[ahma_mcp] fix: drop the hardcoded path separator in expand_home tests - #554

What

test_expand_home asserted expanded.ends_with("/test"). #542 routed this module's expand_home through ahma_common::config::expand_home, which joins with PathBuf::push instead of the previous replacen("~", home, 1).

On Windows that changed the result from C:\Users\x/test (mixed separators — the literal / survived from the input) to C:\Users\x\test, so the assertion failed.

Why fix the test, not the code

The new behaviour is the correct one: a canonical platform separator beats a mixed-separator path, which is the sort of thing that later trips Path::starts_with comparisons. The test carried the assumption AGENTS.md explicitly rules out:

Use MAIN_SEPARATOR/Path APIs, never string separator assumptions.

Both test_expand_home and its ~\ sibling now compare against std::path::MAIN_SEPARATOR.

Release impact

This was the only failure in the post-merge Windows matrix for 0.19.1 — 4352/4353 passed — and it cascaded through CI green to skip Publish Release. v0.19.1 was never published.

job-release-gate keys on whether tag v0.19.1 exists rather than on the version changing in the push, so landing this re-triggers the 0.19.1 build and publish with no further bump.

Verification

• cargo fmt --all, cargo clippy --all-targets — clean
• cargo nextest run — 4669/4669 passed
• cargo nextest run --workspace --run-ignored all — 4680/4680 passed
• cargo deny not run: no Cargo.toml/Cargo.lock change

Local runs are macOS, so they confirm no regression but cannot prove the Windows fix — the post-merge matrix is the real check.