Story 1532: Whose Filing Is This? (FN-2 — extend the document→filing derive)

Why this exists (the catastrophe it prevents). The Record shows counsel every piece of a matter — our filings, the opponent's filings, the court's orders, and the loose documents underneath. Story-1502 (FN-FILING-LINK) taught the register to answer "is this filed, and as what?" But it left a more dangerous blank: whose filing is it? A reviewer scrolling 400 rows who cannot instantly tell our Statement of Claim from the opponent's Statement of Defence will, sooner or later, read the wrong side's pleading as their own and brief on it. The tempting shortcut — stamp a "party" string onto each document — is the same lie ADR-125 already forbade for filing state: a document has no party of its own; the filing it belongs to was lodged by a party. This Story extends the read-time derive to carry that party — name, role-label, and side — without storing a single new byte on the document.

The one analogy: the return address on the envelope

Keep Story-1502's picture. A Filing is an envelope lodged with the court; inside rides one lead document (the letter) plus its annexures (enclosures A-1, B, C-3). FN-2 reads the return address printed on that envelope: who sent it (the participant's display name, e.g. "Vega Capital"), in what capacity (their label in this proceeding, e.g. "Respondent"), and which side of the table they sit on relative to our client (the side badge: Ours · Opposing · Court/Tribunal · Others). You never write the sender on the enclosure — you read it off the envelope, and every enclosure inherits it. A loose letter in no envelope has no return address: "—".

🛰️ Satellite: what shipped

The same one read endpoint, now richer — no new route, no new write path:

GET /app/documents/{doc_id}/filing  ->  200 DocumentFilingLinkView (+ filedBy)

• DocumentFilingLinkView gains filed_by: a nullable FiledByView = {participant_name, participant_label_name, side}.
• A new system enum FilingSide = ours | opposing | court | others — a fixed structural axis, never a firm-editable vocabulary.
• The derive resolves the linked Filing's filer into that view at read time, reusing the ADR-1179 participant model (matter participant + per-proceeding label). Annexures inherit the parent filing's filed_by. Unlinked, or a filing that names no filer → filed_by = None ("—").

✈️ Airplane: how a request resolves

doc = load document (firm-scoped; 404 if not in caller's firm via RLS)
effective_id = doc.parent_document_id or doc.id        <- annexure rides its parent
row = SELECT filings.id, filings.status,
             proceeding_filing_types.name           AS filing_type,
             filings.filed_by_participant_id,
             matter_participants.name                AS filer_name,    <- LEFT JOIN
             matter_participants.side                AS filer_side,
             proceeding_participant_labels.name      AS filer_label    <- LEFT JOIN (role)
        FROM business.filings
        JOIN proceeding_filing_types          ON (firm_id, id = filing_type_id)
   LEFT JOIN matter_participants              ON (firm_id, matter_id, id = filed_by_participant_id)
   LEFT JOIN proceeding_participant_roles     ON (firm_id, proceeding_id, participant_id = filed_by_participant_id)
   LEFT JOIN proceeding_participant_labels    ON (firm_id, proceeding_id, id = role.participant_label_id)
       WHERE firm_id = caller AND document_id = effective_id
if row is None              -> isFiling=false, filed_by=None        ("Not a filing / —")
elif filed_by_participant_id-> filed_by = {filer_name, filer_label, FilingSide(filer_side)}
else                        -> filed_by = None                     (filing names no filer)

Four turns make this correct:

• The filer joins are LEFT, never inner. A filing may name no filer; a named filer may carry no label in this proceeding. An inner join would silently drop the whole filing row in either case — the document would read "not a filing" the instant a filer was missing. The base filing facts (type, state) must survive a blank return address.
• Name + side come off the matter participant; the label comes off the proceeding role. "Claimant" is Ours or Opposing depending on whom we act for, so side lives on the participant (set once per matter), while the label is per-proceeding vocabulary (ADR-1179). The derive reads both through the one filed_by_participant_id.
• Annexures inherit the return address. The effective_id indirection already resolves an annexure to its parent's filing; filed_by falls out of the same row, so an exhibit shows its parent's filer and can never claim a sender of its own.
• Nothing is stored on the document. filed_by is a join projected at read time, single-source-of-truth on the Filing — impossible to desync, exactly like filing state (ADR-125 D5).

🔬 Microscopic: the boundary lines that matter

One-sentence recall

FN-2 reads the return address off the envelope — who filed, in what capacity, on which side — as a read-time join over FN-1's filer FK, so the Record can tell our filings from the opponent's without ever stamping a party onto a document.