feat(browse): generalize the in-pane tool embed to fold classifier/transmittal/archive

grid.js was classifier-only; make it embed ANY embeddable full-page tool the
cascade resolves as default_tool — classifier (incoming/), transmittal
(staging/), archive (the index) — as an iframe scoped to the current dir
(<dir>/<tool>.html). This is the browse-as-shell bridge from the ADR: browse
stays the top-level app and the heavy tools open in-pane (the gridView), so
navigating to staging/ or archive/ inside browse shows transmittal/archive
without leaving the shell, with ?view=browse falling back to the folder
listing (and the standalone tools still served directly at the no-slash URL).

EMBEDDABLE = {classifier, transmittal, archive}; tables/forms embed in the
preview pane instead, landing/browse don't self-embed. resolveViewMode keys
off grid.availableHere() (now generic). Validated in a containerized browser:
each dir embeds its tool, ?view=browse overrides to the listing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

browse/js/events.js

@@ -1121,11 +1121,12 @@
 
     // View mode is URL-driven, not UI-driven.
     //
-    //   ?view=grid    → grid mode (only honored where classifier is
-    //                   available; otherwise falls back to browse)
-    //   ?view=browse  → browse mode (always)
-    //   default       → path-based: grid when inside an incoming/
-    //                   subtree, browse everywhere else
+    //   ?view=grid    → embedded-tool view (only honored where the cascade's
+    //                   default_tool is an embeddable full-page tool —
+    //                   classifier/transmittal/archive; else falls back to browse)
+    //   ?view=browse  → browse listing (always)
+    //   default       → embedded-tool view when the dir's default_tool is one
+    //                   of those tools, browse listing everywhere else
     //
     // resolveViewMode reads the current location and returns the mode
     // to render; applyResolvedViewMode toggles the panes accordingly.
@@ -1134,10 +1135,10 @@
         var qs = new URLSearchParams(window.location.search);
         var explicit = (qs.get('view') || '').toLowerCase();
         var grid = window.app.modules.grid;
-        var classifierHere = !!(grid && grid.availableHere && grid.availableHere());
-        if (explicit === 'grid') return classifierHere ? 'grid' : 'browse';
+        var toolHere = !!(grid && grid.availableHere && grid.availableHere());
+        if (explicit === 'grid') return toolHere ? 'grid' : 'browse';
         if (explicit === 'browse') return 'browse';
-        return classifierHere ? 'grid' : 'browse';
+        return toolHere ? 'grid' : 'browse';
     }
 
     function applyResolvedViewMode() {

browse/js/grid.js

@@ -1,48 +1,53 @@
-// grid.js — "Grid mode" plugin for browse. Loads the classifier tool
-// as an iframe scoped to the current directory so users get classifier's
-// full bulk-rename workflow without leaving browse.
+// grid.js — in-pane tool embed for browse (the browse-as-shell bridge; see
+// ARCHITECTURE.md's ADR). Loads a heavy, full-page tool as an iframe scoped to
+// the current directory so the user gets that tool's full workflow without
+// leaving the browse shell. browse stays the top-level app; the cascade's
+// default_tool decides which tool embeds here.
 //
-// Availability: the cascade decides. Grid auto-activates wherever the
-// .zddc cascade resolves default_tool=classifier (defaults.zddc.yaml
-// declares this for archive/<party>/incoming/). Operators can extend
-// — e.g. setting default_tool=classifier on a custom dir activates
-// grid mode there too — without touching this code.
-//
-// Iframe src resolution: <currentDirURL>/classifier.html. Iframe
-// embedding only works in server mode; file:// pages don't get the
-// Grid toggle.
+// Availability: the cascade decides — `state.scopeDefaultTool` (the
+// X-ZDDC-Default-Tool header) must name one of the EMBEDDABLE full-page tools:
+// classifier (archive/<party>/incoming/), transmittal (…/staging/), archive
+// (the archive index). tables/forms embed in the preview pane instead
+// (table-leaf / form view); landing/browse don't self-embed. Operators extend
+// by setting default_tool on a dir — no code change. Iframe src:
+// <currentDirURL>/<tool>.html. Server mode only (file:// has no server).
 (function () {
     'use strict';
 
     var state = window.app.state;
     var mounted = false;
 
-    function classifierAvailableHere() {
-        // state.scopeDefaultTool is set by the loader from the
-        // X-ZDDC-Default-Tool response header on every listing fetch.
-        // Grid mode is meaningful exactly where the cascade picks
-        // classifier as the default — no client-side path matching.
-        return state.scopeDefaultTool === 'classifier';
+    // Full-page tools that embed in the gridView pane when they're the dir's
+    // default_tool. (tables/form embed in the preview pane; landing/browse are
+    // not in-pane embeds.)
+    var EMBEDDABLE = { classifier: 1, transmittal: 1, archive: 1 };
+
+    // The cascade-resolved default tool for the current dir when it's an
+    // embeddable full-page tool; "" otherwise.
+    function embedToolHere() {
+        var t = state.scopeDefaultTool;
+        return (t && EMBEDDABLE[t]) ? t : '';
     }
 
     function activate() {
         var host = document.getElementById('gridView');
         if (!host) return;
         if (mounted) return;
-        if (state.source !== 'server' || !classifierAvailableHere()) return;
+        var tool = embedToolHere();
+        if (state.source !== 'server' || !tool) return;
 
-        // Compute the iframe src: current page's directory + classifier.html.
+        // Compute the iframe src: current page's directory + <tool>.html.
         var pathname = window.location.pathname || '/';
         if (!pathname.endsWith('/')) {
             var lastSlash = pathname.lastIndexOf('/');
             pathname = lastSlash >= 0 ? pathname.substring(0, lastSlash + 1) : '/';
         }
-        var src = pathname + 'classifier.html';
+        var src = pathname + tool + '.html';
 
         host.innerHTML = '';
         var frame = document.createElement('iframe');
         frame.src = src;
-        frame.title = 'ZDDC Classifier (Grid mode)';
+        frame.title = 'ZDDC ' + tool;
         frame.style.cssText = 'width:100%;height:100%;border:0;display:block;'
             + 'background:var(--bg);';
         host.appendChild(frame);
@@ -61,9 +66,12 @@
     window.app.modules.grid = {
         activate: activate,
         reset: reset,
-        // Hook for events.js to show/hide the Grid toggle button.
+        // Hook for events.js's view-mode resolution: is an embeddable tool the
+        // default here?
         availableHere: function () {
-            return state.source === 'server' && classifierAvailableHere();
-        }
+            return state.source === 'server' && !!embedToolHere();
+        },
+        // The embeddable tool name (or "") — lets the shell label the view.
+        toolHere: embedToolHere
     };
 })();