docs: spec onboarding-wow-burst + ADR-028 (better picks, stronger model)

Phase-1 live-DB investigation found the connect-time burst (ADR-018) fires
but delivers a weak first impression: pure newest-first selection picks junk
(a livestream + regional news for pilot user Jonte), and all burst summaries
run on the weak koala/phi4-mini instead of the validated iguana/gemma4-26b.
Cached-first was investigated and rejected — ~3% cross-user overlap, 0
cached-and-unsummarized, newest-20 all uncached (newest-first and cached-first
are structurally incompatible).

ADR-028 records: persist duration_s at discovery (ADR-023 already fetches it,
just stops discarding), junk-avoiding burst selection (drop known too-short/
too-long), and a stronger burst-only summarizer chain. Not a throughput change.

DECISIONS.md

@@ -1060,6 +1060,74 @@ no migration, no stored state to unwind. Spec: `docs/specs/chat-with-transcript.
 
 ---
 
+## ADR-028 — Onboarding burst: pick likely-good videos, summarize them with a stronger model
+
+**Status:** Accepted (2026-06-11). **Refines ADR-018** (the connect-time burst) and **ADR-020**
+(recency-bounded auto-summarize). **Builds on ADR-022** (the endpoint chain), **ADR-023**
+(the discovery-time `videos.list` enrichment), and **ADR-021** (the shared transcript cache).
+Triggered by a Phase-1 investigation of the live pilot DB.
+
+**Context.** A new user's first session decides whether they return (the Stage-0 gate, ADR-016).
+The connect-time burst (ADR-018: summarize ≤`TAPIR_ONBOARD_SUMMARIZE_COUNT` newest videos so the
+feed isn't empty) *fires* in production, but a live-DB investigation of the second pilot user
+("Jonte") found it delivers a weak first impression for two reasons, and ruled out a third idea:
+
+1. **Junk picks.** Selection was pure newest-first (`NewestUnsummarizedVideoIDs`,
+   `ORDER BY published_at DESC`) with **no quality signal**. Jonte's live burst-3 were a
+   stock-ticker **livestream** + two regional news clips — newest, not best. The cheap signals
+   that *could* gate this (duration, live status) are fetched by ADR-023's `videos.list`
+   enrichment at discovery and then **thrown away**: the `videos.duration_s` column (migration
+   001) was never written.
+2. **Weakest model on the first impression.** All burst summaries ran on `koala/phi4-mini` — the
+   documented weak link (ADR-022 was born from its failures). The stronger, brain-validated
+   `iguana/gemma4-26b` was never used, even though the burst is only ~3 summaries.
+3. **Cached-first instant summaries — REJECTED.** The idea: skip the fetch, summarize
+   already-cached transcripts (ADR-021) instantly. The pilot numbers kill it — only **11 videos**
+   overlap between the two users (~3% of each ~350–400-video library), **0** cached-and-
+   unsummarized, and a new user's newest-20 unsummarized are **20/20 NOT cached**. Newest-first
+   and cached-first are structurally incompatible: fresh uploads are exactly what nobody has
