cost-projection

Forward-looking cost projection that pairs with `cost-budget-check`: - **`cost-budget-check`** answers "have we crossed the line?" — reactive - **`cost-projection`** answers "when will we cross the line?" — predictive ## Algorithm 1. Read all `session-*` records from the `cost-tracking` namespace (same source `cost-budget-check` uses). 2. Filter to a measurement window (default last 7 days on `capturedAt`/`startedAt`). 3. Compute the per-day burn rate: `windowSpend / windowDays`. 4. Linear-extrapolate to each requested horizon (default 7d/30d/90d/365d). 5. If a budget is configured (`budget-config` key set by `cost-budget set`): - Compute "days until 75% / 90% / 100% consumed" at the current rate. - Surface as a separate table block with `ALREADY REACHED` markers for thresholds already exceeded. ## Flags --window <duration> Measurement window. `Nh|Nd|Nw|Nm`. Default `7d`. --horizons <csv> Projection horizons. Default `7d,30d,90d,365d`. --format table|json Default `table` (markdown). Env: `PROJECTION_NAMESPACE` override (default `cost-tracking`), `PROJECTION_QUIET=1` (alias for `--format json`). ## Smoke transcript (3 sessions × $1 over 7d, $20 budget) ``` | Sessions in window | 3 | | Window spend | $3.000000 | | **USD per day** | **$0.428571** | | All-time spend | $3.000000 across 3 sessions | ## Projected spend (linear extrapolation) | Horizon | Days | Projected spend | |---|---:|---:| | 7d | 7 | $3.0000 | | 30d | 30 | $12.8571 | ## Budget exhaustion ($20.00 configured) | Threshold | Target | Remaining | Time at current rate | |---|---:|---:|---| | 75% | $15.00 | $12.00 | 28.0 days | | 90% | $18.00 | $15.00 | 35.0 days | | 100% | $20.00 | $17.00 | 39.7 days | ``` ## When to use - **Finance / SRE planning**: hand the JSON output to a budget dashboard for "are we on track for the quarter?". - **CI gates**: `cost-projection --format json | jq '.budget.exhaustion[2].daysUntilReached < 7'` → fail builds when 100% exhaustion is < 1 week away. - **Post-workload-shift sanity check**: after a big feature lands, re-run to verify the rate hasn't accelerated past expectations. ## Stationarity assumption Linear extrapolation assumes the current rate holds. The footer reminds operators to re-run after workload shifts. For drift detection over MULTIPLE windows, pair with `cost-trend` (which already covers benchmark-drift).