get_linkedin_engagement_source_types

List the LinkedIn engagement source types and their triggers. STEP 1 of building a
                LinkedIn Engagement Retargeting audience.

                WHAT THIS AUDIENCE TYPE IS:
                An audience of people who ALREADY interacted with this advertiser on LinkedIn or on
                their website: watched a video ad, opened a lead form, clicked a document ad, visited
                the company page, or hit specific URLs. It is warm-traffic retargeting, built from
                first-party engagement, and it needs no contact list and no CSV.

                NOT THE SAME AS create_retargeting_audience. That tool IMPORTS an audience that
                already exists inside the native ad account. This flow BUILDS a new LinkedIn DMP
                segment from an engagement rule you define. If the user says "import my existing
                LinkedIn audience", use the other tool. If they describe PEOPLE WHO DID SOMETHING
                ("watched", "clicked", "visited", "opened", "engaged with"), use this flow.

                **THE THREE-STEP FLOW:**
                1. get_linkedin_engagement_source_types (this tool) — choose a source type + trigger
                2. search_linkedin_engagement_sources — choose which campaigns / pages to retarget
                   (SKIP THIS STEP for the WEBSITE source type, which uses URL rules instead)
                3. create_linkedin_engagement_retargeting_audience — build it

                SOURCE TYPES AND WHAT EACH RETARGETS (verified live; the response is authoritative
                and may differ per account, so never assume a value that is not in it):
                - VIDEO_ADS ........... viewers of the account's video ads
                - SINGLE_IMAGE_ADS .... people who engaged with single-image ads
                - DOCUMENT_ADS ........ people who engaged with or downloaded document ads
                - CONVERSATION_ADS .... people who opened or clicked a conversation ad
                - LEAD_GEN_FORMS ...... people who opened or submitted a lead gen form
                - ORGANIZATION_PAGES .. visitors to the LinkedIn company page
                - WEBSITE ............. visitors to specific URLs on the advertiser's own site

                TRIGGERS DEFINE INTENT DEPTH, and each source type has its own set:
                - VIDEO_ADS: FIRST_QUARTILE (>=25% viewed, the default) · MIDPOINT (>=50%) ·
                  THIRD_QUARTILE (>=75%) · FULL_COMPLETE (>=97%). Deeper means smaller and warmer.
                - SINGLE_IMAGE_ADS / DOCUMENT_ADS: ENGAGEMENT (any interaction, default) ·
                  CLICK (chargeable clicks only). DOCUMENT_ADS adds DOWNLOAD_CLICK (downloaded it).
                - CONVERSATION_ADS: OPEN (default) · ANY_CTA_CLICK (clicked a call-to-action).
                - LEAD_GEN_FORMS: VIEW_FORM (opened it, includes submitters, default) ·
                  LEAD_FORM_SUBMIT (submitted only — the hottest signal available).
                - ORGANIZATION_PAGES: VIEW (visited the page, default) · CTA_CLICK (clicked the
                  page header CTA).
                - WEBSITE: VISIT.

                CHOOSING FOR THE USER'S INTENT:
                - "warm up a broad audience" / top of funnel → a shallow trigger (ENGAGEMENT, VIEW,
                  FIRST_QUARTILE, VIEW_FORM) and a long lookback.
                - "high intent" / "ready to buy" / bottom of funnel → a deep trigger
                  (LEAD_FORM_SUBMIT, FULL_COMPLETE, DOWNLOAD_CLICK, ANY_CTA_CLICK) and a short one.
                - When the user does not say, prefer the trigger marked `default` — it is LinkedIn's
                  own recommended choice for that source type.
                - **Only ever use a trigger from the source type you picked.** The pairing is not
                  validated anywhere downstream, so a trigger borrowed from another source type
                  builds a permanently empty audience with no error to warn you.

                LOOKBACK WINDOW is both how far back engagement counts AND how long someone stays in
                the audience. Longer means bigger and colder; shorter means smaller and warmer.
                30 / 60 / 90 / 180 / 365 days, except WEBSITE which LinkedIn caps at 180.
                90 is a reasonable default when the user does not say.

                WHEN TO USE:
                - "Create an engagement retargeting audience"
                - "Retarget people who watched my LinkedIn video ads"
                - "Build an audience of people who opened / submitted my lead gen form"
                - "Retarget visitors to our pricing page" (WEBSITE)
                - "Who visited our LinkedIn company page?" (ORGANIZATION_PAGES)
                - "Retarget everyone who engaged with our ads last quarter"
                - Any request to retarget people by something they DID, on LinkedIn or the site

                PARAMETERS: none. It always reports the whole catalog for the caller's account.

                RETURNS:
                - sourceTypes[]: `engagementSourceType`, a human `description`, and the `triggers`
                  valid for it (`engagementTrigger`, `description`, `default`). Only entries
                  LinkedIn reports as ACTIVE are returned; inactive ones are filtered out.
                - lookbackWindowDays: the windows the platform accepts, with WEBSITE listed
                  separately because of its 180-day cap.
                - next_step: which tool to call next.

                IMPORTANT NOTES:
                - Requires a connected LinkedIn channel. With none connected this returns nothing
                  useful, and the fix is to connect LinkedIn (connect_channel), not to retry.
                - The catalog is LinkedIn's own and is read live, so it can change. Treat the
                  response as the only source of truth and never pass a value absent from it.
                - EVENT_PAGES is deliberately not offered. LinkedIn advertises it but returns no
                  sources for it, so an audience cannot be built from it.
                - A source type may come back with `triggersError` instead of `triggers` if its
                  trigger list could not be read. The other source types are still usable; either
                  retry or choose one of them.