# Brief — RE-R3e: brief history + day-over-day diff (R3 slice d)

> **Slice:** RE-R3e (research-engine rung-2, R3 slice **(d)** in the operator's `(a)→(c)→(b)→(d)→(e)`
> sequence — the doc is numbered r3e by creation order, the concept is slice (d)). It closes **hull #7**
> (substrate §1 hull list: *"ingen brief-historikk"*): the dated morning brief already writes one Markdown
> file per day (`morning-brief/YYYY-MM-DD.md`), but the file is **prose-only** — nothing records *which*
> trends a brief showed in a machine-readable form, and no run reads yesterday's brief, so the engine cannot
> answer the one question a daily motor exists to answer: **"what is new since I last looked?"**
> **Predecessor:** RE-R2b (the dated brief artifact + `surfacedIds(ranking)` — the exact set a brief shows:
> `brief.ts:305`) + RE-R3b (the per-day-idempotent seen-log `surfacedCount`/`lastSurfacedAt`, which already
> records *that* a trend was surfaced but not *with which cohort*) + RE-R3c (the autonomous trigger that makes
> the dated files **accumulate day-over-day on their own** — the dependency that makes a day-over-day diff a real
> signal, not a once-in-a-while comparison) + RE-R3d (the temporal overlay — the within-brief recency/saturation
> class the diff is orthogonal to).
> **Substrate:** `docs/research-engine-concepts.local.md` §1 hull **#7** (*"ingen brief-historikk"*) + §B3
> (*"Dated-digest som flat plain-text-artefakt … diffbar, grep-bar, lenkbar … Senere sesjon laster «gårsdagens
> brief» trivielt"* — the dated file is **explicitly designed to be diffed**, R3e is the diff B3 anticipated) +
> §B4 (*"append-only seen-log → ikke re-overflate samme sak"* — R3e is the per-cohort complement: not "have I
> seen this ever" but "was this in the PRIOR brief").
> **The core decisions (operator-confirmed, AskUserQuestion 2026-06-26 — baked):**
> - **SD1 — persist membership in the brief's own frontmatter, NOT a sidecar.** Each brief writes a single
>   `surfaced: <id-csv>` line into its YAML frontmatter — the ids it actually showed (`surfacedIds(ranking)`).
>   This keeps **one self-describing, grep-bar artifact** per day (B3), mirrors the existing `store: { … }`
>   frontmatter idiom, and is **hook-safe** (the SessionStart `extractYaml` is `^summary:`-anchored and
>   line-scoped — a new `surfaced:` line cannot perturb it). The diff reads the prior brief's `surfaced:` line
>   via one pure regex. **No sidecar `.json`; no second artifact.** `BRIEF_SCHEMA_VERSION` bumps **1 → 2** (the
>   frontmatter gained a field — the first bump since R2b; the store's `SCHEMA_VERSION` stays **4**).
> - **SD2 — `added` with titles + `dropped` as a count; `brief.ts` stays store-free.** The diff is the symmetric
>   set difference of today's surfaced ids against the prior brief's: **added** (in today, not prior — the
>   headline "what's new", rendered with titles resolved from the ranking the brief already holds), **carried**
>   (in both), **dropped** (in prior, not today). `added` is the value; `dropped`/`carried` render as a one-line
>   tally (counts). The dropped ids are **not** resolved against the store for an acted/skipped/aged *reason* —
>   that would require injecting store records into the render and is the one explicit follow-up (§4). The render
>   needs **only the ranking** it already has → `brief.ts` stays pure (no store, no fs). The framing is **honest**:
>   "ikke vist i dag" (not shown today), never "resolved" (which the count cannot prove).
> **TDD-order (two-phase RED, light-Voyage discipline, inherited from R3c/R3d):** Phase A — `diffSurfaced`,
> `parseSurfacedFrontmatter`, `selectPriorBriefFile` (+ the `BriefDiff` type) are NEW named exports of the
> EXISTING `brief.ts`; under Node16 ESM a missing named import throws at module-load (every `brief.test.ts` test
> would error, not assert), so land **non-throwing stubs** FIRST (`diffSurfaced → {priorDate:null,added:[],
> carried:[],dropped:[]}`, `parseSurfacedFrontmatter → []`, `selectPriorBriefFile → null`; `renderBrief` gains an
> optional `diff` param it ignores in the stub), then record value-assertion RED against them (the stubs' constant
> returns fail the diff/parse/select/section/marker assertions — true assertion-RED). Phase B — the CLI two-day
> diff test is value-RED against the existing `brief` handler (today it writes no `surfaced:` line, reads no prior
> brief, and its `--json` carries no `diff` key → the day-2 diff assertions fail). See plan Step 1.

## 1. Operator decision context (2026-06-26)

The research engine is **Tier-1** (operator, 2026-06-23). R1→R3d built the deterministic spine, the trend's life
after capture, the autonomy that runs it, and the within-brief temporal overlay: item-schema + triage (R1) →
capture bridge (R2a) → dated morning brief + surfacing (R2b) → persisted relevance + composite ranking (R3a) →
status lifecycle + seen-log + re-score (R3b) → autonomous trigger + headless entry (R3c) → temporal overlay
(first-mover + saturation, R3d). The brief now **regenerates itself every morning** (R3c) and ranks each trend by
its frozen relevance composite, its pillar overlap, and a live first-mover/saturation class (R3d). But every
morning's brief is a **standalone snapshot**: it cannot say *"these three are new since yesterday; the two you
saw yesterday are gone."* The accumulated dated files are a pile of snapshots, not a **history with a diff**.

