fix: propagate exit code from REPL to process exit status

[cdprice02]

Summary

• Shell::run() return type changed from anyhow::Result<()> to anyhow::Result<ExitCode>
• lib::run() propagates the new return type
• main() returns anyhow::Result<std::process::ExitCode>; the ? operator propagates fatal errors with full anyhow context, and the Termination impl exits the process with the shell's actual exit code
• Added From<ExitCode> for std::process::ExitCode in exit.rs to keep main clean
• Fixed stdin EOF handling: run() now returns Ok(ExitCode::SUCCESS) on a 0-byte read instead of spinning the REPL loop
• Resolves Propagate exit code from REPL to process exit status #16

Test plan

• test_exit_zero_propagates — exit 0 returns ExitCode(0)
• test_exit_nonzero_propagates — exit 1 returns ExitCode(1)
• test_exit_arbitrary_code_propagates — exit 42 returns ExitCode(42)
• TestResult in the harness now exposes exit_code() for future tests
• All existing tests pass

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates ferrish’s control flow so the REPL’s exit <code> value becomes the actual process exit status, and extends the integration-test harness to assert on exit codes.

Changes:

• Change Shell::run() and ferrish::run() to return ExitCode instead of ().
• Update main() to exit the process with the returned ExitCode.
• Extend the test harness (TestResult) and add REPL tests that assert exit-code propagation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/shell.rs	Propagates ExitCode out of the interactive REPL loop.
src/lib.rs	Updates public run() API to return ExitCode.
src/main.rs	Exits the process using the propagated exit code.
tests/harness.rs	Captures ExitCode in TestResult for assertions.
tests/repl.rs	Adds integration tests verifying exit N propagates correctly.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.