feat(move-log): accept timestamps

packages/move-log/README.md

@@ -4,7 +4,8 @@ A **game-agnostic** container for a recorded run of move events. It wraps any ga
 
 ```js
 import {
-  createMoveLog, serializeMoveLog, deserializeMoveLog, isMoveLog, SCHEMA_VERSION
+  createMoveLog, withReceivedTs,
+  serializeMoveLog, deserializeMoveLog, isMoveLog, SCHEMA_VERSION
 } from '@cozy-games/move-log'
 
 // `T` is your game's own event vocabulary — supplied by you, unknown to us.
@@ -16,23 +17,39 @@ const log = createMoveLog([
 
 const json = serializeMoveLog(log)          // → JSON string
 const restored = deserializeMoveLog(json)    // → validated MoveLog, or throws
+
+// A consumer records WHEN it received events (host clock), additively:
+const stamped = withReceivedTs(restored, () => hostNow())
+// → each event now also carries `receivedTs`; still a valid v1 log
 ```
 
 ## Shape
 
-| field            | type              | meaning                                       |
-| ---------------- | ----------------- | --------------------------------------------- |
-| `schema_version` | `1`               | the move-log container version                |
-| `events`         | `MoveEvent<T>[]`  | ordered, each `{ seq, t, event }`             |
+| field            | type              | meaning                                            |
+| ---------------- | ----------------- | -------------------------------------------------- |
+| `schema_version` | `1`               | the move-log container version                     |
+| `events`         | `MoveEvent<T>[]`  | ordered, each `{ seq, t, event, receivedTs? }`     |
 
-`MoveEvent<T> = { seq: number, t: number, event: T }` — the log owns the
-per-event recording metadata (a strictly increasing `seq` and a timestamp `t`),
-so `T` stays a pure game payload with no required shape.
+`MoveEvent<T> = { seq: number, t: number, event: T, receivedTs?: number }` — the
+log owns the per-event recording metadata (a strictly increasing `seq`, a
+source-side timestamp `t`, and an **optional** received-side `receivedTs`), so
+`T` stays a pure game payload with no required shape. `receivedTs` is
+purpose-neutral: it records only *that* a consumer received the event at some
+time, never why or from where.
 
 `deserializeMoveLog` round-trips a serialized log with full fidelity (order,
-timestamps, sequence numbers) and rejects malformed input — bad JSON, missing or
-wrong-typed fields, or non-monotonic `seq` — with a clear error, never returning
-a partially-parsed log.
+timestamps, sequence numbers, and any `receivedTs`) and rejects malformed input —
+bad JSON, missing or wrong-typed fields, or non-monotonic `seq` — with a clear
+error, never returning a partially-parsed log.
+
+## Versioning: `receivedTs` is additive within `schema_version: 1`
+
+`receivedTs` was added **without** bumping `schema_version`. It is optional and
+purely additive: a v1 log is valid whether every event, some events, or no
+events carry a `receivedTs`, and a reader that doesn't know the field simply
+ignores it. A version bump is reserved for *breaking* container changes (a
+renamed/removed field or a newly required one), which would be dispatched on in
+`deserializeMoveLog`. See the `SCHEMA_VERSION` doc comment for the full policy.
 
 ## Invariant: zero game-specific imports
 

packages/move-log/index.js

@@ -8,16 +8,23 @@
  *
  * This module imports NO game types — that independence is the whole point and
  * is enforced by a dependency-graph guard in the tests. The log owns the
- * per-event recording metadata (`seq` + `t`) so `T` can stay a pure game payload
- * with no required shape; the module never inspects the inside of an `event`.
+ * per-event recording metadata (`seq` + `t`, and an optional received-side
+ * `receivedTs`) so `T` can stay a pure game payload with no required shape; the
+ * module never inspects the inside of an `event`.
  *
  * Extraction to a standalone published package comes later; for now it lives as
  * a shared workspace module alongside `packages/utils`.
  */
 
 /**
- * The move-log schema version. Bump ONLY on a breaking change to the container
- * shape itself — never for changes to a game's `T` vocabulary.
+ * The move-log schema version.
+ *
+ * Versioning policy: OPTIONAL, purely additive fields (an event gaining an
+ * optional `receivedTs`, say) do NOT bump this — a v1 reader ignores fields it
+ * doesn't know, and a log written with them stays a valid v1 log. Bump ONLY on a
+ * breaking change to the container shape (a renamed/removed field, a newly
+ * *required* field), which would need dispatch on read. Never bump for changes
+ * to a game's `T` vocabulary.
  *
  * @typedef {1} SchemaVersion
  */
@@ -25,11 +32,14 @@ export const SCHEMA_VERSION = /** @type {SchemaVersion} */ (1)
 