R3e closes **hull #7** — the **brief history + day-over-day diff** — which the operator chose as slice **(d)** of
the full-R3 build-out (2026-06-24, *"ALLE gjenstående R3-slices … i rekkefølge (a) → (c) → (b) → (d) → (e)"*). It
is sequenced **after** R3c for a load-bearing reason: a day-over-day diff is only meaningful when a brief is
**produced every day on its own** — R3c's nightly trigger is what makes "yesterday's brief" reliably exist. (c)
makes (d) a real signal; without the daily trigger, "since last brief" could mean "since whenever the operator
last happened to ask."

**The concrete value — turning a pile of snapshots into a feed.** A daily motor's job is to surface the *delta*:
the operator does not want to re-read the full ranked list every morning and diff it in their head — they want
the engine to say **"3 nye siden i går"** at the top of the brief (and on the one-line SessionStart surfacing,
for free). R3e makes the dated file a genuine **history rung**: each brief records what it showed
(`surfaced:` frontmatter), and the next brief reads the most recent prior one and renders **"Nytt siden sist."**
This is the smallest honest step from *"a brief is written daily"* (R3c) to *"the brief tells me what changed"*
(the point of a feed) — and it is exactly the diffable dated-digest §B3 said the artifact was designed to be.

## 2. The gap — grounded in code

- **The dated brief is prose-only; membership is not machine-readable.** `cli.ts:341-343` writes
  `morning-brief/${day}.md` from `renderBrief(ranking)`; the body embeds each trend's `id` inside a rendered
  bullet (`brief.ts:242`, `:251` — `` `${e.trend.id}` ``), but there is **no structured record** of *the set a
  brief showed*. `surfacedIds(ranking)` (`brief.ts:305`) computes that set and feeds it to `markSurfaced`
  (`cli.ts:348`), but it is **never persisted to the artifact** — so a later run that wants "what did yesterday's
  brief show" would have to scrape prose. The seen-log (`surfacedCount`/`lastSurfacedAt`, R3b) records *that* and
  *how many days* a trend was surfaced, but **not which cohort it appeared with** — it cannot reconstruct
  "yesterday's brief contained {A, B, C}."
- **No run reads a prior brief.** The only consumer of the dated files is the SessionStart hook's
  `latestMorningBrief` (`session-start.mjs:60-77`), which reads the **single newest** file's `date`+`summary` and
  surfaces it verbatim. Nothing reads the **second-newest** to compare. There is no diff, anywhere.
- **"New since last" is not derivable from the store alone.** The seen-log gives "never surfaced ever"
  (`surfacedCount` absent ⇒ a first-ever sighting) — but that is **not** "new since the last brief": a trend
  surfaced once three days ago, absent from yesterday's brief, reappearing today is *new to yesterday's reader*
  yet has `surfacedCount 1` (not 0). Only a **per-brief membership record** (the prior `surfaced:` set) answers
  "was this in the immediately-prior brief," and only it can compute **dropped** (in the prior cohort, gone
  today) — which the store cannot express at all. This is precisely the gap §B3's "diffbar … dated-digest" and
  §1 hull #7 name.
- **The brief's own summary cannot signal a delta.** `briefSummary` (`brief.ts:204-216`) describes today's top
  match in isolation; the SessionStart surfacing (`session-start.mjs:534-536`) shows that line verbatim. There is
  no "N nye siden sist" the operator could see *without opening the file* — the one number a feed leads with.

## 3. Scope — what is IN (RE-R3e)

**Zero new source/test files** (the two tracked slice docs aside). R3e is pure EDITs: the diff lives beside
`surfacedIds` in `brief.ts` (the module that already owns the brief's pure read logic — surgical, no new module
to wire into the gate), its unit tests in `brief.test.ts`, its CLI wiring (prior-file discovery) in
`cli.ts`/`cli.test.ts`, plus the wiring docs + gate.

