Claude-native telemetry: durable telemetry ledger (trends past log rotation)

Problem

Claude prunes session JSONL on a rolling window. A retrospective that reads only live logs cannot compute cross-sprint trends because old data disappears. Trend tracking (#18) needs durable, deduplicated history under our control.

Capability

Snapshot normalized, deduplicated telemetry into a local store that is the source of truth for historical aggregates and trends, surviving log rotation.

Behaviour

• Local store (SQLite recommended) with uniqueness constraints (e.g. (sessionId, message_id)); idempotent insert-or-ignore; recompute aggregates from rows, never additively.
• Incremental scan via per-file mtime / line counts.
• Retain rows beyond Claude's rolling window for cross-sprint trends.
• Optional opt-in Stop-hook (via hooks/hooks.json) ingests after each response.

Acceptance criteria

• Re-ingesting the same sessions twice yields identical aggregates (idempotency).
• A trend query spans sprints whose source JSONL is gone, using stored rows.
• Incremental re-scan skips unchanged files (no-op second run).
• Stop-hook is opt-in and a no-op when disabled.

Privacy: store lives under .logs/ (gitignored), never committed. Enables trends for all dimensions. Tier 4. Depends on #36, #37. PRD: docs/prd/features/07-durable-telemetry-ledger.md.

Start with docs/prd/features/07-durable-telemetry-ledger.md and review the existing trend-tracking work in #18, then inspect how session JSONL is currently read. Check hooks/hooks.json for the opt-in Stop-hook path. Done means durable deduplicated rows under .logs/, idempotent and incremental ingestion, trends that survive log rotation, and a disabled hook that does nothing.