 /**
  * A single recorded event: the log-owned recording metadata — a strictly
- * increasing sequence number `seq` and a timestamp `t` (milliseconds) — plus the
- * game's opaque payload `event`. Generic over the game's event type `T`.
+ * increasing sequence number `seq`, a source-side timestamp `t` (milliseconds),
+ * and an OPTIONAL received-side timestamp `receivedTs` a consumer may attach when
+ * it received the event — plus the game's opaque payload `event`. Generic over
+ * the game's event type `T`. `receivedTs` is purpose-neutral: the log records
+ * only THAT it was received at some time, never why or from where.
  *
  * @template T
- * @typedef {{ seq: number, t: number, event: T }} MoveEvent
+ * @typedef {{ seq: number, t: number, event: T, receivedTs?: number }} MoveEvent
  */
 
 /**
@@ -70,10 +80,29 @@ function assertEvents(events) {
     if (e.seq <= prevSeq) {
       throw new RangeError(`move-log: events[${i}].seq must be strictly increasing (got ${e.seq} after ${prevSeq})`)
     }
+    if (e.receivedTs !== undefined && (typeof e.receivedTs !== 'number' || !Number.isFinite(e.receivedTs))) {
+      throw new TypeError(`move-log: events[${i}].receivedTs must be a finite number when present (got ${JSON.stringify(e.receivedTs)})`)
+    }
     prevSeq = e.seq
   })
 }
 
+/**
+ * Copy one event record to the canonical field set, carrying `receivedTs`
+ * through only when it's actually present (so absent stays absent — no
+ * `receivedTs: undefined` keys leak into the log or its JSON).
+ *
+ * @template T
+ * @param {MoveEvent<T>} e
+ * @returns {MoveEvent<T>}
+ */
+function copyEvent(e) {
+  /** @type {MoveEvent<T>} */
+  const out = { seq: e.seq, t: e.t, event: e.event }
+  if (e.receivedTs !== undefined) out.receivedTs = e.receivedTs
+  return out
+}
+
 /**
  * Assert a value is a well-formed move log — correct `schema_version` and a valid
  * events array — throwing a clear, specific error otherwise. Returns the value
@@ -101,17 +130,42 @@ export function assertMoveLog(value) {
  * entries are copied, so the log never aliases the caller's array.
  *
  * @template T
- * @param {MoveEvent<T>[]} [events] - ordered events, each `{ seq, t, event }`
+ * @param {MoveEvent<T>[]} [events] - ordered events, each `{ seq, t, event, receivedTs? }`
  * @returns {MoveLog<T>}
  */
 export function createMoveLog(events = []) {
   assertEvents(events)
   return {
     schema_version: SCHEMA_VERSION,
-    events: events.map(({ seq, t, event }) => ({ seq, t, event }))
+    events: events.map(copyEvent)
   }
 }
 
+/**
+ * Return a new move log with a received-side timestamp attached to each event
+ * for which `stamp` returns a finite number; events where `stamp` returns
+ * `undefined` are left as-is (keeping any existing `receivedTs`). This is how a
+ * consumer records WHEN it received events — the log never cares where the value
+ * came from. Pure: the input log is not mutated.
+ *
+ * @template T
+ * @param {MoveLog<T>} log
+ * @param {(event: MoveEvent<T>, index: number) => number | undefined} stamp
+ * @returns {MoveLog<T>}
+ */
+export function withReceivedTs(log, stamp) {
+  assertMoveLog(log)
+  const events = log.events.map((e, i) => {
+    const rt = stamp(e, i)
+    if (rt === undefined) return copyEvent(e)
+    if (typeof rt !== 'number' || !Number.isFinite(rt)) {
+      throw new TypeError(`withReceivedTs: stamp must return a finite number or undefined (got ${JSON.stringify(rt)} at index ${i})`)
+    }
+    return { ...copyEvent(e), receivedTs: rt }
+  })
+  return { schema_version: log.schema_version, events }
+}
+
 /**
  * Non-throwing type guard: is `value` a well-formed move log of the current
  * schema version? Checks the container invariants only — remains blind to `T`.

packages/move-log/test/move-log.test.js

@@ -7,7 +7,8 @@ import { dirname, join } from 'node:path'
 // Imported via the PACKAGE NAME (not a relative path) to prove the workspace
 // module resolves and is importable by other packages.
 import {
-  createMoveLog, serializeMoveLog, deserializeMoveLog, isMoveLog, assertMoveLog, SCHEMA_VERSION
+  createMoveLog, withReceivedTs,
+  serializeMoveLog, deserializeMoveLog, isMoveLog, assertMoveLog, SCHEMA_VERSION
 } from '@cozy-games/move-log'
 
