRIOR()`), `isBlank()` (not `ISBLANK()`).
+> **Only the functions above are callable.** An UNKNOWN function — `PRIOR()`, a
+> legacy `ISBLANK()`, a typo'd `isBlnk()` — **fails `objectstack build`** with a
+> "no matching overload" type error (#1877), rather than silently no-op'ing the
+> predicate at run time. Use `previous.x` (not `PRIOR()`), `isBlank()` (not `ISBLANK()`).
 
 ---