feat(graceful-handoff): 2.0 — statusLine context-percent hint [skip-docs]

Step 4 of v2.0 plan. statusLine hook reads context_window.used_percentage
from stdin payload and prints display-only hint at 60% / 70%. NEVER runs
git (research/03 — statusLine scripts can be cancelled mid-flight, unsafe
for side effects). 9 tests cover thresholds, null payload, malformed JSON.
Includes hook-helper.mjs copied from llm-security as test infrastructure.

plugins/graceful-handoff/hooks/scripts/statusline-monitor.mjs

@@ -0,0 +1,51 @@
+#!/usr/bin/env node
+// statusline-monitor.mjs — graceful-handoff v2.0
+// statusLine hook: prints a context-percent hint, never runs git.
+//
+// Reads JSON from stdin (Claude Code statusLine payload). If
+// context_window.used_percentage is available:
+//   < 60%   → no output
+//   60-69%  → "kontekst NN% — vurder /graceful-handoff"
+//   ≥ 70%   → "kontekst NN% — kjør /graceful-handoff NÅ"
+//
+// Exit 0 always. statusLine is display-only — never run git here
+// (research/03 — statusLine scripts can be cancelled mid-flight).
+
+import { readFileSync } from 'node:fs';
+
+function readStdin() {
+  try {
+    return readFileSync(0, 'utf-8');
+  } catch {
+    return '';
+  }
+}
+
+function main() {
+  const raw = readStdin();
+  if (!raw.trim()) {
+    process.exit(0);
+  }
+  let payload;
+  try {
+    payload = JSON.parse(raw);
+  } catch {
+    process.exit(0);
+  }
+
+  const ctx = payload?.context_window;
+  const pct = ctx?.used_percentage;
+  if (typeof pct !== 'number' || isNaN(pct)) {
+    process.exit(0);
+  }
+
+  if (pct >= 70) {
+    process.stdout.write(`kontekst ${Math.round(pct)}% — kjør /graceful-handoff NÅ`);
+  } else if (pct >= 60) {
+    process.stdout.write(`kontekst ${Math.round(pct)}% — vurder /graceful-handoff`);
+  }
+  // < 60 → no output (silent)
+  process.exit(0);
+}
+
+main();