Cost Projections Skill

Overview

Projects remaining workflow cost based on per-phase averages from completed work. Displays cost data in the HUD/statusline and warns when projected totals exceed a configured budget ceiling.

Minimum data requirement: Needs 2+ completed steps before projecting. With fewer than 2 data points, the average is unreliable, display actual spend only and skip projection.

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Step 1: Collect Completed Phase Costs

Read cost data from ~/.claude-octopus/metrics/ or from metrics-tracker.sh output. Each completed phase/step should have an associated cost entry.

# Read metrics from the session metrics directory
METRICS_DIR="$HOME/.claude-octopus/metrics"
SESSION_METRICS="$METRICS_DIR/session-$(date +%Y%m%d).jsonl"

# Each line contains: {"phase": "discover", "cost": 0.42, "tokens_in": 12000, "tokens_out": 3400, "timestamp": "..."}
# Sum costs from completed steps
completed_costs=$(jq -s '[.[].cost]' "$SESSION_METRICS")
completed_count=$(jq -s 'length' "$SESSION_METRICS")
total_spent=$(jq -s '[.[].cost] | add' "$SESSION_METRICS")

Data sources (in priority order):

1. ~/.claude-octopus/metrics/session-*.jsonl, structured per-phase cost entries
2. metrics-tracker.sh output, fallback for legacy sessions
3. HUD accumulated cost counters, last resort

If fewer than 2 completed steps are available, display only actual spend:

💰 Spent: 0.42 USD (1 step complete, need 2+ for projection)

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Step 2: Compute Average Cost Per Step

Calculate the mean cost across all completed steps.

avg_cost=$(echo "$total_spent / $completed_count" | bc -l)

Formula:

avg_cost = total_cost / completed_steps

Example: If 3 steps cost 0.30 USD, 0.50 USD, 0.40 USD → avg = 1.20 USD / 3 = 0.40 USD/step

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Step 3: Project Remaining Cost

Multiply the average cost per step by the number of remaining steps.