peter
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`test_only_a_show_row_pays_for_a_resolution` seeded no watch state, so every rail query inner-joined its way to zero rows and the loop body — with it the assertion — never ran. It now seeds a video, a movie and an episode, and asserts all three kinds are present before the loop, so it cannot go vacuous again. The Plex half of the surprise rail had no test for either of its promises: every test that reached `plex_surprise` passed budget="any" against a library with no state rows, so the duration bounds and the already-started exclusion could both be deleted with the suite green. The YouTube half has had tests for the same two rules since S1 — the asymmetric half of one principle. `plex_item` and `plex_show` — two of the five pinnable kinds — were pinned by no test at all, leaving the rating_key → internal-id translation and both shelf arms uncovered, including the self-reference cycle that once 500'd the shelf. And `GET /api/discover/pick` was exercised only through its domain function, so the route's own query-string translation could regress silently; the new test excludes all three candidates, which is what proves the whole list parsed rather than one unsplit string. `PIN_COLUMNS`/`PIN_KINDS` claimed in a comment to be the one place the pin vocabulary is spoken and had no readers anywhere: `resolve_ref` re-spelled the column names and the route re-typed the kind list. Both now drive off the constants. The `_NO_TS` sentinel was introduced as a crash fix and is not one. The key it replaced, `(ts is not None, ts)`, cannot raise — tuple comparison finds the first UNEQUAL element via `==`, so two null keys compare equal and `None < None` is never reached; three independent runs confirmed it over every permutation. The rationale now says what the sentinel actually buys, lives once in `plex.rollup`, and the third rail that was still on the older spelling has been swept to match. Its test is renamed and re-scoped to the mutation it does catch. Frontend: the reroll's second press asserted `expect.any(Array)`, which cannot tell an accumulating exclusion window from a replacing one — both that and SEEN_WINDOW = 1 (each reinstating the measured nine-card cycle) left the suite green. And `onInfo`'s jump type was untested while `onPlay`'s was pinned twice, so pointing the ⓘ affordance at the player typechecked and shipped green. All eight fixes mutation-checked; every mutant died on its intended test.
Backend conventions
The rules below are already followed across backend/app — they lived only in a few module
docstrings (demo.py, userscope.py, routes/_common.py) until this file collected them (E3 S3,
B-core-20). When you add code, match these so the next reader doesn't have to guess "which pattern do
I copy".
Module layering
Three layers, by who runs the code — not by feature:
-
routes/…— request-only. A route module holds HTTP concerns: auth dependencies, request/ response models, status-code mapping, serialization. It owns logic that runs only on a request. Business logic that a request happens to trigger does not live here if anything else runs it too. -
plex/,downloads/,sync/— domain logic shared by more than one caller. Anything the scheduler or the worker runs (not just a request) lives in one of these domain packages, so the route, the worker, and the scheduler share one definition. Examples from this codebase:downloads/service.pyowns enqueue + the job state transitions (routes call it);plex/sync.pyis run by both the admin route and the scheduler;downloads/pipeline.pyis the worker's child pipeline. -
Flat
app/*.pycore modules — cross-cutting primitives.auth,sysconfig,quota,audit,notifications,userscope,realtime,ratelimit,progress, … are single-file primitives many layers import. They depend on nothing above them (a core module must never import aroutes/…module).
Extraction trigger: the SECOND consumer. Keep new logic inline in its first caller. The moment a second caller needs it (a worker as well as a route; a scheduler as well as a route), extract it down a layer — into the relevant domain package, or a flat core module if it's cross-cutting. Don't pre-abstract for a single caller; don't leave shared logic duplicated once there are two.
Transaction ownership
This follows CLAUDE.md's canonical rule verbatim — "the handler/job-wrapper commits; helpers flush
(only quota owns its session)" — so read it that way, not as an exception to it. The commit belongs
to the operation owner; anything called inside another transaction only stages its change
(db.add / flush) and lets the owner commit, so the whole operation is one transaction.
audit.record() is the reference: it adds the audit row and the caller commits it together with the
mutation it records, so an audit entry can never exist without its change (or vice-versa).
- The operation owner is usually the route handler. A
service.*operation the handler delegates a whole transition to (e.g.service.cancel) is that owner and commits its one transition — it isn't a mid-operation helper. A helper that owns its OWN short-lived session (the worker'sjobdbwrites, the same carve-out CLAUDE.md grantsquota) commits that session. Everything else flushes. SessionLocalisexpire_on_commit=False: after a rawUPDATE+ commit, an ORM object you already loaded is stale. Read the fresh value from the row (RETURNING, or a re-SELECT), not the ORM attribute — seeservice.decr_ref_count.
Shared counters and status: do it atomically at the DB
- Never read-modify-write a shared counter in Python (
x.count = x.count + 1). Concurrent sessions lose an update. Use a DB-atomic statement —col = col + 1, orgreatest(col - 1, 0)withRETURNINGso the caller branches on the post-value under the row lock (service.incr_ref_count/decr_ref_count). - Download job status is a
JobStatusStrEnum (downloads/status.py), not bare strings. TheHOLDINGset defines which states hold aMediaAsset(so release accounting stays correct);STOPPED_BY_ROUTEis the route-initiated stop set. A worker child's terminal write goes throughservice.finalize_if_running(an atomicUPDATE … WHERE status='running') so a finishing child can't resurrect a job a route just stopped.
Config: one home per kind
app.config.settings— boot/env config (DB URL, download root, worker concurrency): read once at startup, not user-tunable at runtime.sysconfig.SPECS— the runtime admin knobs (DB-override-or-default). A new admin-tunable value goes inSPECS; don't invent a fourth store. (state.py'smaintenance_batchpredates this and is slated to fold intosysconfig— do not add more like it.)
The gate
Everything below must be green before a change is done (run via siftlode check):
ruff (backend) · tsc ×3 + eslint + prettier + knip (frontend) · vitest · pytest. The
pytest lane runs in backend/docker-compose.test.yml — an ephemeral Postgres + the backend tree
bind-mounted — so the DB-backed integration tests (the db fixture) actually run; SIFTLODE_TEST_ REQUIRE_DB=1 there turns a would-be silent skip into a hard failure. See docs/development.md.