Add /graph G2: resumable budget, GraphUpdated status chip, PTY + turn-level coverage

BudgetLimited is now a resumable state: a budget trip demotes in-flight
nodes to Ready (a resource stop, not a verdict — no forever-Running node is
ever persisted) and '/graph resume --budget <tokens>' re-arms the graph with
fresh headroom (new budget = spent-so-far + extra). The tripped node's
partial burn is charged into tokens_spent_nodes at BOTH cascade sites before
the demotion clears current_node, so the top-up arithmetic never runs on an
under-counted ledger. Any input starting with 'resume' resolves to a resume
(case-insensitive; malformed top-ups surface the usage hint) and setup_graph
refuses to replace any non-Complete graph — a typo can no longer silently
destroy a resumable graph. An explicit --budget on a merely-paused graph is
rejected loudly instead of silently discarded; all trip-time messages now
advertise the top-up.

The pager gains a graph status chip: a new GraphUpdated wire variant
(extensions/notification.rs, old pagers degrade via #[serde(other)]) is
emitted from the single persist_graph_state chokepoint — every transition is
both a checkpoint and a badge tick — with a 'cleared' sentinel on /graph
clear and a one-shot re-emit after session restore (the replayed updates log
otherwise shows the pre-shutdown Active state that from_snapshot just
demoted in memory). TUI side: GraphDisplayState, session-notification arm,
and a goal-idiom chip with node progress, clamped current-node title, and
budget-aware spend. Pre-session command availability now advertises /graph
from the flags (it was fail-closed to the in-session path only, so the
welcome-screen slash menu never showed it).

Coverage: GraphUpdated wire round-trip + minimal-payload + unknown-tag
tests; PTY scenarios graph_slash_presession{,_disabled}.yaml (both run
green against the real pager binary); handle_prompt-level e2e for terminal
slash outcomes (/graph status|resume|pause, /goal refusals while the graph
owns the engine); budget top-up e2e driving a BudgetLimited diamond back to
Complete. Not shimmed: pre-G2 persisted snapshots with budget-Failed nodes
(the KIGI_GRAPH flag has never shipped enabled, so none exist).

kigi-shell 4927 and kigi-tui 6610 lib tests green; workspace clippy clean.

crates/codegen/kigi-shell/src/session/acp_session_impl/goal.rs

@@ -1908,11 +1908,21 @@ impl SessionActor {
         // budget, so a node-level budget trip is the graph-level trip.
         if self.graph_harness_enabled() && self.graph_tracker.lock().is_active() {
             tracing::warn!("graph: node goal budget trip cascades to graph BudgetLimited");
-            self.graph_tracker.lock().budget_limit();
+            {
+                let mut tracker = self.graph_tracker.lock();
+                // Budget integrity: charge the tripped node's partial burn
+                // BEFORE budget_limit clears current_node — otherwise the
+                // top-up arithmetic runs on an under-counted ledger.
+                if let Some(node_id) = tracker.current_node_id().map(str::to_owned) {
+                    tracker.charge_node_tokens(&node_id, tokens_used);
+                }
+                tracker.budget_limit();
+            }
             self.persist_graph_state();
             self.send_slash_command_output(&format!(
                 "Graph token budget reached ({tokens_used} tokens this node) — graph \
-                 stopped. Use /graph clear, then /graph <objective> to start a new one."
+                 stopped. Top up with /graph resume --budget <tokens>, or /graph clear \
+                 to abandon."
             ))
             .await;
             return true;