feat: run CPU isolation and the memory instrument inside the macro-agent sandbox

[GuillaumeLagrange]

Runner-side changes to make CPU isolation and the memory instrument work
unprivileged inside the macro-agent sandbox. Two issues, combined here because
they share the sandbox's privilege model and the same branch.

CPU isolation (COD-3012). Drop the runner's built-in systemd-run /
CGROUP: isolation for a hook-based one: an Isolation type invokes
codspeed-{pre,wrap,post}-bench and stays oblivious to how cores are attributed.
If codspeed-wrap-bench exists it takes the (unprivileged) hook path; otherwise
it falls back to systemd-run --scope --slice=codspeed.slice, so non-sandbox
hosts are unchanged.

Memory instrument (COD-3047). Let memtrack run off a delegated BPF token
instead of root: attach via bpf()-native links (uprobe_multi + tp_btf),
resolve tracked PIDs in the tracker's PID namespace, and accept
LIBBPF_BPF_TOKEN_PATH as a privilege source.

Closes COD-3012
Closes COD-3047

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 17 untouched benchmarks

---

_{Comparing macro-agent-sandbox (d81db8d) with main (aebdbbc)}

[greptile-apps]

Greptile Summary

This PR makes two sandboxed-runner features work without host privileges: CPU isolation now uses hook scripts (codspeed-{pre,wrap,post}-bench) instead of systemd-run, and memtrack now loads its eBPF programs via a delegated BPF token instead of requiring root or file capabilities.

• CPU isolation (Isolation enum): The old HookScriptsGuard + hardcoded systemd-run path is replaced by a tri-state Isolation::resolve() that prefers machine-installed hooks (no sudo needed; benchmark stays a descendant of the profiler) and falls back to Systemd for gen-1 images.
• eBPF token path (BpfVariant::Token): Two BPF skeletons are compiled from the same source. The token variant uses uprobe_multi links and tp_btf/sched_process_fork (all delegatable via BPF token), while the legacy variant keeps perf_event_open-based uprobes. A new variant.h provides namespace-aware PID helpers so probes resolve PIDs in the tracker's own PID namespace.
• Privilege-free proc_fs attach: candidate_paths() falls back from map_files/ (needs CAP_CHECKPOINT_RESTORE) to the pathname column so libraries are discoverable inside the sandbox.

Confidence Score: 5/5

Safe to merge; the isolation refactor preserves the systemd fallback and the dual-skeleton approach is mechanically correct across all probe sites.

The dual-skeleton dispatch, namespace-aware PID helpers, and proc_fs fallback path are all consistently implemented and well-tested. The previously flagged UPROBE_ARGS_RET namespace bug is fixed here. The only finding is a single eprintln! in a test helper.

Files Needing Attention: No files require special attention.

Important Files Changed

Filename	Overview
src/executor/wall_time/isolation.rs	Tri-state Isolation enum replaces HookScriptsGuard; Hooks path runs pre/post-bench hooks via Drop and wraps the benchmark leaf with codspeed-wrap-bench, Systemd path falls back to systemd-run.
crates/memtrack/src/ebpf/c/utils/variant.h	New header providing UPROBE_SEC/URETPROBE_SEC and namespace-aware PID helpers; task_ns_tgid level<4 bound is correct for BPF verifier.
crates/memtrack/src/ebpf/c/utils/process_tracking.h	sched_process_fork migrated from classic tracepoint to tp_btf for token delegation; follow_fork uses task_ns_tgid correctly.
crates/memtrack/src/ebpf/c/allocator.h	All probe SEC() annotations parameterised; UPROBE_ARGS_RET and all other probes now use current_task_ids().tgid instead of global PID.
crates/memtrack/src/ebpf/memtrack/mod.rs	Dual-skeleton Skel enum with with_skel! dispatch; open_and_load! sets pidns rodata before load; variant selected by has_delegated_bpf_token().
crates/memtrack/src/bpf_token.rs	Shared has_delegated_bpf_token() helper (is_dir check included) now used by both the eBPF loader and the memory executor.
crates/memtrack/src/ebpf/proc_fs.rs	candidate_paths() falls back from map_files to pathname column for privilege-free library discovery.
crates/memtrack/tests/shared.rs	for_each_variant cross-checks BPF variants; one eprintln! violates the project tracing-macro rule.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Isolation::resolve] --> B{CODSPEED_ISOLATION=false?}
    B -- yes --> C[Isolation::None]
    B -- no --> D{codspeed-wrap-bench executable?}
    D -- yes --> E[run_pre_bench hook]
    E --> F[Isolation::Hooks]
    D -- no --> G{forced=true OR passwordless sudo?}
    G -- yes --> H[Isolation::Systemd]
    G -- no --> I[Isolation::None - log warning]
    F --> J[wrap_bench: prepend wrap-bench]
    H --> K[wrap_bench: systemd-run scope]
    C --> L[wrap_bench: passthrough]
    J --> M[benchmark child of profiler]
    K --> N[benchmark reparented - profiler needs sudo]
    F -.->|Drop| P[run post-bench hook]

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_{Reviews (6): Last reviewed commit: "chore: make tests run release builds of ..." | Re-trigger Greptile}

[GuillaumeLagrange]

@greptileai review

[not-matthias]

Overall, already pretty good. I think we can improve the naming a bit and let's check if we can keep the tests unified.

Lmk if you have some other thoughts on some comments.

[not-matthias]

LGTM!