Add sub-question branching + document summary modals

- Source modal now shows LLM-generated document summary (lazy-gen + cached
  in documents.summary) instead of raw chunk text; toggle reveals matched
  chunk; "View all chunks" button fetches every chunk of the document via
  new api/document-chunks.php endpoint
- Each sub-question card gets a "Branch ↓" button that pre-fills the query
  with that sub-question and shows a context panel with the prior brief
  summary; prior_context + branch_notes are injected into interpretSeed()
  and synthesise() so the LLM knows where the research is coming from
- Upload document summaries generated at synthesis time and attached to
  upload sources alongside corpus summaries
- DB: documents.summary TEXT column added to bnl_corpus on chloe

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/js/advocate.js

@@ -6,6 +6,7 @@
   let lang = 'en';
   let uploadFiles = [];
   let lastResult = null;
+  let branchContext = null;
 
   const SLICE_DEFS = [
     { id: 'family_core',      label: 'Family Law Core' },
@@ -65,6 +66,11 @@
       modalEyebrow: document.getElementById('advSourceModalEyebrow'),
       modalMeta: document.getElementById('advSourceModalMeta'),
       modalText: document.getElementById('advSourceModalText'),
+      branchPanel: document.getElementById('advBranchPanel'),
+      branchClear: document.getElementById('advBranchClear'),
+      branchOrigin: document.getElementById('advBranchOrigin'),
+      branchSummary: document.getElementById('advBranchSummary'),
+      branchNotes: document.getElementById('advBranchNotes'),
     });
 
     if (!els.form) return;
@@ -75,7 +81,12 @@
     bindRanges();
     bindUpload();
     bindModal();
+    bindBranch();
     els.form.addEventListener('submit', onSubmit);
+    els.results.addEventListener('click', (e) => {
+      const btn = e.target.closest('.dr-branch-btn');
+      if (btn) branchFromSubQ(btn.dataset.question || '');
+    });
 
     renderTrace(STEP_LABELS.map((label) => ({ label, detail: 'Waiting…', status: 'idle' })));
   });
@@ -214,7 +225,62 @@
       source.matched_sub_questions?.length ? ['Matched sub-Q', source.matched_sub_questions.join(', ')] : null,
     ].filter(Boolean);
     els.modalMeta.innerHTML = '<dl>' + metaRows.map(([k, v]) => `<dt>${escapeHtml(k)}</dt><dd>${escapeHtml(String(v))}</dd>`).join('') + '</dl>';
-    els.modalText.textContent = source.chunk_text || source.excerpt || '';
+
+    const summary = source.summary || '';
+    const chunkText = source.chunk_text || source.excerpt || '';
+    const isUpload = source.source_origin === 'upload';
+    const hasDocId = source.document_id != null;
+
+    let html = summary
+      ? `<div class="dr-modal-summary">${escapeHtml(summary)}</div>`
+      : `<div class="dr-modal-summary dr-modal-summary--empty"><em>Summary not yet generated — showing raw chunk below.</em></div>`;
+
+    if (chunkText) {
+      html += `<button class="dr-modal-chunk-toggle" type="button">Show matching chunk ▼</button>`;
+      html += `<div class="dr-modal-chunk-text is-hidden">${escapeHtml(chunkText)}</div>`;
+    }
+    if (!isUpload && hasDocId) {
+      html += `<button class="dr-modal-all-chunks" type="button" data-document-id="${source.document_id}">View all document chunks →</button>`;
+      html += `<div class="dr-modal-chunks-list"></div>`;
+    }
+
+    els.modalText.innerHTML = html;
+
+    const chunkToggle = els.modalText.querySelector('.dr-modal-chunk-toggle');
+    const chunkDiv = els.modalText.querySelector('.dr-modal-chunk-text');
+    chunkToggle?.addEventListener('click', () => {
+      const isHidden = chunkDiv.classList.toggle('is-hidden');
+      chunkToggle.textContent = isHidden ? 'Show matching chunk ▼' : 'Hide matching chunk ▲';
+    });
+
+    const allChunksBtn = els.modalText.querySelector('.dr-modal-all-chunks');
+    const chunksListDiv = els.modalText.querySelector('.dr-modal-chunks-list');
+    if (allChunksBtn && chunksListDiv) {
+      allChunksBtn.addEventListener('click', async () => {
+        allChunksBtn.disabled = true;
+        allChunksBtn.textContent = 'Loading…';
+        try {
+          const res = await fetch(`api/document-chunks.php?document_id=${source.document_id}`, { credentials: 'same-origin' });
+          const data = await res.json();
+          if (data.ok && data.chunks) {
+            chunksListDiv.innerHTML =
+              `<div class="dr-modal-chunks-head">${escapeHtml(data.document?.title || '')} · ${data.chunks.length} chunks</div>` +
+              data.chunks.map((c) => `<div class="dr-modal-chunk-item">
+                <span class="dr-modal-chunk-idx">#${c.chunk_index + 1}${c.section_title ? ' · ' + escapeHtml(c.section_title) : ''}</span>
+                <p class="dr-modal-chunk-preview">${escapeHtml(truncate(c.content, 300))}</p>
+              </div>`).join('');
+            allChunksBtn.remove();
+          } else {
+            allChunksBtn.textContent = 'Could not load chunks.';
+            allChunksBtn.disabled = false;
+          }
+        } catch (_) {
+          allChunksBtn.textContent = 'Error loading chunks.';
+          allChunksBtn.disabled = false;
+        }
+      });
+    }
+
     els.modal.classList.remove('is-hidden');
   }
 
