feat: add --sidecar global flag (#25)

[mikkeldamsgaard]

Summary

• Adds --sidecar global flag (env: INITIUM_SIDECAR) that keeps the process alive after task completion, for use as a Kubernetes sidecar container
• On success: logs completion message and sleeps indefinitely
• On failure: exits with code 1 immediately (no sleep)
• Fixes pre-existing clippy warnings for newer Rust toolchain (inconsistent_digit_grouping, manual_main_separator_str, unnecessary_map_or)

Closes #25

Test plan

• cargo clippy --all-targets --all-features -- -D warnings passes
• cargo fmt -- --check passes
• cargo test --all-features — all 163 tests pass
• New tests: test_sidecar_flag_on_failure_exits_immediately, test_sidecar_flag_on_success_sleeps, test_sidecar_env_var, test_sidecar_logs_message_on_success, test_without_sidecar_exits_on_success

How to verify

# Build
cargo build

# Verify --sidecar keeps process alive on success (Ctrl+C to stop)
./target/debug/initium --sidecar exec -- true

# Verify --sidecar exits immediately on failure
./target/debug/initium --sidecar wait-for --target tcp://localhost:1 --timeout 1s --max-attempts 1

# Verify env var works (Ctrl+C to stop)
INITIUM_SIDECAR=true ./target/debug/initium exec -- true

# Run tests
cargo test --all-features
cargo clippy --all-targets --all-features -- -D warnings

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a new global --sidecar / INITIUM_SIDECAR flag so initium can stay alive after successful completion (useful for Kubernetes sidecar-container patterns), plus a few small Rust/clippy-modernization tweaks.

Changes:

• Add --sidecar global flag that logs a completion message and then sleeps indefinitely on success.
• Add integration tests covering --sidecar behavior (success sleeps; failure exits; env var support; log message).
• Fix a few clippy warnings / minor stdlib API modernizations in tests.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/main.rs	Adds --sidecar flag and the post-success infinite sleep behavior.
tests/env_var_flags.rs	Adds test coverage for --sidecar and INITIUM_SIDECAR.
docs/usage.md	Documents the new flag and sidecar mode usage.
README.md	Adds a quick “sidecar container” usage section.
tests/integration_test.rs	Minor clippy-related refactor (map_or → is_ok_and).
src/safety.rs	Minor clippy-related refactor (MAIN_SEPARATOR usage).
src/duration.rs	Minor clippy-related refactor (digit grouping).

Comments suppressed due to low confidence (3)

src/main.rs:36

• The project design/contribution guide calls out updating CHANGELOG.md for new user-facing features (see docs/design.md:101-106), but this PR introduces a new global flag without adding an entry. Please add a short note under the Unreleased section describing the new --sidecar / INITIUM_SIDECAR behavior.

    #[arg(
        long,
        global = true,
        env = "INITIUM_SIDECAR",
        help = "Keep process alive after task completion (for sidecar containers)"
    )]
    sidecar: bool,

docs/usage.md:398

• This Kubernetes YAML example is invalid as written: restartPolicy is not a field under spec.containers[]. If the intent is to document KEP-753 sidecar containers (K8s 1.29+), the snippet should be under initContainers: (where per-initContainer restartPolicy: Always is supported), or otherwise drop restartPolicy and keep it as a normal containers: entry.

# Kubernetes sidecar example (requires K8s 1.29+)
containers:
  - name: initium-sidecar
    image: ghcr.io/kitstream/initium:latest
    restartPolicy: Always
    args: ["--sidecar", "wait-for", "--target", "tcp://postgres:5432"]

**README.md:220**
* This Kubernetes snippet uses `containers:` with `restartPolicy: Always`, but `restartPolicy` is not valid under `spec.containers[]`. For KEP-753 sidecar containers (K8s 1.29+), this should likely be shown under `initContainers:` with `restartPolicy: Always`, or else remove `restartPolicy` if you intend a regular long-running container.

containers:
  - name: initium-sidecar
    image: ghcr.io/kitstream/initium:latest
    restartPolicy: Always
    args: ["--sidecar", "wait-for", "--target", "tcp://postgres:5432"]

</details>



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