sfm: stored-event browser at /events

New standalone HTML page (sfm/event_browser.html, ~470 lines, Chart.js)
that lets you browse persisted events from the SeismoDb + WaveformStore.
Companion to the existing live-device viewer at /waveform:

  /waveform  — connect to a unit and pull events in real time
  /events    — browse events already stored in the DB

Flow:
  1. Page loads → GET /db/units → populate serial dropdown
  2. Select serial → GET /db/events?serial=X&limit=500 → event list
  3. Click event → GET /db/events/{id}/waveform.json → render

Layout is Instantel-printout-ready: channels stacked vertically in
Tran / Vert / Long / MicL order, trigger line at t=0, peak labels,
clean dark theme.  Frames the future PDF-export feature without
needing extra layout work.

Smoke-tested against the dev prod-snapshot — 4 channels render with
correct peaks for K558 events (L=0.3 in/s = the offset-fault peak
we've been chasing all week).

CHANGELOG entry added under [Unreleased] per the v0.20.0 release plan.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,30 @@ All notable changes to seismo-relay are documented here.
 
 ---
 
+## [Unreleased]
+
+### Added
+
+- **Stored-event browser** — new standalone HTML page at `GET /events` (`sfm/event_browser.html`).  Pick a serial from the unit dropdown, scroll through that unit's events (newest-first), click any event to render its decoded waveform via the existing `/db/events/{id}/waveform.json` endpoint.  Dark-themed Chart.js viewer, channels stacked vertically (Tran / Vert / Long / MicL — Instantel printout order, designed PDF-export-ready), trigger line at t=0, peak labels, search/filter, false-trigger flag honored.  Companion to the existing live-device viewer at `/waveform`; the two routes are now clearly delineated in their docstrings.
+- **Histogram body codec — uint8 peak count fix.**  Per-channel peak fields at `block[6]/[10]/[14]/[18]` are `uint8`, not `uint16 LE` spanning `block[6:8]` etc.  The original interpretation was byte-exact on the N844 fixture corpus only because every annotation byte (`block[7]/[11]/[15]/[19]`) in those fixtures was zero.  On non-N844 events with non-zero annotation bytes (observed across BE9558 Tran-drift and BE18003 Histogram+Continuous units), the old interpretation produced peaks up to 268 in/s per channel and 35× inflated PVS sums when first deployed to prod (rolled back same day; properly fixed in this release).  Cross-correlated against BW's per-interval ASCII export on K558 / T003 / N599 / N844 corpora — 100% byte-exact on T/V/L, 99%+ on M (sub-precision rounding).  Annotation byte preserved on each record as `record["annotations"]` for future RE.  Verified against ~3,500 blocks across 5 in-repo fixtures + a synthetic K558 interval-12 regression block.
+- **`apply_bw_report_dict_to_event` helper** in `minimateplus.event_file_io`.  Mirror of `apply_report_to_event` for the projected sidecar dict shape — used by the backfill path, which has the preserved `bw_report` block but not the original `.TXT` file.  BW's reported peaks (and `sample_rate` / `record_time`) now win over codec output during `--force` backfill, matching ingest-path behavior.
+- **`scripts/check_bw_report_preservation.py`** — two-step snapshot/diff tool to verify that `backfill_sidecars.py` doesn't wipe the `bw_report` block from existing sidecars.  Classifies every sidecar as PRESERVED / CHANGED / WIPED / STILL_MISSING / NEW / ADDED / REMOVED.  Exit code 1 if any WIPED or CHANGED entries are found, so it can gate a CI step or deploy script.
+
+### Fixed
+
+- **`scripts/backfill_sidecars.py` no longer wipes `bw_report`.**  Before this fix, `event_to_sidecar_dict` silently dropped the preserved `bw_report` block during every backfill, since the function only emits a `bw_report` when called with a live `BwAsciiReport` dataclass (which the backfill doesn't have — only the projected sidecar dict).  Now we read the existing sidecar's `bw_report` and overlay it onto the regenerated sidecar, alongside the existing `review` and `extensions` preservation.
+- **`scripts/backfill_sidecars.py --force` no longer overwrites BW-overlaid DB peaks with codec output.**  The backfill path now calls `apply_bw_report_dict_to_event` before the DB upsert, mirroring what the ingest path does (`/db/import/blastware_file` parses the `.TXT` into a `BwAsciiReport`, calls `apply_report_to_event`, then upserts).  Without this, events where the codec doesn't fully decode (waveform walker edge cases on SP0/SS0/SV0-style events, histogram `byte[5]!=0` sub-format) ended up with PVS=0 in the DB after a `--force` backfill; bit on prod 2026-05-22, rolled back the same day.
+- **Thor IDF files no longer attempted as BW events in backfill.**  `scripts/backfill_sidecars.py` now filters out `.IDFW` / `.IDFH` files in `_looks_like_event_file()`; they share the `.X0W` / `.X0H` suffix shape but use a separate ingest path (`WaveformStore.save_imported_idf`) and aren't decodable by `event_file_io.read_blastware_file`.
+
+### Docs
+
+- **CLAUDE.md** — added a three-tier conceptual architecture model (SFM / SDM / shared codec library) near the top of the file, with a placement rule for where new code goes.  Documents that what is conceptually SDM (database, waveform store, ingest, `/db/*` endpoints) still lives under `sfm/` for historical reasons; rename deferred until the codebase is quiet enough for a clean refactor.
+- **README.md** — added a "Strategic direction" lead-in to the Roadmap that frames seismo-relay as a suite of cooperating components (not a single app), and an explicit "Terra-View ↔ SFM device control" roadmap section with a concrete implementation checklist (auth as hard prerequisite, embedded live-monitor view, action history, Series IV live-device support).
+- **`docs/histogram_codec_re_status.md`** updated with the uint8 retraction and the annotation-byte status.
+- Three known issues recorded in the Roadmap that were discovered during prod validation: (1) `bw_ascii_report` parser misses PPV / `vector_sum` on some `.TXT` formats (5 events on prod); (2) NULL-timestamp duplicate-row dedup needed (2 events on prod); (3) histogram body sub-format with `byte[5] != 0` not yet decoded (~3 events on prod with empty `.h5` plots).
+
+---
+
 ## v0.19.0 — 2026-05-20
 
 The "device-family separation" release.  Tightens the boundary between Series III (MiniMate Plus / Blastware) and Series IV (Micromate / Thor) so the UI and storage layer dispatch deterministically by family instead of sniffing filename extensions or magnitude heuristics.