feat: apply pre-flight chaos to proxy mode (phase 1)

[marthakelly]

Summary

Applies chaos before routing so it affects proxy mode. This introduces pre-flight chaos (drop, disconnect) that runs before fixture matching and proxying.

Changes

• Run applyChaos pre-flight with fixture = null
• Preserve existing post-match chaos to maintain fixture-level behavior
• Set _endpointType once early (removed duplicate assignment later in flow)
• Add test ensuring drop prevents proxy call
• Add disconnect test
• Add fixture-mode pre-flight chaos test
• Fix test resource cleanup (no leaked servers or temp dirs)

Scope

• drop
• disconnect

Why

Previously, chaos was skipped for proxy paths, making proxied responses unrealistically reliable.

This change ensures chaos applies consistently across fixture and proxy flows.

Behavior Note

Chaos is evaluated both pre-flight and post-match, which can increase effective trigger probability for non-boundary rates (p → p(2 - p)). This is an intentional tradeoff to enable pre-flight chaos without refactoring the existing flow.

Tests

• New: drop in proxy mode prevents upstream call
• New: disconnect in proxy mode prevents upstream call
• New: fixture-mode pre-flight chaos short-circuits matching
• Fixed: test cleanup (no leaked servers or temp dirs)
• All existing tests pass

Notes

• Minimal change: no modifications to proxy or writer layers
• Future work will split pre/post phases to remove double evaluation (and add latency handling)

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@copilotkit/aimock@119

commit: 7994ba8

[marthakelly]

close b/c i combined two drafts