### S-history — `scripts/trends/src/brief.ts` (EDIT) — the pure diff + the persisted membership

- **`BRIEF_SCHEMA_VERSION` bumps 1 → 2** (`brief.ts:23`) — the frontmatter gained the `surfaced:` field. (The
  store's `SCHEMA_VERSION` is untouched at **4** — R3e adds **no store field**; the membership lives in the
  artifact, the diff is derived.)
- **`export interface BriefDiff { priorDate: string | null; added: string[]; carried: string[]; dropped: string[] }`**
  — `priorDate` = the date of the brief diffed against (`null` ⇒ no prior brief, i.e. the first ever / a fresh
  data dir); `added`/`carried`/`dropped` = the three partitions of the set difference, each **order-stable**
  (added/carried preserve today's `surfacedIds` order; dropped preserves the prior set's order).
- **`export function diffSurfaced(currentIds: string[], priorIds: string[], priorDate: string | null): BriefDiff`**
  — pure (no clock/fs/env; both id lists + the prior date are injected by the CLI edge). `added` = `currentIds`
  not in `priorIds`; `carried` = `currentIds` in `priorIds`; `dropped` = `priorIds` not in `currentIds`. Uses a
  `Set` for membership; preserves input order in the output arrays. When `priorIds` is empty (first brief),
  `added === currentIds` and `dropped === []`.
- **`export function parseSurfacedFrontmatter(md: string): string[]`** — pure; extracts the `surfaced:` value
  from a brief's full text via a single line-anchored regex (mirrors the hook's `extractYaml` idiom:
  `/^surfaced: *([^\n]*)/m`), splits on `,`, trims, drops empties. Returns `[]` when the line is **absent, blank,
  or malformed** (a pre-R3e brief, or a hand-edited file) — degrades to "empty prior," never throws. Real ids are
  comma-free hex (`store.ts:69-72`), so the CSV is unambiguous.
- **`export function selectPriorBriefFile(filenames: string[], today: string): string | null`** — pure; from a
  directory listing, returns the **lexicographically greatest** filename matching `^\d{4}-\d{2}-\d{2}\.md$` whose
  date is **strictly less than** `today` (ISO dates sort lexicographically, so string compare = date compare),
  else `null`. Mirrors the hook's `latestMorningBrief` filter+sort (`session-start.mjs:63-66`) but **excludes
  today and any future-dated file** — so a same-day re-run diffs against the true previous day, not its own
  just-written file (the byte-determinism guarantee, SC8).
- **`renderBrief` gains an optional `diff` param** (`brief.ts:259`): `renderBrief(ranking: BriefRanking, diff?:
  BriefDiff)`. Two additive emissions:
  - **Frontmatter `surfaced:` line** — `surfaced: ${surfacedIds(ranking).join(",")}` inserted **before**
    `schemaVersion:` (always emitted, even for an empty store → `surfaced: ` blank; this is the record the *next*
    day's diff reads, independent of whether *today* had a prior). `schemaVersion:` now renders **2**.
  - **A `## 🆕 Nytt siden sist` section** (the header gains ` (<prior-date>)` when a prior brief exists, per SC9),
    placed **after the intro line and before `## 🎯 Topp-treff`** (the
    delta leads, then the full ranked list). Branches (all deterministic):
    - **no diff arg / `priorDate === null` with added** → `_Første brief — alt nedenfor er nytt._`
    - **`priorDate === null` with no added** (empty first brief) → `_Første brief._`
    - **`priorDate !== null`, `added` non-empty** → one bullet per added id, its entry resolved from the ranking
      (title + matched pillars + date + link + id, reusing the bullet idiom), then a tally line
      `_${carried.length} båret over, ${dropped.length} ikke vist i dag._`
    - **`priorDate !== null`, `added` empty** → `_Ingenting nytt siden ${priorDate}._` (+ the same tally line)
  - When `diff` is omitted (a bare `renderBrief(ranking)` call, e.g. a unit test that does not exercise the diff),
    it defaults to the empty diff (`{priorDate:null,added:[],carried:[],dropped:[]}`) → the **`_Første brief._`**
    section branch (`priorDate===null`, `added` empty). The `surfaced:` frontmatter line is **independent of the
    diff** — always `surfacedIds(ranking).join(",")` (blank **only** for an empty store), so a non-empty ranking
    still emits its real surfaced ids. (This keeps existing single-arg call sites compiling and semantically valid.)
- **`briefSummary` gains an optional `diff` param** (`brief.ts:204`): `briefSummary(ranking, diff?)`. When `diff`
  is present, `priorDate !== null`, and `added.length > 0`, it appends ` ${added.length} nye siden sist.` to the
  one-line headline — so the **SessionStart hook surfaces the delta for free** (it already shows the `summary:`
  line verbatim; no hook edit). The marker is suppressed on the first brief (`priorDate === null`) and when
  nothing is new (no noise). It carries **no double-quote and no newline** (the `^summary: *"?([^"\n]*)"?`
  hook-regex invariant, `brief.ts:200-203`). `renderBrief` passes its `diff` through to `briefSummary` so the
  frontmatter `summary:` and the `--json summary` agree.

### S-cli — `scripts/trends/src/cli.ts` (EDIT) — prior-brief discovery + the diff in `--json`

- **The `brief` handler discovers the prior brief and computes the diff** (between the ranking at `cli.ts:339`
  and the render at `:340`): `readdirSync(outDir)` (guarded by `existsSync` — a first run has no dir) →
  `selectPriorBriefFile(files, day)` → if found, `readFileSync` it and `parseSurfacedFrontmatter` → build
  `diffSurfaced(surfacedIds(ranking), priorIds, priorDate)`; on any fs error, degrade to the empty-prior diff
  (`priorDate: null`). Pass the diff into `renderBrief(ranking, diff)`. Adds `readdirSync` to the existing
  `node:fs` import (`cli.ts:51`).
- **`--json` gains a `diff` object** (`cli.ts:352`): `diff: { priorDate, added: added.length, carried:
  carried.length, dropped: dropped.length }` — counts, not id lists (the headless `run-daily.sh` collapses
  `--json` to one cron-log line). The non-JSON console line (`cli.ts:355`) appends `, N nye siden sist` when
  `added > 0 && priorDate !== null`.
- **`--no-mark` is unchanged in meaning** — it still governs only the **store** seen-log write (`cli.ts:347-349`).
  The artifact's `surfaced:` frontmatter records what the brief showed **regardless** of `--no-mark` (it is a
  property of the rendered brief, not of the store mutation). No new flag.

