feat(tui,server,config): live config editor + artifact viewer

Two operator features over the existing WebSocket protocol, plus a tui-go nav fix.

Config editor (g / palette "config"):
- core:config gains a thin registry stack: OrchestrationKnobs ([orchestration]
  block), CorrexConfigWriter (round-trip TOML serializer; parseToml(write(c))==c),
  ConfigHolder (AtomicReference live config), and EditableConfig (allowlist of
  editable fields + patch applier; security fields are absent so they can never
  be patched).
- ConfigService validates -> persists (atomic temp+move) -> swaps the holder ->
  rebuilds config-derived services. Live-apply is scoped to safe seams: stage
  timeout, compaction threshold (now a supplier), router knobs (routerFacade
  rebuild), and personalization/project toggles all take effect on the next
  session/turn; in-flight sessions keep the config they started with.
  server.host/port are persisted + badged "restart required", not hot-swapped.
- Protocol: GetConfig / UpdateConfig / ConfigSnapshot; TUI overlay with
  type-aware editing (bool toggle, enum cycle, inline int/string edit) and save.

Artifact viewer (v / palette "artifacts"):
- Server assembles a session's artifacts from the event log and resolves bytes
  from the CAS store (StreamQueries.listArtifacts) — a replay-neutral snapshot
  read. TUI overlay lists artifacts and shows scrollable content.

tui-go fix: workflow failure no longer clears selectedID (which yanked the user
to the list); listNav lands on the first session when nothing is selected
instead of wrapping to a random one.

Config is not event-sourced (it lives in TOML); editing stays outside the log.

apps/tui-go/internal/app/update.go

@@ -167,6 +167,10 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 		m.overlayEventIdx = 0
 	case "t":
 		m.overlay = OverlayToolPalette
+	case "v":
+		m.openArtifacts()
+	case "g":
+		m.openConfig()
 	case "m":
 		m.openModelsOverlay()
 	case "w":
@@ -340,6 +344,10 @@ func (m Model) autoApprove() (tea.Model, tea.Cmd) {
 }
 
 func (m Model) handleOverlayKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
+	// Config overlay owns all its keys (esc cancels an in-progress edit rather than closing).
+	if m.overlay == OverlayConfig {
+		return m.handleConfigKey(k)
+	}
 	if k.Type == tea.KeyEsc {
 		m.overlay = OverlayNone
 		return m, nil
@@ -376,6 +384,29 @@ func (m Model) handleOverlayKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 		if runeIs(k, "t") {
 			m.overlay = OverlayNone
 		}
+	case OverlayArtifacts:
+		switch {
+		case k.Type == tea.KeyUp || runeIs(k, "k"):
+			if m.artifactsIndex > 0 {
+				m.artifactsIndex--
+				m.artifactScroll = 0
+			}
+		case k.Type == tea.KeyDown || runeIs(k, "j"):
+			if m.artifactsIndex < len(m.artifacts)-1 {
+				m.artifactsIndex++
+				m.artifactScroll = 0
+			}
+		case k.Type == tea.KeyPgUp:
+			if m.artifactScroll > 0 {
+				m.artifactScroll--
+			}
+		case k.Type == tea.KeyPgDown:
+			if m.artifactScroll < m.artifactContentMaxScroll() {
+				m.artifactScroll++
+			}
+		case runeIs(k, "v"):
+			m.overlay = OverlayNone
+		}
 	case OverlayModels:
 		switch {
 		case k.Type == tea.KeyUp || runeIs(k, "k"):
@@ -401,6 +432,23 @@ func (m Model) handleOverlayKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 	return m, nil
 }
 
+// openArtifacts opens the artifact viewer for the selected session and requests its
+// artifacts from the server. No-op when no session is selected.
+func (m *Model) openArtifacts() {
+	if m.selectedID == "" {
+		return
+	}
+	m.overlay = OverlayArtifacts
+	m.artifactsIndex = 0
+	m.artifactScroll = 0
+	// Reuse a cached listing only if it's for this session; otherwise show a loading state.
+	if m.artifactsFor != m.selectedID {
+		m.artifacts = nil
+		m.artifactsLoading = true
+	}
+	m.client.Send(protocol.ListArtifacts(m.selectedID))
+}
+
 // openModelsOverlay opens the model picker, pre-selecting the resident model.
 func (m *Model) openModelsOverlay() {
 	m.overlay = OverlayModels
@@ -452,6 +500,8 @@ func paletteCommands() []paletteCmd {
 		{"tools", "tool palette", "tools for the current stage"},
 		{"models", "swap model", "pick / pin the local model"},
 		{"events", "event inspector", "browse the event stream"},
+		{"artifacts", "view artifacts", "browse this session's artifacts"},
+		{"config", "edit config", "view / change correx settings"},
 		{"mode", "toggle mode", "switch chat / steering"},
 		{"cancel", "cancel session", "stop the selected session"},
 		{"back", "back to list", "leave the current session"},
@@ -486,6 +536,10 @@ func (m Model) execPalette(id string) (tea.Model, tea.Cmd) {
 	case "events":
 		m.overlay = OverlayEventInspector
 		m.overlayEventIdx = 0
+	case "artifacts":
+		m.openArtifacts()
+	case "config":
+		m.openConfig()
 	case "mode":
 		m.cycleChatMode()
 	case "cancel":
@@ -683,6 +737,13 @@ func (m *Model) listNav(dir int) {
 			break
 		}
 	}
+	// No current selection (e.g. nothing entered yet): start at the first
+	// session rather than wrapping off the end into an arbitrary entry.
+	if idx < 0 {
+		m.selectedID = list[0].ID
+		m.wfIndex = -1
+		return
+	}
 	n := idx + dir
 	if n < 0 {
 		n = len(list) - 1