fix(ui): uniform header bar height on chat, sources, and the document viewer

frontend/assets/styles.css

@@ -152,6 +152,10 @@ body::after {
   position: sticky;
   top: 0;
   z-index: 20;
+  /* Phase 12: body is a definite-height flex column; without this the
+     header shrinks (flex-shrink:1) to its content minimum on any page
+     whose content overflows the viewport (e.g. Sources at ≤640px). */
+  flex-shrink: 0;
 }
 /* 2px brand→cyan gradient hairline under the sticky header (phase 08;
    shared by the app header and the document-viewer header, phase 10). */
@@ -550,14 +554,20 @@ body::after {
 .docs-table tbody tr:last-child td { border-bottom: 0; }
 
 /* ---------- Document viewer (phase 10) ---------- */
+/* Phase 12: the same fixed-height bar as .app-header (--header-h, 64px /
+   58px mobile) — the header must never change size between chat,
+   sources, and the document viewer (owner report 2026-08-22). */
 .doc-header {
   position: sticky;
   top: 0;
   z-index: 20;
   background: var(--surface);
+  height: var(--header-h);
+  /* Phase 12: same guard as .app-header — the bar never shrinks. */
+  flex-shrink: 0;
 }
 .doc-header-inner {
-  padding-block: 0.7rem;
+  height: 100%;
   display: flex;
   align-items: center;
   gap: 0.9rem;
@@ -589,15 +599,21 @@ body::after {
   overflow: hidden;
   text-overflow: ellipsis;
 }
-/* Meta row: source badge · format badge · mono path · indexed · chunks. */
+/* Meta row: source badge · format badge · mono path · indexed · chunks.
+   Phase 12: it may clip, but it must NEVER wrap — a wrapped meta row
+   would grow the header past the shared --header-h bar. */
 .doc-meta {
   display: flex;
-  flex-wrap: wrap;
+  flex-wrap: nowrap;
   align-items: center;
   gap: 0.4rem;
   margin-top: 0.35rem;
   font-size: 0.78rem;
   color: var(--ink-soft);
+  /* Overflowing content (badges + path + dates) clips at the bar edge;
+     nowrap keeps text on one line so the row can never grow the header. */
+  white-space: nowrap;
+  overflow: hidden;
 }
 .doc-source-badge {
   background: var(--brand-soft);
@@ -622,6 +638,9 @@ body::after {
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
+  /* The path is the meta row's designated ellipsis target: with a floor it
+     keeps a visible box on narrow screens while the trailing badges clip. */
+  min-width: 6rem;
 }
 .doc-chunks { font-family: var(--mono); }
 
@@ -743,7 +762,7 @@ body::after {
   .suggestions { flex-wrap: nowrap; overflow-x: auto; justify-content: flex-start;
     padding-bottom: 0.4rem; -webkit-overflow-scrolling: touch; scrollbar-width: thin; }
   .suggestion-chip { flex: 0 0 auto; }
-  .doc-header-inner { flex-wrap: wrap; gap: 0.5rem; padding-block: 0.6rem; }
+  .doc-header-inner { flex-wrap: nowrap; gap: 0.5rem; }  /* phase 12: fixed-height bar — no wrap, no extra padding */
   #doc-title { font-size: 1.1rem; }
   .doc-path { max-width: 16rem; }
   .doc-md { padding: 1.1rem 1rem; }