Changes Internals

This document describes the implemented structured change comparison boundary.

Purpose

internal/changes compares current and prior structured briefing snapshots and produces compact change records for prompt input data packages.

Inputs and Outputs

Inputs:

prior briefing package
current briefing package
configured Recent Changes thresholds

Output:

ordered changes.Change records with type, message, previous value, and current value where useful

Boundaries

This package compares structured briefing data only.
It does not read state directly, render Markdown, invoke scriptorium, or compare generated report text.

Config Fields Used

The app maps these config fields into comparison thresholds:

recent_change.temperature_degrees
recent_change.precip_probability_points
recent_change.wind_gust_miles_per_hour
recent_change.precip_timing_shift_minutes

Behavior

Daily, 3-Day, and Weekend comparison currently detect:

temperature changes crossing configured thresholds
precipitation probability and timing changes
alert additions and removals
peak wind gust changes
snow, ice, and thunder risk changes

When no prior comparable snapshot exists, the app sends an empty Recent Changes section in the data package. Daily Today and Daily Tomorrow are compatible for same-valid-date comparison through the report registry. 3-Day Outlook compares with prior 3-Day Outlook snapshots for the same valid local date. Weekend Outlook compares with prior Weekend Outlook snapshots for the same weekend window.

Failure Behavior

Daily comparison requires both inputs to contain Daily briefing content. 3-Day comparison requires both inputs to contain 3-Day briefing content. Weekend comparison requires both inputs to contain Weekend briefing content.

Tests

Inspect:

internal/changes/daily_test.go
internal/changes/three_day_test.go
internal/changes/weekend_test.go
internal/app/app_test.go

Invariants

Recent Changes are based on structured snapshots, not Markdown report text.
Comparison thresholds come from configuration.
The comparison output remains compact enough for prompt input.

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