[test-improver] Improve tests for proxy.New and proxy.Handler

[github-actions]

Summary

Adds unit tests for two completely uncovered functions in internal/proxy/proxy.go.

File Analyzed

internal/proxy/proxy_server_test.go (new file)
Implementation: internal/proxy/proxy.go

Improvements Made

Added 4 tests covering previously untested code paths:

Test	Path Covered
TestNew_EmptyWasmPath	cfg.WasmPath == "" guard (lines 90-92)
TestNew_InvalidWasmPath	WASM load error + GitHubAPIURL default fallback
TestNew_InvalidDIFCMode	difcParseErr != nil warning branch (lines 104-106)
TestHandler_ServesRequests	Handler() constructor + verifies /health response

TestHandler_ServesRequests reuses the existing newTestServer helper from handler_test.go (a NoopGuard-based server), so no WASM file is needed. The test routes a real /health request through the wrapped handler to confirm it responds correctly.

Coverage Before / After

Function	Before	After
proxy.go:New	0.0%	64.0%
proxy.go:Handler	0.0%	100.0%
Package total	92.7%	94.9%

The remaining gap in New (36%) covers the full success path which requires loading a real WASM guard module — not feasible in unit tests.

Test Output

=== RUN   TestNew_EmptyWasmPath
--- PASS: TestNew_EmptyWasmPath (0.00s)
=== RUN   TestNew_InvalidWasmPath
--- PASS: TestNew_InvalidWasmPath (0.00s)
=== RUN   TestNew_InvalidDIFCMode
--- PASS: TestNew_InvalidDIFCMode (0.00s)
=== RUN   TestHandler_ServesRequests
--- PASS: TestHandler_ServesRequests (0.00s)
PASS
ok  	github.com/github/gh-aw-mcpg/internal/proxy	0.010s

All existing proxy tests continue to pass (go test -count=3 ./internal/proxy/ — stable across 3 runs).

Warning

Firewall blocked 1 domain

The following domain was blocked by the firewall during workflow execution:

• index.crates.io

To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
  allowed:
    - defaults
    - "index.crates.io"

See Network Configuration for more information.

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