+   fetched. An empty lever at pilot scale.
+
+**Decision.**
+1. **Persist `duration_s` at discovery.** `filterLowValue` (ADR-023) already has each candidate's
+   duration in hand; carry it onto the kept `domain.Video` and have `UpsertVideo` write it,
+   COALESCE-preserving a known value (the channel-title backfill stance, migration 014). No new
+   migration — the column exists. The connect-triggered discovery pass runs *before* the burst,
+   so a fresh user's candidates are enriched in time.
+2. **Junk-avoiding selection.** A new `OnboardBurstVideoIDs(userID, limit, minSeconds, maxSeconds)`
+   keeps the newest-first order but drops a video when its duration is *known* and outside
+   `[minSeconds, maxSeconds]` — `minSeconds` = `TAPIR_MIN_VIDEO_SECONDS` (60, the Shorts floor),
+   `maxSeconds` = new `TAPIR_ONBOARD_MAX_VIDEO_SECONDS` (default 14400 = 4h, to drop multi-hour
+   livestream VODs that pass the live filter once ended). A NULL duration is **unknown** — kept
+   (degrade-open) but ranked after known-good rows. **has-captions stays un-gateable pre-fetch**
+   (only knowable after a gate fetch or a ~0-probability cache hit); selection only *avoids
+   known-junk*, it does not *promise* captions.
+3. **Stronger model for the burst only.** `TAPIR_ONBOARD_SUMMARIZER_MODEL` (default
+   `iguana/gemma4-26b`) leads a burst-specific summarizer chain (onboard model first, then the
+   standard ADR-022 chain as resilience, deduped), wrapped in a burst-specific processor over the
+   *same* store/cache/sink — a pure wiring choice; the engine and ports are unchanged (ADR-003).
+   Empty or equal-to-primary collapses the burst back onto the shared processor.
+
+**Not a throughput change.** The caption rate gate (ADR-014) and the foreground priority lane
+(ADR-026) are untouched — same pacing, same cap. This changes *which* ≤3 videos the burst spends
+its fetches on and *which model* summarizes them, never how fast or how many. The engine's
+existing read-stored-first (ADR-021) is unchanged and still yields a free instant summary on the
+rare cache hit — we simply do not *select* for cache hits.
+
+**Consequences.** Better odds of a strong first session: the burst avoids the obvious junk and
+runs the better model on the one impression that decides return. The selection improvement is
+forward-looking — existing rows have NULL `duration_s` until their next discovery pass backfills
+it (lazy, like channel_title); a brand-new user benefits immediately because connect-discovery
+runs first. `duration_s` becoming live also unblocks future length-aware features (feed sorting,
+"long read" badges) for free.
+
+**Reversibility.** Pure config + wiring + one column write + one query, no migration.
+`TAPIR_ONBOARD_MAX_VIDEO_SECONDS=0` (and `TAPIR_MIN_VIDEO_SECONDS=0`) restores pure newest-first;
+`TAPIR_ONBOARD_SUMMARIZER_MODEL=""` collapses the burst back to the shared processor.
+Spec: `docs/specs/onboarding-wow-burst.md`.
+
+---
+
 ## Rejected alternatives
 
