craft-crw: Canon CRW (CIFF) raw decoder, moved from LightCraft with its clean-room record

The clean-room Canon CRW decoder written in LightCraft (crates/raw/src/vendor/crw.rs,
crw_tables.rs, branch clean-room-crw-format-decode, revision 70c755e4) becomes the shared
crate craft-crw: the CIFF heap container, the entropy coding derived by black-box analysis
(frozen code tables for selectors 0-2), sensor black and white levels, as-shot white
balance, orientation and the make/model/time records. Public types are the crate's own
(Error, Limits, Cfa, Rect, BlackLevel, Header, Image); the capture time is handed on as
Unix seconds so no calendar code lives here; LightCraft's shared plateau estimate is
copied as saturation_plateau. Algorithm, tables and thresholds are unchanged.

Tests: the ported synthetic round-trip, table-structure and hostile-input tests; a
proptest mutation sweep (tests/robust.rs); and tests/samples.rs, which pins the eleven
CC0 raw.pixls.us sample files (tests/samples.json: URL, SHA-256, licence) to the SHA-256
of the verified decode plus levels, white balance and metadata, so the port is proven
byte-identical to the LightCraft decode without redistributing the reference TIFFs.
scripts/fetch-crw-samples.py downloads the files outside the checkout; CRAFT_CRW_SAMPLES
and CRAFT_CRW_ORACLE point the tests at them. The crate builds for wasm32.

The whole derivation record (starting assumptions, plan with the maintainer's decisions,
source log, container and payload notes, derivation log, frozen format, verification,
colour/levels notes, private-corpus and chart notes, scripts, logs and the frozen table
JSON) moves verbatim to crates/crw/clean-room/ with a README that indexes it and maps the
LightCraft paths it cites; tools/gen_tables.py regenerates src/tables.rs from the JSON,
byte for byte.

Repository: .github/workflows/crw.yml (fmt, clippy, tests on Linux, Windows and macOS;
wasm check; the sample-file job with cached downloads), README and ATTRIBUTION rows,
NOTICE source provenance, docs/clean-room.md (the clean-room standard a format crate
follows here), and AGENTS.md expanded with the start-of-session steps, the new-crate
checklist, clean-room, assets and test rules; CLAUDE.md points at it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.github/workflows/crw.yml

@@ -0,0 +1,79 @@
+name: Shared CRW
+
+on:
+  push:
+    branches: [main]
+    paths: ["crates/crw/**", "scripts/fetch-crw-samples.py", "Cargo.toml", "Cargo.lock", ".github/workflows/crw.yml"]
+  pull_request:
+    paths: ["crates/crw/**", "scripts/fetch-crw-samples.py", "Cargo.toml", "Cargo.lock", ".github/workflows/crw.yml"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: shared-crw-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  native:
+    timeout-minutes: 20
+    name: CRW lint and tests (${{ matrix.os }})
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - uses: dtolnay/rust-toolchain@b725eda525362e7cf34af9a7243cac1e3f01a7ec # stable
+        with:
+          components: rustfmt, clippy
+      - uses: Swatinem/rust-cache@d1527c8f67ef9af357290475d4af4b0fab8f12e0 # v2.9.3
+        with:
+          key: craft-crw-${{ matrix.os }}
+      - run: cargo fmt -p craft-crw --check
+      - run: cargo clippy -p craft-crw --all-targets --locked -- -D warnings
+      - run: cargo test -p craft-crw --locked
+
+  wasm:
+    timeout-minutes: 10
+    name: CRW WASM
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - uses: dtolnay/rust-toolchain@b725eda525362e7cf34af9a7243cac1e3f01a7ec # stable
+        with:
+          targets: wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@d1527c8f67ef9af357290475d4af4b0fab8f12e0 # v2.9.3
+        with:
+          key: craft-crw-wasm
+      - run: cargo check -p craft-crw --locked --target wasm32-unknown-unknown
+
+  samples:
+    timeout-minutes: 20
+    name: CRW sample files decode exactly
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+        with:
+          persist-credentials: false
+      - uses: dtolnay/rust-toolchain@b725eda525362e7cf34af9a7243cac1e3f01a7ec # stable
+      - uses: Swatinem/rust-cache@d1527c8f67ef9af357290475d4af4b0fab8f12e0 # v2.9.3
+        with:
+          key: craft-crw-samples
+      - name: Cache the CC0 sample files
+        uses: actions/cache@v4
+        with:
+          path: ${{ runner.temp }}/crw-samples
+          key: crw-samples-${{ hashFiles('crates/crw/tests/samples.json') }}
+      - name: Fetch the pinned CC0 sample files (raw.pixls.us)
+        run: python scripts/fetch-crw-samples.py "$RUNNER_TEMP/crw-samples"
+      - run: cargo test -p craft-crw --release --locked --test samples -- --nocapture
+        env:
+          CRAFT_CRW_SAMPLES: ${{ runner.temp }}/crw-samples
+          CRAFT_CRW_REQUIRE_SAMPLES: "1"