v0.4.0

What's Changed

• docs(benches): refresh Scenario 4 baseline with N=5 aggregation by @avifenesh in #144
• RFC-012 Round-7: trait-shape gap-fills (append_frame widen, create_waitpoint, report_usage replace) by @avifenesh in #145
• feat(ff-core, ff-sdk, ff-backend-valkey): extend Frame for append_frame SDK-forwarder parity by @avifenesh in #147
• bench(apalis): use apalis-workflow DAG for scenario 4 comparison (#51) by @avifenesh in #148
• docs(rfc-009): operator mitigation note for adversarial cap distributions by @avifenesh in #149
• feat(ff-core, ff-sdk, ff-backend-valkey): seal ferriskey::Error leak via BackendError wrapper (#88) by @avifenesh in #151
• docs: fill cairn-migration gaps for 0.4.0 (BackendError seal + Round-7 + T1 + Frame) by @avifenesh in #152
• docs(changelog): group [Unreleased] entries thematically for 0.4.0 readability by @avifenesh in #153
• feat(ff-sdk): RFC-012 Stage 1c — BackendConfig carveout + ff-core feature scaffold (tranche 1 of ~4) by @avifenesh in #146
• chore(rfcs): archive 2026-04-23 session exploration records by @avifenesh in #156
• docs(changelog): fill missing [Unreleased] entries since v0.3.4 by @avifenesh in #155
• docs, feat(ff-core, ff-backend-valkey): DX polish — re-exports + ScannerFilter::with_namespace ergonomics by @avifenesh in #157
• docs(cairn-migration): add T4 section + final 0.4.0 delta polish by @avifenesh in #161
• docs: draft 0.4.0 release notes by @avifenesh in #163
• feat(ff-core, ff-backend-valkey, ff-sdk): seal FlowFabricWorker::client() + migrate stream fns through trait (#87) by @avifenesh in #158
• docs: polish stale rustdoc references post-Stage-1c + Round-7 by @avifenesh in #159
• test(ff-test): trait-boundary coverage for describe_execution, describe_flow, list_edges, report_usage (#154 offshoot) by @avifenesh in #165
• feat(ff-core): UsageDimensions constructor + builders; docs: fix BackendError match pattern by @avifenesh in #162
• test(ferriskey): fix test_client.rs compile under --all-features by @avifenesh in #166
• chore: bump workspace to 0.4.0 + CHANGELOG section flip by @avifenesh in #167

Full Changelog: v0.3.4...v0.4.0