feat: live visibility into what the agent is running (no more silent waiting)

Operator: "I'd like to be able to see in the chat what the agent is actually
running, right now I just wait while nothing happens." Two compounding gaps:

1. The auto-continuation worker (cmd/nomos/continue.go) had zero live push —
   its result only appeared on a manual page reload, so approving a plan and
   watching the chat looked completely dead even while the agent was actively
   working.
2. Even with polling, continueSession only persisted ONE message at the very
   end of a continuation — a continuation that runs several tool calls before
   concluding would still show total silence for however long that took.

Fixed both:
- web/src/lib/stores/chat.ts: polls the current session's messages every 3s
  between turns (never while a live stream owns the message list) and merges
  in anything new. Started after a live turn ends and when a session loads;
  stopped on new-chat/session-switch.
- cmd/nomos/store.go: insertMessageReturningID/updateMessage — lets a message
  be created as a placeholder and updated in place.
- cmd/nomos/continue.go: continueSession now inserts a placeholder the
  instant it starts (renders as the existing "thinking" dots — immediate
  feedback that something is happening) and updates that SAME row after
  EVERY tool call, not just at the end. A poll within ~3s of any tool call
  landing shows it — individual `run` commands appear as the agent issues
  them, not just the final rolled-up summary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/lib/stores/chat.ts

@@ -95,11 +95,8 @@ function mergeToolCalls(raw: ToolCallResult[] | undefined): ToolCallResult[] {
   return Array.from(byId.values())
 }
 
-export async function loadSessionMessages(sessionId: string) {
-  currentSession.set(sessionId)
-  const msgs = await fetchMessages(sessionId)
-  sessionMessages.set(msgs)
-  const chatMsgs: ChatMessage[] = msgs.map((m) => {
+function toChatMessages(msgs: Message[]): ChatMessage[] {
+  return msgs.map((m) => {
     const tools = mergeToolCalls(m.content?.tool_calls)
     return {
       id: m.id,
@@ -109,7 +106,50 @@ export async function loadSessionMessages(sessionId: string) {
       pendingApprovals: extractApprovals(tools)
     }
   })
-  messages.set(chatMsgs)
+}
+
+export async function loadSessionMessages(sessionId: string) {
+  currentSession.set(sessionId)
+  const msgs = await fetchMessages(sessionId)
+  sessionMessages.set(msgs)
+  messages.set(toChatMessages(msgs))
+  startPolling(sessionId)
+}
+
+// Live visibility for autonomous work: the auto-continuation worker (see
+// cmd/nomos/continue.go) runs entirely server-side and has no live push —
+// previously the only way to see its result was to manually reload the
+// session, so approving a plan and then waiting felt like nothing was
+// happening even while the agent was actively working. This polls the
+// session's persisted messages every few seconds and merges in anything new
+// (an auto-continuation's result, a fresh pending approval it queued, etc.)
+// so the transcript updates on its own. Only runs between turns — never
+// while a live streaming turn owns the message list, to avoid clobbering the
+// in-progress optimistic UI.
+let pollTimer: ReturnType<typeof setInterval> | null = null
+let pollingSessionId: string | null = null
+
+function startPolling(sessionId: string) {
+  stopPolling()
+  pollingSessionId = sessionId
+  pollTimer = setInterval(async () => {
+    if (get(streaming)) return
+    if (pollingSessionId !== sessionId || get(currentSession) !== sessionId) return
+    const msgs = await fetchMessages(sessionId)
+    if (get(streaming) || pollingSessionId !== sessionId) return // re-check: the fetch itself takes time
+    const current = get(messages)
+    if (msgs.length === current.length) return
+    sessionMessages.set(msgs)
+    messages.set(toChatMessages(msgs))
+  }, 3000)
+}
+
+export function stopPolling() {
+  if (pollTimer) {
+    clearInterval(pollTimer)
+    pollTimer = null
+  }
+  pollingSessionId = null
 }
 
 export function sendMessage(text: string) {
@@ -202,7 +242,12 @@ export function sendMessage(text: string) {
           }
           return [...ms]
         })
-        currentSession.set(ev.data?.session_id ?? ev.session_id)
+        const sid = ev.data?.session_id ?? ev.session_id
+        currentSession.set(sid)
+        // Start polling for auto-continuation results now that the live turn
+        // is over — this is what makes an approved plan's later steps show up
+        // on their own instead of requiring a manual reload.
+        if (sid) startPolling(sid)
       } else if (ev.type === 'error') {
         error.set(ev.data)
       }
@@ -220,6 +265,7 @@ export function sendMessage(text: string) {
 
 export function newChat() {
   cancelStream()
+  stopPolling()
   currentSession.set(null)
   messages.set([])
   error.set(null)