 Approaches considered during the 2026-06-02 planning + grill session and **deliberately not
@@ -1083,6 +1151,7 @@ maps to the ADR that settles it.
 | Feedback-based Stage 0 gate (friends saying it's useful) | Politeness bias makes asked-for feedback the least reliable signal; return-usage is the real test | ADR-016 |
 | Reverse the Dex-write invite flow (Google OIDC only) | Some intended Future-B users won't use Google; OIDC-only leaves them with no onboarding path — invite flow is load-bearing | ADR-017 |
 | k8s CronJob for scheduled discovery (vs in-process) | At Future-B scale the in-process scheduler is simpler to deploy; CronJob's failure-isolation benefit was weighed and traded away knowingly (revisit if >1 replica or load grows) | ADR-018 |
+| Cached-transcript-first onboarding burst (instant, zero-fetch picks) | Live pilot DB: ~3% cross-user video overlap, 0 cached-and-unsummarized, a new user's newest-20 are 20/20 uncached — newest-first and cached-first are structurally incompatible. Empty lever at pilot scale | ADR-028 |
 
 If a future case genuinely reopens one of these, that's a new ADR superseding the relevant one —
 not a silent reversal.

docs/specs/onboarding-wow-burst.md

@@ -0,0 +1,116 @@
+# Spec — Onboarding "wow" burst: better picks, stronger model
+
+**Repo:** tapir · **Size:** medium · **Solo session** (not a swarm).
+
+**Why this exists.** A new user's first session decides whether they return (the Stage-0 gate,
+VISION.md). On connect, Tapir fires a capped burst (≤`TAPIR_ONBOARD_SUMMARIZE_COUNT`, default 3)
+that summarizes the user's newest unsummarized videos so the feed isn't empty (the burst itself
+works — wired in `cmd/tapir/discovery.go` → `cmd/tapir/main.go` `onboard`). A Phase-1
+investigation of the live pilot DB found the burst *fires* but delivers a **weak first
+impression** for two concrete reasons, and ruled out a third idea:
+
+1. **Picks are junk.** Selection is pure newest-first (`videos.NewestUnsummarizedVideoIDs`,
+   `ORDER BY published_at DESC`) with **zero quality signal**. Pilot user "Jonte"'s live burst-3
+   were a stock-ticker **livestream** + two regional news clips — the newest, not the best.
+2. **Weakest model on the first impression.** All of Jonte's summaries ran on
+   `koala/phi4-mini` (the documented weak link — ADR-022 was born from its failures). The
+   stronger, brain-validated `iguana/gemma4-26b` was never used for the burst.
+3. **Cached-first is empty at pilot scale — REJECTED.** The idea (summarize already-cached
+   transcripts instantly, zero fetch) dies on the numbers: only **11 videos** overlap between the
+   two pilot users (~3% of each library), **0** cached-and-unsummarized, and a new user's
+   newest-20 unsummarized are **20/20 NOT cached** — newest-first and cached-first are
+   structurally incompatible (fresh uploads are exactly what nobody has fetched yet). Not built.
+
+Read `CLAUDE.md`, `DECISIONS.md` (esp. ADR-014, ADR-018, ADR-020, ADR-021, ADR-022, ADR-023,
+and the new **ADR-028**), and `VISION.md` (the Stage-0 gate) first. TBD — commit directly to
+`main`, one logical change per commit, conventional commits, `task check` green before each
+commit, `templ generate` if any view changes (none expected).
+
+## Decisions already made (do not reopen)
+- **Not a throughput change.** The caption rate gate (ADR-014) is untouched — same pacing, same
+  priority lane (ADR-026). This slice changes *which* ≤3 videos the burst spends its fetches on
+  and *which model* summarizes them, never how fast or how many.
+- **Cached-first is dropped** (ADR-028, the 3% overlap). The engine's existing read-stored-first
+  (ADR-021, `resolveTranscript`) stays — it already gives a free instant summary on the rare
+  cache hit, transparently. We do not *select* for cache hits.
+- **has-captions is not a pre-fetch signal.** It is only knowable after a gate fetch (or a cache
+  hit, ~0 for new videos). Selection can only *avoid known-junk* (Shorts/live/over-long) — it
+  cannot *guarantee* captions. The spec is honest about this: better odds, not a promise.
+- **No credentialed caption fetch** (ADR-010/ADR-026 dead end). **No client extension.**
+
+## 1. Persist `duration_s` at discovery (the enabling change)
+The `videos.duration_s` column exists (migration 001) but is **never written** — ADR-023's
+`filterLowValue` (`internal/adapters/youtube/youtube.go`) already fetches each candidate's
+duration via the cheap quota `videos.list` call, uses it to drop Shorts/live, then **discards
+it**. Stop discarding:
+- Add `DurationSeconds int` to `domain.Video`.
