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>
Implements Spor C of post-v3.4.0 roadmap. Zero-dep harness measures
CLAUDE_CODE_FORK_SUBAGENT cache-prefix preservation across 3 fork-children
with identical --allowedTools at 150-250K parent context.
Harness uses --append-system-prompt-file (avoids stdin buffer cap at
>200K bytes) + --exclude-dynamic-system-prompt-sections (prevents
per-child cache-prefix divergence from cwd/env/git-status).
Companion analyser summarizes accumulated ultraexecute-stats.jsonl:
percentile wall_time (p50/p90/max), total events, ISO time range.
Output: JSON via --json <path> CLI shim.
Result file is gitignored (*.local.md). Master-plan thresholds
(<= 1.5K positive / >= 3.5K negative) gate the v3.5.0 Path C decision.
Brief: .claude/projects/2026-05-04-spor-c-q3-cache-prefix-experiment/brief.md
Master-plan: .claude/projects/2026-05-04-post-v3.4.0-roadmap/master-plan.md
