[Bug]: `container build` transfers an empty local context and `COPY` cannot find files

[zebrapurring]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

mkdir container-context-repro
cd container-context-repro

printf '%s\n' \
  'FROM scratch' \
  'COPY staged-run.sh /run.sh' >Dockerfile

printf '%s\n' '#!/bin/sh' >staged-run.sh

container build \
  --platform linux/arm64 \
  --progress plain \
  --tag local/container-context-repro:latest \
  .

There is no .dockerignore.

Current behaviour

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 2B 0.0s done
#1 DONE 0.0s

#2 [internal] load .dockerignore
#2 transferring context: 2B done
#2 DONE 0.0s

#3 [internal] load build context
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [linux/arm64/v8 1/1] COPY staged-run.sh /run.sh
#4 ERROR: failed to calculate checksum ... "/staged-run.sh": not found

Expected behaviour

The local context should include staged-run.sh, and the image should build
successfully.

Problem description

container build transfers a 2B local build context and fails every COPY,
even for a root-level file in a minimal context with no .dockerignore.

The failure persists after stopping and deleting the builder, pulling
ghcr.io/apple/container-builder-shim/builder:0.12.0 again, and starting a new
builder.

Environment

- macOS 26.6 (25G72)
- Xcode 26.6 (17F113)
- Swift 6.3.3
- container CLI 1.1.0
- container-apiserver 1.1.0
- builder image ghcr.io/apple/container-builder-shim/builder:0.12.0
- architecture arm64
- builder resources: 8 CPUs, 12288 MB

Code of Conduct

• I agree to follow this project's Code of Conduct

[rupinajay]

Hey @zebrapurring !
The root cause was a path prefix mismatch in BuildFSSync: the context root was canonicalized (e.g. /tmp to /private/tmp), while Archiver enumerated files using unresolved paths, causing relativeChildPath to drop all files from the build context tar stream.

I have opened PR #2124 with a fix for this issue.
The PR canonicalizes the enumerated URLs before checking containment, and includes both unit and end-to-end integration regression tests.

[rupinajay]

Hi @zebrapurring, When you get the chance, you could take a look at this PR. Thanks.