fix(web,hub): surface inactive-session error on text-only send (closes #918) (#922)

Sending text via the web composer to an archived/inactive session
silently dropped on the floor: the hub returned 409 but the web client
swallowed the failure with a console.error in the resolveSessionId catch
branch, leaving the operator with no signal and no recovery path.

Hub: add a machine-readable `code: 'session_inactive'` to the 409 body
so the web client can discriminate this branch without string-matching
the i18n-able human message.

Web (router.tsx, useSendMessage.ts, HappyComposer.tsx):

  - useSendMessage now fires `onError` on resolveSessionId rejection,
    not just on POST /messages failure -- closes the visibility hole
    when the inactive session has no resume target or resume itself
    fails.

  - The route classifies the thrown error: a 409 + session_inactive
    code or a synthetic ApiError thrown from resolveSessionId attaches
    a Reopen action to the existing inline composer-error affordance.
    Plain 4xx / 5xx / network keep the legacy text-restore UX
    untouched.

  - Reopen calls api.reopenSession (the same path as SessionList's
    Reopen menu item), invalidates the session queries, and navigates
    to the resumed sessionId.  Per the orchestrator brief's friction
    pass on #917 the affordance does NOT auto-replay the send; the
    operator re-clicks Send on the restored composer text.

Tests:

  - hub messages.test.ts: 409 carries `code: 'session_inactive'`.
  - useSendMessage.test.tsx: ApiError(409, session_inactive) from POST
    flows through onError; resolveSessionId rejection flows through
    onError keyed by the original sessionId; 500 keeps the legacy
    fallback path with no code attached.

AI disclosure: implemented by an AI agent (Claude Opus 4.7) acting on
operator instructions; tests pass locally (bun typecheck + bun run
test for hub and web).

Co-authored-by: Cursor <cursoragent@cursor.com>

web/src/lib/locales/en.ts

@@ -240,6 +240,8 @@ export default {
   'chat.terminal': 'Terminal',
   'chat.switchRemote': 'Switch to remote mode',
   'chat.sendError.fallback': "Couldn't send your message. Edit and try again.",
+  'chat.sendError.sessionInactive': 'This session is archived. Reopen it to send your message.',
+  'chat.sendError.sessionInactive.action': 'Reopen',
 
   // Codex review
   'codexReview.title': 'Codex review',