Purpose

tenbackward.config.load_config() is the single boundary that turns process environment + optional .env file into a typed Config dataclass. Job 1083 changes every variable that ships in .env.example so that it is explicitly required at every layer (entrypoint.sh, config.validate_config, and the rendered cron).

Required Environment Variables

The following keys must be present and non-empty in the merged dotenv/process environment before application defaults are applied.

Key	Purpose	Validation
`MASTODON_BASE_URL`	Mastodon instance to post against.	Valid `http` or `https` URL.
`MASTODON_ACCESS_TOKEN`	OAuth token used by the Mastodon client.	Required string; redacted in logs.
`MASTODON_VISIBILITY`	Post visibility.	`public` or `unlisted`.
`SITE_URL`	Source blog URL.	Valid `http` or `https` URL.
`HASHTAGS`	Comma-separated hashtags.	Required string.
`THROWBACK_PREFIX`	Prefix prepended to each status.	Required string.
`MAX_RETRIES`	Maximum number of pipeline attempts.	Non-negative integer; defaults to `5` when absent.
`RUN_AT`	Daily cron fire time.	`HH:MM` 24-hour format.
`TZ`	Cron and application timezone.	Valid IANA timezone.

BLOG_REPO_URL and BLOG_DIR are optional and receive defaults after this required-key check. DATA_DIR is read separately from the process environment and defaults to /app/data.

Defaults

Defaults are applied only after required-key validation. The current defaults are:

Default key	Default value
`MAX_RETRIES`	`5`
`BLOG_REPO_URL`	`https://git.chaospott.de/Chaospott/site`
`BLOG_DIR`	`blog` (resolved relative to `data_dir`)

Application-facing required values are not silently supplied by config.py; the container environment may still provide TZ=Europe/Berlin and Compose may provide development fallback values.

`Config` Dataclass

Field	Type	Source
`mastodon_base_url`	`str`	`MASTODON_BASE_URL`
`mastodon_access_token`	`str`	`MASTODON_ACCESS_TOKEN`
`mastodon_visibility`	`str`	`MASTODON_VISIBILITY`
`site_url`	`str`	`SITE_URL`
`hashtags`	`str`	`HASHTAGS`
`throwback_prefix`	`str`	`THROWBACK_PREFIX`
`max_retries`	`int`	`MAX_RETRIES` (parsed as non-negative int)
`run_at`	`str`	`RUN_AT`
`tz`	`str`	`TZ`
`data_dir`	`Path`	`DATA_DIR`, default `/app/data`
`blog_repo_url`	`str`	`BLOG_REPO_URL`
`blog_dir`	`Path`	`BLOG_DIR` resolved against `data_dir`

Validation Behaviour

validate_config(values) collects all failures before raising so the operator sees every problem at once. A single ConfigError lists each problem joined with "; ". Validation covers:

Required keys are non-empty.
RUN_AT parses as HH:MM.
MASTODON_BASE_URL and SITE_URL parse via urllib.parse.urlparse with an http/https scheme and a non-empty netloc.
VISIBILITY is one of {"public", "unlisted"} (ALLOWED_VISIBILITY).
BLOG_REPO_URL (optional, has default) parses via urllib.parse.urlparse with an http/https scheme and a non-empty netloc when present.
TZ resolves via zoneinfo.ZoneInfo.
MAX_RETRIES parses as a non-negative integer (rejects bools).

Exit Codes

Code	Source	Meaning
`1`	`main.main()` (retry budget exhausted)	Pipeline failed on every attempt after `MAX_RETRIES + 1` tries.
`2`	`main.main()` (`ConfigError`)	Configuration was present but invalid; details are logged.

Citations

[1] src/tenbackward/config.py — REQUIRED_KEYS, DEFAULTS, ALLOWED_VISIBILITY, Config, load_config, validate_config.
[2] .env.example — canonical env-var list.
[3] entrypoint.sh — shell-side mirror of the required keys.

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