### Wiring (D-default — WIRE, mirrors R3a/R3b/R3c/R3d)

- `agents/trend-spotter.md` (EDIT, **prose-only, minimal**): one line — the morning brief now records which trends
  it showed (frontmatter `surfaced:`) and renders a **day-over-day diff** ("Nytt siden sist") against the most
  recent prior brief — no new capture step; the agent's polling/capture path is unchanged. Domain-general (no
  vendor/sector token).
- `scripts/trends/README.md` (EDIT): add a `## Brief history + diff (RE-R3e)` section between the R3d temporal-
  overlay section and `## Tests`: the `surfaced:` frontmatter record, the `selectPriorBriefFile` prior-discovery
  (strict `< today`, same-day re-run determinism), the `diffSurfaced` partitions, the section + the summary
  marker, and the `BRIEF_SCHEMA_VERSION 1→2` boundary (artifact-only; store `SCHEMA_VERSION` stays 4).
- `scripts/test-runner.sh` (EDIT): bump `TRENDS_TESTS_FLOOR` (**live `:716`**, currently **216**) to the `tests N`
  line reported after the suite runs — **recounted live**, **append** `+ RE-R3e: brief +N, cli +N (brief history
  + diff)` to the inline breakdown comment. Add **Section 16n** ("Trends Brief History / Diff", RE-R3e) **between
  Section 16m's closing `echo ""` and the Section 18 header** (anti-erosion must stay last). Mirror 16m's shape:
  **unconditional**, deps-absent-safe (`grep -qF` + a non-vacuity self-test emitting **one** pass/fail). **6
  emitters** (all on tracked source, no `tsx`, all literals **ASCII** — the section header emoji `🆕` is **never**
  grepped; the shell stays ASCII-clean for bash 3.2 `set -u`): (1) self-test; (2) `export function diffSurfaced`
  in `brief.ts`; (3) `parseSurfacedFrontmatter` in `brief.ts`; (4) the section header literal `Nytt siden sist`
  in `brief.ts`; (5) `selectPriorBriefFile` in `cli.ts` (the diff wiring); (6) the frontmatter emit `surfaced: `
  in `brief.ts`. **6 unconditional emitters → bump `ASSERT_BASELINE_FLOOR` 117 → exactly 123** (**live `:1473`**;
  "live recount" is the safety net; the expected value is the pinned 117 + 6). Insert the 16n clause into the
  **header-enumeration prose chain (`:53-64`)** before "…the assertion-count anti-erosion floor (SC6) in Section
  18," and **append the R3e (→123) narration** to the Section-18 floor-history comment (which ends "= 117").

## 4. Non-goals — what is OUT (deferred)

- **A sidecar `.json` membership manifest** — OUT (SD1). Membership lives in the brief's own frontmatter
  (`surfaced:`), keeping one self-describing artifact (B3). No second file per day.
- **`dropped` resolved to an acted/skipped/aged *reason*** — OUT (SD2), and the **one explicit follow-up**.
  `dropped` renders as a **count** ("N ikke vist i dag"). Labelling *why* each dropped id left (acted/skipped via
  `status`, or aged past `freshDays`) would require injecting the store records into the render — `brief.ts` would
  no longer be store-free. Honest framing for R3e: "ikke vist i dag," never "resolved." A small, clearly-scoped
  follow-up (CLI resolves dropped ids → `{title, status}` and passes them to a richer render) if the loop-closing
  signal proves worth the coupling.
- **A browsable history INDEX file** (e.g. a rolling `history.md` of all past briefs) — OUT. The dated files +
  the `surfaced:` frontmatter **are** the history (grep-bar, lenkbar — B3); an index is a presentation nicety, not
  a capability gap.
- **A SessionStart hook change to render the diff** — OUT. The "N nye siden sist" marker rides the **existing**
  `summary:` surfacing (`session-start.mjs:534-536`) — no hook edit, no hook test, no new frontmatter field the
  hook must learn. (The hook still reads only `date`+`summary`.)
- **`schedule` / `run-daily.sh` changes** — OUT. The nightly run calls `brief` (`run-daily.sh:33`), which now
  computes the diff internally → the scheduled brief gets "Nytt siden sist" **automatically**, with **no**
  scheduler edit (no R3c regression surface).
- **A new store field / schema bump / store mutation for the diff** — OUT. `SCHEMA_VERSION` stays **4**;
  `types.ts`/`store.ts` are **untouched**. The membership is an artifact property; the diff is derived at the CLI
  edge.
- **"New" defined as first-ever-sighting (`surfacedCount === 0`)** — OUT (rejected as less correct). R3e's "new"
  is **relative to the immediately-prior brief** (artifact diff), which also flags a trend *re-emerging* after a
  gap — the honest meaning of "siden sist." (`surfacedCount` stays the R3d saturation input, a different
  question.)
- **Diffing against an arbitrary historical brief (`--since <date>`)** — OUT. R3e diffs against the **most recent
  prior** brief only (the "since last" a daily feed needs). An arbitrary baseline is a later nicety.
- **A new module / new test file** — none. The diff lives in `brief.ts`; its tests in `brief.test.ts`. (No
  pathguard surface — all EDITs.)
- **New agent / new command / new reference doc** — none. R3e EDITs `brief.ts` + `cli.ts` + their tests + one
  agent (prose) + README + gate. Counts stay **29/19/27**. (The SSOT `trend-scoring-modes.md` is **not** touched —
  the diff is not a scoring concern; scope fence.)

