feat: scaffold redsen-lean-harness v0.1.0

Recovered from crashed session (Node OOM). Repo contains full P0-P6 scaffold: plugin.json/marketplace.json, AGENTS.md, ADRs 0001-0006, lh CLI (init/index/graph/lane/run/memory/host/report/doctor), 10 .github/agents, 12 CLI skills, instructions, context7 mcp.json, and unit/e2e test suite. Fixed: run.mjs read --in-tokens/--out-tokens but tests and CLI docs use --input-tokens/--output-tokens, so telemetry totals were always 0. Now accepts both forms. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-09-09 22:44:15 +02:00
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+# ADR 0006 — Local NDJSON telemetry, no server, no budget cap
+
+- **Status**: Accepted
+- **Date**: 2026-09-09
+
+## Context
+
+Requirement: the harness must be *fast, observable and benchmarkable*. Scope was explicitly set to
+**telemetry only** — per-run token counts, latency, tool-call traces, pass/fail — not an external
+benchmark suite.
+
+Separately, the operator chose **no budget cap** on parallel fan-out, combined with **fully
+dynamic** re-planning. That combination is the single largest cost risk in the system.
+
+## Decision
+
+1. **Append-only NDJSON** at `.agents/runs/<runId>/events.ndjson`. One JSON object per line,
+   written with `O_APPEND` so concurrent lanes cannot interleave partial lines.
+2. **OpenTelemetry GenAI-inspired attribute names** (`gen_ai.usage.input_tokens`,
+   `gen_ai.request.model`, …) **without an OTEL dependency**. The data is portable to a real
+   tracing backend later; today it costs nothing.
+3. **Tolerant reader.** Malformed lines are skipped, never thrown on. A crashed agent must not
+   destroy the log.
+4. **Live board.** `board.md` is regenerated on every event and shows lanes in flight, ralph
+   iterations, elapsed time, tokens, and — prominently — **burn rate in tokens/min**. Board
+   rendering is wrapped in try/catch so it can never break a telemetry write.
+5. **`lh report`** renders the markdown summary; **`lh report --journal`** renders the committed,
+   self-documenting per-run journal.
+
+### On the absent budget cap
+
+No hard cap is enforced, per the operator's explicit choice. The mitigation is **visibility, not
+prevention**: live burn rate in `board.md`, a post-run cost breakdown in `lh report`, and an
+advisory `concurrency.maxWriteLanes` ceiling that warns and only blocks under `--strict`.
+
+## Consequences
+
+- Zero infrastructure. Telemetry works offline and in CI with no setup.
+- `lh run event` is on the hot path (dozens of calls per run) and must stay well under 100 ms.
+- Cost overrun is possible by design. Accepted and documented; visibility is the control.
+- Because the schema is OTEL-shaped, exporting to Langfuse/OpenLLMetry later is a transform, not a
+  re-instrumentation.
+
+## Alternatives considered
+
+- **OpenTelemetry SDK** — rejected: heavy dependency and a collector to run, for data we currently
+  only read locally.
+- **SQLite event store** — rejected: native dependency (see ADR 0005), and NDJSON is already
+  append-safe and greppable.
+- **Hard credit cap** — rejected by the operator. Revisit if real runs overrun.