 // A REAL mnswpr session/event stream — imported by the TEST, never the module.
@@ -142,6 +143,89 @@ describe('serialization round-trip', () => {
   })
 })
 
+describe('received timestamps (additive receivedTs)', () => {
+  const base = [
+    { seq: 1, t: 0, event: { type: 'reveal', r: 0, c: 0 } },
+    { seq: 2, t: 50, event: { type: 'flag', r: 1, c: 2 } }
+  ]
+
+  it('accepts an optional receivedTs per event and round-trips it', () => {
+    const log = createMoveLog([
+      { seq: 1, t: 0, event: { k: 'a' }, receivedTs: 1000 },
+      { seq: 2, t: 50, event: { k: 'b' }, receivedTs: 1060 }
+    ])
+    expect(log.events[0].receivedTs).toBe(1000)
+    const restored = deserializeMoveLog(serializeMoveLog(log))
+    expect(restored).toEqual(log)
+    expect(restored.events.map(e => e.receivedTs)).toEqual([1000, 1060])
+  })
+
+  it('is valid with receivedTs on only some events', () => {
+    const log = createMoveLog([
+      { seq: 1, t: 0, event: { k: 'a' }, receivedTs: 1000 },
+      { seq: 2, t: 50, event: { k: 'b' } } // no receivedTs
+    ])
+    expect(isMoveLog(log)).toBe(true)
+    expect('receivedTs' in log.events[1]).toBe(false)
+    expect(deserializeMoveLog(serializeMoveLog(log))).toEqual(log)
+  })
+
+  it('REGRESSION: a log with no receivedTs anywhere stays fully valid and leaks no key', () => {
+    const log = createMoveLog(base)
+    expect(isMoveLog(log)).toBe(true)
+    expect(log.events.every(e => !('receivedTs' in e))).toBe(true)
+    const restored = deserializeMoveLog(serializeMoveLog(log))
+    expect(restored).toEqual(log)
+    expect(restored.events.every(e => !('receivedTs' in e))).toBe(true)
+  })
+
+  it('rejects a non-finite / non-numeric receivedTs', () => {
+    expect(() => createMoveLog([{ seq: 1, t: 0, event: {}, receivedTs: 'soon' }])).toThrow(TypeError)
+    expect(() => createMoveLog([{ seq: 1, t: 0, event: {}, receivedTs: Infinity }])).toThrow(TypeError)
+    expect(() => deserializeMoveLog(JSON.stringify({
+      schema_version: 1,
+      events: [{ seq: 1, t: 0, event: {}, receivedTs: 'later' }]
+    }))).toThrow(TypeError)
+  })
+
+  it('withReceivedTs attaches host-received times additively without mutating the input', () => {
+    const log = createMoveLog(base)
+    let clock = 900
+    const stamped = withReceivedTs(log, () => (clock += 10))
+
+    // input untouched
+    expect(log.events.every(e => !('receivedTs' in e))).toBe(true)
+    // output stamped, still a valid v1 log, round-trips
+    expect(stamped.events.map(e => e.receivedTs)).toEqual([910, 920])
+    expect(stamped.schema_version).toBe(1)
+    expect(deserializeMoveLog(serializeMoveLog(stamped))).toEqual(stamped)
+  })
+
+  it('withReceivedTs leaves events unstamped when the stamp returns undefined', () => {
+    const log = createMoveLog(base)
+    const stamped = withReceivedTs(log, (e) => (e.seq === 1 ? 1234 : undefined))
+    expect(stamped.events[0].receivedTs).toBe(1234)
+    expect('receivedTs' in stamped.events[1]).toBe(false)
+    expect(isMoveLog(stamped)).toBe(true)
+  })
+
+  it('withReceivedTs rejects a stamp that returns a non-finite number', () => {
+    const log = createMoveLog(base)
+    expect(() => withReceivedTs(log, () => NaN)).toThrow(TypeError)
+  })
+
+  it('VERSIONING: receivedTs is additive — same schema_version with or without it', () => {
+    const without = createMoveLog(base)
+    const withRt = withReceivedTs(without, () => 1000)
+    expect(without.schema_version).toBe(SCHEMA_VERSION)
+    expect(withRt.schema_version).toBe(SCHEMA_VERSION)
+    expect(SCHEMA_VERSION).toBe(1)
+    // a v1 reader accepts both shapes
+    expect(isMoveLog(without)).toBe(true)
+    expect(isMoveLog(withRt)).toBe(true)
+  })
+})
+
 describe('integration: wraps a real mnswpr event stream (core-06)', () => {
   // 3x3, single mine at (0,0); adjacency computed. Lets us script exact moves.
   const layout = {