diff --git a/.github/workflows/backend-test.yml b/.github/workflows/backend-test.yml
index 3d6d7d8dee..58905b0b1b 100644
--- a/.github/workflows/backend-test.yml
+++ b/.github/workflows/backend-test.yml
@@ -245,7 +245,19 @@ jobs:
           RUST_LOG: "off"
           RUST_LOG_STYLE: never
           CARGO_NET_GIT_FETCH_WITH_CLI: true
-          CARGO_BUILD_JOBS: 12
+          # Cap parallel rustc/link jobs below the 16 available cores. The tail of
+          # the build links ~128 full-graph test binaries (one per tests/*.rs file
+          # across the workspace); at high parallelism enough heavy codegen+link
+          # units (rustc ~2.6GB, mold ~1GB each) overlap to exhaust the 64GB
+          # runner. Matches backend-test-windows.yml, which already uses 8.
+          CARGO_BUILD_JOBS: 8
+          # Incremental compilation is per-run dead weight in CI: rust-cache
+          # (cache-workspaces above) restores compiled dependency artifacts but
+          # never persists target/**/incremental, so there is no prior state to
+          # reuse in a one-shot `cargo test`. It only adds per-crate memory
+          # overhead and extra disk. Off here (kept on for local dev via
+          # .cargo/config.toml). Matches backend-test-windows.yml.
+          CARGO_INCREMENTAL: "0"
           # backend/Cargo.toml leaves profile.dev at the default debug = 2 for
           # the (large) windmill workspace crates; that debug info is emitted
           # into every object file and embedded in each test binary. Across the