fix: harden WAL flush workers and merge-scan teardown under load

.cargo/config.toml

@@ -0,0 +1,12 @@
+# Faster local `cargo build` on nightly:
+# - Parallel rustc frontend (`-Z threads=8`)
+#
+# rust-toolchain.toml selects nightly so these flags are valid for `cargo`.
+# Do not put `profile.dev.codegen-backend` here: Cargo 1.96 rejects that
+# unstable key, and CI/Docker pin rustc 1.96.0 via `RUSTUP_TOOLCHAIN`.
+# Optional local Cranelift (nightly only):
+#   export CARGO_PROFILE_DEV_CODEGEN_BACKEND=cranelift
+# CI and Docker set `CARGO_ENCODED_RUSTFLAGS` empty so stable rustc never
+# receives `-Z`.
+[build]
+rustflags = ["-Z", "threads=8"]

.github/workflows/benchmarks.yml

@@ -9,6 +9,8 @@ env:
   CARGO_TERM_COLOR: always
   PGRX_VERSION: "0.19.1"
   PG_VER: "16"
+  RUSTUP_TOOLCHAIN: "1.96.0"
+  CARGO_ENCODED_RUSTFLAGS: ""
 
 jobs:
   benchmarks:
@@ -104,6 +106,9 @@ jobs:
         env:
           DATABASE_URL: "host=/var/run/postgresql user=runner dbname=runner"
           KOLDSTORE_BENCH_START_PGRX: "0"
+          # Packaged Postgres runs as OS user `postgres` and cannot write under
+          # $GITHUB_WORKSPACE; keep cold Parquet in /tmp (world-writable).
+          KOLDSTORE_BENCH_STORAGE_ROOT: /tmp/koldstore-bench-cold
           # Enable Criterion extension microbenches (default in run.sh skips them).
           KOLDSTORE_BENCH_SKIP_CRITERION: "0"
           BENCH_ROWS: "100000"

.github/workflows/chat-penetration.yml

@@ -45,6 +45,8 @@ env:
   CARGO_TERM_COLOR: always
   PGRX_VERSION: "0.19.1"
   PG_VER: "16"
+  RUSTUP_TOOLCHAIN: "1.96.0"
+  CARGO_ENCODED_RUSTFLAGS: ""
 
 jobs:
   chat-penetration:

.github/workflows/ci.yml

@@ -21,6 +21,10 @@ on:
 env:
   CARGO_TERM_COLOR: always
   PGRX_VERSION: "0.19.1"
+  # rust-toolchain.toml is nightly for local Cranelift; CI must not follow it.
+  RUSTUP_TOOLCHAIN: "1.96.0"
+  # Ignore repo `.cargo/config.toml` `-Z threads=8` (nightly-only).
+  CARGO_ENCODED_RUSTFLAGS: ""
 
 # Needed so EnricoMi can publish check runs + PR comments from JUnit.
 permissions:
@@ -223,6 +227,8 @@ jobs:
     steps:
       - uses: actions/checkout@v7
       - uses: dtolnay/rust-toolchain@1.96.0
+        with:
+          components: clippy
       - uses: Swatinem/rust-cache@v2
       - uses: taiki-e/install-action@v2
         with:

.github/workflows/deep-hammerdb.yml

@@ -60,6 +60,8 @@ permissions:
 env:
   CARGO_TERM_COLOR: always
   PGRX_VERSION: "0.19.1"
+  RUSTUP_TOOLCHAIN: "1.96.0"
+  CARGO_ENCODED_RUSTFLAGS: ""
 
 jobs:
   deep-hammerdb:

.github/workflows/nightly-readiness.yml

@@ -9,6 +9,8 @@ env:
   CARGO_TERM_COLOR: always
   PGRX_VERSION: "0.19.1"
   KOLDSTORE_SQLSMITH_SECONDS: "30"
+  RUSTUP_TOOLCHAIN: "1.96.0"
+  CARGO_ENCODED_RUSTFLAGS: ""
 
 jobs:
   nightly: