dev_container: Prefer canonical compose project on multi-match

[antont]

Stacking

upstream/main
  └─ fix-docker-ps-multi-container        (PR #54068 — detection, unchanged)
     └─ fix-compose-project-name-derivation (PR #6 — derivation)
        └─ prefer-canonical-compose-project  (this PR — tiebreak)

Each PR is separately reviewable. The detection layer from zed-industries#54068 stays byte-identical (parse_find_process_output, the MultipleMatchingContainers variant, its Display, the pass-through arm in start_dev_container_with_config). The tiebreak is a new match arm inside check_for_existing_container, backed by a new pick_canonical_container helper.

How it works

match self.docker_client.find_process_by_filters(filters).await {
    Ok(v) => Ok(v),
    Err(DevContainerError::MultipleMatchingContainers(ids)) => {
        self.pick_canonical_container(ids).await
    }
    Err(other) => Err(other),
}

pick_canonical_container inspects each id, partitions into {canonical, others} by com.docker.compose.project, returns Ok(Some(canonical)) on unique canonical, falls through to MultipleMatchingContainers(ids) otherwise. Log message on recovery names both the canonical id and the orphans.

Prerequisite: DockerConfigLabels gained an Option<String> compose_project field serde-renamed to com.docker.compose.project. All existing inspect struct literals updated with compose_project: None.

Test plan

• cargo test -p dev_container --lib check_for_existing_container — 3 passed (safety net, tiebreak, none-canonical-error).
• cargo test -p dev_container --lib — 78 passed (was 76 on dev_container: Align compose project name with reference CLI and recover from mixed-version duplicates #6's head; +2 new tests).
• ./script/clippy -p dev_container — clean.
• TDD flow: RED commit captures the failing MultipleMatchingContainers output before the logic exists; GREEN commit adds the helper and routes through it.

Live reproduction TODO (defer to approval): against /Users/antont/src/devcontainer-compose-test, manually create a legacy-named container under compose_duplicate_repro and a CLI-named container under devcontainer-compose-test_devcontainer, then open in Zed — expect the canonical one reused and the orphan id named in the log.

Release Notes:

• Fixed Multiple dev container matches error when a workspace has two containers with identical dev container labels but different compose projects (e.g. one left by the devcontainer CLI and one by Zed's Rust implementation). Zed now reuses the container under the canonical ${folder}_devcontainer compose project and logs the orphan; two non-canonical matches still surface the error.

[antont]

Auto-merged by fast-forwarding onto fix-compose-project-name-derivation (PR #6's branch). The three commits (RED test, GREEN tiebreak, serde coverage) are now part of #6. See #6 for the combined review.