Feature compatibility

Which write path a run takes, and whether a combination is allowed at all, comes from one table in faucet_core::compat. Pipeline::run picks the fastest path every active feature supports, and faucet validate refuses a combination no path honours before anything runs.

• ✓ — supported on that path.
• falls back — that path would skip the feature, so the run takes a slower path that honours it (native → columnar → row).
• refused — the combination is rejected when the config is loaded.

A pair the table does not list is supported.

Write paths

Feature	native	columnar	row	exactly-once watermark	overwrite staging
transforms:	falls back	✓	✓	✓	✓
masking:	falls back	✓	✓	✓	✓
masking: rule that retypes a value	falls back	falls back	✓	✓	✓
quality:	falls back	✓	✓	✓	✓
contract:	falls back	✓	✓	✓	✓
schema: (any on_drift)	falls back	✓	✓	✓	✓
schema: { on_drift: fail }	falls back	✓	✓	✓	✓
schema: { on_drift: evolve }	falls back	✓	✓	✓	refused
dlq: (on_batch_error: propagate)	falls back	✓	✓	refused	✓
dlq: (on_batch_error: dlq_all)	falls back	falls back	✓	refused	✓
dlq: with a sink reporting per-row outcomes	✓	falls back	✓	✓	✓
delivery: exactly_once (atomic watermark)	falls back	falls back	✓	✓	✓
write_mode: upsert / delete	falls back	✓	✓	✓	✓
write_mode: overwrite	✓	falls back	✓	refused	✓
write_mode: overwrite shared by fan-out rows	falls back	falls back	✓	refused	✓
adaptive batch sizing	falls back	falls back	✓	✓	✓
resilience:	falls back	falls back	✓	✓	✓
complete_for: { on_missing: delete }	falls back	falls back	✓	✓	refused
policy: rule with on_runtime: quarantine	falls back	falls back	✓	refused	✓
policy:	falls back	✓	✓	✓	✓
budget:	falls back	✓	✓	✓	✓
profiling:	falls back	✓	✓	✓	✓
metadata_columns:	falls back	falls back	✓	✓	✓

The exactly-once watermark and overwrite staging columns apply only when the run uses them (delivery: exactly_once against an idempotent sink, write_mode: overwrite).

Sink capabilities

A sink declares its capabilities (Sink::capabilities, faucet list --json). These combinations depend on them:

Feature	Sink	Verdict
schema: { on_drift: fail }	sink drops unknown fields	refused
schema: { on_drift: evolve }	sink without schema evolution	refused
complete_for: { on_missing: delete }	sink without cleanup	refused

Refusal reasons

• dlq: (on_batch_error: propagate) × exactly-once watermark: delivery: exactly_once (atomic watermark) is not compatible with a DLQ in this version.
• write_mode: overwrite × exactly-once watermark: delivery: exactly_once (atomic watermark) is not compatible with write_mode: overwrite.
• policy: rule with on_runtime: quarantine × exactly-once watermark: a policy rule with on_runtime: quarantine is not compatible with delivery: exactly_once (atomic watermark): a quarantined row would fail the whole page’s atomic commit instead of reaching the DLQ (only a rule whose when can match the row’s sink kind and attributes counts).
• complete_for: { on_missing: delete } × overwrite staging: write_mode: overwrite replaces the whole destination, so scoped cleanup has nothing to do.
• schema: { on_drift: evolve } × overwrite staging: write_mode: overwrite stages into a copy of the destination taken before the run, so schema.on_drift: evolve cannot apply to it.
• schema: { on_drift: fail } × sink drops unknown fields: schema.on_drift: fail cannot be enforced against this sink: it reports no destination schema and silently drops fields its schema lacks, so a drift would never be detected and the fields would be lost.
• schema: { on_drift: evolve } × sink without schema evolution: schema.on_drift: evolve requires a sink that can evolve its destination schema.
• complete_for: { on_missing: delete } × sink without cleanup: scoped cleanup requires a sink that can delete a scope.