Proxy engine: persistent CA, capped capture, upgrade tunnel

[gschier]

First engine PR for Yaak Proxy (crates/yaak-proxy).

• CaStore::load_or_create(dir) persists the CA (ca.pem, ca.key at 0600, CN "Yaak Proxy CA", 10 years). Leaf certs are 365 days with serverAuth EKU, picked by SNI.
• start_proxy(ProxyConfig { port, ca, capture_body_limit, upstream_root_certs }). Client-facing ALPN is http/1.1 only; upstream still negotiates h2 or h1.
• Bodies stream in both directions. RequestBodyChunk / ResponseBodyChunk events carry each frame's bytes up to the cap (10 MB default); completion events carry size, truncated, timing and error. The engine stores nothing.
• Upgrade requests inside CONNECT are spliced into a blind tunnel after the 101. Non-TLS CONNECT payloads, and hosts whose client rejected the TLS handshake (pinning), are tunneled without interception.
• Flow metadata: started_at, elapsed to headers and to end, sizes, HTTP versions on both sides, remote address, error. log replaces eprintln!.
• yaak-proxy-lib is only adapted to the new API.

CI already builds yaak-app-proxy (cargo test --all) and type-checks apps/yaak-proxy (npm run lint), so ci.yml is unchanged.

Tests (cargo test -p yaak-proxy), against a local HTTPS server signed by a throwaway CA:

• CA persisted, reloaded, key mode 0600
• HTTPS GET (upstream HTTP/2, remote address, timings)
• POST with a body
• 404
• request and response bodies over the cap: truncated capture, full delivery
• WebSocket upgrade passes through
• pinned client falls back to passthrough
• plain HTTP GET
• unreachable upstream: 502 and an Error event

[greptile-apps]

Confidence Score: 5/5

[High impact] The PR appears safe to merge, with no new actionable issues or outstanding previous findings.

Summary

The PR adds a saved CA, streamed body capture with a size cap, and blind tunnels for upgrades and traffic that cannot be inspected.

• Yaak Proxy keeps its certificate authority across restarts.
• Proxy bodies stream through while captured copies stay capped.
• CONNECT connections can pass through or switch to upgraded streams.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  Client[Client] --> Proxy[Local proxy]
  Proxy --> Plain[Plain HTTP]
  Proxy --> Connect[CONNECT]
  Connect --> Inspect[Inspect HTTPS]
  Connect --> Blind[Blind tunnel]
  Inspect --> Upgrade[101 upgrade tunnel]
  Plain --> Capture[Capped body events]
  Inspect --> Capture
  Capture --> Adapter[Save exchange and errors]

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_{Reviews (2) · Last reviewed commit: "Address review: server-first tunnels, pa..." · Reviewed by Greptile}

[gschier]

@greptileai review