## 5. Boundaries / invariants (must hold)

- **TDD iron law (two-phase RED):** failing tests land **BEFORE** implementation. Phase A — the new named exports
  (`diffSurfaced`/`parseSurfacedFrontmatter`/`selectPriorBriefFile`/`BriefDiff`) need non-throwing **stubs** first
  (Node16 ESM throws a missing named import at module-load), THEN value-assertion RED against the constant stubs.
  Phase B — the CLI two-day diff test is value-RED against the existing handler (no `surfaced:` write, no prior
  read, no `diff` in `--json` today). The plan does **not** claim a single "everything fails before any code" run.
- **`brief.ts` stays pure** (no clock, no fs, no env, no AI): `diffSurfaced`/`parseSurfacedFrontmatter`/
  `selectPriorBriefFile` all take strings/arrays and return values — the directory read + file read live in
  `cli.ts` (the edge), exactly like `today`/`pillars` are injected. The module's "No fs, no clock, no AI, no
  network" header claim is preserved.
- **Determinism of the brief:** given `(store, pillars, today, freshDays, firstMoverDays, saturationAt, diff)` the
  rendered `.md` is **byte-identical** (the diff is now an injected input, like `today`). Critically, a **same-day
  re-run is byte-identical**: `selectPriorBriefFile` excludes `${today}.md` (strict `<`), so the re-run diffs
  against the same previous day's brief and re-writes the same `surfaced:` line (R3c SC7 preserved).
- **`surfaced:` records the shown set, `--no-mark`-independent:** the frontmatter line is `surfacedIds(ranking)`
  joined — what the brief *showed* — regardless of whether the store seen-log was written (`--no-mark` governs the
  store mutation only). The artifact is always self-consistent.
- **Frozen composite + temporal overlay untouched (R3a + R3d):** R3e adds **no** `cmp` key and changes **no**
  ranking — `rankForBrief` is unchanged. The diff is a **post-ranking, render-time** layer over the same surfaced
  set. `score.composite` is never read for mutation; the R3d `temporal` overlay is orthogonal (it orders within
  the brief; the diff compares across briefs).
- **Schema boundary:** `BRIEF_SCHEMA_VERSION` bumps **1 → 2** (the artifact's frontmatter gained `surfaced:`);
  the store's `SCHEMA_VERSION` stays **4**; `types.ts`/`store.ts`/`score.ts`/`item.ts`/`schedule.ts`/
  `run-daily.sh` are **untouched**.
- **Hook unaffected:** the SessionStart surfacing reads `date`+`summary` only (`session-start.mjs:60-77`). The new
  `surfaced:` frontmatter line is `^surfaced:`-keyed (the `^summary:`-anchored, line-scoped `extractYaml` cannot
  match it), and the `summary:` marker carries no `"`/`\n` — so the regex still captures the summary whole. R3e
  touches neither the hook nor the field set the hook reads; the hook suite must still pass untouched (regression
  sanity; R3e adds no hook test).
- **ASCII-only gate literals:** `scripts/test-runner.sh` must stay ASCII (a multibyte char crashes bash 3.2 under
  `set -u`). The Section-16n sentinels grep the **ASCII** literals (`export function diffSurfaced`,
  `parseSurfacedFrontmatter`, `Nytt siden sist`, `selectPriorBriefFile`, `surfaced: `) — **never** the `🆕` emoji
  (which lives only in `brief.ts` source + rendered output, asserted by the TS tests, not by the shell gate).
- **Domain-general:** no hard-coded user/repo path, no vendor/sector token in any edit. The section header +
  Norwegian copy (`Nytt siden sist`, `båret over`, `ikke vist i dag`, `nye siden sist`, `Første brief`) are
  domain-general UI copy (the brief's existing language); pillars/topics remain config. Section 17 de-niche stays
  green.
- **Pathguard:** R3e adds **no new files** — every change is an EDIT of an existing file (write-allowed). (No
  `.mjs`-under-`hooks/scripts/` surface, no new `scripts/` file.)
- **Counts** (refs/agents/commands 27/19/29) unchanged — **recounted live at land**, never pinned/guessed.

