Delta Briefing Skill

The failure mode of every recurring report is that edition 6 reads like edition 5. This skill structures a recurring brief around the delta: read the last edition's state, diff the world against it, lead with what changed, and save state for the next run.

What This Skill Produces

• A changes-first brief: new / changed / resolved / unchanged-but-watched
• A state record (compact, machine-readable) that the next edition diffs against
• An explicit "nothing changed" edition format — short, honest, and still useful

Required Inputs

Ask for (if not already provided):

• The brief's subject and audience (competitive landscape, product metrics, account health…)
• The previous edition or state record — if none exists, this run is the baseline: say so in the output and produce the first state record
• Current sources for this cycle
• Where state lives between runs (a file next to the brief, a Brain folder — see BRAIN.md if using this library's memory)

Delta Method

1. Load last state. Parse the previous state record (or previous edition if that's all there is). List the items it tracked and their status.
2. Re-observe. Gather this cycle's facts from the sources — independently of the old state, so removals are caught too.
3. Diff into four buckets:
   • New — present now, absent last time
   • Changed — tracked before, materially different now (state what moved, old → new)
   • Resolved / gone — tracked before, no longer present or no longer a concern
   • Watching — unchanged but still worth tracking (compressed to one line each)
4. Judge materiality. A delta makes the brief only if the audience would act differently knowing it. Trivia goes to the state record, not the brief.
5. Write state for next time. Every tracked item, its current status, the date, and the sources read.

Output Format

[Brief name] — [date] (edition [n], previous: [date])

TL;DR: [1-2 sentences: the most consequential delta, or "no material changes"]

New since last edition

• [item] — [why it matters, one line]

Changed

• [item]: [old] → [new] — [implication]

Resolved

• [item] — [how it closed]

Still watching (one line each)

• [item] — [status]

{ "edition": n, "date": "YYYY-MM-DD", "sources": ["..."],
  "items": [ { "id": "...", "status": "...", "note": "..." } ] }

If nothing material changed: say exactly that in three lines — TL;DR ("no material changes"), what was checked, next edition date. Do not pad.

Quality Checks

• The brief opens with the delta, not with background the audience read last time
• Every "Changed" item shows both the old and the new value
• Removals were checked by re-observing, not just re-confirming last edition's list
• A state record exists at the end, complete enough that the next run needs no other memory
• The baseline edition (no previous state) is labelled as a baseline, not presented as a delta

Anti-Patterns

• Do not restate unchanged items at full length — one line in "Still watching" or nothing
• Do not fabricate a delta to make a quiet cycle look productive — "nothing changed" is a valid, valuable edition
• Do not diff against memory or vibes — only against the stored state record
• Do not let the state record and the brief disagree — the record is written from the brief's facts
• Do not track everything forever — items resolved two editions ago leave the state record