action=placeholders (default): persist AI-detected fields. placeholders MUST be
    the exact objects from getsign_detect_placeholders_ai (data.placeholders) —
    always call that tool first and pass its output through unmodified except for
    field_assignments. Do NOT hand-author placeholder coordinates yourself
    (e.g. guessing x/y/width/height from where you drew boxes on a generated
    PDF). The wire shape has two separate coordinate fields —
    formField.coordinates (bottom-up, native PDF points) and placeholder (the same
    point converted top-down) — and this route does not validate that they agree.
    A hand-typed placeholder that gets the two conventions wrong is accepted and
    stored (no error), but silently fails to render in the PDF editor and fails to
    resolve any signer in getsign_get_signer_data. If there is no PDF to detect
    against yet, or the user wants manual control, use getsign_get_document_url(action="edit")
    instead of inventing coordinates.

    Route from the ID pair (not from the word "template"):
    - envelope_id + item_id + file_id → POST /files/map-placeholders (item
      document). Default is_template_update=true saves to the shared template
      and every item using it. Pass is_template_update=false when the
      user says this one item, and ALWAYS when the workflow has useFileColumn
      enabled — a document sourced from a monday File column is that item's own
      file with no shared template behind it. A template-scoped save there is not
      rejected: the file is not pinned to a template, so the backend updates only
      that file, takes the template signing-order branch, and still answers
      "Template updated successfully", so reporting that result verbatim tells the
      user about a template-wide change that never happened.
    - template_id (no item) → POST /template-gallery/map-template-placeholder/:id
      (gallery). file_id is optional, and existing_fields is an optional override.
      is_template_update is ignored.
    Pass one shape, not both. merge=true (default) keeps existing fields.
    After a force detect the save replaces instead (merge=false) so new
    field ids do not stack on the previous run.

    Signer assignment (email / people / mirror-email-column only — use
    getsign_monday_item's signer_columns / emailColumn — raw emails are
    not allowed). If you save without an assignee on an item, this tool
    returns those lists so you can follow up:
    - Prefer field_assignments: [{placeholder_id, assignee_column_id,
      assignee_column_type, optional assignee_column_title}] so each
      signature or standard field can get its own column in one save.
    - Or pass a single assignee_column_id(+type) as a default for every
      field that has no per-field assignment.
    Leave both unset to save fields without signers, then map later in
    getsign_get_document_url(action="edit"). Match is_template_update with edit_template
    when opening the editor to review.

    action=signing_order: set who signs first, second, and so on, without
    opening the PDF editor. Needs envelope_id + item_id. Each ordered_signers
    entry must already be a mapped signer (a board column stamped onto a
    signature field). Identify them with email_column_id, label, or email from
    getsign_get_signer_data, in the sequence they should sign. Example: Priya
    (CISO) first, then the CFO. The second person is emailed only after the
    first signs. required=true (default) turns sequential signing on.
    required=false with an empty ordered_signers list turns it off so everyone
    is notified at once. List every mapped signer when turning it on. This
    writes the same signerOrderSettings the editor Save button writes, so
    existing customers who set order in the editor are not broken. Default is
    item-level (is_template_update=false). Pass true only when the user wants
    the order on the shared template. Call getsign_get_signer_data first. Do
    not bounce the user into the editor just to configure order.