Type: duration (records retention / TTL / SLA) + timestamp arithmetic

[rrrodzilla]

Workstream: Type system · Part of #89

Context

CEL has a first-class duration type; SchemaForge has none — @format("Duration") is display-only over an int. Duration is the highest-value missing type for a federal records platform: retention windows, TTLs, SLA timers.

Scope

• New FieldType::Duration + DynamicValue::Duration (crates/schema-forge-core/src/types/field_type.rs, dynamic_value.rs).
• DSL syntax + literal form (e.g. duration("2555d")).
• Timestamp↔duration arithmetic in rules (pairs with existing DateTime).

Acceptance

• A duration field round-trips; rules can compute now() - created_at > duration(...).

Enables records-retention rules in the rules engine (#89).

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Dependencies: Parallelizable now — independent of the substrate decision. Soft.

[rrrodzilla]

Landed in 3a9bc47 — feat(types): add first-class duration field type (#96).

End-to-end duration field type following the DateTime precedent at every layer:

• core: FieldType::Duration + DynamicValue::Duration(chrono::TimeDelta); new pure types/duration.rs (format/parse, accepts ns/us/ms/s/m/h/d/w + sign/fractional/compound).
• DSL: duration type keyword + parse/print round-trip.
• cel: real bidirectional bridge (replaced the old Unsupported("duration") stub); Integration: apply-time type-checking of rule expressions against schema field types #104 type-checker infers/accepts CelType::Duration. Timestamp/duration arithmetic in rules already worked (Type/semantics: CEL timestamp operations (tz-aware accessors, overflow rules) #101).
• storage: Postgres BIGINT signed nanoseconds (lossless, indexable; fails closed past ~±292y); SurrealDB native unsigned duration.
• acton REST: Go-style seconds-string JSON wire form (e.g. "220752000s"), byte-identical to CEL's duration() input; request→persist→response round-trips.

Fidelity fix during review: SurrealDB's native duration is unsigned, so a negative duration is now rejected fail-closed (BackendError::ValidationFailed → HTTP 422 with the field + offending value), recursing through arrays/composites — rather than silently stored as NULL. Postgres stores negatives losslessly. No silent data loss on either backend.

Verified: clippy -D warnings clean; full workspace 2040 tests pass under --features surrealdb.

Note for rule authors: CEL's own duration() literal accepts only ns/us/ms/s/m/h (cel-spec), NOT d/w. So inside a rule, write duration('220752000s'), not duration('2555d') (the REST/core parser is more permissive and accepts d/w).