Add Variant SELECT rewriter and comprehensive architecture docs

.env.example

@@ -51,3 +51,6 @@ OTEL_EXPORTER_OTLP_PROTOCOL=grpc
 OTEL_EXPORTER_OTLP_HEADERS=
 # Optional: Enable/disable tracing (default: true)
 OTEL_SDK_DISABLED=false
+
+# Data Directory (WAL stored in {dir}/wal, cache in {dir}/cache)
+TIMEFUSION_DATA_DIR=./data

.env.minio

@@ -24,7 +24,7 @@ MAX_PG_CONNECTIONS=100
 AWS_S3_LOCKING_PROVIDER=""
 
 # WAL storage directory for walrus-rust
-WALRUS_DATA_DIR=/tmp/walrus-wal
+TIMEFUSION_DATA_DIR=./data/minio
 
 # Foyer cache configuration for tests
 TIMEFUSION_FOYER_MEMORY_MB=256

.env.test

@@ -39,7 +39,7 @@ TIMEFUSION_VACUUM_RETENTION_HOURS=1
 TIMEFUSION_FOYER_MEMORY_MB=64
 TIMEFUSION_FOYER_DISK_GB=1
 TIMEFUSION_FOYER_TTL_SECONDS=60
-TIMEFUSION_FOYER_CACHE_DIR=/tmp/timefusion_test_cache
+TIMEFUSION_DATA_DIR=./data/test
 TIMEFUSION_FOYER_SHARDS=4
 TIMEFUSION_FOYER_FILE_SIZE_MB=8
 TIMEFUSION_FOYER_STATS=true

.github/workflows/ci.yml

@@ -16,10 +16,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@stable
+      # rustfmt.toml uses nightly-only options (wrap_comments, imports_granularity,
+      # group_imports, format_code_in_doc_comments, normalize_doc_attributes,
+      # empty_item_single_line, struct_field_align_threshold). Stable fmt
+      # silently drops them and reformats differently → CI mismatch.
+      # rust-toolchain.toml pins to stable, so install nightly *and* invoke it
+      # explicitly with `+nightly` so cargo doesn't fall back to the pinned channel.
+      - uses: dtolnay/rust-toolchain@nightly
         with:
           components: rustfmt
-      - run: cargo fmt --all --check
+      - run: cargo +nightly fmt --all --check
 
   clippy:
     name: Clippy
@@ -29,6 +35,8 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: clippy
+      - name: Install protoc
+        run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
       - uses: Swatinem/rust-cache@v2
       - run: cargo clippy --all-targets --all-features -- -D warnings
 
@@ -38,6 +46,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - name: Install protoc
+        run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
       - uses: Swatinem/rust-cache@v2
       - run: cargo check --all-targets --all-features
 
@@ -88,6 +98,8 @@ jobs:
         run: sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - name: Install protoc
+        run: sudo apt-get install -y protobuf-compiler
       - uses: Swatinem/rust-cache@v2
 
       - name: Run all tests