IB-WP-0016-T06: OpenRouter live-run guardrails

Add --chapter / --from-chapter / --to-chapter / --chunk selection flags
to generate init and generate from-source, plumb them into
init_generation_infospace via a new _filter_chunks_by_chapter helper,
and refuse to create an infospace when the filters reject every chunk
(InfospaceError "empty_chapter_selection"). The flags use the same
T03/T02 plumbing (chapter labels, roman numerals, chunk ids) so a
single-chapter selection is a one-flag command.

OpenRouter run-record metadata (model, request_id, usage tokens,
retry_count, duration_seconds) already lands in
output/workflows/runs/*.yaml; this task just adds the smoke test that
proves it stays there, plus the parallel guarantee that the same
provider metadata reaches generated artifact provenance via
provenance.provider_metadata.

tests/test_openrouter_live.py covers:
- chapter-filter, from/to-chapter range, and empty-selection failure on
  init (non-live, deterministic)
- CLI smoke through generate from-source with --chapter
- a pytest-skipped live OpenRouter one-chapter end-to-end gated by
  OPENROUTER_API_KEY + INFOSPACE_BENCH_ENABLE_LIVE_OPENROUTER, with
  INFOSPACE_BENCH_LIVE_MODEL override (default openai/gpt-4o-mini)

docs/generic-source-generator.md gains a "Live OpenRouter runs (handle
with care)" section that walks plan-before-run, single-chapter live
run, the budget/usage artifacts, and the checks a reviewer should run
before scaling to the full book.

129 tests pass, 1 skipped (the live smoke, correctly gated).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/generic-source-generator.md

@@ -48,6 +48,52 @@ infospace-bench generate status ./infospaces/book-space
 shows chunk counts, generated artifact counts, evaluations, metrics, history,
 and stale source/profile inputs.
 
+### Live OpenRouter runs (handle with care)
+
+A single-chapter live run is the only OpenRouter shape the test suite
+covers today. Use `--chapter` (or `--from-chapter` / `--to-chapter`) on
+`generate init` or `generate from-source` to scope what gets registered
+before any provider calls happen:
+
+```bash
+export OPENROUTER_API_KEY=...
+
+# Preview the cost first
+infospace-bench generate plan ./infospaces/foo --chapter I --cost-per-1k 0.30
+
+# Run only Chapter I against a cheap model
+infospace-bench generate from-source ./LEFEVRE.epub \
+  --workspace ./infospaces \
+  --slug reminiscences-ch1 \
+  --name "Reminiscences (Ch I)" \
+  --profile trading-literature \
+  --provider openrouter \
+  --model openai/gpt-4o-mini \
+  --chapter I \
+  --apply
+```
+
+`output/budget/plans.yaml`, `usage.yaml`, and `summary.yaml` record what
+was estimated, what was actually spent, and the plan-vs-actual delta.
+`output/workflows/runs/*.yaml` carry the OpenRouter request_id, model,
+token usage, retry count, and per-call duration; the same metadata
+reaches the entity/relation/evaluation artifacts via
+`provenance.provider_metadata`.
+
+Before scaling to the full book:
+
+- Inspect each chapter's outputs and `generation-summary.md`
+- Multiply the per-chapter `total_provider_calls_estimate` and
+  `estimated_cost_usd` by the chapter count and compare to your budget
+- Decide on a final model and confirm the rate-table entry exists in
+  `src/infospace_bench/model_rates.yaml` or your workspace override
+
+The optional live-smoke test in `tests/test_openrouter_live.py` is
+skipped unless both `OPENROUTER_API_KEY` and
+`INFOSPACE_BENCH_ENABLE_LIVE_OPENROUTER=1` are set. It runs a single
+chapter through the same path and asserts the provider metadata
+plumb-through.
+
 ### Budget and usage registry
 
 Every `generate plan` invocation appends a compact snapshot to