## 6. Success criteria (testable)

- **SC1 (diffSurfaced — partitions + order + empty prior)** — `diffSurfaced(["a","b","c"], ["b","c","d"], "2026-
  06-25")` → `{priorDate:"2026-06-25", added:["a"], carried:["b","c"], dropped:["d"]}` (added/carried in current
  order, dropped in prior order). `diffSurfaced(["a","b"], [], null)` → `{priorDate:null, added:["a","b"],
  carried:[], dropped:[]}` (empty prior ⇒ everything added). Pure: same inputs → same output. The three
  partitions are **mutually disjoint** — `Set` membership is binary (an id is in `priorIds` or not), so each id
  lands in exactly one of added/carried and dropped is disjoint from both; within each list, order and any
  duplicates **mirror the input** (`surfacedIds` yields **distinct** ids in production, so within-list dups never
  arise — the cross-partition exclusivity is the real invariant, not within-list dedup).
- **SC2 (parseSurfacedFrontmatter — read + degrade)** — parses `surfaced: 1a2b,3c4d,5e6f` (in a full frontmatter
  block) → `["1a2b","3c4d","5e6f"]`; a **blank** `surfaced: ` → `[]`; an **absent** `surfaced:` line (a pre-R3e
  brief) → `[]`; whitespace around ids is trimmed; the `summary:`/`store:`/`date:` lines are **not** mismatched
  (line-anchored). Never throws on malformed input.
- **SC3 (selectPriorBriefFile — strict-prior selection)** — from `["2026-06-24.md","2026-06-25.md","2026-06-26.md",
  "README.md","2026-06-30.md"]` with `today="2026-06-26"` → `"2026-06-25.md"` (greatest `< today`; **excludes**
  today `2026-06-26.md` and the future `2026-06-30.md`; ignores the non-dated `README.md`). Empty list, or no file
  `< today`, → `null`.
- **SC4 (frontmatter `surfaced:` line + round-trip)** — `renderBrief(ranking, diff)` emits exactly one
  `^surfaced: <csv>$` line, equal to `surfacedIds(ranking).join(",")`, positioned before `schemaVersion: 2`; an
  empty-store brief emits `surfaced: ` (blank); `parseSurfacedFrontmatter(renderBrief(r, d))` round-trips to
  `surfacedIds(r)`. `schemaVersion:` renders `2`.
- **SC5 (Nytt siden sist section — all four branches)** — the rendered body contains `## 🆕 Nytt siden sist`;
  with `priorDate:null` + added → `Første brief — alt nedenfor er nytt`; with `priorDate:null` + no added (empty
  store) → `Første brief.`; with a prior + `added` → one bullet per added entry (its **title** present, resolved
  from the ranking) + `N båret over, M ikke vist i dag`; with a prior + no added → `Ingenting nytt siden <date>`
  + the tally. The section precedes `## 🎯 Topp-treff`.
- **SC6 (summary delta marker)** — `briefSummary(ranking, diff)` with `priorDate !== null` and `added.length > 0`
  ends with ` ${added.length} nye siden sist.`; with `priorDate:null` (first brief) or `added.length === 0`, the
  marker is **absent** (and `briefSummary(ranking)` with no diff === `briefSummary(ranking, emptyDiff)` — no
  marker, so the existing `frontmatter summary === briefSummary(r)` test stays green). The summary contains **no**
  `"` and **no** `\n`.
- **SC7 (schema boundary)** — `BRIEF_SCHEMA_VERSION === 2`; `SCHEMA_VERSION === 4`; `types.ts` untouched; a
  `brief` run does **not** change any record's `score.composite` (only `surfacedCount`/`lastSurfacedAt` move — the
  existing R3b behaviour, since `rankForBrief`/`markSurfaced` are unchanged).
- **SC8 (determinism, incl. same-day re-run)** — two `brief` renders with the same `(store, pillars, today,
  opts, diff)` → byte-identical `.md`. End-to-end via the CLI: running `brief` **twice on the same day** (the
  second after the first wrote `${day}.md`) → byte-identical files, because `selectPriorBriefFile` excludes the
  same-day file and picks the same prior day.
- **SC9 (CLI diff wiring — two-day sequence)** — write a day-1 brief (records `surfaced:` for its cohort), then a
  day-2 brief over a store with one **new** trend: the day-2 `.md` `## 🆕 Nytt siden sist (<day-1>)` section lists
  the new trend, the day-2 `--json` carries `diff: { priorDate:<day-1>, added:≥1, carried:…, dropped:… }`, and the
  console line appends `N nye siden sist`. A **first** run (empty dir) → `diff.priorDate === null`. A **custom
  `--out`** isolates discovery to that dir (the diff reads prior briefs only from `outDir`).
- **SC10 (gate + wiring + de-niche)** — `bash scripts/test-runner.sh` → `FAIL=0`: trends suite green at the
  bumped `TRENDS_TESTS_FLOOR`; new **Section 16n** green (the six ASCII sentinels + non-vacuity self-test);
  `ASSERT_BASELINE_FLOOR` = **123** (117 + 6); Section 17 de-niche green; counts 29/19/27; the hook suite still
  green untouched (`node --test hooks/scripts/__tests__/*.test.mjs`).