@@ -282,6 +348,10 @@
       controls: getControls(),
       advocate_role: advocateRole,
     };
+    if (branchContext) {
+      payload.prior_context = branchContext;
+      payload.branch_notes = (els.branchNotes ? els.branchNotes.value : '').trim();
+    }
 
     const stepKeyToIndex = {
       interpretation: 0,
@@ -370,6 +440,7 @@
       return;
     }
 
+    finalResult.query = query;
     lastResult = finalResult;
     const meta = finalResult.trace_metadata || {};
     const rc = meta.retrieval_counts || {};
@@ -596,6 +667,7 @@
           <div class="dr-subq-report__question">${escapeHtml(sq.question || '')}</div>
           ${sq.rationale ? `<div class="dr-subq-report__rationale">${escapeHtml(sq.rationale)}</div>` : ''}
         </div>
+        <button class="dr-branch-btn" type="button" data-question="${escapeHtml(sq.question || '')}" aria-label="Branch research from this sub-question">Branch ↓</button>
       </div>
       <ul class="dr-mini-source-list">${sourceItems}</ul>
     </div>`;
@@ -611,6 +683,34 @@
     }
   }
 
+  function bindBranch() {
+    if (!els.branchClear) return;
+    els.branchClear.addEventListener('click', clearBranch);
+  }
+
+  function clearBranch() {
+    branchContext = null;
+    if (els.branchPanel) els.branchPanel.classList.add('is-hidden');
+    if (els.branchNotes) els.branchNotes.value = '';
+  }
+
+  function branchFromSubQ(question) {
+    if (!lastResult || !question) return;
+    branchContext = {
+      original_query: lastResult.query || '',
+      brief_summary: (lastResult.brief_markdown || '').slice(0, 600),
+      what_we_found: lastResult.what_we_found || '',
+      top_sources: (lastResult.sources || []).slice(0, 5).map((s) => ({
+        n: s.n, title: s.title, excerpt: (s.excerpt || '').slice(0, 200),
+      })),
+    };
+    els.input.value = question;
+    if (els.branchOrigin) els.branchOrigin.textContent = 'Original query: ' + branchContext.original_query;
+    if (els.branchSummary) els.branchSummary.textContent = branchContext.brief_summary;
+    if (els.branchPanel) els.branchPanel.classList.remove('is-hidden');
+    els.form.scrollIntoView({ behavior: 'smooth', block: 'start' });
+  }
+
   function renderSourceCard(s) {
     const score = s.reranker_score != null ? s.reranker_score : s.similarity;
     const originTagClass = s.source_origin === 'upload' ? 'dr-source-tag dr-source-tag--upload' : 'dr-source-tag';