chore(desktop): dedupe session-color precedence, tighten tileStoredRow

- Extract resolveSessionColor(): the sessionColorFor fallback no longer
  re-implements the override -> project-color precedence that the
  $sessionColorById computed already owns.
- tileStoredRow: collapse the nested project-tree walk into a flatMap +
  find, matching the local style.

apps/desktop/src/app/chat/session-tile.tsx

@@ -286,31 +286,15 @@ export function SessionTilePane({ storedSessionId }: { storedSessionId: string }
  *  activity lands it there — resolving through the tree keeps its tab titled
  *  and tinted instead of a grey "Session" placeholder. */
 export function tileStoredRow(storedSessionId: string): SessionInfo | undefined {
-  const fromList = $sessions.get().find(s => sessionMatchesStoredId(s, storedSessionId))
+  const match = (s: SessionInfo) => sessionMatchesStoredId(s, storedSessionId)
 
-  if (fromList) {
-    return fromList
-  }
-
-  for (const project of $projectTree.get()) {
-    for (const repo of project.repos) {
-      for (const group of repo.groups) {
-        const row = group.sessions.find(s => sessionMatchesStoredId(s, storedSessionId))
-
-        if (row) {
-          return row
-        }
-      }
-    }
-
-    const preview = project.previewSessions?.find(s => sessionMatchesStoredId(s, storedSessionId))
-
-    if (preview) {
-      return preview
-    }
-  }
-
-  return undefined
+  return (
+    $sessions.get().find(match) ??
+    $projectTree
+      .get()
+      .flatMap(p => [...p.repos.flatMap(r => r.groups.flatMap(g => g.sessions)), ...(p.previewSessions ?? [])])
+      .find(match)
+  )
 }
 
 function tileTitle(storedSessionId: string): string {
@@ -416,6 +400,8 @@ export function SessionTabMenu({
   /** Layout-tree pane id — powers the Close-others/right/all verbs. */
   tabPaneId: string
 }) {
+  // Subscribe for reactivity; the row is read imperatively via tileStoredRow
+  // (which spans both sources), so the values themselves are unused here.
   useStore($sessions)
   useStore($projectTree)
   const pinnedSessionIds = useStore($pinnedSessionIds)

apps/desktop/src/store/session-color.ts

@@ -4,7 +4,7 @@ import { sessionProjectColor } from '@/app/chat/sidebar/projects/workspace-group
 import { Codecs, persistentAtom } from '@/lib/persisted'
 import { $projects } from '@/store/projects'
 import { $sessions, sessionPinId } from '@/store/session'
-import type { SessionInfo } from '@/types/hermes'
+import type { ProjectInfo, SessionInfo } from '@/types/hermes'
 
 // Per-session color OVERRIDES — a user-picked color that wins over the inherited
 // project color (#66565 layer 2). Desktop-local like pins, keyed by the DURABLE
@@ -39,13 +39,21 @@ export function setSessionColorOverride(durableId: string, color: null | string)
 //
 // Precedence in one place: an explicit per-session override wins over the
 // inherited project color. Agent-set color (#66565 layer 3) slots in here too.
+function resolveSessionColor(
+  session: SessionInfo,
+  projects: ProjectInfo[],
+  overrides: Record<string, string>
+): string | undefined {
+  return overrides[sessionPinId(session)] ?? sessionProjectColor(session, projects) ?? undefined
+}
+
 export const $sessionColorById = computed(
   [$sessions, $projects, $sessionColorOverrides],
   (sessions, projects, overrides) => {
     const map: Record<string, string> = {}
 
     for (const session of sessions) {
-      const color = overrides[sessionPinId(session)] ?? sessionProjectColor(session, projects)
+      const color = resolveSessionColor(session, projects, overrides)
 
       if (color) {
         map[session.id] = color
@@ -59,17 +67,12 @@ export const $sessionColorById = computed(
 // The color for a single session object (the tabs already hold the SessionInfo
 // they render, so they resolve through the same map the sidebar reads). A row
 // that isn't in `$sessions` — e.g. a project-tree session older than the
-// paginated recents page, opened as a tab — misses the map, so fall back to
-// resolving it directly through the same precedence the map uses.
+// paginated recents page, opened as a tab — misses the map, so fall back to the
+// same resolver the map is built from.
 export function sessionColorFor(session: null | SessionInfo | undefined): string | undefined {
   if (!session) {
     return undefined
   }
 
-  return (
-    $sessionColorById.get()[session.id] ??
-    $sessionColorOverrides.get()[sessionPinId(session)] ??
-    sessionProjectColor(session, $projects.get()) ??
-    undefined
-  )
+  return $sessionColorById.get()[session.id] ?? resolveSessionColor(session, $projects.get(), $sessionColorOverrides.get())
 }