feat(config): a TOML configuration file, for where a person edits it by hand

[wamxx]

RESCRIPTUM_CONFIG names a file that sets the same settings under readable names — the prefix gone, tables doing the grouping. It exists for the platform this project was written for: on DSM there is no environment, there is a file, and RESCRIPTUM_ANSWERS_DIR=… on every line is a poor thing to hand somebody editing in File Station.

answers_dir = "/srv/answers"
log         = "problems"

[store]
kind    = "sqlite"
db_path = "/srv/answers.db"

[admin]
addr  = "127.0.0.1:8001"
token = "…"

The shape of it

src/tomlconfig.rs maps a document onto the RESCRIPTUM_* names and does nothing else. Every value reaches Config::from_lookup under the key it would have had in the environment, so one place still decides what a setting means and this format cannot grow behaviour the environment lacks — which is what keeps two configuration files from becoming two configurations. A unit test asserts MAPPING covers envfile::KNOWN_KEYS exactly: a setting missing from it is one the file silently cannot configure.

Every rule the env file has carries over unchanged — named and never discovered, the real environment wins, an unreadable named file is a startup error. Naming both files is a transition rather than a steady state, so nothing is refused and the order is said out loud at startup: the environment beats the TOML file, which beats the env file. config set writes the TOML file when both are named, because writing the other would be a change that silently does nothing.

What the implementation settled

• Replace the value, never the entry. A setting's explanation lives in the key's decor, so inserting over an existing key throws away the paragraph above it — on a packaged install, the only documentation the configuration has.
• unset empties the value rather than deleting the line, for the same reason. Empty already counts as unset everywhere else here.
• A configuration file must not live in the answers directory. Every servable .toml at the top of it is an answer document and this format shares the extension, so check reports one dropped there as a misplaced answer. Found by writing the tests; pinned by one rather than left to be discovered.

Cost

A mapping, not a dependency — toml_edit already parses every answer document. Measured on armv7: +14,544 bytes (2,799,168 → 2,813,712), 0.5%.

While measuring, both size tables in the repository turned out to be stale by roughly 200 KB and to disagree with each other. All four feature combinations were re-measured in one sitting and both tables corrected. The boot budget question is now written against 1,164,120 rather than the older figure, and says so.

Tests

613 (+31), including the two that were watched failing before being trusted: the precedence between the two files, and the comments surviving a write.

Not in this PR, deliberately

The DSM package still writes its .env. Switching it means a postupgrade that translates the old file once, and packaging/dsm/CLAUDE.md requires that to be watched running on the machine rather than reasoned about at a desk.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KQnAk5r4fLKcWuAwUY6Pa6