fix(up): forward single-file bind mounts to container run

[csaller]

Closes #93.

The bug

configVolume in ComposeUp.swift treated file vs. directory host sources differently: if the host side of a bind mount resolved to a file, the mount was skipped and only a "The 'container' tool does not support direct file mounts" warning was printed. In practice that warning is often masked by the image-fetch/progress output, so users see a container that silently starts with volumes: entries missing.

But Apple container (0.12.3+) does support file-to-file bind mounts. This works today, straight from the CLI:

container run --rm \
  --volume /host/config.yaml:/app/config.yaml:ro \
  myimage

So the gate in container-compose is no longer (and, based on field use, seems to never have been) correct. Common compose idioms like ./config.yaml:/app/config.yaml:ro or ./init.sh:/docker-entrypoint-initdb.d/init.sh have to be worked around by moving the file into a directory that's already mounted.

The fix

• When the host path exists, forward the bind mount regardless of whether it's a file or directory — both are supported by container --volume.
• Preserve the optional mode component (:ro, etc.) when rebuilding the --volume argument. Previously the mode was stripped even for directory mounts, so :ro had no effect there either.

Diff is small and localized to the bind-mount branch of configVolume. The named-volume branch is untouched.

Verification

Minimal reproducer with one directory mount and one file mount:

# docker-compose.yml
services:
  repro:
    image: docker.io/library/alpine:3.20
    command: ["sh","-c","ls -la /app; cat /app/hello.txt; cat /app/data/marker.txt"]
    volumes:
      - ./data:/app/data
      - ./hello.txt:/app/hello.txt:ro

Before (0.11.0): container inspect shows only the directory mount; file mount is absent from configuration.mounts; cat /app/hello.txt → No such file or directory.

After this patch:

[
  { "source": ".../data/",       "destination": "/app/data",       "options": [],     "type": {"virtiofs": {}} },
  { "source": ".../hello.txt",   "destination": "/app/hello.txt",  "options": ["ro"], "type": {"virtiofs": {}} }
]

Container logs:

-rw-r--r-- 1 root root 36 May  8 18:38 hello.txt
hello from a single-file bind mount
hello from a directory bind mount

The :ro on the file mount is now propagated (options: ["ro"]), matching compose semantics.

Test status

Ran swift test. The only failures are in the pre-existing dynamic suite ("What goes up must come down - two containers", "Test WordPress with MySQL compose file", "Test compose with complex dependency chain") — all of those use compose YAMLs with only named volumes (wordpress_data, db_data) and hit the known named-volume bootstrap issue tracked in #52. They reproduce on main without this patch; no code path touched by this change is exercised by them.

I didn't add a unit test because configVolume is a private instance method that pulls from several ComposeUp fields (cwd, fileManager, environmentVariables, projectName). Happy to extract a pure helper and add a static test in a follow-up if you'd prefer that shape.

Test plan

• docker-compose.yml with a single-file bind mount (e.g. ./config.yaml:/app/config.yaml:ro) brings up a container that can read the file.
• docker-compose.yml with a directory bind mount continues to work.
• container inspect <name> shows both mounts in configuration.mounts, with options: ["ro"] preserved for :ro entries.
• Missing host directories are still auto-created (unchanged behavior).

[Mcrich23]

Hi @csaller. Thank you for your PR. I plan to look at it early next week when I have some time (if I don't send something, please ping me!)

For the test, go ahead and add it. Using an @testable import should give you access to any private variables and methods for your evaluation.

[csaller]

Hi @Mcrich23, thanks! I just added the unit test and they are passing locally, also a test build worked exactly as expected with no regressions detected. Lmk if you need everything else from me. Other than that, have a great weekend!