[WIP] feat: roar agent

[christophergeyer]

Summary

• roar agent — new CLI command that traces file I/O without requiring a clean git working tree or even a git repository. Jobs recorded with job_type="agent".
• Process tree in roar show — agent jobs display "Executed commands:" showing the subprocess tree extracted from existing tracer data.
• Preload tracer fork/exec tracking — the LD_PRELOAD tracer now interposes fork() and emits Exec events via a library constructor, so short-lived children like ls appear in the process tree.

Detail

Reuses the entire run pipeline (tracer → provenance → job recording → report) with two differences:

• get_git_root_optional() instead of validate_git_clean() — returns cwd if not in a git repo
• job_type="agent" passed through to job recording

Git info captured best-effort; _get_git_info returns {} outside a repo. Git provider get_status stderr leak suppressed.

Process tree display

The summarized process tree is stored in job metadata as process_tree. roar show renders:

  Executed commands:                                                                                               
    bash -c 'echo test 1; ls; echo test 2'                        
      - ls

Preload fork/exec

Two new NativeTraceEvent variants: Fork { parent_pid, child_pid } and Exec { pid, command }. C shim interposes fork(), library constructor sends Exec with /proc/self/cmdline after successful exec. Launcher reconciles out-of-order events by back-filling parent_pid.

Known limitation: clone3/posix_spawn (used by glibc system() and Python subprocess) bypass fork() interposition.

Shell commands work correctly since bash uses libc fork().

Test plan

• roar agent bash -c "echo test; ls; echo done" in dirty git repo succeeds
• roar agent outside a git repo succeeds with no git error
• roar show @n for agent job displays "Executed commands:" tree
• roar agent --tracer preload bash -c "ls; echo done" — ls appears in tree
• roar agent --tracer ptrace bash -c "ls; echo done" — ls appears in tree
• Existing roar run / roar build unchanged
• cargo test -p roar-tracer-preload passes

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