burn summary: surface fidelity per-cell (partial-coverage notation, footer note, JSON block)

[willwashburn]

Context

PR #76 (#41 first cut) landed summarizeFidelity / hasMinimumFidelity and per-turn fidelity flags. The granular fidelity-aware command follow-ups landed for compare (#95 → PR #135), waste (#100 → PR #133), limits (#105 → PR #132), and plans (#108 → PR #134). `burn summary` was never given its own granular issue.

PR #127 ("Complete fidelity-aware command contracts", closed in favor of the granular PRs) included a substantial `burn summary` block (~119 lines in `packages/cli/src/commands/summary.ts`) that no granular PR covers. This issue tracks porting that work.

Issue #41's "Command behavior contract → burn summary" bullet captures the intent:

`burn summary` should distinguish a literal $0 / 0 tokens from "no cost data" / "no token data" — render `—` (or equivalent) for the latter, and never imply $0.00 attribution where the source is silent.

Proposal

In `packages/cli/src/commands/summary.ts`:

1. Per-field usage coverage accumulator. While building the per-(model, project, …) cells, track `{ knownTurns, missingTurns, unknownTurns }` for each token field (input/output/reasoning/cache_read/cache_create) using the `TurnRecord.fidelity.coverage` flags.
2. Cell rendering.
   • When `knownTurns === 0` and `missingTurns > 0`: render `—` (no number, no $0.00).
   • When `knownTurns > 0` and `missingTurns > 0`: render the value with a `*` suffix (or equivalent partial-coverage marker) and add a footer note explaining the marker.
3. Footer notice. When any cell carries the partial-coverage marker, append a single line: `* partial coverage: N of M turns omitted per-turn token data`. Suppress when every cell is fully covered (avoid noise in the common case).
4. JSON contract. Add a `fidelity` block matching the shape used by sibling fidelity PRs — `{ summary: FidelitySummary, perCell?: { … } }`. Reuse `summarizeFidelity` for consistency with burn compare: honor fidelity (default-exclude aggregate-only/cost-only, annotate, --fidelity flag) #95/burn waste: honor fidelity (refuse aggregate-only/cost-only, name missing prerequisites) #100/burn limits: honor fidelity (mark forecasts low-confidence on partial usage) #105/burn plans: honor fidelity (mark monthly spend totals low-confidence on partial usage) #108.

Acceptance criteria

• A summary over mixed-fidelity input shows `*` markers on cells where some turns lacked token data, plus a single footer note.
• A summary over fully-missing fields renders `—` and never `$0.00` / `0%` for those fields.
• Full-fidelity summaries show no marker and no footer note.
• `--json` payload includes a `fidelity` block keyed off `summarizeFidelity` (same shape as `compare --json` from PR Honor fidelity in burn compare (#95) #135).
• Tests in `packages/cli/src/commands/summary.test.ts` cover all-full, all-missing, and mixed cases.

Out of scope

• Codex / OpenCode reader fidelity (already landed in PRs Populate TurnRecord.fidelity from Codex parser (#84) #115/Populate TurnRecord.fidelity from OpenCode parser (#89) #116).
• Compare / waste / plans / limits fidelity surfacing (already landed in PRs Honor fidelity in burn compare (#95) #135/Honor fidelity in burn waste (#100) #133/Honor fidelity in burn plans (#108) #134/Honor fidelity in burn limits (#105) #132).

Refs

• Spun out of Coverage and fidelity metadata: distinguish missing, zero, aggregate-only, and partial usage #41 (PR Complete fidelity-aware command contracts #127, closed)
• Reference implementation: PR Complete fidelity-aware command contracts #127's `packages/cli/src/commands/summary.ts` diff
• Sibling: PRs Honor fidelity in burn compare (#95) #135 (burn compare: honor fidelity (default-exclude aggregate-only/cost-only, annotate, --fidelity flag) #95), Honor fidelity in burn waste (#100) #133 (burn waste: honor fidelity (refuse aggregate-only/cost-only, name missing prerequisites) #100), Honor fidelity in burn limits (#105) #132 (burn limits: honor fidelity (mark forecasts low-confidence on partial usage) #105), Honor fidelity in burn plans (#108) #134 (burn plans: honor fidelity (mark monthly spend totals low-confidence on partial usage) #108)