cost-model

# Cost model — make cost claims defensible great_cto reports cost numbers on the board. Those numbers MUST be auditable, because a wrong "7,638×" claim killed credibility (see docs/blog/cost-dashboard-rebuild.md). This skill defines the format. ## The 4-line cost section Every PLAN-*.md and ARCH-*.md cost section follows this exact template: ```markdown ## Cost estimate **LLM**: $<low>–<high> (<N> calls × $<per-call avg>) **Human equiv**: $<low>–<high> (<hours> × $<rate>/h) **Infra delta**: $<low>–<high>/month **Time to ship**: <hours> agent-time, <hours> wall-clock > Methodology: <one-sentence rationale for each range> ``` ### Why this exact format? The board's `getCostHistory()` parser anchors on **line-start** "LLM" and "Human" labels. Mid-line references are ignored to prevent the $240-trap regression. Stick to the template. ## How to estimate each line ### LLM cost For each agent in the pipeline, estimate: - **Prompt tokens** = (system prompt size) + (context the agent receives) - **Completion tokens** = (typical output for that agent type) Quick reference for Sonnet 4 ($3/M in, $15/M out): | Agent | Typical prompt | Typical output | Per-call cost | |---|---|---|---| | architect | 14k | 1.5k | ~$0.06 | | pm | 6k | 0.6k | ~$0.03 | | senior-dev | 8k | 0.8k | ~$0.04 | | qa-engineer | 11k | 0.5k | ~$0.04 | | reviewer (avg) | 8-12k | 0.6k | ~$0.04 | | security-officer | 12k | 1k | ~$0.05 | | devops | 9k | 0.8k | ~$0.04 | For Haiku ($0.80/M / $4/M), divide by ~4....