phase: 99_kb_tree_table_and_back_nav

All verification is complete and green. Final report:

**Phase 99 — final verification pass (all 3 tasks already in `complete/`)**

- Verified the one-line Description clamp: `.kb-desc-cell` flex wrapper + `.kb-desc-text` ellipsis triad + `nowrap` column + in-cell Edit button + hover `title` + untouched level block (source diffs match D1; unit pins present)
- Verified the back-button breadcrumb nav: `applyTarget(target, push)` state-only `pushState`, no-duplicate gate, popstate adopt/reset, `bor:view-refresh` alignment before `loadTree()`, anonymous gate listener-free, router.js untouched (D2)
- `uv run pytest --cov=app`: **2180 passed**, coverage **99%** (>90% gate)
- `uv run ruff check .`: clean; `uv run pyright`: **0 errors, 0 warnings**
- `uv run pytest tests/e2e/test_kb_tree_nav.py -v --no-cov` (isolated, DB up): **4/4 passed** (back-walk, jump-then-back, fresh-nav/active-reclick, measured clamp incl. row-height parity ±4px, computed styles, full text in DOM/title/level block)
- Regression suites isolated: `test_kb_tree.py` 8✓, `test_ls_tree_drilldown.py` 3✓, `test_navbar_refresh.py` 7✓, plus `test_sync_summary_visibility.py` 3✓ (marker pin updated to `kb-desc-text kb-summary-pending` — the sanctioned class-pair change) and `test_edit_summaries.py` 4✓
- Criteria 1–4: **met** (each as above). Criterion 5 (atomic commit): left to the harness per executor rules — no `git add`/`commit` run; all changes left in the working tree
- No defects found in prior phases; no deviations. Stray `__pycache__/test_zz_smoke_tree_ui.*.pyc` is a leftover (no `.py` on disk) — inert, not touched
- Next pending phase: **none** — `todo/` will be empty once the harness moves this phase

frontend/assets/styles.css

@@ -1982,11 +1982,31 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
 .kb-folders-table { min-width: 480px; }
 .kb-folders-table td:nth-child(2) { font-family: var(--font); font-size: inherit; max-width: none; }
 .kb-folders-table td:nth-child(3) {
-  white-space: normal;
+  white-space: nowrap; /* phase 99 (D1): one line — the clamp's budget is the column width */
   min-width: 18rem;
   max-width: 44rem;
   font-size: 0.88rem;
 }
+/* Phase 99 (task 01, D1): the Description cell is ONE flex row — the
+   text span flexes + ellipsizes (the row height is one line, independent
+   of the description's length), the Edit button stays fixed (flex: 0 0
+   auto — it never wraps to a second line). The gap replaces the button's
+   old margin-left (the context-spacing rule below keeps only the level
+   block's margin-top). The clamp is visual only: the full text stays in
+   the DOM + on the span's title (hover). */
+.kb-desc-cell {
+  display: flex;
+  align-items: center;
+  gap: 0.4rem;
+  min-width: 0;
+}
+.kb-desc-text {
+  flex: 1 1 auto;
+  min-width: 0; /* lets the flex item shrink — what engages the ellipsis (the .sync-label pattern) */
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
 .folder-link {
   color: var(--brand-ink); /* 9.0:1 on --surface (the .doc-link pair, row variant) */
   text-decoration: none;
@@ -2024,9 +2044,9 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
 }
 .kb-summary-edit:hover { background: var(--brand-soft); color: var(--brand-ink); border-color: var(--brand); }
 .kb-summary-edit[hidden] { display: none; } /* the hidden attr must beat the display above */
-/* Context spacing: the row cell's button sits after the description
-   text; the level block's sits below the <p>. */
-.kb-folders-table .kb-summary-edit { margin-left: 0.4rem; }
+/* Context spacing: the row cell's button spacing comes from the
+   .kb-desc-cell gap (phase 99, task 01 — the margin-left is gone);
+   the level block's sits below the <p>. */
 .kb-level-body .kb-summary-edit { margin-top: 0.5rem; }
 .kb-summary-editor {
   display: block;
@@ -2041,6 +2061,11 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
   line-height: 1.5;
   resize: vertical;
 }
+/* Phase 99 (task 01): the open editor fills the .kb-desc-cell flex
+   wrapper — as a flex item it needs the explicit grow + min-width: 0
+   (the width: 100% base above still serves the level block's non-flex
+   .kb-level-body). */
+.kb-desc-cell .kb-summary-editor { flex: 1 1 auto; min-width: 0; }
 .kb-summary-actions {
   display: flex;
   align-items: center;