make the editable tab name survive refreshes

sessionStorage is the per-tab store — separate per tab, survives reload and
navigation, dies with the tab. The route title is derived rather than assigned,
so navigating no longer wipes a name you typed.

Duplicating a tab clones sessionStorage, so a `navigate` that arrives already
holding a name is treated as a clone and drops it; fails soft.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/chat-ui-walkthrough.md

@@ -397,6 +397,53 @@ server code, not clicked through.
 
 ---
 
+## 16. The tab you named stays named
+
+`src/apps/officer-web/state/usePageTitle.ts`, `…/Layout/Header/Header.tsx`
+
+The title in the middle of the header has been editable for a while, and it renames the browser tab as
+you type — which is genuinely useful once you have six Officer tabs open and every one of them says
+"Chat". It just didn't last. Two separate reasons: the name lived only in React Query, so a refresh
+took it with the page; and `usePageTitleSync` had an effect that reset the title to the route default on
+every navigation, so clicking anything at all wiped it even without a refresh.
+
+**There is no tab id in the browser.** `chrome.tabs` gives an extension one, but page scripts are
+deliberately not allowed to know which tab they are in, or that other tabs exist — it's the same
+boundary that stops a page enumerating your windows. So there is no id to key the name on.
+
+There doesn't need to be: **`sessionStorage` *is* the per-tab store.** It's separate per tab, it
+survives a refresh and in-place navigation, and it's discarded when the tab closes. That is exactly the
+lifetime a tab name wants. (`localStorage` would be wrong in the obvious way — every tab would share
+one name, which is the problem, not the fix.)
+
+So the name is read from `sessionStorage` at module load and mirrored into a `useGlobal` entry; the
+React Query copy is what re-renders the header, and the storage copy is what survives the reload. The
+route title is no longer *assigned* to the state, it's **derived** — `label ?? titleForPath(pathname)`.
+Navigation therefore retitles the tab by itself when you haven't named it, and leaves it alone when you
+have. Clearing the field is the one way back to the route name, and there's no third state to get stuck
+in.
+
+**The one hole is duplicate-tab**, which you use constantly — and duplicating a tab clones its
+sessionStorage, so the copy would open wearing the original's name. Two tabs called "Platform Arch" is
+precisely what naming one was meant to prevent. `performance.getEntriesByType('navigation')[0].type`
+separates the cases: a refresh reports `reload`, a duplicate reports `navigate`. So a `navigate` that
+arrives already holding a name did not earn it, and the name is dropped. A brand-new tab is `navigate`
+too but has nothing stored, so it's untouched.
+
+That check **fails soft on purpose**: if the timing entry is missing, or some browser labels duplication
+differently, the copy just keeps the name — redundant, not wrong. Nothing else about the tab changes.
+
+The header input also became a draft committed on blur/Enter rather than a live write. It wrote every
+keystroke before, which was fine while the title was a plain string; now that an empty field means "use
+the route name", deleting the last character would have snapped the input to "Chat" under the cursor.
+Escape discards the draft.
+
+**Not verified:** the duplicate-tab navigation type, in an actual browser. The rest — that the name
+survives a refresh and a navigation — follows from sessionStorage's specified behaviour, but the clone
+heuristic is the part I could only reason about.
+
+---
+
 ## Things noticed and deliberately left alone
 
 - **`useChatWebSocket` silently ignores unparseable frames.** That one is intentional and the comment