Adds reference + features-page coverage for the commands that landed
in PRs #199-#203, and populates the CHANGELOG's [Unreleased] section
for the upcoming coordinated release cut.

- `docs/reference/commands/administration.md` — new `rocky cost
  <run_id|latest>` section with JSON + table examples and adapter
  coverage notes (Databricks/Snowflake duration-based; BigQuery bytes;
  DuckDB zero; discovery adapters skipped). Added to the related-
  commands list on `rocky trace` so the three sibling readers
  (replay/trace/cost) cross-link.
- `docs/reference/commands/core-pipeline.md` — added `rocky branch
  compare <name>` to the branch subcommand header and a short usage
  example explaining the `ShadowConfig.schema_override` mechanism it
  shares with `rocky run --branch`.
- `docs/features/all-features.md` — added `cost` to the administration
  command roster and a bullet under Observability for the historical-
  rollup surface.
- `engine/CHANGELOG.md` — populated [Unreleased] with the five PRs
  shipped 2026-04-21 (SIGPIPE, branch compare, POC portability cleanup,
  rocky cost, record_run wiring) plus the Pydantic soft-swap + fixture
  normalizer internals. Ready for the next coordinated release cut.

Docs build: `cd docs && npm run build` — 69 pages built, no warnings.

* chore(engine): release 1.12.0

Arc 1 wave 2 + cleanup cascade. Eight PRs since v1.11.0:

- #199 SIGPIPE handler
- #200 rocky branch compare
- #201 POC target_dialect cleanup
- #202 rocky cost <run_id|latest> (Arc 2 wave 2 first PR)
- #203 rocky run persists RunRecord (Arc 1 wave 2 load-bearing fix)
- #204 docs + CHANGELOG [Unreleased] cascade
- #205 demo-branches-replay.gif refresh
- #206 real per-model started_at on MaterializationOutput

rocky history / replay / trace / cost now return real data end-to-end
for the first time. Full notes in CHANGELOG.

* feat(state): configurable transfer timeout + tracing span + Valkey wrap

- `StateConfig.transfer_timeout_seconds` (default 300s) replaces the hard-
  coded `STATE_TRANSFER_TIMEOUT`. Operators can now tune the wall-clock
  budget in `rocky.toml` for very large state or slow networks without
  recompiling. `StateConfig` gains a manual `Default` impl so
  `StateConfig::default()` yields 300s (not u64's zero).
- `state.upload` / `state.download` tracing spans wrap every transfer
  carrying `backend`, `bucket`, and `size_bytes`. The in-elapse warn event
  inherits those fields automatically, so hung transfers are diagnosable
  from stderr logs alone (which dagster-rocky streams into the Dagster run
  viewer).
- Structured `warn!` on timeout elapse ("state transfer exceeded timeout
  budget") with a `duration_ms` field — replaces silent `Timeout(_)`.
- Valkey read/write paths audited and closed: `redis::Client::get_connection`
  + `redis::cmd(...).query()` are sync and blocked the tokio runtime thread;
  no outer `tokio::time::timeout` could rescue them. Both `upload_to_valkey`
  and `download_from_valkey` now run under `tokio::task::spawn_blocking`
  inside `with_transfer_timeout`, closing the same class of hang the
  object-store paths were already protected against.
- `default_client_options()` in `object_store.rs` honours the standard
  `object_store`-crate env vars `AWS_ALLOW_HTTP` / `AZURE_ALLOW_HTTP` /
  `GOOGLE_STORAGE_ALLOW_HTTP`. Always off in production; the new
  integration test uses it to front-end the S3 SDK with a plain-HTTP
  wiremock server without bypassing the credential chain.
- New `tests/state_sync_timeout_test.rs` integration test: a wiremock S3
  endpoint that holds PutObject for 1h proves `upload_state` returns
  `StateSyncError::Timeout` within the configured 2s budget (+grace).
  A prompt-endpoint negative control guards against regressions.
- CHANGELOG entries added under [1.12.0]. Example config in
  `engine/examples/dagster-integration/rocky.toml` surfaces the new key.

cargo fmt clean; `clippy --workspace --all-targets -- -D warnings` clean;
all 977 rocky-core unit tests + 30 e2e + 20 integration + the 2 new
timeout tests pass.

* chore(codegen): regenerate schemas + pydantic types for StateConfig.transfer_timeout_seconds

* chore(fixtures): regenerate dagster test fixtures for 1.12.0

`just regen-fixtures` — version string bump only (1.11.0 → 1.12.0) across
35 captured fixtures under integrations/dagster/tests/fixtures_generated/.