build: REUSE compliance (§4.3) + reuse lint CI gate

.github/workflows/ci.yml

@@ -119,3 +119,17 @@ jobs:
     steps:
       - uses: actions/checkout@v5
       - uses: EmbarkStudios/cargo-deny-action@v2
+
+  # REUSE (§4.3): every file has license + copyright info (via REUSE.toml) and
+  # the license texts live in LICENSES/. Python tool, independent of the pinned
+  # Rust toolchain.
+  reuse:
+    name: REUSE lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+      - run: pip install reuse
+      - run: reuse lint

CHANGELOG.md

@@ -10,6 +10,13 @@ range may break in any release.
 
 ### Added
 
+- **REUSE compliance (Standard §4.3) + CI gate.** Added `LICENSES/GPL-3.0-or-later.txt`
+  and a `REUSE.toml` (a `path="**"` annotation supplying copyright + license in
+  bulk, mirroring `construct/`), so every file carries license + copyright info
+  and `reuse lint` passes (77/77 files, GPL-3.0-or-later only). A new `REUSE lint`
+  CI job enforces it. Satisfies the §5.2 posture requirement for a `LICENSES/`
+  directory.
+
 - **`justfile` dev gates.** Recipes mirroring CI exactly — `just fmt` / `clippy`
   (fresh-isolated `-D warnings`, the only form that matches the runner) / `test`
   / `headless` / `version-gate` / `deny` / `audit`, with `just ci` running the