feat: capture page views and surface as page_events in selectPlacements

[alexs-mparticle]

Summary

Records page-view events as they are logged, persists them durably to the Rokt local-session-attribute store, and surfaces them as a flat page_events array on the next selectPlacements call as targeting context.

What's included

• Capture (process): page views (EventDataType === 3) are appended to a persisted mpPageViews list (max 25, oldest evicted), guarded so a malformed event can never throw out of the forwarder. Captures EventName, full pageUrl (window.location.href), SourceMessageId, timestamp, ActiveTimeOnSite, and EventAttributes.
• Flatten (buildPageEvents): each stored view is flattened into a page_events entry — event_name, page_name (from the title attribute), and eventAttributes exploded into attr_-namespaced keys so they can't clobber base fields. The raw nested mpPageViews store is stripped so only the flat copy is sent.
• timeOnPage: each entry carries a derived timeOnPage — the active time a page was viewed before the next page view was logged (diff of consecutive activeTimeOnSite). Emitted only when it's a genuine non-negative number; omitted for the still-open last entry, negative diffs, and non-numeric values. Derived at read time — nothing extra persisted.
• Feeding selectPlacements: relaxed returnLocalSessionAttributes() so the store flows through whenever it's available and populated.

Security note (per Rokt secure-coding policy)

pageUrl (full URL incl. query/fragment) and eventAttributes are stored verbatim and may contain PII; they are persisted to browser storage and sent to Rokt. Full-URL was an explicit product choice; sanitizeUrl() isolates the boundary so query/fragment stripping is a one-line change later. The SDK does not run kit user-attribute filters over page-view EventAttributes. Design doc records this in full.

Testing

• Navigate through a page with an MPA and then triggermParticle.getInstance()._Store.getLocalSessionAttributes() in the dev console.

Expected result:

[
    {
        "attr_hostname": "www.domain.com",
        "event_name": "PageView",
        "page_name": "Online Store",
        "pageUrl": "https://www.domain.com/",
        "sourceMessageId": "80588459-ea2c-491a-9f41-2acc15b8cfb8",
        "timestamp": 1785526522349,
        "activeTimeOnSite": 328892,
        "timeOnPage": 35935
    },
    {
        "attr_hostname": "www.domain.com",
        "event_name": "PageView",
        "page_name": "Online Store | Some Page",
        "pageUrl": "https://www.domain.com/page_1",
        "sourceMessageId": "88a1ef32-83fd-41a8-03d8-04c4c67c879d",
        "timestamp": 1785526728989,
        "activeTimeOnSite": 364827,
        "timeOnPage": 11964
    },
    {
        "attr_hostname": "www.domain.com",
        "event_name": "PageView",
        "page_name": "Online Store | Next Page",
        "pageUrl": "https://www.domain.com/page_2",
        "sourceMessageId": "3c755531-1785-4b23-bf6c-fee3a93cc38e",
        "timestamp": 1785526922622,
        "activeTimeOnSite": 376791
    }
]

Verify the expected payload when making a select placements call:

{
  "active_time_on_site_ms": "427361",
  "page_events": "[ /* stringified array of events with timeOnPage value */ ]",
  // other placement attributes
}

[alexs-mparticle]

We should create an explicit type here for safety and it should include timeOnPage as optional.

[alexs-mparticle]

We shouldn't be changing these.

[alexs-mparticle]

Superseded by #109 — branch renamed to feat/capture-page-views to match our naming convention (the rename closed this PR).