Check the dev-proxy file-descriptor limit #1064

Description

The macOS-only ts dev proxy opens connections for browser-facing and origin-facing traffic. A low process soft file-descriptor limit may prevent it from accepting the expected number of simultaneous tunnels. The existing proxy command has no RLIMIT_NOFILE preflight in its source.

Proposed fix

Choose and document an appropriate minimum soft limit from the proxy's expected concurrent connection budget. Before starting listeners, read the current soft RLIMIT_NOFILE. If it is below that threshold, fail with a message that reports the current and required limits, explains that each proxied tunnel uses at least two sockets, and gives a platform-appropriate way to raise the limit. Do not modify the process limit implicitly.

Done when

• The threshold and its connection-capacity rationale are documented.
• A too-low soft limit produces an actionable startup error before the proxy begins accepting traffic.
• A sufficient limit proceeds normally; unavailable limit information has an explicit, tested policy.
• Tests exercise the decision and message through an injectable limit reader, without changing the test process limit.

Affected area

ts dev proxy on macOS.