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siftlode/backend/app/README.md
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peter 8d0083d4e4 feat(diagnostics): the issue composer — draft, review, screenshots, zip export (E16 S3)
After Stop (or at the cap, or from Settings → Diagnosztika's past sessions)
one dialog drafts the issue: title, description, the steps drafted from the
session's markers and page changes (a marker without a label is named by its
time), the environment (version, browser, system, window, language). Beside
it, what goes with it: the browser and server logs — each reviewable line by
line, an unticked line is not sent — and the screenshots, removable, with
paste / drop / pick to add more.

- it saves as it goes (debug_sessions.draft, migration 0090): the rendered
  markdown in the user's language, the excluded rows, and its own fields to
  reopen as it was; a sent session is read-only
- the zip export (issue.md, client.log, server.log, screenshots) is built
  from the saved draft by app/issues/bundle.py — the one definition the Gitea
  delivery (S4) will share; .log, not .jsonl, which Gitea refuses
- the log line's level tags and clock move to components/logLineParts so the
  review list draws a level the way both log viewers do
2026-09-19 22:26:49 +02:00

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# 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:
1. **`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.
2. **`plex/`, `downloads/`, `sync/`, `issues/` — 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.py` owns enqueue + the job state transitions (routes call it); `plex/sync.py` is
run by both the admin route and the scheduler; `downloads/pipeline.py` is the worker's child pipeline;
`issues/bundle.py` is the one definition of a bug report's files, for the zip export and the tracker.
3. **Flat `app/*.py` core modules — cross-cutting primitives.** `auth`, `sysconfig`, `quota`, `audit`,
`notifications`, `userscope`, `realtime`, `ratelimit`, `progress`, `logs` (the one logging
configuration), `logsink` (its `log_events` table), `diagnostics` (a user's consented log
level) and `debugsession` (a recording that tags its user's lines, E16), … are single-file primitives many layers import. They depend on nothing above them (a core
module must never import a `routes/…` 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's `jobdb` writes,
the same carve-out CLAUDE.md grants `quota`) commits that session. Everything else flushes.
- `SessionLocal` is `expire_on_commit=False`: after a raw `UPDATE` + 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 — see `service.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`, or `greatest(col - 1, 0)` with
`RETURNING` so the caller branches on the post-value under the row lock (`service.incr_ref_count` /
`decr_ref_count`).
- **Download job status is a `JobStatus` StrEnum** (`downloads/status.py`), not bare strings. The
`HOLDING` set defines which states hold a `MediaAsset` (so release accounting stays correct);
`STOPPED_BY_ROUTE` is the route-initiated stop set. A worker child's terminal write goes through
`service.finalize_if_running` (an atomic `UPDATE … 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 in `SPECS`; don't invent a fourth store. (`state.py`'s `maintenance_batch` predates this and is
slated to fold into `sysconfig` — 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`.