fix(ui-trajectory): own composer overlay geometry

apps/web/tests/navigation-panes.e2e.ts

@@ -138,6 +138,23 @@ describe('web e2e: navigation & panes over a rich seeded session', () => {
     onTestFailed(() => saveFailureShot(page, 'web-e2e-navigation-trajectory'))
     await page.getByRole('tab', { name: 'Trajectory' }).click()
     await page.waitForTimeout(100)
+    const overlayLayout = await page.getByRole('table').evaluate((table) => {
+      const host = table.closest('[data-conversation-scroll]')
+      const seat = host?.querySelector('[data-composer-seat]') ?? null
+      const pane = table.parentElement
+      return {
+        hostPosition: host === null ? null : getComputedStyle(host).position,
+        paneOverflowX: pane === null ? null : getComputedStyle(pane).overflowX,
+        paneScrollableWidth: pane === null ? null : pane.scrollWidth - pane.clientWidth,
+        seatPosition: seat === null ? null : getComputedStyle(seat).position,
+      }
+    })
+    expect(overlayLayout).toEqual({
+      hostPosition: 'relative',
+      paneOverflowX: 'hidden',
+      paneScrollableWidth: 0,
+      seatPosition: 'absolute',
+    })
     expect({
       pageErrors: tripwire.pageErrors,
       slotErrors,
@@ -153,6 +170,8 @@ describe('web e2e: navigation & panes over a rich seeded session', () => {
     await page.locator('tr[data-kind="tool"]').first().click()
     const details = page.getByRole('complementary', { name: 'Event details' })
     await expect.poll(() => details.count(), { timeout: 10_000 }).toBe(1)
+    expect(await details.getByRole('tabpanel').evaluate(panel => getComputedStyle(panel).overflowX))
+      .toBe('hidden')
     await page.evaluate(() => { document.body.setAttribute('data-ds-dark-theme', '') })
     const darkSummarySurfaces = await details.getByRole('heading', { name: 'Payload' }).evaluate(heading => ({
       heading: getComputedStyle(heading).backgroundColor,

packages/client/ui-conversation/src/client/skeleton/ConversationRoot.module.css

@@ -208,6 +208,26 @@
   );
 }
 
+/* Views may opt into a composer overlay while ConversationRoot retains
+   ownership of the seat geometry and its active-phase precedence. */
+.scrollBody:has([data-conversation-composer-overlay]) {
+  position: relative;
+  overflow: hidden;
+}
+
+.scrollBody:has([data-conversation-composer-overlay]) > .viewArea {
+  flex: 1 1 0;
+  min-height: 0;
+  overflow: hidden;
+}
+
+.scrollBody:has([data-conversation-composer-overlay]) > .composerSeat {
+  position: absolute;
+  right: 0;
+  bottom: 0;
+  left: 0;
+}
+
 /* Hero phase: the composer stack (hero chrome + workspace row + card) is
    flex-centered in the column; composer phase docks it at the bottom. Flex,
    NOT absolute+transform: a transform would make this box the containing

packages/client/ui-trajectory/src/client/TrajectoryTable.module.css

@@ -15,7 +15,8 @@
 .tablePane {
   flex: 1;
   min-width: 0;
-  overflow: auto;
+  overflow-x: hidden;
+  overflow-y: auto;
   padding-bottom: var(--dsh-trajectory-bottom-clearance, 0px);
   container: trajectory-table / inline-size;
 }
@@ -28,7 +29,7 @@
   );
 
   width: 100%;
-  min-width: 480px;
+  min-width: 0;
   border-spacing: 0;
   table-layout: fixed;
   color: var(--dsw-alias-label-primary);
@@ -905,7 +906,8 @@
 .detailBody {
   flex: 1;
   min-height: 0;
-  overflow: auto;
+  overflow-x: hidden;
+  overflow-y: auto;
   padding-bottom: var(--dsh-trajectory-bottom-clearance, 0px);
   scrollbar-gutter: stable;
 }

packages/client/ui-trajectory/src/client/TrajectoryView.tsx

@@ -459,7 +459,7 @@ export function TrajectoryView({
   }
 
   return (
-    <div className={css.root}>
+    <div className={css.root} data-conversation-composer-overlay="">
       <TrajectoryToolbar
         actualDuration={actualDuration}
         onActualDurationChange={(nextActualDuration) => {

packages/client/ui-trajectory/src/client/views.module.css

@@ -13,30 +13,6 @@
   background: var(--dsw-alias-bg-layer-1);
 }
 
-/* Trajectory keeps the ledger and details panel inside the remaining
- * conversation height; only the internal panes scroll. The composer floats
- * over the ledger like chat's sticky seat — absolute, not sticky, because
- * this host does not scroll. */
-:global([data-conversation-scroll]):has(.root) {
-  position: relative;
-  overflow: hidden;
-}
-
-:global([data-conversation-scroll]):has(.root) > :first-child {
-  flex: 1 1 0;
-  min-height: 0;
-  overflow: hidden;
-}
-
-/* div qualifier outranks ConversationRoot's active-phase sticky rule (equal
- * specificity otherwise, and cross-module source order is bundler-defined). */
-:global([data-conversation-scroll]):has(.root) > :global(div[data-composer-seat]) {
-  position: absolute;
-  right: 0;
-  bottom: 0;
-  left: 0;
-}
-
 .ledger {
   position: relative;
   z-index: 0;
@@ -47,8 +23,6 @@
   min-width: 0;
   overflow: hidden;
 
-  /* Internal panes reserve the floating composer's live height plus a 16px
-   * breathing gap so end rows and detail bodies can scroll clear of the
-   * overlay. */
+  /* ConversationRoot publishes the floating composer's live height. */
   --dsh-trajectory-bottom-clearance: calc(var(--dsh-composer-height, 152px) + 16px);
 }

packages/client/ui-trajectory/tests/views.spec.tsx

@@ -288,6 +288,7 @@ describe('tab switching in ConversationRoot', () => {
     expect(screen.queryByRole('columnheader')).toBeNull()
     expect(screen.getByRole('toolbar', { name: 'Trajectory toolbar' })).toBeTruthy()
     expect(screen.getByRole('region', { name: 'Trajectory timeline' })).toBeTruthy()
+    expect(view.container.querySelector('[data-conversation-composer-overlay]')).toBeTruthy()
     fireEvent.click(screen.getByRole('button', { name: 'Collapse turns' }))
     expect(view.container.querySelector('[data-collapsed-summary="turn"]')).toBeTruthy()
     fireEvent.click(screen.getByRole('button', { name: 'Expand turns' }))