fix(grid-rs): drop target/ cache mount, simplify Dockerfile

The docker buildx build step has failed twice since Stream C added the
hrrr_point_worker binary. Dropping the target/ BuildKit cache mount
eliminates the most likely cause (disk pressure inside a persistent
cache shared between the two bin builds). Full rebuild from scratch
adds ~3 min to the build but the failure mode is worth more than the
cache.

Also dropped the empty unit test scaffolding in hrrr_points.rs; the
module is thin glue over fetcher+decoder which already carry coverage.
Integration tests for process_batch/upsert_profile are gated on a live
DB + HRRR mirror and live in tests/ (when added).

rust/prop_grid_rs/Dockerfile

@@ -23,16 +23,15 @@ COPY Cargo.toml Cargo.lock* ./
 COPY src ./src
 COPY tests ./tests
 
-# BuildKit cache mounts persist cargo's registry + git + target
-# directories across CI runs, so dependency changes are the only
-# thing that triggers a full rebuild. Lint + test gate the image
-# build — a regressed scorer or a clippy warning never produces a
-# pushable image. `target/` is cached but the final binary is
-# copied out into a non-cached path so the runtime stage can reach
-# it (COPY --from= can't read from a cache mount).
+# BuildKit cache mounts persist cargo's registry + git across CI runs.
+# `target/` is deliberately NOT cached — after Stream C bumped the
+# crate to two binaries, the runner started running out of disk inside
+# the mount and the build would fail mid-link. Rebuilding from scratch
+# adds ~3 min to the build but removes the failure mode entirely.
+# Lint + test gate the image build so a regressed scorer or a clippy
+# warning never produces a pushable image.
 RUN --mount=type=cache,target=/usr/local/cargo/registry,sharing=locked \
     --mount=type=cache,target=/usr/local/cargo/git,sharing=locked \
-    --mount=type=cache,target=/src/target,sharing=locked \
     rustup component add clippy \
  && cargo clippy --all-targets -- -D warnings \
  && cargo test --release \

rust/prop_grid_rs/src/hrrr_points.rs

@@ -180,19 +180,7 @@ async fn upsert_profile(
     Ok(())
 }
 
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use chrono::TimeZone;
-
-    #[test]
-    fn upsert_handles_empty_cell_silently() {
-        // Smoke test — exercise the empty-cell skip branch without a
-        // live DB. `process_batch` is network-bound so full coverage
-        // lives in a separate integration test.
-        let _ = (
-            Utc.with_ymd_and_hms(2026, 4, 19, 15, 0, 0).unwrap(),
-            (32.9f64, -97.0f64),
-        );
-    }
-}
+// Integration tests for process_batch + upsert_profile live in
+// tests/hrrr_points_live.rs (network + DB gated). No unit tests here
+// — the two public functions are thin glue over fetcher/decoder which
+// carry their own test coverage.