/insights never populates facets/ cache — at_a_glance stays "_No insights generated_" across repeated runs

Claude Code version: 2.1.221 (BUILD_TIME 2026-08-03T03:19:26Z)
Platform: macOS (Darwin 25.5.0)

Summary
Running /insights produces a report with correct raw stats (session/message/hour/commit counts) but the at_a_glance narrative section is always empty, falling back to "_No insights generated_". This persists across repeated runs on the same session pool.

Repro

1. Have 100+ eligible sessions (≥2 user messages, ≥1 min duration — per the CLI's own filter) spanning several weeks.
2. Run /insights 3 times in a row (same day).
3. Observe: all 3 generated report-*.html files are byte-identical (confirmed via file size + diff), and the facets/ directory referenced in the tool's own output never exists on disk afterward (test -d .../usage-data/facets fails every time).

Expected: facet extraction runs for up to 50 uncached sessions per invocation (per the batching cap visible in the bundled source), caches results to disk, and at_a_glance synthesizes from the accumulated facets map after one or a few runs.

Actual: facets/ is never created, at_a_glance is always empty, and re-running does not change the outcome — suggesting the per-session facet-extraction call (the LLM sub-analysis step) is failing silently rather than hitting a real data threshold.

Additional context: 196 total sessions on disk, 141 meeting the eligibility filter — well above the 50-session batch cap, so this isn't a "too little data" case.