perf(sandbox): streaming SHA256 and spawn_blocking for identity resolution

[koiker]

Summary

The proxy's TOFU (Trust-On-First-Use) identity resolution performs synchronous /proc scanning and SHA256 hashing of binaries on every cold-cache network request. For large binaries like Node.js (~124 MB), this blocks the async Tokio runtime for nearly a second — stalling all concurrent connections — and allocates the entire file contents in memory just to hash them.

This PR fixes both issues:

• Streaming SHA256: Replace std::fs::read() + Sha256::digest() (which loads the full binary into RAM) with a 64 KB buffered streaming read+hash loop. For a 124 MB binary this eliminates a 124 MB heap allocation per cold-cache check.
• spawn_blocking wrapper: Wrap the entire evaluate_opa_tcp() call in tokio::task::spawn_blocking() in both handle_tcp_connection and handle_forward_proxy. The identity resolution does heavy synchronous I/O (/proc scanning, file hashing) that must not run on the async executor.
• Profiling instrumentation: Add a lightweight file-based perf_log() helper that writes timestamped phase timings to /var/log/openshell-perf.log (or /tmp), providing visibility into proxy latency without depending on the tracing pipeline.

Context

Commit f88aecf ("avoid repeated TOFU rehashing for unchanged binaries") added fingerprint-based caching that made the warm path fast (0 ms TOFU, 11 ms total evaluate_opa_tcp). However:

1. The cold path still reads the entire binary into memory before hashing — a 124 MB allocation for Node.js.
2. The hashing and /proc I/O run synchronously on the Tokio runtime, blocking all other connections during the ~1 s cold-cache window.

Profiling Data (Node.js binary, 124 MB)

Phase	Cold cache	Warm cache
file_sha256	~890 ms	0 ms (fingerprint hit)
evaluate_opa_tcp total	1002 ms	11 ms
OPA evaluation	1 ms	1 ms
DNS + TCP connect	166–437 ms	166–437 ms

Files Changed

• crates/openshell-sandbox/src/procfs.rs — streaming SHA256 in file_sha256(), phase timing in resolve_tcp_peer_identity() and find_pid_by_socket_inode()
• crates/openshell-sandbox/src/proxy.rs — spawn_blocking wrapper around evaluate_opa_tcp() in both call sites, phase timing throughout
• crates/openshell-sandbox/src/identity.rs — phase timing in verify_or_cache()

Test Plan

• cargo build --release succeeds (cross-compiled for x86_64-unknown-linux-gnu)
• Deployed to live NemoClaw sandbox and verified with curl and node requests through the proxy
• Cold-cache: ~1 s total (dominated by SHA256 of 124 MB binary, now non-blocking)
• Warm-cache: 11 ms total (fingerprint cache hit, unchanged from baseline)
• No functional regressions — policy allow/deny decisions unchanged
• cargo test -p openshell-sandbox (existing identity and procfs tests)

Made with Cursor

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