… 2 wave-2 PR 3)

Explicit warm-up path for the Arc 7 wave 2 wave-2 schema cache (design
doc §4.2 route B). When `--with-schemas` is set, `rocky discover` walks
each unique `(catalog, schema)` pair reachable via the source's
`BatchCheckAdapter`, issues one `batch_describe_schema` round-trip, and
persists every returned table as a `SchemaCacheEntry` via
`StateStore::write_schema_cache_entry` (the infra PR 1a shipped in
#223). Downstream `rocky compile` / `rocky lsp` invocations pick up
those entries via the read path wired in #228 (PR 1b), so leaf models
that reference the cached source stop typechecking as `Unknown`.

What the flag does NOT do:

- Does not touch the `rocky run` write tap (PR 2, parallel agent).
- Does not add `clear-schema-cache` or a CLI TTL override (PR 4).
- Does not alter the read path, the cache-entry format, or the
  `state_path` resolution.

Error handling (design doc §4.2 + trust positioning):

- `--with-schemas` + `[cache.schemas] enabled = false` in rocky.toml
  → hard error with an actionable message. The two signals are
  contradictory; silently skipping would leave the user guessing why
  `schemas_cached=0`. Erroring keeps the user's mental model aligned
  with what the cache actually does.
- Missing `source.catalog` → warn once, skip writes (cannot key
  entries without a catalog).
- `BatchCheckAdapter` not registered for the source adapter (DuckDB
  today) → warn once, skip writes.
- Per-schema `batch_describe_schema` failure → warn and continue.
- Per-entry `write_schema_cache_entry` failure → warn and continue.

DiscoverOutput schema change:

- New `schemas_cached: usize` field (skipped from the wire format
  when zero — fixtures captured without the flag stay byte-stable).
  Full codegen cascade run: `schemas/discover.schema.json`,
  `integrations/dagster/.../types_generated/discover_schema.py`, and
  `editors/vscode/src/types/generated/discover.ts` all regenerated.

Tests:

- 5 new unit tests (`discover::tests`) covering the dedup helper and
  the inner warm-up loop against a stub `BatchCheckAdapter`: writes
  one entry per table, continues past describe failures, handles the
  empty schema list, and lowercases key components. DuckDB adapter
  has no `BatchCheckAdapter` so playground integration tests hit the
  warn-and-skip path; the stub gives meaningful assertions for the
  happy path that would otherwise require a live warehouse.

Test plan:

- `cargo test -p rocky-cli -p rocky-core` — 1236 tests green.
- `cargo clippy --all-targets -- -D warnings` — clean on full
  workspace.
- `cargo fmt --all --check` — clean.
- `just codegen` — schemas regenerated, only the expected
  `schemas_cached` node added to `discover`.
- `uv run pytest` in `integrations/dagster/` — 370 tests green after
  Pydantic regeneration.
- `npm run compile` in `editors/vscode/` — clean.
- `scripts/regen_fixtures.sh` — fixtures byte-stable (field skipped
  when zero).
- Smoke-tested against the 00-playground-default POC: discover
  without the flag returns the same JSON as before (no
  `schemas_cached` field); discover with `--with-schemas` warns
  about the missing DuckDB `BatchCheckAdapter` and returns the same
  JSON (no entries written, `schemas_cached=0` elided); discover
  with `enabled = false` + `--with-schemas` errors cleanly.