test: add coverage for MCP mount/docker-arg warning propagation

[github-actions]

Test Gap Fixes

Test suite snapshot: 3322 unit tests, ~700 integration tests, 40+ test fixtures (baseline cargo test run before this change)

Added Coverage

Module	Function/Path	Why It Matters	Test Added
src/validate.rs	validate_mount_source (docker.sock detection), surfaced via validate_stdio_mcp in src/compile/common.rs	Detects a mount that grants full host Docker access / container escape; unit-tested in isolation but the full front-matter → compile → stderr path was never exercised	test_compile_warns_on_docker_socket_mount
src/validate.rs	validate_docker_args (--privileged flag detection)	Detects privilege-escalating Docker args; only unit-tested against the raw function, not through the CLI	test_compile_warns_on_privileged_docker_arg
src/validate.rs	validate_docker_args → validate_mount_source delegation (-v/--volume smuggling a sensitive host path)	Confirms args-based mount smuggling that bypasses the dedicated mounts: field still gets the delegated sensitive-path warning, end-to-end through compile	test_compile_warns_on_volume_arg_smuggling_sensitive_mount

These three security-relevant validators (container escape via docker socket mounts, privilege escalation via docker args, and mounts-validation bypass) previously had only direct unit tests in src/compile/common.rs exercising the functions in isolation. Nothing asserted that the warnings actually reach the compiled CLI's stderr output when triggered through real front matter, so a regression in the validate_stdio_mcp wiring (e.g. dropping an eprintln! call or no longer iterating opts.mounts/opts.args) would have gone unnoticed by the existing suite.

Validation

• cargo test (3322+ tests, all passing, including the 3 new tests)
• cargo clippy --all-targets --all-features (no warnings)

---

This PR was created by the automated test gap finder. Modules audited this cycle: secure.rs, validate.rs (focus: MCP docker/mount validators), sanitize.rs, execute.rs, fuzzy_schedule.rs, compile/ado_bundle.rs, compile/pr_filters.rs, compile/filter_ir.rs.

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