.dockerignore

@@ -1,10 +1,16 @@
-// Ignore everything
+# Ignore everything
 *
 
-// Allow what is needed
+# Allow what is needed
 !crates
 !tests
 !resources
 
+# The patched dependency Cargo.toml's [patch.crates-io] points at. Without
+# it the build context has no vendor/, and `cargo chef cook` fails on
+# "failed to load source for dependency sieve-rs" -- which CI cannot see,
+# because CI builds from a checkout and only the image build has a context.
+!vendor
+
 !Cargo.lock
 !Cargo.toml

.gitea/workflows/ci.yml

@@ -35,6 +35,11 @@ jobs:
       - run: python3 tools/fork/name-check.py
       - if: always()
         run: python3 tools/fork/notice-check.py
+      # Cargo can patch a dependency to a directory in this repository, and
+      # the image builds from a context .dockerignore prunes to almost
+      # nothing. CI never sees the difference; a release does.
+      - if: always()
+        run: python3 tools/fork/context-check.py
 
   build:
     # Either runner (host1 or host2): the build needs no docker socket.

tools/fork/context-check.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+# SPDX-FileCopyrightText: 2026 Coffey Labs
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Every path Cargo patches has to be in the image's build context.
+
+Cargo.toml's [patch.crates-io] can point at a directory in this repository,
+and the Dockerfile builds from a context that .dockerignore prunes to almost
+nothing. Those two facts met on 2026-09-23: a vendored, patched sieve-rs
+landed, CI stayed green -- it builds from a checkout, where the directory is
+simply there -- and the release build failed on
+
+    failed to load source for dependency `sieve-rs`
+    failed to read /build/vendor/sieve-rs/Cargo.toml
+
+after a tag had already been pushed. This is seconds, and it runs beside the
+other fork checks rather than waiting for a release to find out.
+"""
+
+import re
+import sys
+from pathlib import Path
+
+root = Path(__file__).resolve().parents[2]
+
+
+def patched_paths(manifest: Path) -> list[str]:
+    """Directories named by a [patch...] section's `path = "..."` entries."""
+    out, in_patch = [], False
+    for line in manifest.read_text().splitlines():
+        stripped = line.strip()
+        if stripped.startswith("["):
+            in_patch = stripped.startswith("[patch")
+            continue
+        if not in_patch:
+            continue
+        m = re.search(r'path\s*=\s*"([^"]+)"', stripped)
+        if m:
+            out.append(m.group(1))
+    return out
+
+
+def allowed(dockerignore: Path) -> set[str]:
+    """The first path segment of every re-inclusion rule."""
+    keep = set()
+    for line in dockerignore.read_text().splitlines():
+        stripped = line.strip()
+        if stripped.startswith("!"):
+            keep.add(stripped[1:].strip("/").split("/")[0])
+    return keep
+
+
+def main() -> int:
+    paths = patched_paths(root / "Cargo.toml")
+    if not paths:
+        print("no patched paths to check")
+        return 0
+    keep = allowed(root / ".dockerignore")
+    bad = []
+    for p in paths:
+        top = p.strip("/").split("/")[0]
+        if top not in keep:
+            bad.append((p, top))
+        elif not (root / p).is_dir():
+            bad.append((p, None))
+    for path, top in bad:
+        if top is None:
+            print(f"Cargo.toml patches {path}, which does not exist", file=sys.stderr)
+        else:
+            print(
+                f"Cargo.toml patches {path}, but .dockerignore does not re-include {top!r}:\n"
+                f"  the image build would not see it, and cargo would fail on it.\n"
+                f"  Add `!{top}` to .dockerignore.",
+                file=sys.stderr,
+            )
+    if bad:
+        return 1
+    print(f"build context includes every patched path: {', '.join(paths)}")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())