feat: virtual fallback for archive/<party>/* folders + incoming fixture data

Three coupled fixes:

1. landing MDL card: Open button now navigates to /<project>/archive/
   <party>/mdl (no trailing slash) so the tables tool loads. The
   slash form would route to browse instead, which is not what users
   want when they click "Open MDL".

2. zddc-server canonical-folder fallback extended to
   archive/<party>/{mdl,incoming,received,issued}. New
   zddc.IsArchivePartyFolder() recognises any of the four party
   folders at depth 4. fs.ListDirectory returns [] for missing
   on-disk variants (mirroring the project-root behavior added in
   commit 3fc3717); the dispatcher routes slash forms to
   ServeDirectory and the no-slash mdl form to ServeTable, with
   non-mdl no-slash forms 302'ing to the slash form.

   So /Project-N/archive/<party>/incoming/ now lands on an empty
   browse listing rather than 404 when nobody has dropped files yet.

3. Fixture seeded with 3 files per party under incoming/ — naming
   intentionally NOT in transmittal-envelope form, so classifier
   (loaded automatically by browse's grid mode at /incoming/
   per the URL-driven view convention) has something to rename.

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

landing/js/landing.js

@@ -704,7 +704,11 @@
         function openSelectedMdl() {
             var party = mdlSelect.value;
             if (!party) return;
-            var url = '/' + p + '/archive/' + encodeURIComponent(party) + '/mdl/';
+            // No trailing slash: per the convention, the no-slash form
+            // serves the tables tool with the MDL view. The slash form
+            // would serve browse, which is not what the user wants when
+            // they click "Open MDL".
+            var url = '/' + p + '/archive/' + encodeURIComponent(party) + '/mdl';
             window.location.assign(url);
         }
         mdlOpenBtn.addEventListener('click', openSelectedMdl);

tests/data/test-archive.sh

@@ -447,10 +447,29 @@ cmd_build() {
 
         for party in $parties; do
             party_dir="$proj_dir/archive/$party"
-            mkdir -p "$party_dir/received" "$party_dir/issued"
+            mkdir -p "$party_dir/received" "$party_dir/issued" "$party_dir/incoming"
-            chmod 0777 "$party_dir" "$party_dir/received" "$party_dir/issued"
+            chmod 0777 "$party_dir" "$party_dir/received" "$party_dir/issued" "$party_dir/incoming"
             write_zddc_config "$party_dir/.zddc" party
 
+            # Seed incoming/ with a couple of unclassified files (no
+            # transmittal envelope yet) so the grid view has data to
+            # exercise. Stays small — incoming is the staging surface
+            # for files dropped by counterparties; classifier turns
+            # them into named transmittal folders.
+            incoming_seed_count=3
+            j=0
+            while [ "$j" -lt "$incoming_seed_count" ]; do
+                j=$((j + 1))
+                seed_ext=$(pick_word "$EXTENSIONS_WEIGHTED")
+                seed_title="$(random_title)"
+                seed_name="incoming-${j}-${seed_title}.${seed_ext}"
+                seed_path="$party_dir/incoming/$seed_name"
+                # Use the per-transmittal renderer with dummy
+                # tracking/rev/status. classifier reads the bytes,
+                # not the envelope, when renaming.
+                render_file "$seed_ext" "drop-${j}" "_A" "(IFR)" "$seed_title" "$seed_path"
+            done
+
             i=0
             while [ "$i" -lt "$per_party" ]; do
                 i=$((i + 1))

