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-tui/src/app/agent.rs

@@ -385,6 +385,25 @@ impl GoalDisplayPhase {
         }
     }
 }
+/// Graph mode display state — the pager-side mirror of the
+/// `GraphUpdated` session notification (see the shell's
+/// `extensions/notification.rs`). Deliberately lean: the status chip
+/// shows counts + the current node; details live in `/graph status`.
+#[derive(Debug, Clone)]
+pub struct GraphDisplayState {
+    pub objective: String,
+    /// Reuses the goal display-status vocabulary (same wire strings).
+    pub status: GoalDisplayStatus,
+    pub total_nodes: u32,
+    pub achieved_nodes: u32,
+    pub failed_nodes: u32,
+    pub running_nodes: u32,
+    pub current_node_title: Option<String>,
+    pub token_budget: Option<i64>,
+    pub tokens_spent: i64,
+    pub pause_message: Option<String>,
+}
+
 /// Display state for an active goal, populated from `GoalUpdated`
 /// session notifications emitted by the goal orchestrator.
 #[derive(Debug, Clone)]