Refuse an unregistered --symbols instead of reporting wrote=0

[mspinola]

The problem

The three providers disagreed about what to do with a symbol the registry does not carry.

• databento refuses it — KeyError: not in the marketdata registry: [...]
• yfinance and norgate filtered it out of their target list and returned ok=True, wrote=0

main() turns ok=True into exit 0. So a fetch scoped to a symbol that is not in registry.yaml printed one line and reported a successful run:

$ marketdata-update --bars --symbols VIX
yfinance: no registry symbols resolve to this provider among ['VIX']

bars_yahoo: wrote=0 failed=0
$ echo $?
0

That matters because of how the producer wrappers read it. run-equities.cmd and run-prices.cmd both branch on if not errorlevel 1, so exit 0 means "fetch succeeded, go on to sync" — and the replica syncs run against a store nothing was written to.

The sharp edge is what it does to a symbol removed from registry.yaml. The removal itself is quiet and local; the failure surfaces later, wherever something still asks for that symbol, as a wrote=0 that looks like a typo rather than a consequence.

The change

--symbols is validated against the registry in main(), before dispatch, and refused via p.error — exit 2, matching the other malformed-request guards, so a fetch failure (1) stays distinguishable from a request that could never have fetched anything.

$ marketdata-update --bars --symbols NOTASYMBOL
marketdata-update: error: not in the marketdata registry: NOTASYMBOL. Nothing
would be fetched for these, so this is refused rather than reported as a run
that wrote 0 rows. Check the spelling, or add them to registry.yaml.
$ echo $?
2

This is not a new policy. It is the rule the file already applies to --require-final and --windowed-n1-stats — "a modifier that cannot modify anything is refused, not ignored" (update.py) — extended to the one argument still exempt from it.

Two decisions worth review

The check is in main(), not in each provider. An unscoped --bars runs every domain, so an equities symbol legitimately resolves to nothing in norgate and a futures symbol resolves to nothing in yfinance. A per-provider refusal would fail a run the other half handled perfectly well. test_an_equities_symbol_does_not_fail_the_futures_half pins that.

A partially satisfiable request is refused whole. --symbols SPY NOTASYMBOL fetches nothing rather than fetching SPY. Three of four symbols arriving is not the request that was made, and which half to keep is the caller's call, not the producer's.

Tests

tests/test_cli_symbols.py, 5 cases: unknown symbol refused; refused even when other requested symbols are valid; a registered symbol is not refused (the guard must not over-fire); cross-domain unscoped runs unaffected; no --symbols means no check.

Suite: 215 passed, 2 skipped (was 210 passed, 2 skipped).

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