zddc/cmd/zddc-server/main.go

@@ -884,15 +884,16 @@ func dispatch(cfg config.Config, idx *archive.Index, ring *handler.LogRing, apps
 					// block → ServeDirectory → embedded browse.html.
 				}
 			}
-			// Default-MDL virtual directory at archive/<party>/mdl[/].
+			// Per-party canonical folders at archive/<party>/{mdl,incoming,
-			// Shape rule mirrors the other canonical folders:
+			// received,issued}[/]. The on-disk folder may not exist yet —
-			//   - no slash  → tables app (default tool for mdl/)
+			// dispatch lands on a usable view regardless:
-			//   - slash     → browse (ServeDirectory → empty listing for
+			//   - no-slash mdl   → tables app (default-MDL fallback)
-			//                  the not-yet-materialised folder)
+			//   - no-slash else  → not yet a registered tool → falls
-			// The dispatcher works without the on-disk dir existing
+			//                       through to 302 (slash form)
-			// thanks to fs.ListDirectory's empty-listing fallback +
+			//   - slash, all     → browse (ServeDirectory → fs.ListDirectory
-			// RecognizeTableRequest's default-MDL fallback.
+			//                       empty-listing fallback)
 			if r.Method == http.MethodGet || r.Method == http.MethodHead {
+				rel := strings.Trim(strings.TrimPrefix(urlPath, "/"), "/")
 				if !strings.HasSuffix(urlPath, "/") {
 					synth := urlPath + "/table.html"
 					if tr := handler.RecognizeTableRequest(cfg.Root, http.MethodGet, synth); tr != nil {
@@ -904,8 +905,14 @@ func dispatch(cfg config.Config, idx *archive.Index, ring *handler.LogRing, apps
 						handler.ServeTable(cfg, tr, w, r)
 						return
 					}
-				} else if zddc.IsArchivePartyMdlDir(
+					// No-slash forms for non-mdl party folders 302 to
-					strings.Trim(strings.TrimPrefix(urlPath, "/"), "/")) {
+					// the slash form so they consistently land on the
+					// browse listing.
+					if zddc.IsArchivePartyFolder(rel) {
+						http.Redirect(w, r, urlPath+"/", http.StatusFound)
+						return
+					}
+				} else if zddc.IsArchivePartyFolder(rel) {
 					handler.ServeDirectory(cfg, appsSrv, w, r)
 					return
 				}

zddc/internal/fs/tree.go

@@ -57,7 +57,7 @@ func ListDirectory(ctx context.Context, decider policy.Decider, fsRoot, dirPath,
 		// virtualUserHomeEntry below still fires for working/ so the
 		// user sees their own home placeholder.
 		if os.IsNotExist(err) &&
-			(zddc.IsProjectRootFolder(dirPath) || zddc.IsArchivePartyMdlDir(dirPath)) {
+			(zddc.IsProjectRootFolder(dirPath) || zddc.IsArchivePartyFolder(dirPath)) {
 			entries = nil
 		} else {
 			return nil, err

zddc/internal/handler/tables.html

@@ -1300,7 +1300,7 @@ body.help-open .app-header {
             </svg>
             <div class="header-title-group">
                 <span class="app-header__title" id="table-title">ZDDC Table</span>
-                <span class="build-timestamp"><span style="color:red;font-weight:bold">v0.0.17-alpha · 2026-05-11 18:10:39 · e85d5fc-dirty</span></span>
+                <span class="build-timestamp"><span style="color:red;font-weight:bold">v0.0.17-alpha · 2026-05-11 18:30:39 · ab44d75-dirty</span></span>
             </div>
         </div>
         <div class="header-right">

zddc/internal/zddc/special.go

@@ -49,6 +49,36 @@ var AutoOwnCanonicalNames = []string{"working", "staging", "incoming"}
 // MkdirAll for it.
 var VirtualOnlyCanonicalNames = []string{"reviewing"}
 
+// IsArchivePartyFolder reports whether dirPath (relative, forward-
+// slash-separated) names a canonical per-party folder at exactly
+// depth 4: <project>/archive/<party>/<folder>, where <folder> is one
+// of mdl/incoming/received/issued (case-insensitive). The party
+// segment is verbatim.
+//
+// Used by listing + dispatch fallbacks so a fresh party that hasn't
+// yet had files written to each subfolder still lands on a usable
+// empty browse view rather than 404.
+func IsArchivePartyFolder(dirPath string) bool {
+	clean := strings.Trim(filepath.ToSlash(dirPath), "/")
+	if clean == "" {
+		return false
+	}
+	parts := strings.Split(clean, "/")
+	if len(parts) != 4 {
+		return false
+	}
+	if !strings.EqualFold(parts[1], "archive") {
+		return false
+	}
+	leaf := strings.ToLower(parts[3])
+	for _, name := range PartyFolders {
+		if leaf == name {
+			return true
+		}
+	}
+	return false
+}
+
 // IsArchivePartyMdlDir reports whether dirPath (relative, forward-
 // slash-separated) names the default-MDL pattern at exactly depth 4:
 // <project>/archive/<party>/mdl. Match is case-insensitive on the