claude@clouddev1
e22f933e02
Adds `Severity` (Error / Warning, ordered so Error > Warning)
and `Diagnostic { severity, span, message }` in
`walker::outcome`, plus a `diagnostics` field on `WalkResult`
— the schema-aware findings layered on a structurally-valid
parse (ADR-0027 §2).
`input_verdict(source, schema)` is the validity-indicator
entry point: `None` when the input would run clean (and for
empty input), `Some(Error)` for a parse failure or unknown
command, `Some(Warning)` for the ADR-0026 expression flags.
The verdict is the highest severity across the parse outcome
and the diagnostics set.
`diagnostics` is empty at this step — the schema-existence
(ERROR) and expression (WARNING) passes that fill it land
next. Covered by `input_verdict` unit tests.