## 7. Verification

**Deterministic:** `bash scripts/test-runner.sh` → `FAIL=0`; trends suite ≥ new floor; Section 16n self-test +
greps pass; `ASSERT_BASELINE_FLOOR` = 123; Section 17 de-niche green; ref/agent/command counts unchanged.
**Regression sanity:** `node --test hooks/scripts/__tests__/*.test.mjs` → still green untouched (R3e touches no
hook). The R3c suite (`schedule.test.ts`/`run-daily.test.ts`) still green untouched (`schedule.ts`/`run-daily.sh`
not edited).
**Behavioural (manual):**
1. `D=/tmp/r3e-mb-$$; S=/tmp/r3e-$$.json` (unique dir, no `rm`). Seed a store with two on-pillar trends and run a
   day-1 brief: `node --import tsx src/cli.ts brief --pillars ai,gov --out "$D" --store "$S"` → inspect the `.md`:
   the frontmatter carries `surfaced: <ids>` and `schemaVersion: 2`; the `## 🆕 Nytt siden sist` section says
   `Første brief — alt nedenfor er nytt`.
2. `capture` a third on-pillar trend into the same store, then run a day-2 brief **with a later `today`** (seed via
   a second dated file is not possible — use `--out "$D"` so day-1's `${day}.md` is the prior; on a real next-day
   run the date advances): inspect the new `.md` → `## 🆕 Nytt siden sist (<prior-date>)` lists the new trend with
   its title, then `N båret over, M ikke vist i dag`; the `--json` shows `diff.added ≥ 1`.
3. Re-run the **same-day** brief → the written `.md` is **byte-identical** (`diff` against the same prior file;
   `surfaced:` re-written identically) — `cmp` the two files.
4. Confirm the seeded records' `score.composite` values are unchanged after the briefs (only `surfacedCount`/
   `lastSurfacedAt` advance) — the diff never mutates the store ranking.
5. Confirm a pre-R3e brief (no `surfaced:` line) as the prior → `parseSurfacedFrontmatter` returns `[]` → every
   trend reads as `added` (graceful degrade, no crash).

## 8. Open questions for the go-gate

Two architectural decisions are **CONFIRMED** (operator, AskUserQuestion 2026-06-26): **SD1** persist membership
in the brief's frontmatter (no sidecar); **SD2** `added` with titles + `dropped` as a count (`brief.ts`
store-free). Residual decisions, all baked to the recommended default — confirm or redirect with "Go":
- **D1 — "new" = relative to the immediately-prior brief (artifact diff), not first-ever (`surfacedCount 0`)?**
  YES (rec). It is the honest meaning of "siden sist" and catches re-emergence; it is also what unlocks `dropped`.
  Re-open only to redefine "new" as first-ever.
- **D2 — diff against the most recent prior brief only (no `--since` baseline)?** YES (rec). The "since last" a
  daily feed needs. Re-open only to add an arbitrary historical baseline.
- **D3 — `## 🆕 Nytt siden sist` placed before `## 🎯 Topp-treff` (delta leads)?** YES (rec). The one thing a feed
  leads with. Re-open only to place it after the ranked list (appendix) or omit the header on a first brief.
- **D4 — summary marker ` N nye siden sist.` (suppressed on first brief / when nothing new)?** YES (rec). The
  delta the SessionStart hook surfaces for free, with no hook edit. Drop only to keep the summary minimal.
- **D5 — `surfaced:` frontmatter always emitted (incl. `--no-mark`, incl. empty store → blank)?** YES (rec). It is
  the record the *next* diff reads; gating it on `--no-mark` or non-empty would silently break tomorrow's diff.
  Re-open only to gate it.
- **D6 — `dropped`/`carried` render as a one-line count (no titles); `dropped` framed "ikke vist i dag"?** YES
  (rec, = SD2). Keeps `brief.ts` store-free; honest (a count cannot prove "resolved"). Re-open only to pull the
  reason-labeled follow-up into R3e now.
- **D7 — `BRIEF_SCHEMA_VERSION` 1 → 2; store `SCHEMA_VERSION` stays 4?** YES (rec). The frontmatter gained a
  field (the first artifact-schema change since R2b); no store field. Re-open only to add a store field instead.
- **D8 — README gets the R3e section; `trend-spotter.md` gets one prose line; the SSOT is NOT touched?** YES
  (rec). The diff is not a scoring concern — touching `trend-scoring-modes.md` would be scope creep. Re-open only
  to add an SSOT note.
- **D9 — commit split?** Docs commit first, then **one** code commit (rec) — the diff (helpers + render + CLI
  wiring + gate) is one coherent feature. Re-open only for a helpers-then-wiring split.

## 9. Light-Voyage review — folded

Three Opus reviewers ran COLD on this brief + the plan against live `scripts/trends/` code (scope-guardian,
brief-reviewer, plan-critic — the R3c/R3d discipline). **Verdicts:** scope-guardian **MIXED** · brief-reviewer
**PROCEED_WITH_RISKS** · plan-critic **REWORK (0.88)**. They **converged on 2 MAJOR** (both re-verified against
live code before folding) + 4 MINOR. Every line-cite, the floors, the regex/lex/hook safety, and the §3 scope
fence were **confirmed correct** by all three and left untouched.

