fix(stats): M6 — trekbrief and trekplan records land where the yardstick reads

New lib/stats/stats-append.mjs: one record on stdin, appended to
<data dir>/<kind>-stats.jsonl. The data dir is CLAUDE_PLUGIN_DATA, else
~/.claude/plugins/data/voyage-ktg-plugin-marketplace (the yardstick's
default). A failed write exits 1 with a reason: reported, never silent.
/trekbrief Phase 7 and /trekplan Phase 12 now run it instead of
"append to ${CLAUDE_PLUGIN_DATA}/…; skip silently". intent-approval's
resolveApprovalDataDir delegates to the same resolver.

Chose a stdin heredoc over a --json argument because a JSON record in a
shell argument breaks on quotes in task text. Only trekbrief and trekplan
are rewired (økt 2's countable form needs exactly those two); the other
commands' stats prose is unchanged and docs/architecture.md says so.

Red a358059 7/7 → green 7/7. Suite 1208: 1206 pass / 0 fail / 2 skip.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/stats/stats-append.mjs

@@ -0,0 +1,70 @@
+// lib/stats/stats-append.mjs
+// Append one command-stats record to <data dir>/<kind>-stats.jsonl.
+//
+// Why this exists: the commands' stats phases said "append to
+// ${CLAUDE_PLUGIN_DATA}/<kind>-stats.jsonl; if it is not set, skip silently".
+// The Bash tool's env carries no CLAUDE_PLUGIN_DATA, so the record was skipped
+// whenever the model did not guess the directory itself — the same silent skip
+// that left brief-approved at 0 records. This writer resolves the directory
+// the way scripts/yardstick.mjs reads it, and a failed write is REPORTED
+// (exit 1 + reason), never swallowed. Stats still never block the workflow:
+// the command prose reports the failure and carries on.
+//
+// CLI (the record is read from stdin, so no shell quoting of JSON):
+//   node lib/stats/stats-append.mjs <kind> <<'JSON'
+//   { ...record... }
+//   JSON
+//   → prints {"written":true,"path":...} exit 0 | {"written":false,"reason":...} exit 1
+
+import { appendFileSync, mkdirSync, readFileSync } from 'node:fs';
+import { homedir } from 'node:os';
+import { join } from 'node:path';
+
+export const STATS_KINDS = Object.freeze([
+  'trekbrief', 'trekresearch', 'trekplan', 'trekexecute', 'trekreview', 'trekcontinue',
+]);
+
+/**
+ * The plugin data directory: CLAUDE_PLUGIN_DATA when the harness provides it,
+ * otherwise the directory the hooks write to and scripts/yardstick.mjs reads.
+ */
+export function resolveStatsDir(env = process.env) {
+  if (env.CLAUDE_PLUGIN_DATA) return env.CLAUDE_PLUGIN_DATA;
+  const home = env.HOME && env.HOME.length > 0 ? env.HOME : homedir();
+  return join(home, '.claude', 'plugins', 'data', 'voyage-ktg-plugin-marketplace');
+}
+
+/**
+ * @returns {{ written: boolean, path: string|null, reason?: string }}
+ */
+export function appendStatsRecord(kind, record, env = process.env) {
+  if (!STATS_KINDS.includes(kind)) {
+    return { written: false, path: null, reason: `unknown kind "${kind}" (one of ${STATS_KINDS.join(', ')})` };
+  }
+  if (!record || typeof record !== 'object' || Array.isArray(record)) {
+    return { written: false, path: null, reason: 'record must be a JSON object' };
+  }
+  const dir = resolveStatsDir(env);
+  const path = join(dir, `${kind}-stats.jsonl`);
+  try {
+    mkdirSync(dir, { recursive: true });
+    appendFileSync(path, JSON.stringify(record) + '\n');
+  } catch (e) {
+    return { written: false, path, reason: `${e.code || 'write-failed'}: ${e.message}` };
+  }
+  return { written: true, path };
+}
+
+if (import.meta.url === `file://${process.argv[1]}`) {
+  const kind = process.argv[2];
+  let record = null;
+  let reason = null;
+  try {
+    record = JSON.parse(readFileSync(0, 'utf8'));
+  } catch (e) {
+    reason = `stdin is not JSON: ${e.message}`;
+  }
+  const r = reason ? { written: false, path: null, reason } : appendStatsRecord(kind, record);
+  process.stdout.write(JSON.stringify(r) + '\n');
+  process.exit(r.written ? 0 : 1);
+}