[dlebauer]

Cal-Adapt WRF ingestion currently lives in draft #3967 as a downloader that also extracts, converts units, and writes CF files, with a source-specific bypass in met.process(). This replacement keeps download and CF conversion separate and uses the normal site-level dispatch.

• download.CalAdaptWRF() stages native Zarr chunks through caladaptaer::cae_stage_zarr() and writes annual JSON manifests. It does not convert weather values.
• met2CF.CalAdaptWRF() reads the manifests and delegates extraction, conversion, provenance, and validated output reuse to cae_build_met_drivers(). It publishes annual files with PEcAn prefixes that retain model, scenario, and resolution.
• Registration metadata supplies defaults and a product-prefix template, identifies the raw JSON format, and disables statistical gap filling. There is no CalAdaptWRF branch or skip-list entry in met.process().
• General ingestion changes forward climate options for site downloads, distinguish products during database lookup, allow explicit creation of a named raw format, and carry the CF result forward when standardization is disabled.

The source defaults to CESM2 / ssp370 / d03. d01 and d02 remain selectable. Source calendars and missing values are preserved. The JSON manifests reference local cache paths, so keep the cache until conversion finishes. Shared-cache downloads should run serially; this PR does not add cache locking.

Dependency / merge order: keep this PR in draft until the caladaptaer stack #25–30 lands. The adapter requires the runtime APIs in #25–28; it was tested against stack head f5d50dacb71fbe88052f7b30b7b3b39ba29b85cf. Dependencies point to the normal upstream repository, assuming those changes have merged, rather than pinning a temporary stack branch. The functions fail explicitly when the source-staging API is absent. Remote Zarr access requires R-linked GDAL >=3.9.

Validation:

• 45 assertions passed across the new ingestion tests and nearby dispatcher/registration tests, using the actual proposed CF builder with a local eight-variable fixture and mocked remote staging.
• Checks cover native 365-day calendars, retained missing values, precipitation totals, humidity conversion, wind speed, reuse and corrupted-output repair, preceding precipitation records, character site IDs, product identity, normal CF dispatch, and handoff to model conversion.
• Roxygen documentation regenerated; package build and git diff --check passed.
• R CMD check --no-manual --no-vignettes --no-tests --no-examples completed with no errors, 4 warnings and 3 notes. Reports concern unchanged datasets/compression, unbuilt vignettes, the license stub, existing global bindings, and a local PROJ diagnostic. The focused tests above were run separately; the full package test suite and live downloads were not run.

This PR does not fix SIPNET's assumption of complete Gregorian years or connect the direct-file UCLA reanalysis APIs. The documentation identifies the downstream calendar limitation.

Supersedes #3967; retains credit for Akash B V's original contribution.