core: make EnvClient WebSocket keepalive configurable

[sergiopaniego]

Summary

Adds ping_interval_s / ping_timeout_s to EnvClient, forwarded to the WebSocket ws_connect. Default is 20.0 (the websockets default, so existing behavior is unchanged); passing ping_interval_s=None disables client-side keepalive, which sandbox tunnels that drop WebSocket ping/pong frames require to stay connected. Surfaced in #821 (Modal), where the E2E previously needed a monkeypatch of ws_connect.

Closes #875.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• New environment
• Refactoring

Alignment Checklist

Before submitting, verify:

• I have read .claude/docs/PRINCIPLES.md and this PR aligns with our principles
• I have checked .claude/docs/INVARIANTS.md and no invariants are violated
• I have run /pre-submit-pr (or bash .claude/hooks/lint.sh and tests) and addressed all issues

RFC Status

• Not required (bug fix, docs, minor refactoring)
• RFC exists: #___
• RFC needed (will create before merge)

Test Plan

New unit tests (no network) patch ws_connect and assert the keepalive args are forwarded:

• default → ping_interval=20.0, ping_timeout=20.0 (behavior unchanged)
• ping_interval_s=None / ping_timeout_s=None → forwarded as None (keepalive disabled)

PYTHONPATH=src:envs pytest tests/test_core/test_generic_client.py -m "not integration" → 68 passed. Lint clean (ruff format --check, ruff check).

Claude Code Review

N/A

---

Note

Low Risk
Small, backward-compatible addition to core WebSocket connect options with targeted unit tests; no auth or data-path changes.

Overview
EnvClient (and subclasses like GenericEnvClient) now accept ping_interval_s and ping_timeout_s, which are passed through to ws_connect on connect. Defaults stay 20s for both, so behavior is unchanged unless callers override.

Setting either to None turns off client-side keepalive / pong timeout—needed when sandbox tunnels (e.g. Modal) drop WebSocket ping/pong frames and would otherwise drop the session on timeout.

Unit tests patch ws_connect to assert default forwarding and None when keepalive is disabled.

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[bot-ci-comment]

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[burtenshaw]

Addressed in #878