**MAJOR-1 — a hard schema literal breaks at the 1→2 bump (the §6/Step-1 "no existing assertion breaks" scoping
missed it).** `tests/brief.test.ts:574` is `assert.equal(BRIEF_SCHEMA_VERSION, 1)` — a **hard literal**, not the
constant-tracking RegExp at `:163` (`new RegExp("\\nschemaVersion: " + BRIEF_SCHEMA_VERSION + "\\n")` auto-tracks).
It lives in the `rankForBrief — no schema/score mutation` block (`:568-577`), **outside** the frontmatter tests
§6/plan-Step-1 enumerated, so the "every frontmatter assertion auto-tracks" claim did not cover it. **Resolution:**
the GREEN schema bump (`BRIEF_SCHEMA_VERSION = 2`) must **also flip `:574` → `, 2)`** in the same step (plan
Step 3). `:575` (`assert.equal(SCHEMA_VERSION, 4)`, the store schema) is untouched. Folded into plan Step 3 + R1 +
Step 1's enumeration. (Swept live: `:574` is the *only* hard `BRIEF_SCHEMA_VERSION` literal in the suite;
`cli.test.ts:102` asserts the **store** `persisted.schemaVersion === SCHEMA_VERSION` (4) — unrelated, stays green.)

**MAJOR-2 — the `--json summary` would diverge from the file frontmatter on day-2 (the "one source" invariant).**
The file's frontmatter `summary:` is built inside `renderBrief` (`brief.ts:265`), which Step 3 routes through
`briefSummary(ranking, diff)` → on day-2 it carries the ` N nye siden sist.` marker. But the CLI's `--json`
`summary` field reads a **separate** `const summary = briefSummary(ranking)` (`cli.ts:350`, comment `// SAME source
the frontmatter carries`) that Step 4 left unthreaded → no marker. `cli.test.ts:268` asserts
`fileFrontmatter.summary === json.summary` ("one source") → would **break** on day-2. **Resolution:** Step 4
changes `cli.ts:350` to `briefSummary(ranking, diff)` (the `diff` is in scope — Step 4 computes it between the
ranking at `:339` and the render at `:340`). **Safe on day-1:** `priorDate === null` ⇒ the marker is suppressed ⇒
byte-identical to today's string. Folded into plan Step 4 + the files-touched table.

**MINOR (folded):**
- **M1 — `BriefDiff` is an interface (type-only export).** Anywhere it is referenced as a type (tests or `cli.ts`),
  import it with **`import type { BriefDiff }`**, never a value import — under Node16 ESM + tsx a type-only export
  is stripped from the emitted JS, so a value-import named binding fails to resolve at **module-load** (the same
  Phase-A hazard as a missing named import). The plan's Step-4 code does **not** annotate `: BriefDiff` (it infers
  from `diffSurfaced`'s return) and the SC tests pass object literals — so in practice no `BriefDiff` import is
  needed; the rule is the guardrail if one is added. Folded into plan Step 2/4.
- **M2 — SC9's prior brief is a real renamed brief, not a hand-fixture (rename-real-write).** Replace the "pre-write
  a `<prior-date>.md` fixture carrying a `surfaced:` line" mechanism (plan Step 4 note / Phase B / Step 7) with:
  run `brief` once (writes `${today}.md` with a genuine `surfaced:` line), `mv ${today}.md → 2026-06-20.md` (a fixed
  past date) **in the same `--out`**, then run `brief` again. This (a) closes the write→read loop **clock-free** (no
  `today()` manipulation), and (b) **guarantees the prior `surfaced:` ids are real store ids** (they came from a
  real run), so `carried` is non-trivial and `added` is *exactly* the newly-captured trend — a hand-fixture risks an
  id mismatch that makes everything read as added/dropped (a weaker, possibly-vacuous test). Folded into plan Step 4
  note, Phase B, Step 7, SC9.
- **M3 — SC1 "repeated id" wording.** `diffSurfaced` uses `currentIds.filter(...)`/`priorIds.filter(...)`, which
  **preserve** within-list duplicates — so "not double-counted" is wrong as within-list dedup. What the `Set`
  membership actually guarantees is **cross-partition disjointness** (added/carried/dropped are mutually exclusive).
  Reworded in §6 SC1 + plan Step 1/verification. (Production `surfacedIds` yields distinct ids, so within-list dups
  never arise.)
- **M4 — §3 "empty `surfaced:`" self-contradiction.** The bare `renderBrief(ranking)` default-diff prose said it
  yields "an empty `surfaced:` reflecting the ranking" — contradictory: `surfaced:` is always
  `surfacedIds(ranking).join(",")` (**non-empty** for a non-empty ranking; blank only for an empty store),
  independent of the diff; the default empty diff only drives the **`_Første brief._`** section branch. Reworded in
  §3 (the `renderBrief` default-diff bullet).

**Confirmed correct by all three — left untouched:** every line-cite (`brief.ts:23/204/265/305`,
`cli.ts:339/340/350/352`, `session-start.mjs:60-77/534-536`); the floors (`TRENDS_TESTS_FLOOR` 216 @ live `:716`,
`ASSERT_BASELINE_FLOOR` 117 @ live `:1473` → 123 = 117 + 6 unconditional 16n emitters); Section 16m is the last
trends section (16n sits between its `echo ""` and Section 18); the 6 ASCII sentinels are non-vacuous; the
`/^surfaced: *([^\n]*)/m` regex, the ISO-lex compare, the `^surfaced:` ≠ `^summary:` hook-safety, the `--json`
shape, and the same-day-determinism strict `<`.