+- In `filterLowValue`, set `DurationSeconds` on each kept video from the `videos.list` `meta`.
+- `UpsertVideo` writes `duration_s`, **COALESCE-preserving** a known value (never overwrite a
+  real duration with 0/unknown), mirroring the `channel_title` backfill stance (migration 014).
+- No new migration — the column is already there.
+
+Consequence: a fresh user's connect-triggered discovery pass runs **before** the onboard burst
+(`Enqueue`: `run()` then `onboard()`), so duration is populated for the burst's candidates at
+connect. Existing rows backfill on their next discovery pass; until then their `duration_s` is
+NULL and treated as "unknown" (§2).
+
+## 2. Junk-avoiding burst selection
+New store method, RLS-scoped via `withUser`:
+
+```
+OnboardBurstVideoIDs(ctx, userID string, limit, minSeconds, maxSeconds int) ([]string, error)
+```
+
+- Same base as `NewestUnsummarizedVideoIDs`: the user's videos with no summary yet,
+  `ORDER BY published_at DESC NULLS LAST, seen_at DESC`, `LIMIT limit`.
+- **Exclude known-junk**: a row is dropped only when `duration_s IS NOT NULL` **and**
+  (`duration_s < minSeconds` OR `duration_s > maxSeconds`). A NULL duration is **unknown** — kept
+  (degrade-open: never starve the burst because metadata is missing), but ordered *after* rows
+  with a known-good duration so a freshly-enriched good pick wins when both exist.
+- `minSeconds` reuses `TAPIR_MIN_VIDEO_SECONDS` (default 60 — the Shorts floor, ADR-023).
+  `maxSeconds` is new: `TAPIR_ONBOARD_MAX_VIDEO_SECONDS` (default 14400 = 4h) — drops the
+  multi-hour livestream VODs that pass the live filter once ended.
+- `minSeconds<=0` and `maxSeconds<=0` each disable that bound (so `0/0` == the old
+  newest-first behaviour, the reversibility lever).
+- `NewestUnsummarizedVideoIDs` stays (still correct for any caller that wants pure-newest); the
+  burst switches to the new method.
+
+## 3. Stronger model for the burst
+The burst summarizes only ≤3 videos, so a slower, stronger model is affordable exactly here.
+- New config `TAPIR_ONBOARD_SUMMARIZER_MODEL` (default `iguana/gemma4-26b` — the brain-validated
+  homelab general-purpose model, already the ADR-022 fallback).
+- Build a **burst-specific summarizer chain** that puts the onboard model **first**, then the
+  standard chain (primary → local fallback → cloud) as resilience, deduped. Wrap it in a
+  burst-specific `engineProcessor` reusing the same store/transcript-cache/sink — a pure wiring
+  choice, engine and ports unchanged (Clean Architecture, ADR-003).
+- The `onboard` closure uses the burst processor instead of `app.Processor`.
+- **Collapse cleanly**: when `OnboardSummarizerModel` is empty or equals `SummarizerModel`, the
+  onboard path reuses `app.Processor` (no separate chain) — the reversibility lever.
+- Local-first preserved: the onboard model is a local alias; the cloud endpoint stays last in the
+  chain, so a client/NDA deployment with `TAPIR_CLOUD_FALLBACK_MODEL=""` keeps burst content
+  local too.
+
+## 4. Behaviour spec + docs
+- Add a scenario to `docs/use-cases/connect_account.feature` (the connect → burst flow) covering:
+  burst skips a too-long/live video in favour of a reasonable-length one; burst summaries record
+  the onboard model. Map it in `scenarioCoverage` (or tag `@pending` with a reason) so
+  `TestScenarioCoverage` stays green.
+- Update `docs/architecture/architecture.md` (the onboarding-burst / newest-first ordering
+  section) to describe the junk-avoiding selection + the burst model override.
+- ADR-028 in `DECISIONS.md` records the rationale (incl. the rejected cached-first lever).
+
+## Success criteria
+- `task check` green (fmt, vet, lint, `go test -p 1 ./...`).
+- A unit test proves `OnboardBurstVideoIDs` drops a known too-long / sub-min video and keeps a
+  good one, newest-first, RLS-scoped.
+- A test proves discovery persists `duration_s` and does not clobber it on re-upsert.
+- A test proves the burst processor records the onboard model on its summaries (chain ordering).
+- Config defaults + bounds tested (`OnboardMaxVideoSeconds`, `OnboardSummarizerModel`).
+- No change to the rate gate, fetch pacing, or burst cap. `0/0` + empty model == prior behaviour.
+
+## Explicitly NOT in this slice
+- Cached-first selection (rejected, ADR-028).
+- Any caption-availability *guarantee* (impossible pre-fetch).
+- Backfilling `duration_s` for existing rows via a migration (it backfills lazily on discovery).
+- Return-nudges / digests (ADR-020: poisons the unprompted-return signal).
+- Raising fetch throughput, multi-IP, or Whisper (out of scope; the gate is deliberate).