fix: --show-config stops flagging documented [session] persist as an unknown TOML key (gh #112)

[dkedar7]

Summary

Fixes #112. langstage-cli --show-config contradicted itself about [session] persist: in one run it listed session.persist under "unknown TOML keys (ignored - a typo or wrong table?)" and, one line later, attributed persist = ... [toml (session.persist)] to that same key.

[session] persist is a documented key (README: disable persistence with [session] persist = false) and it is honored — so the "unknown/typo/ignored" warning is a false positive on the very diagnostic verb a user runs to trust their config.

Root cause

langstage-core 1.0.32 added unknown-TOML-key detection (HostConfig.unknown_toml_keys()), which flags any TOML key that maps to no config field. persist is resolved out-of-band by cli._resolve_persist (flag > LANGSTAGE_PERSIST > [session] persist > default-on) and rendered by its own --show-config block (gh #102/#108), so it is deliberately not a CodeConfig dataclass field — hence absent from _toml_map() and false-flagged.

The fix

Register the dotted key session.persist in CodeConfig._TOML's known-key set. This is a map entry, not a dataclass field — core's resolve() / describe() / config_dict() all iterate dataclass fields, so this adds no phantom field and does not double-render persist; it stays resolved and rendered out-of-band exactly as before.

A _TOML_PASSTHROUGH [session] table was rejected on purpose: it would silence the whole table and hide real typos. Registering the single key keeps the detector honest — a typo like [session] perssist (or any unknown table [bogus] x) is still flagged.

Verification

langstage.toml	Before	After
[session] persist = false	flagged as unknown ❌	not flagged ✓, persist = False [toml (session.persist)]
[session] perssist = true	flagged	still flagged ✓
[bogus] x = 1	flagged	still flagged ✓

Tests

• Full suite: 176 passed, ruff check + format --check clean.
• Adds two regression tests in tests/test_show_config.py: documented [session] persist shows no unknown-key warning; typo'd [session] perssist and [bogus] x are still flagged.

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https://claude.ai/code/session_011HWCfJii6gXd3XL3Gq3W8B