feat(zddc): add ParseTransmittalFolder + IsTrnOrSubTracking helpers

Extracts the YYYY-MM-DD_<tracking> (<status>) - <title> grammar into a
reusable parser in the zddc package, and exposes a tracking-type
predicate for -TRN- / -SUB- (case-fold). The transmittal-folder regex
was previously only inside archive/index.go where it captured just the
date; the new ParseTransmittalFolder also returns tracking, status, and
title so handlers can recognise transmittal envelopes for upcoming
staging↔working mirror logic.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

zddc/internal/zddc/folder.go

@@ -0,0 +1,48 @@
+package zddc
+
+import (
+	"regexp"
+	"strings"
+)
+
+// transmittalFolderRE matches the canonical ZDDC transmittal-folder shape:
+//
+//	YYYY-MM-DD_<tracking> (<status>) - <title>
+//
+// where <tracking> has no spaces or underscores, <status> is anything inside
+// parentheses, and <title> is anything after the dash. Capture groups:
+//
+//	1: date (YYYY-MM-DD)
+//	2: tracking number (e.g. proj-EM-TRN-0042)
+//	3: status (e.g. IFR, IFA, RSA, DFT)
+//	4: title
+var transmittalFolderRE = regexp.MustCompile(
+	`^(\d{4}-\d{2}-\d{2})_([^_\s]+(?:-[^_\s]+)*)\s*\(([^)]+)\)\s*-\s*(.+)$`,
+)
+
+// ParseTransmittalFolder splits a folder basename into its ZDDC transmittal
+// components. The fourth return is true iff name is a well-formed transmittal
+// folder. Trailing slashes on name are tolerated.
+//
+// Used by handlers that need to recognise a staging-folder mkdir as a
+// transmittal envelope (to mirror it under working/), and by the archive
+// indexer that scans for transmittal folders on disk.
+func ParseTransmittalFolder(name string) (date, tracking, status, title string, ok bool) {
+	name = strings.TrimRight(name, "/")
+	m := transmittalFolderRE.FindStringSubmatch(name)
+	if m == nil {
+		return "", "", "", "", false
+	}
+	return m[1], m[2], m[3], m[4], true
+}
+
+// IsTrnOrSubTracking reports whether tracking contains a "-TRN-" or "-SUB-"
+// segment (case-insensitive). These two tracking types are the ones whose
+// staging folders get a paired drafting folder under working/.
+//
+// "-MDL-" and other tracking types do NOT match — MDL deliverables are
+// tracked via per-party mdl/ rows, not via the working↔staging mirror.
+func IsTrnOrSubTracking(tracking string) bool {
+	upper := strings.ToUpper(tracking)
+	return strings.Contains(upper, "-TRN-") || strings.Contains(upper, "-SUB-")
+}

zddc/internal/zddc/folder_test.go

@@ -0,0 +1,89 @@
+package zddc
+
+import "testing"
+
+func TestParseTransmittalFolder(t *testing.T) {
+	type expect struct {
+		date, tracking, status, title string
+		ok                            bool
+	}
+	cases := map[string]expect{
+		"2026-06-15_proj-EM-TRN-0042 (DFT) - Foundation Plans": {
+			date: "2026-06-15", tracking: "proj-EM-TRN-0042", status: "DFT", title: "Foundation Plans", ok: true,
+		},
+		"2026-01-15_123456-EM-SUB-0001 (IFR) - Submittal Title.with.dots": {
+			date: "2026-01-15", tracking: "123456-EM-SUB-0001", status: "IFR", title: "Submittal Title.with.dots", ok: true,
+		},
+		"2026-01-15_proj-EM-SUB-0001 (RSA) - Response Notes": {
+			date: "2026-01-15", tracking: "proj-EM-SUB-0001", status: "RSA", title: "Response Notes", ok: true,
+		},
+		// Whitespace variations around "(" and "-".
+		"2026-01-15_proj-EM-TRN-1(IFC)-Title": {
+			date: "2026-01-15", tracking: "proj-EM-TRN-1", status: "IFC", title: "Title", ok: true,
+		},
+		// MDL is a valid transmittal name even though it doesn't match TRN/SUB.
+		"2026-01-15_proj-EM-MDL-0001 (IFR) - Master Deliverables List": {
+			date: "2026-01-15", tracking: "proj-EM-MDL-0001", status: "IFR", title: "Master Deliverables List", ok: true,
+		},
+		// Negatives.
+		"":                     {ok: false},
+		"scratch":              {ok: false},
+		"2026-06-15 missing-underscore": {ok: false},
+		"NotADate_proj-EM-TRN-0042 (DFT) - Title": {ok: false},
+		"2026-06-15_no-status - Title":            {ok: false},
+		"2026-06-15_no-dash (IFC) Title":          {ok: false},
+		// Tracking with whitespace must not parse — tracking has no spaces.
+		"2026-06-15_proj EM TRN (IFC) - Title": {ok: false},
+	}
+	for in, want := range cases {
+		date, tracking, status, title, ok := ParseTransmittalFolder(in)
+		if ok != want.ok {
+			t.Errorf("ParseTransmittalFolder(%q) ok=%v, want %v", in, ok, want.ok)
+			continue
+		}
+		if !ok {
+			continue
+		}
+		if date != want.date || tracking != want.tracking || status != want.status || title != want.title {
+			t.Errorf("ParseTransmittalFolder(%q) = (%q,%q,%q,%q), want (%q,%q,%q,%q)",
+				in, date, tracking, status, title, want.date, want.tracking, want.status, want.title)
+		}
+	}
+}
+
+func TestParseTransmittalFolderTrailingSlash(t *testing.T) {
+	date, tracking, _, _, ok := ParseTransmittalFolder("2026-06-15_proj-TRN-1 (DFT) - x/")
+	if !ok || date != "2026-06-15" || tracking != "proj-TRN-1" {
+		t.Errorf("trailing slash not tolerated: ok=%v date=%q tracking=%q", ok, date, tracking)
+	}
+}
+
+func TestIsTrnOrSubTracking(t *testing.T) {
+	yes := []string{
+		"proj-EM-TRN-0042",
+		"proj-EM-SUB-0001",
+		"PROJ-em-trn-0001", // case-fold
+		"vendor-sub-9",
+		"a-TRN-b-SUB-c", // either qualifies
+	}
+	no := []string{
+		"",
+		"proj-EM-MDL-0001",
+		"trn-without-dashes",
+		"sub-without-dashes",
+		"prefixTRN",     // no dashes around TRN
+		"-TRN",          // missing trailing dash
+		"TRN-",          // missing leading dash
+		"proj-TRNX-001", // not exactly -TRN-
+	}
+	for _, s := range yes {
+		if !IsTrnOrSubTracking(s) {
+			t.Errorf("IsTrnOrSubTracking(%q) = false, want true", s)
+		}
+	}
+	for _, s := range no {
+		if IsTrnOrSubTracking(s) {
+			t.Errorf("IsTrnOrSubTracking(%q) = true, want false", s)
+		}
+	}
+}